Arylamine-modified thiazoles as donor-acceptor dyes: Quantum chemical evaluation of the charge-transfer process and testing as ligands in ruthenium(II) complexes

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FULL PAPER

DOI: 10.1002/ejoc.201200688

Arylamine-Modified Thiazoles as Donor–Acceptor Dyes: Quantum Chemical

Evaluation of the Charge-Transfer Process and Testing as Ligands in

Ruthenium(II) Complexes

Roberto Menzel,^[a][‡]Stephan Kupfer,^[b,c][‡]Ralf Mede,^[a]Dieter Weiß,^[a]Helmar Görls,^[d]

Leticia González,*^[c]and Rainer Beckert*^[a]

Keywords: N,S-Heterocycles / Heterocycles / Chromophores / Dyes / Charge transfer / Density functional calculations /

Ruthenium complexes

A series of new 4-hydroxy-1,3-thiazole-based chromophores

bearing different arylamine components (triarylamines, carb-

azole, and phenothiazine) as electron donors and azahetero-

cycle components (pyridine, pyrazine and pyrimidine) as

electron-acceptor moieties have been synthesized. Elaborate

quantum chemical calculations were carried out with two se-

lected compounds to identify the natures of the HOMO/

LUMO transition and of the intramolecular charge-transfer

state. The electrochemical properties were investigated: the

dyes show reversible first oxidation and reduction peaks,

with the former strongly dominated by the type of arylamine.

The donor moieties were synthesized under Buchwald–Hart-

wig conditions. Several of the presented X-ray structures

provide deeper insight into the geometries of the ligands.

The bidentate nature of the chromophores makes them suit-

able as ligands in transition metal complexes. The corre-

spondingruthenium(II)polypyridinecomplexes–Ru(dmbpy)₂-

(L)(PF₆)₂(dmbpy = 4,4Ј-dimethyl-2,2Ј-bipyridine) – were suc-

cessfully synthesized for seven of the ligands. The MLCT

bands in these complexes are significantly broadened, re-

sulting in improved light-harvesting efficiencies.

have been developed since then. Thanks to their easy func-

tionalization and tunable optical properties they have been

successfully incorporated as blue-emitting species in a poly-

mer backbone,^[4]as a FRET energy donor in a terpolymer

together with a Ru^IIcomplex as the acceptor unit,^[5]and

as chromophores in donor-π-acceptor (D-π-A) dyes in dye-

sensitized solar cells (DSSCs).^[6]In addition, they were very

recently reported to be fast and specific systems for fluoride

ion detection^[7]and have been employed as light-harvesting

ligands in Ru^IIpolypyridyl complexes.^[8]

The last of these in particular is of significant interest,

due to the potential application of Ru^IIdyes as sensitizers

in DSSCs, which usually lack chromophores to harvest sun-

light efficiently. Furthermore, ruthenium(II) complexes, es-

pecially Ru^IIpolypyridine complexes, have attracted con-

siderable interest due to their outstanding properties, such

as good chemical stability, reversible redox behavior, and

long-lived excited states with distinct reactivities and

unique, tunable emission characteristics.^[9]This has opened

the doorway to numerous applications.^[10]Nonetheless, the

investigation of new complexes is still an evolving field and

is one part of this contribution.

Introduction

The classical heterocyclic 4-hydroxy-1,3-thiazole core

was described by R. Dodson and H. Turner in 1951.^[1]Since

then, several compounds have been synthesized^[2]but only

a few data relating to applications of these compounds ex-

ist. Some of the derivatives have been tested as drugs (e.g.,

as cyclooxygenase, 5-lipoxygenase, and cyclin-dependent

kinase 5 inhibitors).^[3]

Our group revived the 4-hydroxy-1,3-thiazole unit as a

chromophore and fluorophore, due to its similarities to the

naturally occurring luciferin and its remarkable spectro-

scopic characteristics. Several applications of its derivatives

[a] Friedrich Schiller University Jena, Institute of Organic and

Macromolecular Chemistry,

Humboldtstraße 10, 07743 Jena, Germany

Fax: +49-3641-948212

E-mail: c6bera@uni-jena.de

Homepage: http://ww w .agbeckert.uni-jena.de/

[b] Friedrich Schiller University Jena, Institute of Physical

Chemistry,

Helmholtzweg 4, 07743 Jena, Germany

[c] University of Vienna, Institute of Theoretical Chemistry,

Waehringer Str. 17, 1090 Vienna, Austria

Homepage: http://theochem.univie.ac.at/

[d] Friedrich Schiller University Jena, Institute of Inorganic and

Analytical Chemistry,

Additionally, arylamines have also been the focus of in-

tense research, due to potential applications in various

functional materials. They have been used as materials that

show photoconductive and nonlinear optical (NLO) prop-

erties,^[11]and were employed for that purpose as chromo-

Humboldtstraße 8, 07743 Jena, Germany

[‡] Both authors contributed equally to this article

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejoc.201200688.

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FULL PAPER

phores in ultrafast electro-optic (EO) applications.^[12]sen as a promising candidate. For the coupling reaction,

Furthermore, they can act as photoconductors and hole- bis(dibenzylideneacetone)palladium(0) [Pd(dba)₂] was used

transporting materials in organic light-emitting diodes as the precatalyst, KOtBu as the base to deprotonate the

(OLEDS),^[13]and are promising cores both in bulk hetero- amine in the catalytic cycle, and toluene as solvent. Fortu-

junction (BHJ) solar cells^[14]and in Grätzel-type DSSCs.^[15]nately, the desired products were obtained with use of

The synthesis and characterization of different dyes P(tBu)₃in good yields (76–90%). In addition, the two-step

based on the 4-methoxy-1,3-thiazole core as a chromophore nature of the reaction was demonstrated. As representative

with an arylamine donor in the 5-position (i.e., with a examples, for A1 and B1 the monosubstituted products

phenyl-, p-anisole-, p-tolyl-, or phenothiazine-based aryl- A1m (69%) and B1m (88%) were obtained. This opens the

amine) and a pyridine, pyrimidine, or pyrazine moiety in door for the construction of unsymmetrically substituted

the 2-position as acceptor is presented. Two of the dyes triarylamines useful for photonic applications.^[22]Unlike the

were further investigated by quantum chemical methods in double N-arylation of the amines 3a–3c, the Buchwald–

order to assign their longest-wavelength absorptions either Hartwig reaction starting with 2d, in which the aryl halide

to a twisted (TICT) or to a planar (PICT) intramolecular is connected to the thiazole, was not successful by the de-

charge-transfer process. The successful synthesis of seven scribed method: with the commonly used diphenylamine as

heteroleptic Ru^IIcomplexes was achieved by use of the acti- the amine component no conversion to the substituted

vated precursor cis-Ru(dmbpy)₂(acetone)₂(PF₆)₂.^[16]The product was observed under various conditions. The biaryl-

complexes were synthesized in order to test the abilities and phosphane ligand 2-(dicyclohexylphosphanyl)-2Ј,6Ј-di-

characteristics of these dyes as ligands, which is considered methoxy-1,1Ј-biphenyl (SPHOS) was therefore chosen as a

a first step to establishing this class of chromophores as promising ligand.^[20b,23]SPHOS has already been success-

electron-donating and light-harvesting ligands in Ru^IIcom- fully applied in the amination of chloro-terpyridine and is

plexes utilized as sensitizers in DCCSs.^[17]All compounds widely used in the Suzuki–Miyaura reaction.^[24]Finally, the

were investigated with regard to their electronic and electro- coupling reaction with employment of SPHOS yielded the

chemical properties. Furthermore, the emission behavior of arylamines D1–D3 (69 to 88%).

the dyes was characterized in terms of lifetime and quan-

tum efficiency measurements.

The synthesis of the heteroleptic Ru^IIcomplexes is also

depicted in Scheme 1. The standard procedure – heating of

precursor cis-(dmbpy)₂RuCl₂(1 equiv.) in EtOH with the

appropriate ligand (1 equiv.) for 24 h under reflux condi-

tions and precipitating the product with NH₄PF₆– yielded

an inseparable mixture of products, so the precursor was

activated with AgPF₆prior to the complexation reaction

Results and Discussion

Synthesis

The synthesis of the dyes/ligands is depicted in Scheme 1. with the ligand. The synthesized complexes can easily be

The new 4-hydroxy-1,3-thiazoles 1a–1c were prepared by purified by size exclusion chromatography either with Bio-

Hantzsch thiazole cyclizations between the thioamides of Beads^®S-X1 with DCM or with Sephadex^®LH-20 with

the corresponding azaheterocycles and ethyl 2-bromo-2-(4- acetone as solvent if they are only sparingly soluble in

nitrophenyl)acetate, which can in turn easily be prepared DCM. After precipitation of the products with diethyl

from the commercially available 2-(4-nitrophenyl)acetic acid ether, they were obtained as deep red solids in moderate to

by a standard protocol.^[18]Compound 1d was prepared good yields (75–93%). Although several attempts were

similarly, from ethyl 2-bromo-2-(4-bromophenyl)acetate made, it was not possible to obtain pure samples of all pos-

and pyridine-2-carbothioamide, as described in the litera- sible complexes. No homogeneous products were obtained

ture.^[19]Alkylation of the “phenolic” 4-hydroxy group was in the cases of compounds B1 and B2. Most likely unfavor-

achieved in a manner similar to the Williamson ether syn- able complexation at the second pyrazine nitrogen atom led

thesis, by treatment of the deprotonated thiazole with to a mixture of differently substituted complexes. The com-

methyl iodide in DMSO. The reduction of the nitro group plexation was also unsuccessful in the case of ligand A3.

in 2a–2c was accomplished with freshly prepared Raney

nickel and hydrazine as the hydrogen source in EtOH in

excellent yields (Ͼ95%).

X-ray Structures

The bottleneck for the synthesis of the arylamines was

the Buchwald–Hartwig cross-coupling reaction, involving a

X-ray structures of the molecules A1, B1, C1, and D2

double N-arylation. Although thoroughly described in the were obtained from crystals grown directly in NMR tubes

literature, the reaction depends strongly on the natures of by slow evaporation of CHCl₃/EtOH solvent mixtures. The

the catalysts and ligands and on the conditions used.^[20]structures are depicted in Figure 1 and data are listed in

Several attempts with, for example, triphenylphosphane or Table 1 (additional refinement data are reported in

1,1Ј-bis(diphenylphosphanyl)ferrocene as ligand together Scheme S1 in the Supporting Information). Each dye shows

with NaH or KOtBu as base have failed completely. There- a more or less planar geometry along the acceptor 1,3-thi-

fore, the electron-rich ligand tri-tert-butylphosphane azole unit, with the nitrogen atoms arranged in a transoid

[P(tBu)₃], which had already been successfully applied in conformation due to N–H hydrogen-bonding interactions

the synthesis of different carbazole derivatives,^[21]was cho- between N1 of the 1,3-thiazole and the hydrogen of the ap-

2

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Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

Scheme 1. Synthesis and structure of the ligands and the complexes.

propriate N-heterocycle (except for C1). The torsion angles

The triarylamines display propeller-type geometries of

are 9.10(7)° for C1 with the pyrimidine moiety (no hydro- the aromatic rings. They are twisted in a well-known fash-

gen bond possible) and are decreased to 2.86(6), 7.79(8), ion out of the plane into conformations with fewest steric

and 2.48(9)° for A1, B1, and D2, respectively. Each dye is interactions with the adjacent rings, as reported for several

also twisted to some extent along the 1,3-thiazole-phenyl arylamines.^[25]The nitrogen N3 of the triarylamine in each

single bond. Because there is no appreciable steric hin- case adopts an almost planar geometry, in agreement with

drance it can be assumed that free rotation occurs at room the sp²hybridization and the resulting intramolecular p–π

temperature, leading to an unsteady torsion angle in the interactions. The interatomic distances and angles both in

crystalline state, from almost planar with 9.10(7)° in the the arylamine donor and in the 4-methoxy-1,3-thiazole core

case of C1 to highly twisted with 37.89(10)° in that of A1.

are all in the expected range.^[26]Additionally, the X-ray

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Figure 1. ORTEP plots of the arylamines A1, B1, C1, and D2. The numbering of A1 also applies for the other compounds. Hydrogen

atoms are omitted; ellipsoid probability 50%.

Table 1. Selected interatomic distances [Å] and angles [°] in A1, B1, contribute only marginally to the π-conjugated system, as

C1, and D2.

is also supported by the absorption spectra and quantum

chemical calculations.

A1

B1

C1

D2

Bonds

N2–C4

C4–C1

C1–S1

S1–C2

C2–C3

C3–N1

C3–O1

C2–C9

C12–N3

1.345(2)

1.467(2)

1.725(1)

1.727(1)

1.376(2)

1.358(2)

1.353(2)

1.467(2)

1.414(2)

1.342(2)

1.462(2)

1.723(2)

1.733(2)

1.377(2)

1.358(2)

1.355(2)

1.466(2)

1.427(2)

1.342(2)

1.471(2)

1.725(1)

1.730(1)

1.388(2)

1.359(2)

1.350(2)

1.465(2)

1.417(2)

1.342(3)

1.463(3)

1.722(2)

1.727(2)

1.383(3)

1.360(3)

1.354(3)

1.468(3)

1.446(3)

Electronic Absorption Spectra of the Dyes

The UV/Vis spectra of the ligands are shown in Figure 2

(see also Table 2). Every triarylamine dye shows several

high energy transitions below 250 nm where the assign-

ments are tentative (not shown) and two main transitions

at 305 and 420 nm. The bands located at 305 nm are due to

mixtures of π–π* transitions in the triarylamines. They are

not affected either by the donor or by the acceptor. The

bands located in the visible part are of charge-transfer (CT)

character, as recently shown for similar 4-methoxy-1,3-thi-

azole dyes.^[6]The lowest-energy absorption maxima are in-

fluenced both by the donors and by the acceptors. The ab-

sorption λ_maxvalues are slightly bathochromically shifted

by approx. 10 nm for the dyes with the pyrazine instead of

the pyridine acceptors. Further shifts of these bands can be

observed for the derivatives with more strongly electron-

donating arylamines. For A1–A3, the absorption λ_maxval-

ues are bathochromically shifted from 405 nm for the phen-

yl- to 417 nm (0.09 eV) for the p-anisole-, and further to

Angles

C1–S1–C2

S1–C2–C3

C2–C3–N1

C3–N1–C1

N1–C1–S1

89.76(6)

89.83(8)

90.17(7)

90.10(10)

107.95(10)

117.56(12)

109.60(11)

115.13(10)

107.70(12) 107.41(10) 107.76(15)

117.45(15) 117.51(12) 117.40(19)

109.93(14) 109.89(12) 109.71(18)

115.08(12) 115.03(10) 115.02(16)

Torsion angles

N2–C4–C1–S1

S1–C2–C9–C10

C11–C12–N3–C15 40.21(11)

C12–N3–C15–C16 34.97(11)

2.86(6)

37.89(10)

7.79(8)

18.04(12) 1.65(10)

62.88(14) 48.35(12) 112.21(18)

20.10(14) 48.14(12) 6.50(18)

9.10(7)

2.48(9)

18.47(15)

structure of the monosubstituted product A1m is given in 433 nm (0.20 eV) for the p-N,NЈ-dimethylaniline-based tri-

Scheme S2 in the Supporting Information. It features a arylamine. This coincides with the behavior of the thiazoles

geometry very similar to those of the doubly substituted with the pyrazine and pyrimidine acceptor. For compounds

derivatives.

D1–D3, the λ_maxvalues of this transition are significantly

In order to describe the butterfly conformation of the shifted towards higher energies. This can be explained by

phenothiazine dye D1, it is necessary to introduce the fold- the very weak participation of the annulated arylamines in

ing angle θ and the tilt angle α.

the conjugation pathway, as can be seen from the X-ray

The former refers to the extent of the butterfly conforma- structure of D2. The extinction coefficients (ε) of the long-

tion, whereas the latter represents the deviation of these pla- est-wavelength absorptions are high, varying from 18000

nes from coplanarity (α = 0°). For D1, θ is 153°, corre- (D1) to 30000 m^–1cm^–1(B1). Additionally, the absorption

sponding to α = 27°, which conforms very well with unsub- spectra of D2 and D3 display a very strong, typical n–π*

stituted (θ = 159°) or N-phenyl-substituted (θ = 155°) phe- transition for D2 (λ = 257 nm, ε = 53000 m^–1cm^–1) and a

nothiazine.^[27]Additionally, the phenothiazine is almost strong π–π* transition for D3 (λ = 240, ε = 58000 m^–1cm^–1)

completely twisted out of the plane of the attached phenyl for the phenothiazine or phenoxazine moieties, as described

ring [112.21(18)°]. This corroborates the assumption that for various N-aryl-substituted derivatives.^[28]The emission

the annulated arylamines (the same applies for D1 and D3) spectra of the dyes are depicted in Scheme S3 in the Sup-

4

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Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

porting Information. The emission quantum yields (Φ_F) are Table 2. Spectroscopic properties of the dyes measured in CH₃CN

at room temp.

also strongly dependent on the arylamine donors. In con-

trast with the phenyl-based triarylamines, with Φ_F= 40–

47%, the p-anisole-based triarylamines show Φ_Fvalues be-

low 1%, and consequently no fluorescence was detected for

the p-N,NЈ-dimethylaniline derivative in CH₃CN solution at A3

room temp. The obtained Φ_Fvalues corresponded well with

λ_abs[nm] [logε]

λ_em[nm]^[a]

Φ_F[%]

τ_F[ns]

A1

A2

301 [4.33], 405 [4.44]

299 [4.35], 417 [4.43]

307 [4.43], 433 [4.36]

303 [4.40], 425 [4.47]

302 [4.40], 439 [4.46]

302 [4.32], 426 [4.36]

301 [4.38], 433 [4.46]

292 [4.11], 380 [4.24]

547

605

n.d.

593

611

601

630

478

47

Ͻ1

n.d.

40

Ͻ1

8

Ͻ1

90

2

3.83

0.26

n.d.

2.99

0.13

1.26

Ͻ 0.1^[c]

3.12

0.11

0.13

B1

B2

the measured emission lifetimes (τ_F). They were signifi-

C1

cantly decreased for the compounds with the lower Φ_Fval-

ues. This prompts the assumption that several radiationless

deactivation processes must efficiently depopulate the S₁

state if additional donors (p-methoxy A2, B2, C2, p-dimeth-

ylamino A3, or even p-methyl C1) are present in the triaryl-

amine. More complicated behavior was observed for the de-

rivatives D1–D3. As a result of the weak overlap of the two

chromophores (thiazole and carbazole, phenothiazine, or

phenoxazine) the emission spectra are hypsochromically

shifted relative to those of the triarylamines A1–A3. The

emission bands for D2 and D3 each show several peaks,

most likely from transitions into different vibronic states of

the electronic ground state. Only one main emission band

can be observed for compound D1 in the polar solvent

CH₃CN, with a very high Φ_Fof 90%, coincidently with an

emission due to the carbazole moiety,^[29]whereas for D2

and D3 the emissions are very weak.

C2

D1

D2

D3

257 [4.72], 377 [4.42]^[b]484 sh, 507

240 [4.77], 373 [4.40] 455 sh, 470

Ͻ1

[a] λ_maxof emission after excitation in the maximum of the longest

wavelength absorption. [b] Measured in THF. [c] Below demand in-

terval, n.d.: not detected, sh: shoulder.

D1. This behavior has been explained in the literature in

terms of a conformational transformation from a planar

locally excited (LE) state to an intramolecular charge-trans-

fer (ICT) or, consequently, to a twisted intramolecular

charge-transfer (TICT) state.^[30]

In our case, the ground-state conformations of the dyes

are not planar, as is supported by the X-ray structures. The

energies of the S₀states are basically independent of the

solvents used and are only marginally decreased in polar

solvents, such as MeOH, leading to small hypsochromic

shifts in the absorption spectra for A2 (Table 3) and D1

(Table 4). According to the Franck–Condon principle, the

geometries of the LE states of S₁do not change during

excitation, leading to very similar energies for these transi-

tions for all solvents. LE states in nonpolar solvents are not

stabilized through interactions with solvent molecules, and

their conformations are predominately affected by the

ground state geometries [sometimes considered partial

charge-transfer (PCT) transitions].^[12,31]In contrast, the

charge-separated ICT states (excitation leads to a formal

Table 3. Spectroscopic behavior of A2 in different solvents.

Solvent

λ_abs[nm] [logε] λ_em[nm] Φ_F

Stokes

τ_F

[%]

shift [cm^–1] [ns]

Heptane

Dioxane

CHCl₃

THF

MeOH

CH₃CN

427 [4.585]

425 [4.441]

428 [4.422]

425 [4.485]

421 [4.456]

417 [4.434]

483, 512 63

3900

4700

5500

5400

6500

7400

2.6

3.8

4.0

3.8

0.1

530

561

552

581

603

59

40

43

Ͻ 1

1

Figure 2. Absorption spectra of the ligands at room temp.

In order to investigate the longest-wavelength absorp-

tions (and emissions) of the dyes in more detail, measure-

ments in different solvents were carried out for compounds

A2 and D1. If a simple π–π* transition takes place, both

the absorption and the emission maximum should be ba-

thochromically shifted with higher solvent polarities. Sur-

prisingly, it was shown for both compounds (for spectra see

Scheme S4 in the Supporting Information) that the absorp-

tion λ_maxvalues are slightly shifted toward shorter wave-

lengths with increasing solvent polarity, but the emission

maxima are shifted toward longer wavelengths. Conse-

quently, the Stokes shifts increased significantly from 2700

(heptane) to 7400 cm^–1(CH₃CN) for A2 and (less pro-

Table 4. Spectroscopic behavior of D1 in different solvents.

[a]

Solvent

λ_abs[nm] [logε] λ_em[nm]

Φ_FStokes

τ_F

[%] shift [cm^–1] [ns]

Heptane

Dioxane

CHCl₃

THF

CH₃CN

MeOH

387 [4.466]

385 [4.399]

387 [4.235]

384 [4.474]

380 [4.244]

456, 464

472

475

473

475

97 4300

100 4800

95 4800

100 4900

90 5300

81 5700

2.4

2.7

2.9

2.8

3.1

3.3

[a]

382

489

[a] Extinction coefficient could not be measured, due to poor solu-

nounced) from 4300 (heptane) to 5700 cm^–1(MeOH) for bility.

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cation radical at the arylamine and an anion radical at the separation, occur. It was found here that the S₁states are

acceptor) in polar solvents are extraordinarily stabilized by sufficiently stabilized by a polar solvent after planarization

solvent molecules. It is assumed that the ICT transitions are along the phenyl-1,3-thiazole bonds, which leads to slightly

facilitated by planarization along the phenyl-1,3-thiazole broadened and red-shifted emission bands, as observed in

bond during the vibrational cooling process (see quantum the UV/Vis measurements. It is noteworthy that no concen-

chemical section). This accounts for the energy gain due to tration dependencies of either the absorption or the emis-

electronic conjugation (mesomeric interactions) and, conse- sion spectra were observed, ruling out excimer formation.

quently, the bathochromic shifts of the emission maxima The bathochromic shifts of the emission are also ac-

and increased Stokes shifts in solvents with higher polarit- companied by decreased quantum yields and increased

ies. In order to clarify whether a TICT is likely to occur, we emission lifetimes (no clear trend of τ_Fwas observed for

used the Lippert–Mataga equation to estimate the change A1, unlike for D2). Two possible apparently conflictive as-

in the dipole moment between S₀and S₁.^[32]

sumptions can be made to explain this behavior: i) stabiliza-

tion of the excited state from polar solvent molecules might

raise the energy barrier (increased “activation” energy) for

the deactivation process (in polar solvents the CT state di-

rectly decays radiationlessly to the ground state by the back

CT reaction), leading to an increase in τ_F,^[31]or ii) various

nonradiative quenching processes might be accessible due

to additional conformational twists.^[30a]The first is consis-

tent with the τ_Fmeasured for D2. The second fact was de-

scribed and discussed in detail by Hu et al. for dyes bearing

additional dimethylamino groups on their arylamine donor

components (similar to A3).^[30b]It is assumed that the p-

dimethylamino (or for A2 the p-methoxy) groups give rise

to additional rotatable junctions and radiationless deactiva-

tion pathways if the charge-separated states are sufficiently

stabilized by polar solvent molecules. The latter explanation

would also be consistent with the significantly decreased Φ_F

and τ_Fvalues and the lack of emission of the triarylamines

in which the donor component is a p-dimethylamino, p-an-

isole, or even p-tolyl system rather than a phenyl group,

as described above. Additionally, it is noteworthy that no

wavelength dependency of τ_Fwas observed in the transient

emission spectroscopy for A2 and D1 in heptane, ruling out

second emissive states (dual fluorescence).

The Lippert–Mataga plots obtained are shown in Fig-

ure 3 and further details are summarized in Scheme S5 in

the the Supporting Information. It is known that protic sol-

vents (hydrogen bonding) and 1,4-dioxane do not yield re-

producible values,^[33]so they were excluded from the analy-

sis. The main uncertainty in this equation is the Onsager

cavity radius (a). As described in the pioneering work by

Lippert, a was calculated from the major axis of the mole-

cule (simplified as an ellipsoid) and the correction value 0.8

(according to a equal energetic sphere).^[34]The lengths of

the two molecules can both be derived from the X-ray

structures as 17 Å, and the cavity radii are then 13.6 Å. The

changes in dipole moment (Δμ = μ_E– μ_G) were calculated

to be 4.6 D for A2 and 2.8 D for D1. This is a strong hint

that a planar ICT (PICT) process is taking place rather

than a TICT. TICT states usually show significantly higher

changes in dipole moments (ΔμՆ 20 D) then those ob-

served here.^[35]

Electronic Absorption Spectra of the Ru^IIComplexes

The studied complexes each show several intense absorp-

tion bands due to the different possible electronic transi-

tions of Ru^IIpolypyridyl complexes. The spectra are shown

in Figure 4 and the data are summarized in Table 5. The

high-energy bands at 258 nm can be assigned to spin-al-

lowed metal-to-ligand charge-transfer (MLCT) transitions.

The intense ligand-centered (LC) π–π* transitions (ε Ͼ

65000 m^–1cm^–1) of the two dmbpy ligands are located at

285 nm. The high-energy LC transitions of the triaryl-

amines A1–C2 can be observed at approximately 325 nm,

and they are presumably superimposed with weak metal-

centered (MC) transitions.^[9a]

Figure 3. Lippert–Mataga plots for A1 (solid) and D2 (dashed).

Solvents: heptane, CHCl₃, THF, and MeOH, at room temp.

The broad absorption bands of the complexes in the vis-

ible region at 400–600 nm are due to MLCT transitions and

Quantum chemical calculations were carried out in order LC transitions of the thiazole-based ligands. It is not pos-

to evaluate the spatial distributions and energies of the sible to assign any distinct transition to these broad feature-

HOMO and LUMO orbitals and whether or not rotations less bands (ε Ͼ 28000 m^–1cm^–1) for the complexes Ru1–Ru4.

(TICTs) about either the phenyl-1,3-thiazole bonds or the For Ru5–Ru7 the different transitions are better resolved.

phenyl-amine bonds in the excited states, leading to charge The bands of the LC transitions for Ru5, Ru6, and Ru7 are

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Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

Ru5, and Ru6 are shown as representative examples in Fig-

ure 5. The unexpected behavior of Ru1–Ru4, although it vi-

olates Kasha’s rule, is not new (especially at a temperature

of 77 K) and has been described in the literature. Two pos-

sible mechanisms have been discussed as an explanation.

Firstly, two emitting ³MLCT states might be present, as

documented for, for example, heteroleptic Ru^IIcomplexes

containing two bpy and one 2,3-bis(2-pyridyl)pyrazine li-

gand^[37]or two bpy and different phenanthroline-based li-

gands^[38]or for acetylene-linked dinuclear Ru^IIcom-

plexes.^[39]This behavior can usually be assigned only by

time-resolved emission dynamics measurements, due to the

superimposition of the two emission bands. Secondly, one

3

emitting MLCT and one emitting ligand localized triplet

excited state (³IL) might be present, as extensively discussed

in a review by Wang et al.^[40]

Figure 4. Absorption spectra of the complexes measured in

CH₃CN at room temp.

Table 5. Spectroscopic properties of the complexes measured in

CH₃CN at room temp.

λ_abs[nm] [logε]

λ_em[nm]^[a]

Ru1

Ru2

Ru3

Ru4

Ru5

Ru6

Ru7

258 [4.47], 287 [4.92], 319 [4.59], 447 [4.48] 606, 689

258 [4.41], 286 [4.86], 324 [4.52], 457 [4.45] 619, 710

258 [4.54], 285 [4.99], 326 [4.64], 471 [4.53] 629, 727

258 [4.57], 285 [5.00], 328 [4.63], 473 [4.55] 627, 736

258 [4.52], 286 [4.85], 389 [4.29], 486 [4.00] 676

286 [4.82], 362 [4.29], 434 [4.24], 485 [4.05] 679

286 [4.82], 327 [4.47], 446 [4.12], 483 [4.05] 667

[a] Measured in ethanol/methanol (4:1, v/v) glass at 77 K after exci-

tation at 450 nm.

located at 390, 370, and 360 nm (broad), respectively. This

is in accordance with the absorption maxima of the free

ligands and leads to the conclusion that the longest-wave-

length ligand-based CT transitions are marginally affected

by complexation. The bands of the MLCT transitions to

the dmbpy ligand are located at approx. 435 nm. Unlike

Figure 5. Emission spectra of the heteroleptic Ru^IIcomplexes Ru1,

Ru2, Ru5, and Ru6 in ethanol/methanol (4:1, v/v) glass at 77 K.

In the cases of the complexes Ru1–Ru4 the two bands

those for Ru1–Ru4, the MLCT bands for the three com- are well resolved. Excitation at 400 nm leads in each case

plexes Ru5–Ru7 are acceptably resolved and each display to an increase in the intensity of the higher-energy emission

an additional shoulder located at 490 nm. This can be ex- at approx. 620 nm whereas excitation at the longest-wave-

plained by absorption into two different ¹MLCT states length absorption Ͼ500 nm leads to an increase in the

caused by the presence of two different ligands (the thi- lower-energy emission band at approx. 710 nm. Two dif-

azole-based and the dmbpy ligands).^[36]

ferent emitting states separated by a distinct energy barrier

In conclusion, as a result of the complexation of the ad- are populated in a manner dependent on the excitation

ditional light-absorbing ligands, leading to several intense wavelength, as was also supported by measurement of exci-

bands in the absorption spectra of the complexes superim- tation spectra. We assume that one of these emissive states

3

posed with the “classic” transitions, the complexes show en- is of MLCT character and is localized on a dmbpy–Ru

3

hanced light-harvesting efficiencies in the UV/Vis and vis- pair and that the other is the lower-energy MLCT state

3

ible regions of the solar spectrum.

localized on the thiazole–Ru pair and not a IL state. The

Unlike the very similar thiazole-based complexes de- latter assumption is also supported by measurement of the

scribed in the literature,^[8]the compounds do not show any emission spectra of the ligands. The locations and differ-

room temperature emission, so emission spectroscopy was ences of the maxima of/and between the ligands do not fit

carried out in EtOH/MeOH (4:1, v/v) glass at 77 K. The with either the short- or the long-wave emissions of the

measured complexes each exhibit emission between 606 and complexes. Nonetheless, unambiguous assignment will be

736 nm. For complexes Ru1–Ru4, with the triarylamine- the subject of further time-dependent measurements carried

based ligands, two different main emission bands can be out at 77 K. For the complexes Ru5–Ru7 only one broad

observed in each case, whereas for Ru5–Ru7 only one main emission band is apparent in each case. Presumably the en-

emission band is present. The emission spectra of Ru1, Ru2, ergies of the two possible ³MLCT states are too close, which

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L. González, R. Beckert et al.

FULL PAPER

would lead to superimposed emission bands, in contrast 56°), whereas the carbazole is completely planar. In general,

with the absorption spectra, in which the two different and consistently with the results of the solvent-dependent

¹MLCT transitions are well resolved.

UV/Vis measurements, the ground-state structures of A2

and D1 are basically invariant to solvation. The optimized

geometries of the S₁states show similarities to the ground-

state equilibrium structures. The reason is the π–π* nature

of the S₁states and the partial occupation of the LUMOs;

Quantum Chemical Calculations on A1 and D1

In order to gain more detailed insight into the structural the excited-state structures therefore show only minor shifts

and the spectroscopic properties of D1 and A2, density in bond lengths and angles. The thiazole-phenyl fragments,

functional theory (DFT) and its time-dependent variant however, are planarized (δ₂≈ –1° for A2 and 2° for D1) as

(TDDFT)^[41]were applied. The influence of solvation was

studied for an apolar (heptane, ε = 1.9113, n = 1.3878) and

Table 6. Calculated torsion angles and dipole moments of the

ground (S₀) and first excited (S₁) states of A2 and D₁.

a polar (MeOH, ε = 32.613, n = 1.3288) solvent with use

of a polarized continuum model.^[42]All calculations were

performed with the GAUSSIAN 09 program.^[43]The

ground-state equilibrium structures of A2 and D1 were op-

timized with a functional based on B3LYP^[44]and denoted

as B3LYP(35),^[45]combining 35% of exact exchange, 58.5%

of non-local B88^[46]exchange, and the LYP correlation

along with the 6–31G(d,p) double-ξ basis set.^[47]Harmonic

vibrational frequencies at the same level of theory con-

firmed that the obtained stationary points corresponded to

the minima of the potential energy surfaces (PESs). Excited

state properties, such as excitation energies, oscillator

strengths, and excited states geometries, were computed by

use of TDDFT and the same exchange-correlation func-

tional and basis set as for the ground states. The absorption

spectra in the Franck–Condon (FC) region were simulated

from the first ten singlet excited states. The S₁states were

optimized to obtain the emission energies. Furthermore,

PESs of the S₀and the S₁states of A2 were generated along

the dihedral angle δ₄(starting from the optimized S₁geome-

tries for heptane and MeOH), describing the internal tor-

sion of the donor group (for a graphic representation of

the angles see Scheme S6 in the Supporting Information) in

order to study the presence of a TICT state in the S₁state.

The PESs were calculated with rotation of the phenyl group

with respect to the bis(4-methoxyphenyl)-N-phenylaniline

moiety with a step size of 2° and at the same level of theory

as the previous calculations.

Geom. Solvent

δ₁[°] δ₂[°]

δ₃[°]

δ₄[°]

μ [D]

A2

S₀

heptane

MeOH

heptane

MeOH

0.32

0.34

–0.43 –1.19

–0.32 –1.58

–17.99

–19.01

30.61

28.09

39.11

32.68

31.56

29.67

38.30

32.10

1.37

1.55

1.58

2.62

S₁

D1

S₀

heptane

MeOH

heptane

MeOH

0.03

0.00

–0.22 –2.22

–0.27 –2.02

–16.65

–17.32

56.42

56.54

44.39

45.46

–0.09

–0.12

–0.09

0.00

5.38

6.12

4.64

5.22

S₁

The ground-state equilibrium geometries of both mole-

cules exhibit similar structural features, as shown in Table 6

and Figure 6. The trans isomer of the thiazole-pyridine

moiety is in each case energetically favored over the cis iso-

mer by approximately 0.3 eV in heptane and by 0.2 eV in

MeOH. As can be seen from the dihedral angles, the 4-

methoxy-1,3-thiazole fragment adopts a configuration al-

most planar to the pyridine. The angle δ₂describes the tor-

sion around the C–C bond between the thiazole fragment

and the donor moiety. It was found that δ₂is almost inde-

pendent both of the donor group [carbazole and bis(4-

methoxyphenyl)-N-phenylaniline] and of the solvent (for A2

δ₂= 18° in heptane and 19° in MeOH, whereas for D1 δ₂

= 17° in both solvents). The phenyl groups of the donor in

both dyes are twisted out of planarity due to steric hin-

drance. This twisting is in the range of ca. 30°, as illustrated

by the angles δ₃and δ₄in A2. The torsion of the carbazole

Figure 6. Potential curves, representations of the HOMO, LUMO,

and SOMO orbitals, and energies of the S₀and S₁states before

and after stabilization through either heptane or MeOH solvent

molecules and experimentally determined (upper values of the ab-

in the case of D1 is significantly more pronounced (δ₃= sorption and emission energies) and calculated energies.

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Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

a result of the bonding characters of the LUMOs in these tional is very well suited to describe the CT in these dyes in

positions. Additionally, the torsions in the donor groups are both polar and apolar solvents. Comparison of the oscil-

slightly changed. In the case of D1, the angle δ₃decreases lator strengths (f) with the experimentally observed ε values

by approximately 12 to 44° in heptane and to 45° in MeOH. shows that they are constant for A2 and D1 in both sol-

This supports the assumption that excitation leads to a vents. The trend of decreasing ε values with increasing sol-

PICT and not a TICT state.

vent polarity was also reproduced in the electronic structure

calculations.

The absorption spectra of the two dyes were calculated

by using FC geometries and the first ten singlet excited

states. Table 7 lists the vertical and adiabatic S₁excitations

for the compounds in both solvents. A summary of the pho-

tophysical properties and a representation of the orbitals of

the higher excited singlet states are given in Schemes S7–

S10 in the Supporting Information. The S₁state of D1 is

mainly characterized by a π–π* excitation with significant

CT participation predominantly from the carbazole donor

(HOMO) to the thiazole/pyridine acceptor (LUMO). The

ratio of this transition in heptane is 87% and it is slightly

enhanced to 89% in MeOH. An additional π–π* transition

of D1 from the HOMO–1 to the LUMO shows a significant

weight of 11% (heptane) and 9% (MeOH).

The adiabatic emission spectra were obtained by use of

the optimized geometries of the first excited singlet states.

The vertical emissions to the S₀were calculated by use of

these structures. The fluorescence energies, measured and

simulated, are listed in Table 7. The energies obtained are

in excellent agreement with the experimental findings. In

the case of A2, the divergences from the simulations to the

experimentally determined values are 0.00 (heptane) and

0.09 eV (MeOH), whereas for D1 they are –0.09 (MeOH)

and –0.08 eV (heptane). Relaxation in the S₁state leads to

a wave function with a significantly increased weight of the

HOMO/LUMO transition. A similar trend was observed

for the two chromophores. In the case of A2, the weight, the

CT nature of the S₁state, of the HOMO/LUMO transition

increases from 94 to 96%, whereas for D1 it rises from 87

Table 7. Calculated absorption/emission properties to/from the first (heptane) and 89% (MeOH) to 97% in both solvents. This

singlet excited states S₁. Main contributions to the wave function

can be explained in terms of the planarization in the dihe-

(weight), vertical (absorption) or adiabatic (emission) excitation en-

dral angle δ₂, which leads to a greater amount of CT char-

ergies (ΔE^ein eV and nm), oscillator strengths (f), and deviations

acter for this transition. The energy of the S₁state is sub-

stantially dependent on the solvent; the polar solvent stabi-

from experimental results (ΔΔE_Exp). H: HOMO, L: LUMO.

Solvent Transition Weight ΔE^e

f

ΔΔE_exp

[eV]

lizes the excited state considerably, by 0.43 and 0.50 eV for

A2 and D1, respectively, whereas the apolar solvent stabi-

lizes the S₁by only 0.27 and 0.33 eV, respectively. The sig-

nificant difference in the emission energies in heptane and

in MeOH can be explained in terms of the enhanced weight

of the HOMO/LUMO transition in the S₁wave function of

the planarized geometry.

[%]

[eV]

[nm]

A2

Abs. heptane HǞL

94

4

94

4

2.90

2.91

428

426

1.021 0.00

1.006 –0.04

H–1ǞL

MeOH HǞL

H–1ǞL

Em. heptane HǟL

MeOH HǟL

96

2.42

2.22

512

559

1.088 0.00

1.341 0.09

Further investigations were carried out in order to study

the likelihood of PICT or TICT states. The optimization in

the S₁states did not affect the arrangements of the donor

groups drastically (see δ₃and δ₄), leading to the conclusion

that no TICT state is observed in these dyes. However, the

TICT is not connected to a barrier-free evolution in the

excited state PES, as described in the literature, so a scan

of the S₀and the S₁states around the dihedral angle δ₄was

performed for the chromophore A2. The PESs obtained for

both solvents are depicted in Figure 7. The minima of the

ground states in both solvents are found at approx. 30 and

210°. These minima are separated by barriers of 1.87

(MeOH) and even 2.55 eV (heptane). The excited state

PESs show similar behavior: the minima here are located at

ca. 34 (MeOH) and 38° (heptane), values consistent with

the angles in the optimized S₁geometries of A2. The PESs

of the S₁state are almost parallel to those of the electronic

D1

Abs. heptane HǞL

87

11

89

9

97

3.24

3.28

382

378

0.986 0.04

0.995 0.03

H–1ǞL

MeOH HǞL

H–1ǞL

Em. heptane HǟL

MeOH HǟL

2.64

2.45

469

506

1.137 –0.08

1.306 –0.09

The HOMO–1/LUMO transition has a less pronounced

CT character than the HOMO/LUMO transition, because

the HOMO–1 is delocalized over the entire molecule. On

the other hand, the S₁state of A2 has a weighting of 94%

in favor of the HOMO/LUMO transition (heptane and

MeOH), whereas the HOMO–1/LUMO transition only has

a weighting of 4%.

In conclusion, the S₁state of A2 has a more pronounced ground state and no evidence for a minimum at 90° was

CT character than that of D1. The wavelength dependency found. In order to support this statement an additional op-

of the first absorption band on solvent polarities is in very timization procedure was performed with a starting torsion

good agreement with the experimental findings (Table 7, of δ₄of 90°. However, the obtained structure evolved to

Figure 6). The excitation energies of the S₁states are mar- that of the optimized geometry at the FC region. In sum-

ginally overestimated by 0.04 eV or underestimated by mary, the appearance of a TICT state in this chromophore

–0.04 eV, respectively, showing that the B3LYP(35) func- can be excluded from the quantum chemical calculations.

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FULL PAPER

influenced by the electronic properties of the arylamine. No

reactions of the radical cations or dications of the triaryl-

amines to form σ-dimers with additional discharging waves

at more negative potentials (at ca. –1.0 V) or carbazole de-

rivatives with additional discharging waves at 0.7 V were

detected under the conditions used.^[49]The half-wave poten-

tials (E_1/2) of the first oxidation are 0.23–0.26 V for the aryl-

amines A2, B2, and C2, with the strongly electron-donating

4-methoxyphenyl groups, 0.36 V for arylamine C1, with the

4-tolyl substituents, and 0.41 and 0.43 V for the tri-

phenylamines A1 and B1, respectively. For A3, with the very

strongly electron-donating dimethylamine groups on the

arylamine, the oxidation potential is significantly lowered

to –0.17 V. This is consistent with the observation that this

compound is already oxidized by atmospheric O₂in solu-

tion (CDCl₃, reduction of the cation radical with Zn in an

NMR tube; see Scheme S12 in the Supporting Infor-

mation). Additionally, A3 shows a reversible second oxi-

dation wave due to the formation of a doubly-charged

quinoid bication at 0.13 V,^[50]whereas all other triaryl-

amines exhibit second irreversible oxidation waves. The E_1/2

values for these second oxidations are located in a very

small range of 0.66–0.77 V and are independent of the triar-

ylamine components. The oxidation wave for the carbazole-

derived dye D1 is completely irreversible, due to the cou-

pling of the cation radical in para-position.^[51]The half-

wave potential (E_1/2) is 0.84 V, which is in accordance with

examples in the literature.^[52]For the phenothiazine-based

dye D2 the oxidation wave is reversible. The E_1/2is 0.31 V

vs. Fc/Fc⁺or 0.68 V vs. the reference electrode used (Ag/

AgCl, KCl, 0.1 m). This is consistent with the electronically

similar arylamine 10-phenylphenothiazine (0.88 V vs. Ag/

AgCl, sat. KCl) and with other phenothiazines reported in

the literature.^[53]

Figure 7. Scan around the dihedral angle δ₄for A2.

Electrochemical Properties of the Dyes

Electrochemical measurements were carried out with

CH₃CN as solvent, with platinum as counter, Ag/AgCl as

reference, and carbon as working electrodes, and with tetra-

butylammonium hexafluorophosphate (TBAPF₆) as the

conducting salt (scan rate 0.2 Vs^–1). Ferrocene was added

as the internal standard after every measurement. All values

discussed here are relative to the Fc/Fc⁺redox couple and

the data are listed in Table 8. The cyclic voltammetry (CV)

spectra of A1–A3 are depicted as representative examples

in Figure 8 (spectra of the other compounds can be found

in Scheme S11 in the Supporting Information). For these

types of compounds it is known that the first oxidations

occur at the triarylamine components, leading to the forma-

tion of positively charged cation species.^[48]Each dye there-

fore shows a first reversible oxidation wave that is strongly

Table 8. Electrochemical data for the donor–acceptor dyes and the Ru^IIcomplexes.

Dye

E_1/2,ox[V]^[a]

E_1/2,red[V]^[a]

E^HOMO[eV]^[b]

E^LUMO[eV]^[b]

ΔE^cv[eV]^[b]

E_g[eV]^[c]

opt

A1

A2

A3

B1

B2

C1

C2

D1

D2

D3

0.41, 0.73^[d]

0.23, 0.66^[d]

–0.17, 0.13

0.43, 0.77^[d]

0.26, 0.77^[d]

0.36, 0.76^[d]

0.25, 0.77^[d]

–2.19

–2.23

–2.25

–1.97

–1.98

–2.03

–2.05

–2.15

–2.11

–2,14

–5.19

–5.02

–4.56

–5.22

–5.06

–5.16

–5.05

–5.65

–5.09

–5.07

–2.74

–2.62

–2.96

–2.95

–2.90

–2.88

–2.78

–2.87

–2.74

2.45

2.28

1.94

2.26

2.11

2.26

2.17

2.87

2.22

2.33

2.67

2.57

2.42

2.54

2.44

2.51

2.49

2.85

2.93

2.92

[d]

0.84

0.31, 1.05^[d]

0.34, 1.00^[d]

Complex

Ru1

Ru2

Ru3

Ru4

Ru5

Ru6

Ru7

0.61, 0.83

0.36, 0.83

0.52, 0.90

0.37, 0.89

0.80^[d], 0.85

0.33, 0.81

0.34, 0.82

–1.58, –1.98, –2.21

–1.61, –1.97, –2.20

–1.42, –1.95, –2.14

–1.44, –1.96, –2.16

–1.53, –1.94, –2.18

–1.53, –1.97, –2.19

–1.52, –1.98, –2.19

–5.37

–5.16

–5.33

–5.14

–5.61

–5.13

–5.07

–3.34

–3.32

–3.52

–3.51

–3.41

–3.35

2.03

1.84

1.81

1.63

2.20

1.77

1.72

2.32

2.25

2.13

2.09

2.39

2.32

2.26

[a] Measurements were performed in CH₃CN containing TBAPF₆(0.1 m). The potentials are given vs. ferrocene/ferrocenium (Fc/Fc⁺).

[b] Determined by use of E^HOMO= –[(E_{onset, ox}– E_{onset, Fc/Fc+}) – 4.8] eV and E^LUMO= –[(E_{onset, red}– E_{onset, Fc/Fc+}) – 4.8] eV.^[59][c] Estimated

from the UV/Vis spectra at 10% of the maximum of the longest-wavelength absorption band on the low-energy side. [d] Derived from

differential pulse polarographic measurements; peaks are irreversible.

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Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

ered in energy after complexation. The Ru^II/Ru^IIIoxi-

dations are shifted slightly towards higher potentials for the

thiazoles with pyrimidine rather than pyridine acceptor

moieties, due to the more strongly electron-accepting prop-

erties of the pyrimidine, lowering the energies of the t_2gor-

bitals. The three reversible reduction waves are well resolved

in each case and are located at approx. –1.42 to –1.61, –2.0,

and –2.2 V. No clear trend is obvious, and assignment to

reduction of the ligand-located antibonding π*-orbitals of

either a thiazole or dmbpy ligand would be tentative. Ad-

ditionally, behavior similar to that of A3 was found for the

complex Ru4. The signals of the arylamine protons are ex-

1

tremely broadened in the H NMR spectra due to partial

formation of the radical cation in aerated CD₃CN solution

(see Scheme S14 in the Supporting Information). The sig-

nals became well resolved after the addition of Zn and re-

duction of the cation radical.

Figure 8. Cyclic voltammetry of dyes A1–A3. Experimental condi-

tions: 0.1 m TBAPF₆/CH₃CN solution, c ≈ 1ϫ10^–4m, room temp.,

scan rate 0.2 Vs^–1. RE: Ag/AgCl. WE: carbon. AE: platinum.

The first oxidation wave for D3 is also reversible and is

located at 0.34 V, consistently with an oxidation of the phen-

oxazine.^[54]The similar E_1/2values for D2 and D3 are in

accordance with the very similar electronic behavior of

phenothiazine and phenoxazine.^[55]Additionally, D2 and

D3 each show a second irreversible oxidation wave located

at approx. 1.0 V.

All dyes show reversible first reductions. The E_1/2values

of the first reduction are slightly dependent on the ac-

ceptors and not on the arylamines. The redox potentials

vary from –2.19 to –2.25 V for the dyes with the pyridine

acceptor (A1–A3). They are shifted to more positive poten-

tials (the reduction is facilitated) when the electron de-

ficiency of the acceptor is increased. The reductions occur

at ca. –1.97 V for the dyes B1 and B2 and at –2.03 and

–2.05 V for C1 and C2, respectively. It can therefore be as-

sumed that the reductions each take place at the acceptor,

leading to a negatively charged azabenzene, as described in

the literature.^[56]Irreversible reduction due to proton ab-

straction of the radical anion from residual water, to form

a free radical that would be immediately reduced at the po-

tential of its formation,^[57]was not observed (the measure-

ments were carried out under water-free conditions).

Figure 9. Cyclic voltammetry of Ru1, Ru2, Ru5, and Ru6. Experi-

mental conditions: 0.1 m TBAPF₆/CH₃CN solution, c ≈ 5ϫ10^–5m,

room temp., scan rate 0.2 Vs^–1. RE: Ag/AgCl. WE: carbon. AE:

platinum.

Conclusions

A series of donor–acceptor dyes featuring different aryl-

amines moieties as electron donating units have been suc-

cessfully prepared by a Buchwald–Hartwig cross-coupling

approach. Different azaheterocycles were employed as ac-

Electrochemical Properties of the Ru^IIComplexes

The complexes Ru1–Ru7 were characterized by CV under ceptor moieties. The spectroscopic and electrochemical

the same conditions as discussed above. The electrochemi- properties, as well as the HOMO/LUMO gaps, of these di-

cal results are presented in Table 8 and the spectra of Ru1, polar compounds are significantly affected by the different

Ru2, Ru5, and Ru6 are given as representative examples in donors used. The natures of the intramolecular charge-

Figure 9 (spectra of the other compounds can be found in transfer states were identified as PICT processes for one of

Scheme S13 in the Supporting Information). They each the triarylamine-based (A2) and one of the tricyclic aryl-

show two reversible oxidation waves (except Ru5) and three amine dyes (D1) with the aid of spectroscopic methods and

reversible reduction waves. The former can be attributed to quantum chemical calculations. Furthermore, the absorp-

oxidation of the arylamines and of the Ru^IIruthenium cen- tion and emission spectra and energies of the transitions,

ter to Ru^{III [58]}

The oxidations of the arylamines of the co- oscillator strengths, and weights were calculated for the op-

.

ordinated ligands are marginally shifted towards higher po- timized ground- and excited-state structures of these two

tentials relative to the free dyes, confirming the assumption dyes. The synthesis and characterization of the correspond-

that the corresponding ligand-centered π-orbitals are low- ing Ru^IIpolypyridyl complexes of seven of the dyes/ligands

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L. González, R. Beckert et al.

FULL PAPER

Fourier synthesis and refined isotropically. The hydrogen atoms of

A1 and A1m were included at calculated positions with fixed ther-

mal parameters. All non-hydrogen atoms were refined anisotropi-

cally.^[62]Crystallographic data and structure solution and refine-

ment details are summarized in Table 1. XP (SIEMENS Analytical

X-ray Instruments, Inc.) was used for structure representations.

CCDC-876513 (for A1), -879865 (for A1m), -876514 (for B1),

-876515 (for C1), and -876516 (for D2) contain the supplementary

crystallographic data for this paper. These data can be obtained

free of charge from The Cambridge Crystallographic Data Centre

are reported. Each complex shows an enhanced absorption

in the visible part of the UV/Vis spectrum, due to ad-

ditional LC and MLCT transitions originating from 4-

methoxy-1,3-thiazole ligands. All compounds were unam-

biguously identified by NMR spectroscopy, elemental

analysis, mass spectrometry, and MALDI-TOF measure-

ments. Further research into the presented dyes will focus

on the synthesis of the analogous Ru(dcbpy)(L)(SCN)₂

(dcbpy = 2,2Ј-bipyridine-4,4Ј-dicarboxylic acid) for DSSC

applications. The dyes will also be tested with regard to via www.ccdc.cam.ac.uk/data_request/cif.

their two-photon excitation behavior, which could open

doorways to several new applications such as two-photon

excitation microscopy. First tests established this ability for

a dye with a methoxy donor group similar to A1.

5-(4-Nitrophenyl)-2-(pyridin-2-yl)thiazol-4-ol (1a): A suspension of

pyridine-2-carbothioamide (1.00 g, 7.24 mmol), ethyl 2-bromo-2-

(4-nitrophenyl)acetate (2.50 g, 8.68 mmol, 1.2 equiv.), and pyridine

(8.58 g, 10.8 mmol, 2 equiv.) in toluene (100 mL) was stirred under

reflux for six hours and a yellow fluffy precipitate was produced.

After the system had cooled to room temperature, the precipitate

was filtered off, washed with EtOH and Et₂O, and dried in vacuo;

Experimental Section

1

yield 3.05 g (10.2 mmol, 71%). H NMR (400 MHz, [D₆]DMSO):

Ethyl 2-bromo-2-(4-nitrophenyl)acetate and 5-(4-bromophenyl)-2-

(pyridin-2-yl)thiazol-4-ol (1d) were synthesized by literature pro-

cedures.^[18–19]Pyridine-2-carbothioamide, pyrazine-2-carbothioam-

ide, and pyrimidine-2-carbothioamide are commercially available

or can be prepared from the corresponding nitriles and H₂S.

Pd(dba)₂and P(tBu)₃(1 m solution in toluene) were purchased

from Sigma–Aldrich. Ru(dmbpy)₂Cl₂was prepared with use of mi-

crowave irradiation by a literature procedure and was readily puri-

fied by column chromatography (Al₂O₃activity 10, CH₂Cl₂to

CH₂Cl₂/MeOH 50:1 as eluent).^[60]All other chemicals used were

reagent grade and purchased from Sigma–Aldrich or Acros. Sol-

vents were purified by standard procedures. Solvents for UV/Vis,

emission spectroscopy, and CV were of analytical grade and bought

from Sigma–Aldrich. ¹H and ¹³C NMR and the corresponding cor-

relation spectra were recorded with Bruker AC-250 (250 MHz) and

AC-400 (400 MHz) spectrometers. Chemical shifts (δ) are given rel-

ative to solvents. UV/Vis data for the compounds were collected

with a Lambda 19 instrument from Perkin–Elmer and emission

spectra were measured with a Jasco FP 6500 instrument. Quantum

δ = 12.44 (s, 1 H), 8.65 (d, J = 4.4 Hz, 1 H), 8.24 (d, J = 8.9 Hz, 2

H), 8.07–7.94 (m, 4 H), 7.52 (t, J = 5.5 Hz, 1 H) ppm. ¹³C NMR

(100 MHz, [D₆]DMSO): 164.0, 161.6, 150.4, 150.0, 145.0, 139.5,

138.4, 126.7, 126.0, 124.7, 119.3, 108.8 ppm. UV/Vis (DMSO): λ_max

[log(ε/m^–1cm^–1)] = 414 [4.40], 609 [3.64] nm. MS (EI): m/z (%) =

299 (100) [M]⁺, 105 (30). C₁₄H₉N₃O₃S (299.30): calcd. C 56.18, H

3.03, N 14.04, S 10.71; found C 56.17, H 3.13, N 13.99, S 10.60.

5-(4-Nitrophenyl)-2-(pyrazin-2-yl)thiazol-4-ol (1b): A solution of

pyrazine-2-carbothioamide (3.75 g, 26.9 mmol), ethyl 2-bromo-2-

(4-nitrophenyl)acetate (9.30 g, 32.3 mmol, 1.2 equiv.), and pyridine

(4.25 g, 53.8 mmol, 2 equiv.) in DMF (100 mL) was stirred at 50 °C

for 24 h and a yellow precipitate was produced. After the system

had cooled to room temperature, the mixture was diluted with

EtOH (100 mL). The precipitate was filtered off, washed with

EtOH and Et₂O, and dried in vacuo; yield 2.95 g (9.83 mmol,

1

37%). H NMR (250 MHz, [D₆]DMSO): δ = 12.30 (s, J = 5.9 Hz,

1 H), 9.22 (s, 1 H), 8.73 (d, J = 13.4 Hz, 2 H), 8.25 (d, J = 7.9 Hz,

2 H), 8.04 (d, J = 8.9 Hz, 2 H) ppm. ¹³C NMR (63 MHz, [D₆]-

DMSO): δ = 160.91, 160.34, 145.64, 144.99, 144.85, 144.23, 139.75,

138.20, 126.29, 123.75, 109.40 ppm. UV/Vis (DMSO): λ_max[log(ε/

yields were determined relative to fluorescein (NaOH, 0.1n, Φ_F

=

0.82) with refractive indices n(NaOH) = 1.334 and n(CH₃CN) =

1.344.^[35d]Elemental analysis was carried out with a Leco CHNS-

932 instrument. Mass spectra were measured either with a Finnigan

MAT SSQ 710 (EI) or a MAZ 95 XL (FAB) system. MALDI-TOF

MS was performed with a Bruker Ultraflex TOF/TOF mass spec-

trometer fitted with a 337 nm nitrogen laser operated in the re-

flectron mode with an acceleration voltage of 25 kV. Dithranol was

used as matrix. Electrochemical measurements were performed

with a Metrohm Autolab PGSTAT30 potentiostat with a standard

three-electrode configuration. The experiments were carried out in

degassed solvents containing Bu₄NPF₆salt (0.1 m). At the end of

each measurement ferrocene (Fc/Fc⁺) was added as an internal

standard. TLC materials were from Merck (Polygram SIL G/

UV254, aluminum oxide 60 F254). The material for column

chromatography was also obtained from Merck (silica gel 60).

m

^–1cm^–1)] = 419 [4.20] nm. MS (EI): m/z (%) = 300 (60) [M]⁺, 106

(100). C₁₃H₈N₄O₃S (300.29): calcd. C 52.00, H 2.69, N 18.66, S

10.68; found C 52.24, H 2.71, N 18.34, S 10.52.

5-(4-Nitrophenyl)-2-(pyrimidin-2-yl)thiazol-4-ol (1c): A mixture of

pyrimidine-2-carbothioamide (2.60 g, 18.7 mmol), ethyl 2-bromo-

2-(4-nitrophenyl)acetate (6.46 g, 22.4 mmol, 1.2 equiv.), and trieth-

ylamine (10 mL) was stirred at room temperature. The suspension

solidified after a few minutes and was allowed to react for 24 h.

The mixture was suspended in EtOH (100 mL). The precipitate was

filtered off, washed with EtOH and Et₂O, and dried in vacuo; yield

1.12 g (3.73 mmol, 18%). ¹H NMR (400 MHz, [D₆]DMSO): δ =

12.34 (s, 1 H), 8.92 (d, J = 4.8 Hz, 2 H), 8.25 (d, J = 8.9 Hz, 2 H),

8.05 (d, J = 8.9 Hz, 2 H), 7.55 (t, J = 4.8 Hz, 1 H) ppm. ¹³C NMR

(100 MHz, [D₆]DMSO): δ = 161.28, 160.61, 157.97, 157.67, 144.85,

138.35, 126.32, 123.76, 121.20, 109.89 ppm. UV/Vis (DMSO): λ_max

[log(ε/m^–1cm^–1)] = 412 [4.10] nm. MS (EI): m/z (%) = 300 (60) [M]⁺,

106 (100). C₁₃H₈N₄O₃S (300.29): calcd. C 52.00, H 2.69, N 18.66, S

10.68; found C 51.64, H 2.81, N 18.54, S 10.72.

Structure Determinations: The intensity data for the compounds

were collected with a Nonius KappaCCD diffractometer and

use of graphite-monochromated Mo-K_αradiation. Data were

corrected for Lorentz and polarization effects but not for absorp-

tion effects.^[61]The structures were solved by direct methods

(SHELXS)^[62]and refined by full-matrix, least-squares techniques

General procedure, illustrated for 2a, for the etherification of the

4-hydroxy-1,3-thiazoles:

against F_o(SHELXL-97).^[62]The hydrogen atoms of B1 (without

4-Methoxy-5-(4-nitrophenyl)-2-(pyridin-2-yl)thiazole (2a): A mix-

ture of 5-(4-nitrophenyl)-2-(pyridin-2-yl)thiazol-4-ol (4.00 g,

13.4 mmol) and K₂CO₃(2.22 g, 16.1 mmol, 1.2 equiv.) in DMSO

2

the methyl group hydrogen atoms at C4), C1, and D2 and the

amine hydrogen atom at N3 of A1m were located by difference

12

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Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

(100 mL) was stirred for 30 min, followed by the addition of CH₃I

(dd, J = 4.8, 7.5 Hz, 1 H), 7.58–7.60 (m, 2 H), 7.74 (dd, J = 7.7,

(2.09 g, 14.7 mmol, 1.1 equiv.). The deep blue mixture was stirred 7.8 Hz, 1 H), 8.10 (d, J = 8.0 Hz, 1 H), 8.57 (d, J = 4.9 Hz, 1

for 24 h at room temperature. The solution was poured into H₂O

(300 mL) and extracted with CHCl₃(3ϫ100 mL). The combined

organic phases were additionally washed with H₂O (3ϫ100 mL) to

remove the DMSO, dried with MgSO₄, and concentrated in vacuo

to give a brown oil, which was further purified by a short gel fil-

tration (silica, CHCl₃to CHCl₃/EtOAc 1:1) to yield the product as

an orange solid; yield 2.86 g (9.11 mmol, 68%). ¹H NMR

(250 MHz, CDCl₃): δ = 8.61 (d, J = 4.2 Hz, 1 H), 8.26–8.18 (m, 2

H), 8.15 (d, J = 7.9 Hz, 1 H), 7.96–7.87 (m, 2 H), 7.81 (td, J = 7.7,

1.7 Hz, 1 H), 7.35 (ddd, J = 7.5, 4.8, 1.1 Hz, 1 H), 4.25 (s, 3

H) ppm. ¹³C NMR (63 MHz, CDCl₃): δ = 163.44, 161.57, 150.65,

149.60, 145.46, 138.63, 137.03, 126.67, 124.85, 124.12, 119.31,

111.62, 57.89 ppm. UV/Vis (CH₂Cl₂): λ_max[log(ε/m^–1cm^–1)] = 226

[4.05], 399 [4.49] nm. MS (EI): m/z (%) = 313 (100) [M]⁺, 166 (45).

C₁₅H₁₁N₃O₃S (313.33): calcd. C 57.70, H 3.54, N 13.32, S 10.23;

found C 57.70, H 3.86, N 13.32, S 10.19.

H) ppm. ¹³C NMR (63 MHz, CDCl₃): δ = 158.63, 158.38, 151.51,

149.37, 145.53, 136.81, 128.28, 123.72, 121.91, 118.77, 115.42,

115.19, 57.58 ppm. UV/Vis (CH₂Cl₂): λ_max[log(ε/m^–1cm^–1)] = 224

[4.01], 277 [3.83], 399 [4.19] nm. MS (EI): m/z (%) = 283 (100)

[M]⁺, 136 (60). C₁₅H₁₃N₃OS (283.35): calcd. C 63.58, H 4.62, N

14.83, S 11.32; found C 63.20, H 4.57, N 14.60, S 11.19.

4-[4-Methoxy-2-(pyrazin-2-yl)thiazol-5-yl]aniline (3b): Yield 89%.

¹H NMR (300 MHz, CDCl₃): δ = 9.32 (d, J = 1.1 Hz, 1 H), 8.51–

8.46 (m, 2 H), 7.58 (d, J = 8.6 Hz, 2 H), 6.70 (d, J = 8.6 Hz, 2 H),

4.17 (s, 3 H), 3.74 (s, 2 H) ppm. ¹³C NMR (75 MHz, CDCl₃): δ =

159.20, 155.24, 147.11, 146.00, 144.16, 143.85, 140.96, 128.52,

121.51, 117.00, 115.25, 57.80 ppm. UV/Vis (CH₃CN): λ_max[log(ε/

m

^–1cm^–1)] = 259 [4.02], 278 [3.98], 317 [3.68], 420 [4.31] nm. MS

(EI): m/z (%) = 284 (100) [M]⁺, 136 (80). C₁₄H₁₂N₄OS (284.34):

calcd. C 59.14, H 4.25, N 19.70, S 11.03; found C 58.84, H 4.18,

N 19.52, S 11.08.

4-Methoxy-5-(4-nitrophenyl)-2-(pyrazin-2-yl)thiazole (2b): The pro-

cedure was similar to that used for 2a, with purification by

recrystallization from EtOH/CHCl₃with slow evaporation of the

4-[4-Methoxy-2-(pyrimidin-2-yl)thiazol-5-yl]aniline (3c): Yield 87%.

¹H NMR (250 MHz, CDCl₃): δ = 8.79 (d, J = 4.9 Hz, 2 H), 7.60

(d, J = 8.6 Hz, 2 H), 7.20 (t, J = 4.8 Hz, 1 H), 6.69 (d, J = 8.6 Hz,

2 H), 4.22 (s, 3 H), 3.78 (s, 2 H) ppm. ¹³C NMR (63 MHz, CDCl₃):

δ = 159.84, 159.80, 157.84, 155.73, 146.13, 128.73, 128.67, 121.60,

119.97, 115.30, 58.10 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 223 [4.16], 243 [3.99], 275 [3.98], 411 [4.33] nm. MS (EI): m/z (%)

= 284 (100) [M]⁺, 136 (80). C₁₄H₁₂N₄OS (284.34): calcd. C 59.14,

H 4.25, N 19.70, S 11.03; found C 59.30, H 4.33, N 19.47, S 11.03.

1

CHCl₃to give the product as yellow needles; yield 45%. H NMR

(250 MHz, CDCl₃): δ = 9.38 (d, J = 1.4 Hz, 1 H), 8.62 (d, J =

2.5 Hz, 1 H), 8.58–8.53 (m, 1 H), 8.28–8.19 (m, 2 H), 7.98–7.88 (m,

2 H), 4.28 (s, 3 H) ppm. ¹³C NMR (63 MHz, CDCl₃): δ = 162.00,

160.55, 146.31, 145.97, 145.53, 144.14, 141.26, 138.22, 127.08,

124.32, 112.98, 58.27 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 245 [397], 403 [4.46] nm. MS (EI): m/z (%) = 314 (100) [M]⁺, 166

(30). C₁₄H₁₀N₄O₃S (314.32): calcd. C 53.50, H 3.21, N 17.82, S

10.20; found C 53.18, H 3.12, N 18.08, S 10.13.

General procedure, illustrated for A1, for the Buchwald–Hartwig

couplings of the arylamines with the corresponding aryl halides:

4-[4-Methoxy-2-(pyridin-2-yl)thiazol-5-yl]-N,N-diphenylaniline (A1):

Bromobenzene (345 mg, 2.2 mmol, 2.2 equiv.) and KOtBu (246 mg,

2.2 mmol, 2.2 equiv.) were added under nitrogen to a solution of

4-[4-methoxy-2-(pyridin-2-yl)thiazol-5-yl]aniline (238 mg, 1 mmol)

in dry toluene (20 mL). The mixture was additionally purged thor-

oughly with nitrogen for 30 min, followed by the addition of

Pd(dba)₂(23 mg, 0.04 mmol, 4 mol-%) and P(tBu)₃(80 μL of a

1.0 m solution in toluene, 0.08 mmol, 8 mol-%). The mixture was

heated to reflux (6 to 24 h) until no starting material was left as

indicated by TLC (silica, CHCl₃, R_fstarting material = 0.1, R_f

monosubstituted product = 0.6, R_fdisubstituted product = 0.8).

After the reaction was complete, the mixture was allowed to cool

down to room temp. and the solvent was evaporated in vacuo. Puri-

fication by column or flash chromatography yielded the product as

a yellow solid. To obtain crystals suitable for X-ray crystallography,

the product was recrystallized from EtOH/CHCl₃to afford the

compound as yellow block crystals; yield 331 mg (0.76 mmol,

76%). ¹H NMR (250 MHz, CDCl₃): δ = 8.59 (d, J = 4.3 Hz, 1 H),

8.12 (d, J = 7.9 Hz, 1 H), 7.77 (td, J = 7.7, 1.7 Hz, 1 H), 7.66 (d,

J = 8.7 Hz, 2 H), 7.34–7.22 (m, 5 H), 7.19–6.95 (m, 8 H), 4.18 (s,

3 H) ppm. ¹³C NMR (63 MHz, CDCl₃): δ = 159.23, 159.24, 151.36,

149.40, 147.47, 146.51, 136.82, 129.26, 127.74, 125.61, 124.51,

123.89, 123.51, 123.03, 118.86, 114.55, 57.58 ppm. UV/Vis

(CHCl₃): λ_max[log(ε/m^–1cm^–1)] = 306 [4.33], 417 [4.44] nm. MS

(EI): m/z (%) = 435 (100) [M]⁺, 288 (55). C₂₇H₂₁N₃OS (435.54):

calcd. C 74.46, H 4.86, N 9.65, S 7.36; found C 74.25, H 4.71, N

9.40, S 7.16.

4-Methoxy-5-(4-nitrophenyl)-2-(pyrimidin-2-yl)thiazole (2c): Yield

44%. H NMR (300 MHz, CDCl₃): δ = 8.84 (d, J = 4.5 Hz, 2 H),

1

8.19 (d, J = 8.3 Hz, 2 H), 7.91 (d, J = 8.3 Hz, 2 H), 7.30 (t, J =

4.5 Hz, 1 H), 4.30 (s, 3 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

= 162.16, 160.63, 158.91, 157.76, 145.79, 137.95, 127.00, 124.06,

120.78, 113.95, 58.29 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 232 [4.03], 396 [4.41] nm. MS (EI): m/z (%) = 314 (100) [M]⁺,

166 (20). C₁₄H₁₀N₄O₃S (314.32): calcd. C 53.50, H 3.21, N 17.82,

S 10.20; found C 53.58, H 3.17, N 17.99, S 10.18.

5-(4-Bromophenyl)-4-methoxy-2-(pyridin-2-yl)thiazole (2d): Yield

1

77%. H NMR (250 MHz, CDCl₃): δ = 9.15–9.10 (m, 1 H), 8.64

(d, J = 4.8 Hz, 1 H), 8.20–8.15 (m, 1 H), 7.61 (dd, J = 6.8 Hz, 2

H), 7.51 (dd, J = 6.8 Hz, 2 H), 7.39–7.34 (m, 1 H), 4.19 (s, 3

H) ppm. ¹³C NMR (63 MHz, CDCl₃): δ = 160.01, 156.92, 150.67,

146.95, 132.63, 131.72, 130.21, 129.42, 128.26, 123.68, 120.43,

110.9, 57.96 ppm. MS (EI): m/z (%) = 346 (45) [M]⁺, 200 (100),

120 (67). C₁₅H₁₁BrN₂OS (347.23): calcd. C 51.89, H 3.19, N 8.07,

S 9.23; found C 51.64, H 3.23, N 8.24, S 9.42.

General procedure, illustrated for 3a, for the reduction of the nitro

groups to afford the corresponding aniline derivatives:

4-[4-Methoxy-2-(pyridin-2-yl)thiazol-5-yl]aniline (3a): A suspension

of 4-methoxy-5-(4-nitrophenyl)-2-(pyridin-2-yl)thiazole (2.66 g,

8.50 mmol) in EtOH (100 mL) was heated to 50 °C. Freshly pre-

pared Raney nickel (catalytic amounts) and N₂H₅OH (several por-

tions approx. 2 equiv. until no starting material was left as indicated

by TLC) were added to the solution. The reaction mixture was

filtered through a frit on which a silica bed (2 cm thick) had been

applied to remove the Raney nickel. The silica bed was washed

Monosubstituted Product of A1. 4-[4-Methoxy-2-(pyridin-2-yl)thi-

azol-5-yl]-N-phenylaniline (A1m): If the reaction to A1 was aborted

with EtOH/CHCl₃1:1. The product was purified by gradient gel earlier (t Ͼ 2 h), the monosubstituted product was obtained in 70%

filtration (silica, CHCl₃to CHCl₃/EtOAc 1:2) to yield the amine as

a yellow solid; yield 2.16 g (7.62 mmol, 90%). ¹H NMR (250 MHz,

CDCl₃): δ = 3.76 (s, 2 H), 4.15 (s, 3 H), 6.68–6.72 (m, 2 H), 7.24

yield after purification (column chromatography, silica, CHCl₃).

Recrystallization from EtOH/CHCl₃yielded the compound as

orange needles suitable for X-ray structure analysis. ¹H NMR

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L. González, R. Beckert et al.

FULL PAPER

(250 MHz, CDCl₃): δ = 8.58 (d, J = 4.8 Hz, 1 H), 8.12 (d, J =

8.0 Hz, 1 H), 7.77 (td, J = 7.8, 1.7 Hz, 1 H), 7.69 (d, J = 8.7 Hz, 2

H), 7.36–7.22 (m, 3 H), 7.16–7.03 (m, 4 H), 6.96 (t, J = 7.3 Hz, 1

8.50–8.48 (m, 1 H), 7.61–7.55 (m, 2 H), 7.10–7.04 (m, 4 H), 6.95–

6.90 (m, 2 H), 6.87–6.81 (m, 4 H), 4.17 (s, 3 H), 3.80 (s, 6 H) ppm.

¹³C NMR (100 MHz, CDCl₃): δ = 159.56, 156.25, 155.61, 148.09,

H), 5.79 (s, 1 H), 4.18 (s, 3 H) ppm. ¹³C NMR (63 MHz, CDCl₃): 147.11, 144.26, 143.91, 141.04, 140.63, 127.95, 126.94, 123.04,

δ = 158.99, 158.93, 151.45, 149.40, 142.58, 142.07, 136.82, 129.38, 120.26, 116.70, 114.90, 57.86, 55.64 ppm. UV/Vis (CH₃CN): λ_max

128.11, 124.14, 123.82, 121.37, 118.84, 118.25, 117.45, 114.91,

57.60 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 229 [4.17],

295 [4.21], 405 [4.44] nm. MS (EI): m/z (%) = 359 (100) [M]⁺, 212

(80). C₂₁H₁₇N₃OS (359.44): calcd. C 70.17, H 4.77, N 11.69, S 8.92;

found C 70.29, H 4.72, N 11.67, S 8.95.

[log(ε/m^–1cm^–1)] = 240 [4.42], 302 [4.40], 439 [4.46] nm. MS (micro-

ESI): m/z = 519.1 [M + Na]⁺. C₂₈H₂₄N₄O₃S (496.58): calcd. C

67.72, H 4.87, N 11.28, S 6.46; found C 67.39, H 4.88, N 11.16, S

6.15.

4-[4-Methoxy-2-(pyrimidin-2-yl)thiazol-5-yl]-N,N-di-p-tolylaniline

(C1): Yield 85%. ¹H NMR (400 MHz, CDCl₃): δ = 8.83 (d, J =

4.9 Hz, 1 H), 7.65 (d, J = 8.8 Hz, 1 H), 7.24 (t, J = 4.9 Hz, 1 H),

7.13–7.07 (m, 2 H), 7.07–7.00 (m, 3 H), 4.26 (s, 2 H), 2.34 (s, 3

H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 160.23, 159.71, 157.85,

156.29, 147.69, 145.01, 133.13, 130.10, 128.08, 125.10, 124.04,

122.10, 120.06, 117.89, 58.11, 20.98 ppm. UV/Vis (CH₃CN): λ_max

[log(ε/m^–1cm^–1)] = 233 [4.21], 302 [4.32], 426 [4.36] nm. MS (EI):

m/z (%) = 464 (30) [M]⁺, 316 (100). HRMS (micro-ESI):

C₂₈H₂₄N₄OS: 464.1671; found 464.1665. C₂₈H₂₄N₄OS (464.58):

calcd. C 72.39, H 5.21, N 12.06, S 6.90; found C 72.30, H 5.33, N

12.47, S 6.03.

4-Methoxy-N-{4-[4-methoxy-2-(pyridin-2-yl)thiazol-5-yl]phenyl}-

1

N-(4-methoxyphenyl)aniline (A2): Yield 90%. H NMR (400 MHz,

CDCl₃): δ = 8.57 (d, J = 4.7 Hz, 1 H), 8.10 (d, J = 8.0 Hz, 1 H),

7.75 (td, J = 7.8, 1.7 Hz, 1 H), 7.63–7.56 (m, 2 H), 7.29–7.22 (m,

1 H), 7.11–7.03 (m, 4 H), 6.93 (d, J = 8.8 Hz, 2 H), 6.88–6.81 (m,

4 H), 4.15 (s, 3 H), 3.80 (s, 6 H) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 159.17, 158.96, 156.21, 151.70, 149.56, 147.77, 140.89,

136.93, 127.85, 126.84, 123.90, 123.80, 120.61, 118.99, 115.31,

114.94, 57.70, 55.67 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 299 [4.35], 417 [4.43] nm. HRMS (ESI): calcd. 518.1514

[C₂₉H₂₅N₃O₃S + Na]⁺; found 518.1517.

N¹-[4-(Dimethylamino)phenyl]-N¹-{4-[4-methoxy-2-(pyridin-2-yl)-

4-Methoxy-N-{4-[4-methoxy-2-(pyrimidin-2-yl)thiazol-5-yl]phen-

yl}-N-(4-methoxyphenyl)aniline (C2): Yield 90 %. ¹H NMR

(250 MHz, CDCl₃): δ = 8.80 (d, J = 4.9 Hz, 2 H), 7.61 (d, J =

8.8 Hz, 2 H), 7.25–7.17 (m, 1 H), 7.13–7.03 (m, 4 H), 6.93 (d, J =

8.8 Hz, 2 H), 6.88–6.79 (m, 4 H), 4.23 (s, 3 H), 3.80 (s, 6 H) ppm.

¹³C NMR (63 MHz, CDCl₃): δ = 160.09, 159.71, 157.82, 156.25,

155.99, 148.20, 140.60, 128.07, 126.95, 122.99, 120.21, 119.99,

118.08, 114.89, 58.08, 55.62 ppm. UV/Vis (CH₃CN): λ_max[log(ε/

thiazol-5-yl]phenyl}-N⁴,N⁴-dimethylbenzene-1,4-diamine (A3): Yield

1

86%. H NMR (400 MHz, CDCl₃): δ = 8.56 (d, J = 4.5 Hz, 1 H),

8.10 (d, J = 7.9 Hz, 1 H), 7.74 (td, J = 7.8, 1.6 Hz, 1 H), 7.56 (d,

J = 8.8 Hz, 2 H), 7.24 (dd, J = 7.0, 5.4 Hz, 1 H), 7.07 (d, J =

8.9 Hz, 4 H), 6.90 (d, J = 8.8 Hz, 2 H), 6.69 (d, J = 8.9 Hz, 4 H),

4.16 (s, 3 H), 2.93 (s, 12 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ

= 158.94, 158.39, 151.78, 149.52, 148.42, 147.63, 137.48, 136.88,

127.74, 127.03, 123.74, 122.34, 119.16, 118.91, 115.87, 113.81,

57.67, 41.10 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 247

[4.30], 206 [4.80], 307 [4.43], 433 [4.36] nm. MS (EI): m/z (%) = 521

(100) [M]⁺, 374 (80). C₃₁H₃₁N₅OS: C 71.37, H 5.99, N 13.42, S

6.15; found C 71.23, H 4.66, N 13.17, S 5.77.

m

^–1cm^–1)] = 231 [4.36], 301 [4.38], 433 [4.46] nm. MS (EI): m/z (%)

= 496 (100) [M]⁺, 348 (90). HRMS (micro-ESI): C₂₈H₂₄N₄O₃S:

496.1569; found 496.1568. C₂₈H₂₄N₄O₃S: C 67.72, H 4.87, N 11.28,

S 6.46; found C 67.69, H 4.83, N 11.46, S 6.03.

5-[4-(9H-Carbazol-9-yl)phenyl]-4-methoxy-2-(pyridin-2-yl)thiazole

(D1): The procedure was similar to that used for A1. Instead of

P(tBu)₃, SPHOS was used as the phosphane ligand. Compound

2d (393 mg, 1.13 mmol), Pd(dba)₂(13 mg, 0.023 mmol, 2 mol-%),

SPOS (18 mg, 0.046 mmol, 4 mol-%), carbazole (208 mg,

1.25 mmol, 1.1 equiv.), KOtBu (140 mg, 1.25 mmol, 1.1 equiv.), and

toluene (dry and degassed, 30 mL) were used. Purification was by

column chromatography (silica, CHCl₃/EtOAc 10:1, R_fstarting

material = 0.7, R_fproduct = 0.75!) and additionally by recrystal-

lization from EtOH/CHCl₃by slow evaporation of the CHCl₃, to

yield the arylamine as a yellow amorphous solid; yield 336 mg

4-[4-Methoxy-2-(pyrazin-2-yl)thiazol-5-yl]-N,N-diphenylaniline

(B1): Yield 90%. ¹H NMR (400 MHz, CDCl₃): δ = 9.34 (d, J =

1.3 Hz, 1 H), 8.53 (d, J = 2.5 Hz, 1 H), 8.52–8.49 (m, 1 H), 7.65

(d, J = 8.8 Hz, 2 H), 7.33–7.18 (m, 4 H), 7.17–7.00 (m, 8 H), 4.19

(s, 3 H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 159.72, 156.18,

147.42, 147.01, 146.92, 144.30, 143.77, 140.96, 129.33, 127.94,

125.01, 124.71, 123.26, 116.11, 109.95, 57.75 ppm. MS (EI): m/z

(%) = 436 (100) [M]⁺, 288 (90). UV/Vis (CH₃CN): λ_max[log(ε/

m

^–1cm^–1)] = 237 [4.01], 303 [4.20], 426 [4.27] nm. C₂₆H₂₀N₄OS

(436.53): calcd. C 71.54, H 4.62, N 12.83, S 7.35; found C 71.27,

H 4.66, N 12.61, S 7.67.

1

(0.78 mmol), 69%. H NMR (400 MHz, CDCl₃): δ = 8.63 (d, J =

4.7 Hz, 1 H), 8.22–8.12 (m, 3 H), 8.03 (d, J = 8.5 Hz, 2 H), 7.81

(td, J = 7.7, 1.4 Hz, 1 H), 7.60 (d, J = 8.5 Hz, 2 H), 7.53–7.38 (m,

4 H), 7.37–7.23 (m, 3 H), 4.27 (s, 3 H) ppm. ¹³C NMR (100 MHz,

CDCl₃): δ = 161.13, 160.25, 151.39, 149.67, 141.00, 137.06, 136.19,

131.12, 128.36, 127.38, 126.12, 124.41, 123.63, 120.44, 120.15,

119.22, 113.59, 110.03, 57.87 ppm. UV/Vis (CHCl₃): λ_max[log(ε/

Monosubstituted Product of B1 – 4-[4-Methoxy-2-(pyrazin-2-yl)thi-

azol-5-yl]-N-phenylaniline (B1m): If the reaction to afford B1 was

aborted earlier (t Ͼ 3 h), the monosubstituted product was ob-

tained in 79% yield after purification (column chromatography, sil-

ica, CHCl₃/EtOAc 4:1). Recrystallization from EtOH/CHCl₃

yielded the compound as orange block crystals. ¹H NMR

(250 MHz, CDCl₃): δ = 8.82 (d, J = 4.9 Hz, 2 H), 7.76–7.68 (m, 2

H), 7.33–7.20 (m, 3 H), 7.17–7.04 (m, 4 H), 7.02–6.91 (m, 1 H),

5.88 (s, 1 H), 4.26 (s, 3 H) ppm. ¹³C NMR (63 MHz, CDCl₃): δ =

160.10, 159.70, 157.83, 156.20, 142.81, 142.44, 129.54, 128.54,

123.57, 121.75, 120.06, 118.65, 117.89, 117.29, 58.11 ppm. MS (EI):

m/z (%) = 360 (50) [M]⁺, 212 (100). C₂₀H₁₆N₄OS (360.43): calcd.

C 66.65, H 4.47, N 15.54, S 8.90; found C 66.60, H 4.45, N 15.60,

S 8.79.

m

^–1cm^–1)] = 293 [4.04], 387 [4.13] nm. UV/Vis (CH₃CN): λ_max

[log(ε/m^–1cm^–1)] = 236 [4.49], 292 [4.11], 380 [4.24] nm. MS (EI):

m/z (%) = 433 (100) [M]⁺, 286 (90). C₂₇H₁₉N₃OS (433.53): calcd.

C 74.80, H 4.42, N 9.69, S 7.40; found C 74.79, H 4.30, N 9.39, S

7.26.

10-{4-[4-Methoxy-2-(pyridin-2-yl)thiazol-5-yl]phenyl}-10H-pheno-

thiazine (D2): The procedure was similar to that used for D1; yield

88%. Purification was achieved by recrystallization from CHCl₃.

¹H NMR (400 MHz, CDCl₃): δ = 8.62 (ddd, J = 4.8, 1.5, 0.8 Hz,

1 H), 8.16 (d, J = 7.9 Hz, 1 H), 8.03–7.97 (m, 2 H), 7.80 (td, J = 7.8,

1.7 Hz, 1 H), 7.42–7.36 (m, 2 H), 7.32 (ddd, J = 7.5, 4.8, 1.1 Hz, 1

4-Methoxy-N-{4-[4-methoxy-2-(pyrazin-2-yl)thiazol-5-yl]phenyl}-N-

1

(4-methoxyphenyl)aniline (B2): Yield 84 %. H NMR (400 MHz,

CDCl₃): δ = 9.33 (d, J = 1.4 Hz, 1 H), 8.51 (d, J = 2.5 Hz, 1 H),

14

www.eurjoc.org

Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20688

/KAP1

Date: 08-08-12 17:05:18

Pages: 18

Arylamine-Modified Thiazoles as Donor–Acceptor Dyes

H), 7.04 (dd, J = 7.4, 1.7 Hz, 2 H), 6.92–6.78 (m, 4 H), 6.34 (dd,

J = 8.1, 1.2 Hz, 2 H), 4.24 (s, 3 H) ppm. ¹³C NMR (100 MHz,

152.88, 152.85, 152.32, 152.12, 151.72, 151.43, 151.42, 151.35,

151.33, 150.75, 140.43, 138.61, 129.63, 129.51, 129.40, 129.29,

CDCl₃): δ = 161.20, 160.27, 151.30, 149.68, 144.28, 139.55, 137.10, 128.93, 128.40, 127.81, 126.13, 125.98, 125.94, 125.59, 125.10,

131.66, 130.74, 129.08, 127.03, 126.94, 124.48, 122.77, 120.85, 124.15, 119.03, 118.90, 116.11, 62.10, 56.25, 21.35, 21.34, 21.28,

119.24, 116.66, 113.38, 57.88 ppm. UV/Vis (THF): λ_max[log(ε/

21.21 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 248 [445],

258 [4.41], 286 [4.86], 324 [4.52], 457 [4.45] nm. MS (MALDI-TOF,

dithranol): calcd. for C₅₃H₄₉F₆N₇O₃PRuS 1110.26 [M – PF₆]⁺;

found 1110.23. HRMS (micro-ESI): calcd. for C₅₃H₄₉F₆N₇O₃PRuS

1104.2335; found 1104.2336.

m

^–1cm^–1)] = 257 [4.72], 377 [4.42] nm. MS (EI): m/z (%) = 465 (100)

[M]⁺, 318 (90). C₂₇H₁₉N₃OS₂(465.59): calcd. C 69.65, H 4.11, N

9.03, S 13.77; found C 69.55, H 4.02, N 9.21, S 13.89.

10-{4-[4-Methoxy-2-(pyridin-2-yl)thiazol-5-yl]phenyl}-10H-phen-

oxazine (D3): Yield 80%. ¹H NMR (400 MHz, CDCl₃): δ = 8.62

(ddd, J = 4.8, 1.5, 0.9 Hz, 1 H), 8.16 (d, J = 7.9 Hz, 1 H), 8.03–

7.97 (m, 2 H), 7.80 (td, J = 7.8, 1.7 Hz, 1 H), 7.39–7.29 (m, 3 H),

6.72–6.57 (m, 6 H), 6.02 (dd, J = 7.7, 1.6 Hz, 2 H), 4.24 (s, 3

H) ppm. ¹³C NMR (100 MHz, CDCl₃): δ = 161.32, 160.32, 151.26,

149.67, 144.11, 137.24, 137.11, 134.47, 132.20, 131.21, 129.40,

124.51, 123.40, 121.46, 119.25, 115.56, 113.49, 113.24 57.88 ppm.

UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 240 [4.77], 276 [4.06],

373 [4.40] nm. MS (EI): m/z (%) = 449 (50) [M]⁺, 302 (100).

C₂₇H₁₉N₃O₂S (449.53): calcd. C 72.14, H 4.26, N 9.35, S 7.13;

found C 72.09, H 4.12, N 9.44, S 7.55.

Ru(dmbpy)₂(C1)(PF₆)₂(Ru3): Yield 60%. ¹H NMR (400 MHz,

CD₃CN): δ = 8.84 (dd, J = 4.8, 1.9 Hz, 1 H), 8.37–8.29 (m, 4 H),

7.93 (d, J = 5.8 Hz, 1 H), 7.86 (dd, J = 5.8, 1.9 Hz, 1 H), 7.75 (d,

J = 5.8 Hz, 1 H), 7.57 (d, J = 5.8 Hz, 1 H), 7.44 (d, J = 5.8 Hz, 1

H), 7.41 (d, J = 8.9 Hz, 2 H), 7.37–7.33 (m, 1 H), 7.33–7.28 (m, 2

H), 7.22 (d, J = 4.9 Hz, 1 H), 7.19–7.13 (m, 5 H), 7.01 (d, J =

8.3 Hz, 4 H), 6.89 (d, J = 8.9 Hz, 2 H), 3.00 (s, 3 H), 2.56 (d, J =

2.6 Hz, 6 H), 2.51 (d, J = 6.2 Hz, 6 H), 2.31 (s, 6 H) ppm. ¹³C

NMR (100 MHz, CD₃CN): δ = 164.05, 161.96, 160.34, 158.28,

158.09, 158.04, 157.86, 157.48, 155.41, 153.13, 152.72, 152.08,

151.89, 151.63, 151.59, 151.54, 150.96, 150.93, 145.00, 135.65,

131.29, 129.71, 129.66, 129.39, 129.36, 129.28, 128.45, 126.89,

126.01, 125.94, 125.61, 125.14, 122.84, 120.65, 120.04, 62.20, 21.31,

21.24, 21.18, 20.93 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 247 [4.58], 258 [4.54], 285 [4.99], 326 [4.64], 471 [4.53] nm. MS

(MALDI-TOF, dithranol): calcd. for C₅₂H₄₈F₆N₈OPRuS

1079.2718 [M – PF₆]⁺; found 1079.2713. HRMS (micro-ESI):

calcd. for C₅₂H₄₈F₆N₈OPRuS 1073.2389; found 1073.2400.

Ru(dmbpy)₂(C2)(PF₆)₂(Ru4): Yield 75%. ¹H NMR (400 MHz,

CD₃CN): δ = 8.83 (dd, J = 4.8, 1.9 Hz, 1 H), 8.34 (s, 2 H), 8.31

(d, J = 8.6 Hz, 2 H), 7.92 (d, J = 5.8 Hz, 1 H), 7.85 (dd, J = 5.8,

1.9 Hz, 1 H), 7.75 (d, J = 5.8 Hz, 1 H), 7.57 (d, J = 5.8 Hz, 1 H),

7.43 (d, J = 5.8 Hz, 1 H), 7.40–7.35 (m, 2 H), 7.35–7.26 (m, 3 H),

7.21 (d, J = 5.8 Hz, 1 H), 7.17 (d, J = 5.8 Hz, 1 H), 7.14–7.07 (m,

4 H), 6.95–6.89 (m, 4 H), 6.82–6.75 (m, 2 H), 3.78 (s, 6 H), 2.98 (s,

J = 6.0 Hz, 3 H), 2.56 (s, 3 H), 2.55 (s, 3 H), 2.52 (s, 3 H), 2.50 (s,

3 H) ppm. ¹³C NMR (100 MHz, CD₃CN): δ = 164.07, 161.79,

160.32, 158.30, 158.27, 158.09, 158.04, 157.87, 157.48, 155.02,

153.12, 152.72, 152.08, 151.89, 151.61, 151.58, 151.53, 150.96,

140.21, 129.72, 129.65, 129.38, 129.27, 128.97, 128.44, 126.01,

125.94, 125.61, 125.14, 122.75, 118.86, 118.61, 116.05, 62.13, 56.19,

21.31, 21.24, 21.18 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 247 [4.62], 258 [4.57], 285 [5.00], 328 [4.63], 473 [4.55] nm. MS

(MALDI-TOF, dithranol): calcd. for C₅₂H₄₈F₆N₈O₃PRuS 1111.23

[M – PF₆]⁺; found 1111.30. HRMS (micro-ESI): calcd. for

C₅₂H₄₈F₆N₈O₃PRuS 1105.2288; found 1105.2274.

General Procedure, illustrated for Ru1, for the synthesis of the

Ru(dmbpy)₂(L)(PF₆)₂complexes:

Ru(dmbpy)₂(A1)(PF₆)₂(Ru1): The activated precursor cis-Ru-

(dmbpy)₂(acetone)₂(PF₆)₂was synthesized by stirring cis-(dmbpy)₂-

RuCl₂(68 mg, 0.126 mmol) and AgPF₆(64 mg, 0.252 mmol,

2 equiv.) in dried and nitrogen-purged acetone (5 mL) for 6 h at

room temp. under inert conditions with use of Schlenk techniques.

The precipitated AgCl was filtered off and the corresponding li-

gand A1 (55 mg, 0.126 mmol) was added to the solution. The mix-

ture was heated under reflux for 24 h. Subsequently, the reaction

mixture was allowed to cool to room temp. and filtered through a

cellulose filter. The solvent was removed in vacuo and the crude

product was purified by size exclusion chromatography (Bio-

Beads S-X1, CH₂Cl₂as eluent) to remove traces of the ligand (if

the complex was not sufficiently soluble in CH₂Cl₂, it was applied

with a 1:1 mixture of CH₂Cl₂/acetone and eluted with CH₂Cl₂).

After evaporation of the solvent, the solid was dissolved in a small

amount of CH₂Cl₂and precipitated with Et₂O (200 mL) to give

the complex as a red solid; yield 99 mg (0.083 mmol, 67%). ¹H

NMR (250 MHz, CD₃CN): δ = 8.39–8.26 (m, 4 H), 8.20 (d, J =

7.9 Hz, 1 H), 7.97 (td, J = 7.9, 1.2 Hz, 1 H), 7.91 (d, J = 5.8 Hz, 1

H), 7.63 (d, J = 5.5 Hz, 1 H), 7.59 (d, J = 5.8 Hz, 2 H), 7.50–6.88

(m, 20 H), 2.99 (s, 3 H), 2.61–2.46 (m, 12 H) ppm. ¹³C NMR

(63 MHz, CD₃CN): δ = 161.39, 158.02, 157.99, 157.94, 157.51,

157.50, 154.59, 152.79, 152.23, 152.01, 151.61, 151.31, 151.23,

151.21, 150.64, 150.22, 147.70, 138.52, 130.66, 129.67, 129.41,

129.29, 129.19, 128.30, 127.85, 126.46, 125.88, 125.83, 125.49,

125.46, 125.42, 124.99, 124.18, 122.23, 121.17, 62.11, 21.24, 21.18,

21.11 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 258 [4.47],

287 [492], 319 [4.59], 447 [4.48] nm. MS (MALDI-TOF, dithranol):

Ru(dmbpy)₂(D1)(PF₆)₂(Ru5): Yield 93%. ¹H NMR (400 MHz,

CH₃CN): δ = 8.41–8.25 (m, 5 H), 8.20 (d, J = 7.8 Hz, 2 H), 8.02

(dd, J = 11.3, 4.4 Hz, 1 H), 7.98 (d, J = 5.8 Hz, 1 H), 7.83 (d, J =

8.6 Hz, 2 H), 7.74 (d, J = 8.5 Hz, 2 H), 7.69 (d, J = 5.5 Hz, 1 H),

7.63 (d, J = 5.8 Hz, 2 H), 7.51–7.41 (m, 5 H), 7.40–7.28 (m, 5 H),

7.24 (d, J = 5.1 Hz, 1 H), 7.19 (d, J = 5.0 Hz, 1 H), 3.09 (s, 3 H),

2.58 (s, 3 H), 2.57 (s, 3 H), 2.54 (s, 3 H), 2.52 (s, 3 H) ppm. ¹³C

NMR (100 MHz, CH₃CN): δ = 162.46, 159.40, 158.15, 158.10,

158.08, 157.62, 154.58, 152.98, 152.94, 152.33, 152.11, 151.70,

calcd. for C₅₁H₄₅F₆N₇OPRuS 1050.209 [M

–

PF₆]⁺; found

1050.345. HRMS (micro-ESI): calcd. for C₅₁H₄₅F₆N₇OPRuS

1044.2124; found 1044.2122.

Ru(dmbpy)₂(A2)(PF₆)₂(Ru2): Yield 67%. ¹H NMR (400 MHz, 151.45, 151.39, 151.37, 150.80, 141.41, 139.72, 138.67, 130.67,

CD₃CN): δ = 8.36–8.31 (m, 3 H), 8.28 (s, 1 H), 8.17 (d, J = 8.0 Hz, 129.50, 129.37, 129.30, 128.53, 128.40, 128.30, 127.91, 127.31,

1 H), 7.96 (td, J = 7.9, 1.3 Hz, 1 H), 7.90 (d, J = 5.8 Hz, 1 H), 7.62

(d, J = 5.6 Hz, 1 H), 7.58 (d, J = 5.8 Hz, 2 H), 7.45 (d, J = 5.8 Hz,

125.97, 125.94, 125.61, 125.11, 124.64, 124.54, 123.88, 121.55,

121.45, 110.72, 62.63, 21.31, 21.30, 21.24, 21.17 ppm. UV/Vis

1 H), 7.36–7.25 (m, 5 H), 7.21 (d, J = 5.8 Hz, 1 H), 7.16 (d, J = (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 238 [4.73], 257 [4.53], 286 [4.85],

5.8 Hz, 1 H), 7.13–7.07 (m, 4 H), 6.96–6.90 (m, 4 H), 6.80 (d, J = 322 [4.38], 338 [4.34], 389 [4.29], 486 [4.00] nm. MS (MALDI-TOF,

8.9 Hz, 2 H), 3.78 (s, 6 H), 2.98 (s, 3 H), 2.56 (s, 3 H), 2.55 (s, 3 dithranol): calcd. for C₅₁H₄₃F₆N₇OPRuS 1110.26 [M – PF₆]⁺;

H), 2.53 (s, 3 H), 2.50 (s, 3 H) ppm. ¹³C NMR (100 MHz, CD₃CN): found 1110.23. HRMS (micro-ESI): calcd. for C₅₁H₄₃F₆N₇OPRuS

δ = 161.20, 158.30, 158.16, 158.13, 158.10, 157.66, 157.01, 154.80, 1042.1968; found 1042.1959.

Eur. J. Org. Chem. 0000, 0–0

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L. González, R. Beckert et al.

FULL PAPER

Ru(dmbpy)₂(D2)(PF₆)₂(Ru6): Yield 57%. ¹H NMR (400 MHz,

CD₃CN): δ = 8.36 (s, 2 H), 8.35 (s, 1 H), 8.31 (s, 1 H), 8.26 (d, J

= 7.9 Hz, 1 H), 8.01 (td, J = 7.9, 1.3 Hz, 1 H), 7.95 (d, J = 5.8 Hz,

1 H), 7.69–7.64 (m, 3 H), 7.63–7.59 (m, 2 H), 7.47 (d, J = 5.8 Hz,

1 H), 7.38–7.32 (m, 4 H), 7.30 (d, J = 4.9 Hz, 1 H), 7.27 (dd, J =

7.6, 1.5 Hz, 2 H), 7.24 (d, J = 5.8 Hz, 1 H), 7.18 (d, J = 4.8 Hz, 1

H), 7.13 (td, J = 7.8, 1.6 Hz, 2 H), 7.05 (td, J = 7.5, 1.3 Hz, 2 H),

6.73 (dd, J = 8.0, 1.0 Hz, 2 H), 3.03 (s, 3 H), 2.58 (s, 3 H), 2.57 (s,

3 H), 2.54 (s, 3 H), 2.52 (s, 3 H) ppm. ¹³C NMR (100 MHz,

CD₃CN): δ = 162.05, 158.80, 158.09, 158.06, 158.03, 157.58,

154.58, 152.93, 152.91, 152.32, 152.09, 151.70, 151.41, 151.34,

151.31, 150.75, 145.18, 143.78, 138.63, 130.92, 129.47, 129.36,

129.26, 128.62, 128.42, 128.37, 128.17, 126.71, 126.34, 125.95,

125.91, 125.59, 125.44, 125.08, 124.52, 124.36, 121.66, 21.33, 21.31,

21.26, 21.18, 15.64 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)]

= 257 [4.76], 286 [4.82], 320 [4.38], 367 [4.27], 434 [4.24] nm.

MS (MALDI-TOF, dithranol): calcd. for C₅₁H₄₃F₆N₇OPRuS₂

1080.17 [M – PF₆]⁺; found 1080.17. HRMS (micro-ESI): calcd.

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[4]

[5]

[6]

[7]

[8]

[9]

for

C₅₁H₄₃F₆N₇OPRuS₂

1074.1692;

found

1074.1711.

C₅₁H₄₃F₁₂N₇OP₂RuS₂(1225.06): calcd. C 50.00, H 3.54, N 8.00, S

5.23; found C 49.98, H 3.76, N 7.87, S 4.87.

Ru(dmbpy)₂(D3)(PF₆)₂(Ru7): Yield 68%. ¹H NMR (400 MHz,

CD₃CN): δ = 8.42–8.28 (m, 5 H), 8.04 (td, J = 7.9, 1.3 Hz, 1 H),

7.98 (d, J = 5.8 Hz, 1 H), 7.88–7.79 (m, 2 H), 7.70 (d, J = 5.3 Hz,

1 H), 7.63 (d, J = 5.8 Hz, 2 H), 7.54–7.47 (m, 3 H), 7.44–7.35 (m,

2 H), 7.32 (dd, J = 5.7, 0.9 Hz, 1 H), 7.25 (dd, J = 5.8, 0.9 Hz, 1

H), 7.20 (dd, J = 5.8, 0.9 Hz, 1 H), 6.73–6.60 (m, 6 H), 5.98 (d, J

= 8.4 Hz, 2 H), 3.07 (d, J = 6.1 Hz, 3 H), 2.59 (s, 3 H), 2.59 (s, 3

H), 2.56 (s, 3 H), 2.54 (s, 3 H) ppm. ¹³C NMR (100 MHz, CD₃CN):

δ = 162.51, 159.65, 158.11, 158.06, 158.03, 157.58, 154.51, 153.00,

152.95, 152.33, 152.11, 151.71, 151.44, 151.37, 151.35, 150.78,

144.78, 141.24, 138.66, 134.93, 132.76, 131.88, 129.49, 129.37,

129.36, 129.29, 128.40, 128.36, 125.97, 125.93, 125.60, 125.09,

124.70, 124.56, 123.57, 122.82, 116.44, 114.40, 62.64, 21.32, 21.26,

21.18 ppm. UV/Vis (CH₃CN): λ_max[log(ε/m^–1cm^–1)] = 286 [4.82],

327 [4.47], 446 [4.12], 483 [4.05] nm. MS (MALDI-TOF, dithranol):

calcd. for C₅₁H₄₃F₆N₇O₂PRuS 1064.19 [M – PF₆]⁺; found 1064.20.

HRMS (micro-ESI): calcd. for C₅₁H₄₃F₆N₇O₂PRuS: 1058.1916;

found 1058.1923.

[10]

[11]

Supporting Information (see footnote on the first page of this arti-

cle): Lippert–Mataga calculation, emission spectra of the dyes and

of A2 and D1 in different solvents, ¹H NMR spectra of the radical

cations of A3 and Ru4, X-ray structure of A1m, refinement data

and X-ray structure files for A1, B1, C1, D2 and A1m, MALDI-

TOF spectra of the complexes, graphical representation of the tor-

sion angles for A2 and D1, summary of the photophysical proper-

ties and representations of the orbitals of the higher excited singlet

[12]

[13]

[14]

[15]

states, CV spectra of the complexes Ru3, Ru4 and Ru7. ¹H and ¹³

C

NMR spectra of the final products.

Acknowledgments

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Mishra, M. K. R. Fischer, P. Bäuerle, Angew. Chem. 2009, 121,

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The authors thank the Thuringian Ministry for Education, Science

and Culture (grant number #B514–09049, project “Photonische

Mizellen [PhotoMIC]”) for financial support. We gratefully

acknowledge the help of Dr. Eckhard Birckner and Erika Kielman

with the emission spectroscopy of the complexes at 77 K.

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Published Online: ᭿

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Job/Unit: O20688

/KAP1

Date: 08-08-12 17:05:18

Pages: 18

L. González, R. Beckert et al.

FULL PAPER

Donor–Acceptor Dyes

R. Menzel, S. Kupfer, R. Mede, D. Weiß,

H. Görls, L. González,*

R. Beckert* ..................................... 1–18

Arylamine-Modified Thiazoles as Donor–

Acceptor Dyes: Quantum Chemical Evalu-

ation of the Charge-Transfer Process and

Testing as Ligands in Ruthenium(II) Com-

plexes

Several 4-hydroxy-1,3-thiazole-based chro-

mophores bearing different arylamine

donor and N-heterocyclic acceptor moiet-

ies were synthesized and their electronic

properties were investigated experimentally

and theoretically (DFT and TDDFT). The

nature of the charge-transfer transition was

identified. Additionally, the dyes were ap-

plied as light-harvesting ligands in hetero-

leptic Ru^IIcomplexes.

Keywords: N,S-Heterocycles

/

Hetero-

cycles / Chromophores / Dyes / Charge

transfer / Density functional calculations /

Ruthenium complexes

18

www.eurjoc.org

Eur. J. Org. Chem. 0000, 0–0

Article Doi

Arylamine-modified thiazoles as donor-acceptor dyes: Quantum chemical evaluation of the charge-transfer process and testing as ligands in ruthenium(II) complexes

DOI: 10.1002/ejoc.201200688

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Article abstract of DOI:10.1002/ejoc.201200688

Full text of DOI:10.1002/ejoc.201200688

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