Synthesis, electronic, and electro-optical properties of emissive solvatochromic phenothiazinyl merocyanine dyes

Article abstract of DOI:10.1002/chem.201100592

Phenothiazinyl merocyanine dyes with variable substitution patterns on the peripheral benzene ring were synthesized in good yields by Knoevenagel condensation of the corresponding phenothiazinyl aldehydes and N-methylrhodanine or indan-1,3-dione. The electronic properties were investigated by cyclic voltammetry, absorption, electro-optical absorption, and emission spectroscopy. All these merocyanines reveal reversible redox behavior that stems from the phenothiazinyl-centered oxidation to give stable radical cations. The redox potentials strongly correlate with Hammett σ_p parameters. All merocyanines reveal large Stokes shifts. They also display a pronounced emissive solvatochromism, which is caused by large dipole moment changes upon excitation from the ground to the excited state. These findings are supported by solvatochromism studies and time-dependent DFT computations. A dye-ing breed: Phenothiazinyl-merocyanine dyes with variable substitution patterns on the peripheral benzene ring were synthesized in good yields by Knoevenagel condensation of the corresponding phenothiazinyl aldehydes and N-methylrhodanine or indan-1,3-dione. Their electronic properties were investigated by various methods (see figure). Copyright

Full text of DOI:10.1002/chem.201100592

DOI: 10.1002/chem.201100592
Synthesis, Electronic, and Electro-Optical Properties of Emissive
Solvatochromic Phenothiazinyl Merocyanine Dyes
Martina Hauck,[a] Matthias Stolte,[b] Jan Schçnhaber,[a] Hans-Georg Kuball,*[b] and
Thomas J. J. Mꢀller*[a]
Abstract: Phenothiazinyl merocyanine
dyes with variable substitution patterns
on the peripheral benzene ring were
synthesized in good yields by Knoeve-
nagel condensation of the correspond-
ing phenothiazinyl aldehydes and N-
methylrhodanine or indan-1,3-dione.
The electronic properties were investi-
gated by cyclic voltammetry, absorp-
tion, electro-optical absorption, and
emission spectroscopy. All these mero-
cyanines reveal reversible redox behav-
ior that stems from the phenothiazinyl-
centered oxidation to give stable radi-
cal cations. The redox potentials
strongly correlate with Hammett sp pa-
rameters. All merocyanines reveal
large Stokes shifts. They also display a
pronounced emissive solvatochromism,
which is caused by large dipole
moment changes upon excitation from
the ground to the excited state. These
findings are supported by solvato-
chromism studies and time-dependent
DFT computations.
Keywords: chromophores
· cyclic
voltammetry · dyes/pigments · elec-
tro-optical absorption spectroscopy ·
fluorescence · heterocycles
Introduction
highly intriguing as electrochemically addressable and
switchable molecular entities (native-doped; ON/OFF),[7]
low-bandgap polymers,[8] and as functional units and build-
ing blocks in single-molecule-based molecular electronics.[9]
For several reasons, phenothiazines,[10]a class of tricyclic ni-
trogen–sulfur heterocycles with a broad pharmaceutical pro-
file,[11] are particularly intriguing for redox systems. They
possess low and highly reversible first-oxidation poten-
tials[10,12] with a pronounced propensity to form stable radi-
cal cations,[13] and their redox and fluorescence properties
can be tuned.[14] Furthermore, the inherent folded conforma-
tion of phenothiazine[15] with a folding angle of 158.58,
which can be transformed into a stable radical cation with a
planar conformation and excellent delocalization,[16] quali-
fies phenothiazine-based Do–Acc chromophores as excel-
lent models for redox-switchable merocyanines. In addition,
phenothiazine derivatives with extended p-conjugated sub-
stituents often display intense luminescence upon UV/Vis
excitation with remarkable Stokes shifts that might be due
to solvent relaxation and, in part, to geometry changes in
the excited state. As a consequence, the favorable electronic
properties of phenothiazines have led to applications as
electrophore probes in supramolecular assemblies[17] for
photoinduced electron transfer (PET) and sensor studies,
and as electron-donor components in material scientific in-
vestigations such as electrically conducting charge-transfer
composites,[18] polymers,[19] Do–Acc arrangements,[20] and
also as chromophores in dye-sensitized photovoltaic cells.[21]
In past years, our interest has focused on understanding
the electronic effects of remote 3-mono- and 3,7-bis-accept-
or substitution with[22] and without[23] ethynyl bridging
(Scheme 1) on phenothiazine oxidation potentials, as well as
absorption and emission behavior. In addition, modular
For the rational design of functional p-electron systems, the
donor–acceptor (Do–Acc) substitution of p-chromophores is
the most fundamental heuristic concept[1] with a well-found-
ed theoretical basis.[2] Hence, the reliable prediction of func-
tional chromophores in molecular photonics for future tech-
nical applications has turned out to be increasingly realis-
tic.[3] Due to their unsymmetrical highly dipolar nature, the
class of neutral merocyanines[4] has adopted a central role
among Do–Acc dyes. In particular, with respect to designed
supramolecular self-organized mesoscopic and macroscopic
morphologies,[5] merocyanines have become increasingly im-
portant as absorbing chromophores in dye-sensitized solar
cells[6] for photovoltaics with a wide range of donor auxo-
chromes. In addition, functional p-electron systems with
Do–Acc topology based upon heterocyclic reversible redox
units that display electronic bi- or multistability (e.g., neu-
tral-radical ion, or even several stable oxidation states) are
[a] Dr. M. Hauck, Dr. J. Schçnhaber, Prof. Dr. T. J. J. Mꢀller
Institut fꢀr Organische Chemie und Makromolekulare Chemie
Heinrich-Heine Universitꢁt Dꢀsseldorf
Universitꢁtsstrasse 1, 40225 Dꢀsseldorf (Germany)
Fax : (+49)211-81-14324
E-mail: ThomasJJ.Mueller@uni-duesseldorf.de
[b] Dr. M. Stolte, Prof. Dr. H.-G. Kuball
FB Chemie
Technische Universitꢁt Kaiserslautern
Erwin-Schrçdinger-Strasse Geb 52/532
67663 Kaiserslautern (Germany)
Fax : (+49)631-2052750
E-mail: kuball@rhrk.uni-kl.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100592.
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Chem. Eur. J. 2011, 17, 9984 – 9998

FULL PAPER
Alternatively, phenothiazine 1 can be formylated by a Vils-
meier reaction with N-methylformanilide and phosphorus
oxychloride to furnish aldehyde 2,[29] which in turn can be
brominated to give bromoaldehyde 4.[22b] The latter can be
submitted to Suzuki coupling to give rise to the p-tolyl-sub-
stituted aldehyde 7, whereas Beller cyanation[14b,30] affords
the cyanoaldehyde 8.
With various phenothiazinyl aldehydes 3–8 in hand, Knoe-
venagel condensation with N-methylrhodanine (9) to render
a favorable acceptor moiety in merocyanine dye-sensitized
organic solar cells,[31] with piperidine as a base in ethanol/
toluene (1:1) or methanol/toluene (2:1), furnishes pheno-
thiazine–rhodanine merocyanines 10 in excellent yields
Scheme 1. 3-Mono- and 3,7-bis-acceptor-substituted phenothiazines and
oligophenothiazines.
strategies
have
enabled
straightforward accesses to
structurally well-defined mono-
disperse electronically coupled
oligophenothiazines with direct
3,7-ligation (Scheme 1) of the
units.[14a,24]
Interestingly, the emission
behavior of phenothiazine de-
rivatives such as cyanoACTHUNTGRENNG(U oligo)-
phenothiazines,[14b] and diphe-
nothiazine dumbbells bridged
by carbo-[25] and heterocy-
cles,[14c] and cruciforms[26] re-
veals enormous Stokes shifts
and, thus, has aroused our inter-
est for a deeper understanding
of the excited-state structure
and properties. Here, we report
the syntheses and investigation
of ground- and excited-state
electronic properties of various
Scheme 2. Synthesis of the phenothiazinyl aldehydes 3–8: a) Br2, AcOH, RT, 18 h; b) N-methylformanilide,
1,2-dichloroethane, POCl3, 08C, then: D, 40 h, 74%; c) Br2, AcOH, RT, 18 h, 91%; d) 1) nBuLi, THF, ꢀ788C;
2) DMF, ꢀ788C to RT, 18 h; e) 1) nBuLi, THF, ꢀ788C; 2) I2, ꢀ788C, 6 h; 3) DMF, ꢀ788C to RT; f) 2.7 mol%
[Pd(PPh3)4], DME/H2O (2:1), K2CO3, 20 h, 908C; g) 1mol% Pd(OAc)2, dppf (1,1’-bis(diphenylphosphanyl)fer-
rocene), K4[Fe(CN)6], N-methylpyrrolidone (NMP), Na2CO3, 1208C, 18 h.
phenothiazinyl
merocyanines
with tunable emission and
redox properties.
Results and Discussion
(Scheme 3). Under the same conditions, the condensation of
1,3-indandione (11) as a methylene-active component with
Syntheses and structure: In a straightforward convergent
retrosynthetic analysis, all phenothiazine merocyanines can
be derived from N-hexyl-10H-phenothiazine (1) as the
common starting material, which can be prepared in high
yield from 10H-phenothiazine by hexylation with hexyl bro-
mide in the presence of potassium tert-butoxide in THF.[14a]
The corresponding aldehydes necessary for suitable Knoeve-
nagel condensations with methylene-active compounds in-
troducing the acceptor moieties are either accessible
through bromine–lithium exchange of the 3,7-dibromo-N-
hexyl-10H-phenothiazine (2) (obtained from 1 by bromina-
tion) with subsequent sequential trapping of the dilithio de-
rivatives[27,28] with DMF to give rise to dialdehyde 5 or with
DMF and iodine to furnish iodoaldehyde 6[27,28] (Scheme 2).
aldehydes 3–8 led to the formation of phenothiazine–indan-
dione merocyanines 12 in moderate to excellent yields. In
addition, and for comparison, the corresponding aniline–
merocyanine dyads 14[32] and 15[20a,33] were synthesized by
Knoevenagel condensation of N,N-disubstituted p-amino-
benzaldehydes 13 with 9 or 11 in good yields (Scheme 4).
The structures of all merocyanines 10, 12, 14, and 15 were
1
unambiguously assigned by H and 13C NMR, UV/Vis, and
IR spectroscopy, mass spectrometry, and by combustion
analysis.[34] Although two geometrical double-bond isomers
of the series 10 and 14 could arise from the condensation,
the appearance of single sets of signals in the NMR spectra
indicates the stereoselective formation of the Z isomers. The
Z configuration of phenothiazinyl–N-methylrhodanine dyes
Chem. Eur. J. 2011, 17, 9984 – 9998
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9985

H.-G. Kuball, T. J. J. Mꢀller et al.
Redox behavior: In all cyclic
voltammograms of the pheno-
thiazinyl merocyanines 10 and
12, the reversible oxidation of
the phenothiazine moiety can
be observed at potentials E00=þ1
ranging from 806 to 1078 mV
(10) and from 823 to 1068 mV
(12) (Table 1, Figure 3, and
Figure 4).
In comparison to the N-hex-
ylphenothiazine
728 mV), the potentials of the
merocyanines are shifted anodi-
Scheme 3. Knoevenagel synthesis of phenothiazine-rhodanines 10 and phenothiazine-indandione merocyanines
12: a) ethanol/toluene, methanol/toluene or 2-propanephosphonic acid anhydride (T3P)/DCE, piperidine, D,
0.5–1 h.
(E00=þ1
=
Scheme 4. Knoevenagel synthesis of aniline–rhodanine 14 and aniline–in-
dandione merocyanines 15: a) ethanol/toluene, piperidine, D (14a,b and
15a) or acetic acid/ammonium acetate, D (15b).
Figure 1. Molecular structure of 10b (left) and 12b (right). Hydrogen
atoms were omitted for clarity.
10 and the crystal packing of both types of merocyanines 10
and 12 was additionally corroborated by two X-ray structure
analyses for compounds 10b and 12b (Figures 1 and 2). The
merocyanine structure is maintained in a perfect coplanar
arrangement of the acceptor component (rhodanine), the
double bond, and the conjugated benzo core of the pheno-
thiazine donor (Figure 1). Due to the pronounced dipolar
character of the merocyanines, the antiparallel orientation
results in an overall herringbone superstructure in the crys-
tal (Figure 2). The nonconjugated phenothiazinyl benzo core
and the hexyl side chains adopt peripheral positions in these
closely packed structures.
Electronic properties: The electronic properties of merocya-
nines 10, 12, 14, and 15 were experimentally studied by
spectroscopic and electroanalytical methods (Table 1). UV/
Vis and fluorescence spectroscopy were also applied to in-
vestigate the solvatochromism of the absorption and emis-
sion behavior of compounds 10b and 10 f and to estimate
the luminescence efficiency of series 10 and 12 by determin-
ing the emission quantum yields with 4-dicyanomethylene-2-
methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) as a
standard.[35] In addition, the ground- and excited-state elec-
tronic structures of selected merocyanines were calculated
on the level of DFT. Finally, electro-optical absorption
(EOA) measurements were performed to elucidate the
dipole moment change upon excitation from the electronic
ground to the excited state.
Figure 2. Elementary cells of 10b (top) and 12b (bottom). Hydrogen
atoms were omitted for clarity.
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Phenothiazinyl Merocyanine Dyes
FULL PAPER
Table 1. Selected absorption and emission spectra,[a] and cyclovoltammetric data[b] of merocyanines 10, 12, 14,
and 15.
cally with increasing strength of
the electron-withdrawing group.
Interestingly, the reversible oxi-
dations E00=þ1 in the series of
merocyanines 10 and 12 reveal
a strong dependence on the
electronic substituent effect and
Compound
Absorption[c]
lmax,abs [nm]
Emission[d]
Stokes shift
E00=þ1
[mV]
Eþ0 1=þ2
[mV]
E00=ꢀ1
[mV]
[f]
lmax,em [nm] (Ff)[e]
Dn˜ [cmꢀ1
]
10a
10b
10c
10d
10e
10 f
12a
12b
12c
12d
12e
12 f
14a
14b
15a
15b
269, 302, 360, 481
252, 303, 366, 472
257, 299, 362, 470
299, 361, 467
300, 365, 466
294, 362, 460
268, 311, 340, 519
254, 268, 314, 332, 360, 506
259, 312, 336, 499
256, 334, 499
271, 312, 326, 363, 495
268, 301, 325, 350, 488
254, 322, 480
660 (0.02)
652 (0.04)
643 (0.10)
638 (0.12)
621 (0.23)
622 (0.51)
685 (<0.01)
688 (<0.01)
668 (<0.01)
669 (<0.01)
656 (<0.01)
644 (0.08)
542
5600
5800
5700
5700
5500
5600
4700
5200
5000
5100
5000
5200
2400
4100
1600
4100
806
859
926
930
1014
1078
823
837
919
920
1017
1068
–
1477
–
–
–
–
ꢀ1327
ꢀ1268
ꢀ1201
ꢀ1211
ꢀ1199
ꢀ1159
ꢀ1130
ꢀ1131
ꢀ1114
ꢀ1110
display
a
reasonably good
linear correlation (r2 =0.9622
for series 10 and r2 =0.9604 for
12, respectively) with the Ham-
–
1473
1542
1577
1583
1633
–
–
–
–
–
mett substitution parameters
[36]
ꢀ1106 sp
(Figure 5). In agreement
with the radical cationic nature
of the oxidation product 10+
and 12+, respectively, the stabi-
lization is achieved by both in-
ductive and resonance effects
as reflected by the linear corre-
lation of E00=þ1 with sp. There-
fore, the redox potentials of
ꢀ1073
–
–
–
–
302, 472
488
264, 293, 486
585
529
608
–
–
–
[a] Recorded in CH2Cl2, T=293 K. [b] Recorded in CH2Cl2, T=293 K, v=100 mVsꢀ1, electrolyte: [Bu4N]
[PF6], Pt working electrode, Pt counterelectrode, Ag/AgCl reference electrode. [c] Recorded in CH2Cl2 at c=
10ꢀ3 m. [d] Recorded in CH2Cl2 at c=10ꢀ6 m. [e] Determined with 4-dicyanomethylene-2-methyl-6-[p-(dimethy-
lamino)styryl]-4H-pyran (DCM) as a standard in DMSO, Ff =0.78. [f] Dn˜ =1/lmax,absꢀ1/lmax,em [cmꢀ1].
phenothiazinyl
merocyanines
Figure 5. Correlation of the half-wave potentials E00=þ1 [mV] and the
Hammett parameters sp of phenothiazine–N-methylrhodaninemerocya-
Figure 3. Cyclic voltammogram of 10 f. Recorded in CH2Cl2; T=293 K;
0.1m electrolyte [Bu4N][PF6]; v=100 mVsꢀ1; Pt working electrode, Ag/
AgCl reference and Pt counterelectrode.
&
*
,
nines 10 ( , c) and phenothiazine-1,3-indanedione merocyanines12 (
a).
can be predicted and represent an interesting feature of re-
versibly redox-switchable push/pull chromophores. Most in-
terestingly, the slightly more electron-rich examples 10a and
12a–12e display a second reversible phenothiazine oxida-
tion that occurs for compound 10a at 1477 mV and increases
with increasing acceptor strength in the series 12a–12e from
1473 to 1633 mV. In the other cases, the second oxidation
presumably lies outside the measurement range of dichloro-
methane and could not be detected. Additionally, an irrever-
sible reduction wave accounts for the acceptor moieties, N-
methyl rhodaninylidene or 1,3-indandionylidene, strongly
dependent on the substitution pattern. With increasing ac-
ceptor strength of the peripheral benzo substituents, the re-
versible reduction potentials of the rhodaninylidene mero-
cyanines 10 are shifted anodically and are detected between
Figure 4. Cyclic voltammogram of 12c. Recorded in CH2Cl2; T=293 K;
0.1m electrolyte [Bu4N][PF6]; v=100 mVsꢀ1; Pt working electrode, Ag/
AgCl reference and Pt counterelectrode.
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9987

H.-G. Kuball, T. J. J. Mꢀller et al.
ꢀ1327 (10a) and ꢀ1159 mV (10 f), whereas the indandion-
ACHTUNGTRENNUNGylidene-substituted chromophores 12 display irreversible re-
duction potentials between ꢀ1130 (12a) and ꢀ1073 mV
(12 f).
Absorption and emission behavior: The phenothiazinyl
meroACHTUNGTRENNUNGcyanines 10 and 12 display three distinct broad, un-
structured absorption bands in the UV/Vis region at 294–
314, 340–366, and 460–519 nm (Figure 6), in which the latter
Figure 6. Absorption (solid line) and emission (dashed line) of compound
10b. Recorded in CH2Cl2; T=293 K, excitation wavelength lexc =472 nm
(a.u.=arbitrary units).
Figure 7. Absorption (solid line) and emission (dashed line) of com-
pounds 14a (top) and 14b (bottom). Recorded in CH2Cl2; T=293 K, ex-
citation wavelength lexc =480 and 472 nm, respectively (a.u.=arbitrary
units).
shows the largest extinction coefficients. Occasionally, in-
tense short wavelength bands can be detected at 252–
271 nm.
The direct comparison between phenothiazine–rhodanine
merocyanine 10b and the N,N-diethyl- and N,N-diphenylani-
line models 14 (Figure 7) reveals that the longest wave-
length absorption arises from the aniline–rhodanine mero-
cyanine substructure, whereas the phenothiazinyl-specific
bands are found at higher energies. For rhodanine-type
ly, N-methylrhodanine-containing dyes 10 display distinctly
higher quantum yields (Ff =0.02–0.51) than the 1,3-indan-
dione-containing merocyanines 12 (Ff =<0.01–0.08). How-
ever, and most interestingly, the peripheral benzo substitu-
ents exert a substantial influence on the observed fluores-
cence quantum yields. Since the iodo and bromo derivatives
10c (Ff =0.10) and 10d (Ff =0.12) unexpectedly show
higher quantum yields than the unsubstituted merocyanine
10b (Ff =0.04) or the electron-rich tolyl derivative 10a
(Ff =0.02), a pronounced electronic substituent effect appa-
rently could rationalize this behavior. Indeed, the electron-
poor substituted merocyanines 10e and 10 f exhibit with 23
and 51% the highest quantum yields in this series, whereas
the cyano-substituted indandione merocyanine 12 f is the
only representative in series 12 to reveal substantial quan-
tum yields over 1%. The aniline merocyanines 14 and 15
that have been chosen as model and reference systems dis-
play a similar behavior, yet with significantly blueshifted
emission maxima and hence considerably smaller Stokes
shifts (1600-4100 cmꢀ1). Therefore, it can be stated that phe-
nothiazinyl-based merocyanines reveal significantly larger
Stokes shifts in comparison to anilines. These special fea-
tures of the merocyanines 10 and 12 are apparently correlat-
ed to the elongated conjugated systems of phenothiazines.
We performed solvatochromism studies in different solvents
for both absorption and emission spectra of the unsubstitut-
meroACHTUNGTRENNUNGcyanines 10, the longest wavelength bands lie between
460 and 481 nm, and the corresponding absorptions of the
indandione-type push/pull systems 12 appear at lower ener-
gies between 488 and 519 nm. In agreement with theoretical
calculations, merocyanines with electron-withdrawing
groups at the peripheral benzo ring of phenothiazine (10e,
10 f, 12e, and 12 f) absorb at higher energy than those with-
out (10b, 12b) or with donor substituents (10a, 12a).
All phenothiazinyl merocyanines 10 and 12 reveal pro-
nounced fluorescence and large Stokes shifts (Dn˜) that
range from 4700 to 5800 cmꢀ1 (Table 1, Figure 6), for which
the N-methylrhodanines 10 display slightly larger Stokes
shifts (5500–5800 cmꢀ1) than the 1,3-indandiones 12 (4700–
5200 cmꢀ1). These large Stokes shifts represent a peculiar
and characteristic behavior of many phenothiazine-based
chromophores.[14b,c,24–26] The broad, unstructured emission
bands show maxima at 621–688 nm. Yet the emission inten-
sity as reflected by the fluorescence quantum yields (Ff)
varies significantly with the type of merocyanine and the pe-
ripheral benzo substituent on the phenothiazine. Interesting-
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Chem. Eur. J. 2011, 17, 9984 – 9998

Phenothiazinyl Merocyanine Dyes
FULL PAPER
ed rhodanine–merocyanine 10b and the cyano-substituted
derivative 10 f. In both cases, the solvatochromism of the ab-
sorption maxima was only modest (Figure 8).
Figure 9. Absorption (top) and emission (bottom) solvatochromism of
merocyanine 10 f. Recorded in methylcyclohexane, dibutyl ether, toluene,
dioxane, THF, CH2Cl2, and benzonitrile; T=293 K, excitation wavelength
lexc =254 nm, handheld UV lamp.
625 nm (benzonitrile) to 555 nm (methylcyclohexane)
(Figure 8, top). Therefore, the Stokes shift is also solvent-de-
pendent and increases with increasing solvent polarity. The
conclusions given above are consistent with the results of
the continuums theory for solvent dependence of the posi-
tion of the absorption and emission maxima and the corre-
sponding solvent dependence of the Stokes shift (see the
Supporting Information). Qualitatively, it can be concluded
that the dipole moments of the merocyanines 10 are smaller
in the electronic ground state than those of the Franck–
Condon excited state. A comparison with quantitative re-
sults from EOA spectroscopy confirms these conclusions as
will be discussed in the following section.
Quantitative evaluation of the solvent dependence of the
Stokes shift: To quantify the variation of color (Figure 9),
Figure 8. Normalized solvent-dependent absorption and emission spectra
of merocyanines 10b (top) and 10 f (bottom). Recorded in methylcyclo-
hexane, dibutyl ether, toluene, dioxane, THF, CH2Cl2, benzonitrile, and
acetonitrile; T=293 K, excitation wavelength lexc =the corresponding
longest-wavelength absorption maximum (a.u.=arbitrary units) (for
color graphics, see the Supporting Information).
the solvatochromism of 10b and 10 f of the absorption (n˜abs
)
and the emission spectra (n˜em; Figure 8) and the solvent-de-
pendent Stokes shift have been analyzed quantitatively
within the assumption of the Onsager continuums theory,[37]
which follows within the approximation described by
Suppan et al. [Eqs. (1) and (2)].[38]
Upon variation from unpolar methylcyclohexane to mod-
estly polar benzonitrile, the longest wavelength absorption
maxima were shifted from 453 to 474 nm (10b) and from
443 to 463 nm (10 f), respectively. In spite of the fact that
the fluorescence is measured at a very low concentration
(10ꢀ6 m), the shoulder observed in the emission spectra of
10b and 10 f in methylcyclohexane may hint at ecximer for-
mation. But in all higher polar solvents, this shoulder disap-
pears, and besides, in all solvents a nearly identical band
shape is observed. Thus, no complex formation, that is, nei-
ther exciplexes nor excimers, influences the band shift. This
conclusion is further confirmed because the dipole moments
of the ground and excited state, determined from the EOA
spectra, fit in the solvatochromism of the Stokes shift (vide
infra). However, most interestingly, upon UV excitation
(Figure 9) and in the solvent-dependent emission spectra of
merocyanine 10 f (Figure 8, bottom), a considerable effect of
the solvent polarity on the emission color and wavelength
can be viewed with the naked eye (Figure 8). A pronounced
positive solvatochromism accounts for emission maxima of
625 nm in benzonitrile and 530 nm in methylcyclohexane.
For merocyanine 10b, the emission maxima range from
1
0
~
~
nabs=em ¼nabs=em
ꢀ
4pe0hca3
ꢀ
ꢁ
ð1Þ
ð2Þ
1
2
mg=e ꢁ ðmeꢀmgÞðfðerÞꢀfðn2ÞÞþ ðme2ꢀmg2Þfðn2Þ
2ðyꢀ1Þ
fðyÞ ¼
y ¼ er or n2
2yþ1
The values of er and n represent the dielectric permittivity
and the refraction index, respectively, whereas the variable
a stands for the radius of the spherical cavity. The function
f(y) allows for the correction of the internal field in a simple
approximation, sufficient for the following discussion. From
the Stokes shift [Eq. (3)]:
~
~
~
nabsꢀnem ¼ DnStokes
¼
ꢀ
ꢁ
ð3Þ
1
0
þ
ðmeꢀmgÞ ꢁ ðmeꢀmgÞðfðerÞꢀfðn2ÞÞ
~
nStokes
4pe0hca3
results the dipole moment difference jmkeꢀmg j by the fit
given in Figure 10 directly from the scalar product
Chem. Eur. J. 2011, 17, 9984 – 9998
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9989

H.-G. Kuball, T. J. J. Mꢀller et al.
(mkeꢀmg)·(mkeꢀmg) for 10b and 10 f (40ꢃ10ꢀ30 and 46ꢃ
10ꢀ30 Cm), respectively (Table 2). Thus, the linear relations
(Figure 10) provide unambiguous evidence for a large shift
Computations: A deeper understanding of the electronic
properties of the merocyanines 10b, 10 f, and 12b was
sought by inspection of the electronic structure of the fron-
tier molecular orbitals. The electron-density distribution in
the HOMO and the LUMO was computed by gas-phase
DFT calculations using Gaussian 03[39] with the B3LYP func-
tional[40] and the Pople basis 6-31+G(d,p)[41] applied to start-
ing geometries obtained from the X-ray structure analyses
of 10b and 12b, in which the n-hexyl substituent was trun-
cated to an ethyl group. The minima structures were con-
firmed by analytical frequency analysis, and hence the fron-
tier orbitals of dyes 10b, 10 f, and 12b have been pictured
(for compound 12b, see the Supporting Information). In
both HOMOs the coefficients are large in the phenothiazin-
yl moiety, whereas only small coefficients are observed at
the rhodanine and the indandione substituents, respectively.
With regards to the LUMOs, it is notable that the peripheral
benzo core of the phenothiazine does not bear significant
orbital coefficients. In contrast to the HOMOs, the coeffi-
cients are now enlarged at the internal benzo core of pheno-
thiazine, the bridging double bond, and the conjugated ac-
ceptor moiety (Figure 11). Assuming a HOMO–LUMO
transition as the dominant longest-wavelength absorption
band, the first excited state appears to originate from a
charge transfer from the phenothiazine moiety to the ac-
ceptor unit.
*
^
Figure 10. Stokes shift Dn˜ of 10b ( , dashed line) and 10 f ( , solid line)
versus f(er)ꢀf(n2). Analysis (line) based upon Onsagerꢄs continuum
theory taking f for spherical particles. Stokes shifts plotted from left to
right: in methylcyclohexane, dibutyl ether, toluene, dioxane, THF, di-
chloromethane, and benzonitrile. Additionally, for compound 10 f the
Stokes shift in acetonitrile is pictured here; see also the Supporting Infor-
mation).
Table 2. Summarized results of dielectric properties and comparison of
experimental and theoretical results for merocyanines 10b and 10 f.[a]
10b
10b
10 f
10 f
experiment
theory
experiment
theory
mSg0(mkgS0 , m?g S0
)
17 (12.0, –)
18.0
16.3
49.1
15 (–, 9.9)
16.1
16.1
45.5
mFgC2
FC1
e
Dm=jDmj=jmSe ꢀmSg
j
40 (34.0, –)
41[b] (–, 6.4)
0
(jDmk j,jDm? j)
EOA spectroscopy
Dm=jDmj=jmSe1 ꢀmeFC2[b]
40
57
49.1
46
–
45.5
Stokes shift
FC2
1
jmSe jꢀjmg
j
49.3
66.4
65.5
19.5
12
18
14
6
28.3
48.2
44.4
21.0
89
90
71
3
mFeC1
meS
meg
1
21.5
34
32
21.8
81
75
a[c]
[d]
#
g[e]
q[e]
Figure 11. HOMOs (bottom) and LUMOs (top) of merocyanines 10b
(left) and 10 f (right) (for color graphics, see the Supporting Informa-
tion).
0
0
[a] The statistical error of the experimentally determined moments is less
or about 5%. The absolute error due to the needed assumption is about
10 to 20%. [b] Dm=jDmj=jmkeꢀmg j is calculated under the assumption
of a=# and q=0. This value is very sensitive to a variation of these
three angles. A variation of a few degree changes the evaluated Dm by a
factor of 2. [c] The value a is the angle between the dipole moment of
the ground state mg and the electric dipole transition moment m of the
CT transition. [d] The value # displays the angle between the dipole
moment of the ground state and the dipole difference Dm, mg, and me in-
clude the angle [e] The values g and q lie between the dipole transition
moment m and the dipole difference Dm (dipole moments in [10ꢀ30 Cm];
1 Debye=^ 3.33562ꢃ10ꢀ30 Cm; angles in [8])
The ground (S0) and excited state (S1) geometries of
meroACTHUNRTGNEUNGcyanine 10b without peripheral substitution and the
cyano-substituted derivative 10 f were optimized by gas-
phase DFT calculations for the ground states and TD-DFT
methods for the excited states using the program package
Turbomole. Furthermore, the relaxed ground and excited
states were obtained and the corresponding Frank–Condon
states SF1C1 and SF0C2 were calculated in addition. The first
Frank–Condon state was obtained by a vertical excitation
using the optimized ground-state geometry in a TD-DFT
calculation. In 10b, the SF1C1 state is about 20922 cmꢀ1
(250.4 kJmolꢀ1) higher in energy than the ground state S0
of charges within the molecule due to the charge-transfer
(CT) transition that results in a dramatic color shift.
9990
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Chem. Eur. J. 2011, 17, 9984 – 9998

Phenothiazinyl Merocyanine Dyes
FULL PAPER
and about 2748 cmꢀ1 (32.9. kJmolꢀ1) higher than the relaxed
S1 state. The comparable values for compound 10 f are
21808 cmꢀ1 (261.0 kJmolꢀ1) for SF1C1 and 2748 cmꢀ1
(32.9 kJmolꢀ1) for S1. The energy of the SF0C2 state is about
planarization in the excited state. In addition, in the pheno-
ꢀ
ꢀ
thiazine core the nitrogen carbon bonds N1 C2 are elon-
ꢀ
ꢀ
gated, whereas the sulfur carbon bonds S10 C11 are con-
tracted upon excitation. With respect to the rhodanine
moiety, in the S1 state the structural changes manifest them-
selves in elongation of the carbonyl bond and the olefinic
double bond with concomitant contraction of adjacent
2766 cmꢀ1
(33.1 kJmolꢀ1)
(10b)
and
2657 cmꢀ1
(31.8 kJmolꢀ1) (10 f), respectively, above the ground-state
energy level of S0. The decrease of the energy from the S1FC1
state to the relaxed S1 state could be rationalized by a signif-
icant change of the geometry after excitation. The most in-
teresting aspects are the structural differences between the
SF1C1 state and the vibrationally relaxed S1 state, which repre-
sent a change of folding angles (Scheme 5) within the phe-
nothiazine core.
ꢀ
single bonds. In the excited state, the carbon carbon bond
lengths in the substituted phenothiazine benzo core exhibit
rather the character of alternating single and double bonds
than that of aromatic bonds. As a consequence, the pheno-
thiazinyl nitrogen atom, which bears a partial charge of
+0.56 in the ground state, is negatively charged in the excit-
ed state, whereas the adjacent atoms reveal an inverse be-
havior. Likewise, the carbonyl oxygen atom in the rhoda-
nine moiety displays a higher negative partial charge in the
excited state compared to the ground state. Hence, the first
excited state SF1C1 of the phenothiazinyl merocyanines pos-
sesses a highly dipolar nature. For a more detailed under-
standing, the dipole moments of the four involved states
were calculated, and for consolidated interpretation electro-
optical absorption measurements (EOAM) have been per-
formed.
Scheme 5. Folding angle and tilt angle in the butterfly structure of pheno-
thiazines.
The phenothiazine folding angle of the S0 and the S1FC1
structures of merocyanines 10b and 10 f is calculated to be
141.08 for both cases. In comparison to the ground-state
structures, the optimized vibrationally relaxed S1 state struc-
tures display significant geometry changes (Schemes 5 and
6, Table 3).
Electro-optical absorption measurements: The large ampli-
tude of the EOA spectra L(n˜f)E(n˜) assigns the longest
wavelength band as a charge-transfer transition. Note that
for all compounds of both series 10 and 12 (Scheme 3) the
fit of L(n˜f)E(n˜) as a function of the line shape of the corre-
sponding UV/Vis band and its first and second derivatives is
of sufficient quality (Figure 12). In contrast to the good fit
for 10 f throughout the CT band, a good fit for 10e is re-
stricted either to the long-wavelength flank or the short-
wavelength region of the CT band (Figure 12). This indi-
cates that the band of 10e is either not uniformly polarized,
or a superposition of contributions from absorption bands of
different conformers or isomers. Fortunately, the effect is
Scheme 6. Numeration of atoms in the PT–merocyanine dyads.
Table 3. Selected bond lengths [ꢅ] of 10b and 10 f in the S0 and the re-
laxed S1 states.
Bonds
10b
10b
10 f
10 f
S0
S1
S0
S1
ꢀ
N1 C2
ꢀ
C2 C3
1.40
1.40
1.38
1.40
1.45
1.35
1.48
1.21
1.78
1.41
1.38
1.40
1.44
1.39
1.38
1.42
1.44
1.37
1.46
1.23
1.76
1.40
1.39
1.40
1.41
1.40
1.38
1.40
1.45
1.35
1.48
1.21
1.79
1.41
1.38
1.41
1.43
1.40
1.38
1.43
1.43
1.37
1.46
1.23
1.76
1.41
1.39
1.40
ꢀ
C3 C4
ꢀ
C4 C5
ꢀ
C5 C6
ꢀ
C6 C7
ꢀ
C7 C8
ꢀ
C8 O9
ꢀ
S10 C11
ꢀ
C11 C2
ꢀ
C11 C12
ꢀ
C12 C5
Figure 12. UV/Vis spectra of the CT transition (10e: dashed line, 10 f:
dotted line), the experimental EOA spectra (f=08C): open symbols;
f=908C: filled symbols) and the multilinear fit (solid line) of the EOA
Most remarkably, the increase of the folding angles to
* *
^ ^
, ), measured in 1,4-dioxane at T=
spectra of 10e (
,
) and 10 f (
157.98 (10b) and to 161.18 (10 f) indicates a considerable
298 K (for color graphics, see the Supporting Information).
Chem. Eur. J. 2011, 17, 9984 – 9998
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9991

H.-G. Kuball, T. J. J. Mꢀller et al.
small, and the electric dipole moment of the ground state mg
and the dipole moment difference Dm=jDmj=jmkeꢀmg j can
be determined from the electro-optical coefficients[42] with
good accuracy by neglecting polarizability effects (Table 2).
The angles between the various dipole moments can also be
estimated (Table 2).
Figure 14 summarizes the results of the theoretical analy-
sis, which are consistent in their tendency with those of the
emission and EOA spectroscopy (Table 2). As expected, the
The dipole moment of the ground state (mg) of 10b with
16.7ꢃ10ꢀ30 Cm is only slightly higher than that of 10 f
(14.7ꢃ10ꢀ30 Cm), although the nitrile group itself possesses
a partial dipole moment of about 13ꢃ10ꢀ30 Cm (Table 2).
Hence, either the dipole moments of the ground mg and ex-
cited state mke and the dipole difference Dm=mekꢀmg are dif-
ferently oriented with respect to each other, or the cyano
substitution has totally changed the electronic structure of
10 f. The latter can be excluded by the results of the DFT
calculations. From Dm, with its angle q deviating approxi-
mately about ꢂ108 to ꢂ208 from the direction of the transi-
tion moment m, it follows for 10b and 10 f that Dm is ap-
proximately aligned parallel to m in both cases. The angle #
results approximately in #ffia (Table 2). Furthermore, the
dipole moment of the ground state is oriented parallel to
the transition moment for 10b, whereas for 10 f the angle a
is about 908 (Table 2).
Because mg and Dm for 10b are oriented parallel, the ab-
solute value of the dipole moment of the excited state mek
can be evaluated to be about 57ꢃ10ꢀ30 Cm. The mek value is
not available for 10 f because Dm and mke (k=CT transition)
are oblique-angled with respect to each other. This is con-
firmed by the DFT calculations, for which the absolute
value of Dm is different from the difference of the absolute
values jmSe1 jꢀjmgFC2 j. Also, the quantitative evaluation of
the Stokes shift yields an increase of jDmj=jmFeC1ꢀmgS0 j of
40ꢃ10ꢀ30 Cm for 10b and 46ꢃ10ꢀ30 Cm for 10 f, which is a
good independent proof for the conclusions from the EOA
spectra (Table 2). The absolute orientations of mg, Dm, and
m with respect to the molecular framework are not available
from the experimental results.
Figure 14. The polarity change of 10 f depicted schematically for the pro-
cess “excitation to the Franck–Condon state SF1C1, internal conversion to
the relaxed S1 state, emission to Franck–Condon state SF0C2, and relaxa-
tion to S0 state:” The comparison of theoretical and experimental results
(SI=^ 1ꢃ10ꢀ30 Cm=^ 3.33562 D); gray: experimental results, measured in
1,4-dioxane; black: theoretical results for gas phase. The scheme of 10b
possesses the same structure. In addition, the complete set of dielectric
data of 10b and 10 f are given in Table 3; the energy differences for 10b
are E(S1FC1, solv)ꢀE(Ss0olv)=21413 cmꢀ1
;
E(S1FC1, gas)ꢀE(S0gas)=20922 cmꢀ1
;
;
E(S1FC1, gas)ꢀE(S1gas)=2748 cmꢀ1
;
E(S1solv)ꢀE(SF0C2, solv)=16420 cmꢀ1
E(S1gas)ꢀE(S0FC2, gas)=15408 cmꢀ1; E(S1FC2, gas)ꢀE(S0gas)=2766 cmꢀ1
.
DFT method overestimates the values of the ground-state
dipole moments mg (18.0ꢃ10ꢀ30 Cm for 10b and 16.1ꢃ
10ꢀ30 Cm for 10 f) in comparison with the EOA data (16.7ꢃ
10ꢀ30 Cm for 10b and 14.5ꢃ10ꢀ30 Cm for 10 f) if additionally
taking into account the solvent interaction, which led to an
increase of the calculated dipole moments due to the reac-
tion field of about 15 to 25%.[43] The transition dipole mo-
ments meg for the excited Franck–Condon CT state SF1C1 are
computed as 19.5ꢃ10ꢀ30 Cm for 10b and 21.0ꢃ10ꢀ30 Cm for
10 f, whereas the UV/Vis measurement display values of
21.5ꢃ10ꢀ30 Cm for 10b and 21.8ꢃ10ꢀ30 Cm for 10 f. Combin-
ing the results of the emission and EOA spectroscopy with
those of the theoretical calculations allows us to discuss the
process (Figure 14): S0!SF1C1!S1!S0FC2!S0; whereas the
EOA spectroscopy yields Dm for the excited molecule in its
Franck–Condon state S0!SF1C1 the solvent dependence of
the emission spectra gives Dm for the transition between an
equilibrated excited state and a Franck–Condon ground
state SF0C2 that possesses the geometry of the equilibrium ex-
cited state. For 10b and 10 f, the dipole difference jmkeꢀmg j
from the EOA measurement and the solvent-dependent
emission is the same within the experimental error
(Table 2).
DFT calculations allow one to correlate the computed
transition moment direction, as depicted in Figure 13, of the
molecular scaffold to the experimental findings. The theoret-
ical calculations also fit the quantitative trend of the experi-
mental results. Here it has to be mentioned that the DFT
calculations are performed for the gas phase, whereas the
experimental data are corrected for solvent effects in the ap-
proximation of the Onsager theory, not taking into account
dispersion interaction and polarizability effects.
This large and nearly identical variation of the dipole mo-
ments by the excitation to the Franck–Condon state S0!
SF1C1 and the emission S1!SF0C2 suggests that during the re-
laxation from S1FC1!S1 and from S0FC2!S0 the polarity of
10b and 10 f is maintained. Thus, the different geometries in
Figure 13. TD-DFT computed orientations of dipole moments mg, mke, and
the transition moment m of the CT transitions of dye 10b (left) and dye
10 f (right) (for color graphics, see the Supporting Information).
9992
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Chem. Eur. J. 2011, 17, 9984 – 9998

Phenothiazinyl Merocyanine Dyes
FULL PAPER
the Franck–Condon states and the equilibrium states do not
essentially determine the dipole moment change Dm. The
dipole moment change is only determined by the charge dis-
location due to the excitation. This conclusion is supported
by calculating only negligible differences between the excit-
ed-state dipole moments me in the SF1C1 and the relaxed S1
state as well for SF0C2 and S0 for 10b (meFC1 66.4ꢃ10ꢀ30 Cm, mSe
1
65.5ꢃ10ꢀ30 Cm) and for 10 f (meFC1 =48.2ꢃ10ꢀ30 Cm, meS1 =
44.4ꢃ10ꢀ30 Cm). Therefore, the change of geometry due to
the relaxation of the SF1C1(S0FC2) into the S1(S0) relaxed state
is only subordinate for the existence of a large dipole
moment of the excited CT state. The extrapolation to the
Stokes shift in nonpolar solvents [Eq. (2)] leads to an energy
change by the equilibration process from SF1C1 to S1 for 10b
to about 900 cmꢀ1, which is consistent with the TD-DFT re-
sults (Figure 14).
*
^
Figure 15. Value of Dm for both sets of compounds 10 ( ) and 12 ( ) as a
function of the Hammett parameter sp (Dm=43.1ꢃ10ꢀ30 Cm to 17.4ꢃ
10ꢀ30 Cm).
The dipole moment of the longest-wavelength excited
state of 10b is strongly enhanced by a displacement of
charge along the direction of the transition dipole moment
as visualized by the dipole moment me (Figure 13), the de-
picted HOMO and LUMO orbitals (Figure 11), and last but
not least experimentally by the angles of about 08 and 328
found for q and #, respectively. It is interesting to see that
the nitrile group in 10 f with its partial dipole moment of
13ꢃ10ꢀ30 Cm does not essentially influence the dipole tran-
sition moment, although this dipole moment lies approxi-
mately perpendicular to m (a=818, #=758, Figure 13). The
Dm value remains approximately parallel to m relative to
10b, and thus, also relative to the displacement of charge
with the excitation process. If the strong polar group is not
able to rotate the transition moment in 10 f, it can be sug-
gested that the substitution is of minor significance for the
charge displacement (i.e., the charge displacement is by ap-
proximation independent from the substitution pattern in
the 7-position of the phenothiazine core). A minor influence
can be seen from the nearly linear dependence of Dm for
both sets of compounds 10 and 12 as a function of the Ham-
mett parameter sp (Figure 15), as shown for the redox po-
tential E00=þ1 in the electronic ground state. Whether Dm is
suitable to characterize phenomenological push/pull chro-
mophores like the redox potential E00=þ1 cannot be answered
at the moment because there is no obvious theoretical sub-
stantiation.
flected by fluorescence quantum yields is strongly depen-
dent on the electron deficiency of the peripheral benzo ring
of the phenothiazine. A peculiar aspect of this class of mero-
cyanines is their distinct difference between absorption and
emission solvatochromism, thus revealing a strong influence
of the solvent polarity on the emission properties and only
minor effects on the absorption behavior, which is based on
the very different dipole moments of the ground and the ex-
cited CT states. A large change in the dipole moment Dm
upon excitation from the ground state to the excited state
could be proven. Theoretical DFT and TD-DFT computa-
tions indicate a charge transfer upon excitation, which re-
sults in a highly polar excited state. As a consequence, the
orientation of the dipole moments in the excited state is
changed. Here, the considerable planarization of the pheno-
thiazine moiety does not influence the polarity of the excit-
ed state. As a consequence, for enhancing or diminishing
the polarity of a merocyanine through excitation, substituent
variation with groups that contain partial dipole moments,
which are not oblique-angled with respect to the transition
moment of the charge-transfer transition, can be proposed.
The value of Dm=mkeꢀmg increases if the partial dipole
moment of a substituent is oriented parallel to the effect of
charge displacement by the excitation. On the other hand,
Dm=mkeꢀmg decreases if the partial dipole moment of a sub-
stituent is oriented antiparallel or oblique-angled with an
angle larger than ꢂ908 with respect to the transition
moment of the charge-transfer transition. Apparently, the
created moment of the CT transition and the moment of the
substituent obey LeFevreꢄs law of additivity.[44] Therefore,
this class of highly fluorescent, polarity-sensitive merocya-
nines can turn into medium-sensitive fluorescence markers,
poling probes, or sensors with simultaneous redox switcha-
blility.
Conclusion
Two series of phenothiazinyl merocyanines were readily syn-
thesized from phenothiazinyl aldehydes and N-methylrhoda-
nine or indan-1,3-dione in good yields. All representatives
display Nernstian behavior of the phenothiazine-centered
oxidation in cyclic voltammetry and display a broad range
of fine-tunable redox properties as reflected by a good cor-
relation between Hammett parameters sp and the oxidation
potentials E00=þ1. Furthermore, all merocyanines display in-
tense deep-colored absorption bands and intense emission
with large Stokes shifts. The fluorescence efficiency as re-
Experimental Section
General: Reagents, catalysts, ligands, and solvents were reagent grade
when purchased and used without further purification. THF and 1,4-diox-
Chem. Eur. J. 2011, 17, 9984 – 9998
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9993

H.-G. Kuball, T. J. J. Mꢀller et al.
ane were dried and distilled according
to standard procedures.[45] The synthe-
ses of the aldehydes 3–6 were per-
formed according to literature proce-
dures, and the syntheses of the alde-
hydes 7 and 8 are reported in the Sup-
porting Information. Column chroma-
tography was performed on silica gel
60, mesh 70–230. TLC used silica gel
plates. 1H and 13C NMR spectra were
Table 4. Experimental details of the synthesis of merocyanines 10, 12, 14, and 15.
Entry
Aldehyde [mg]
(mmol)
9/11 [mg]
(mmol)
Treaction (treaction
)
Merocyanines [mg]
(yield [%])
1[a]
2[b]
253 (0.63) of 7
156 (0.50) of 3
218 (0.50) of 6
390 (1.00) of 4
156 (0.46) of 5
168 (0.50) of 8
241 (0.60) of 7
312 (1.00) of 3
175 (0.40) of 6
390 (1.00) of 4
170 (0.50) of 5
202 (0.60) of 8
89 (0.5) of 13a
274 (1.00) of 13b
30 (0.17) of 13a
274 (1.00) of 13b
102 (0.69) of 9
74 (0.5) of 9
reflux temp (0.5 h)
room temp (1 h)
reflux temp (1 h)
reflux temp (0.5 h)
room temp (1 h)
reflux temp (1 h)
reflux temp (0.5 h)
room temp (1 h)
reflux temp (1 h)
room temp (1 h)
reflux temp (0.5 h)
reflux temp (1 h)
reflux temp (1 h)
reflux temp (1 h)
reflux temp (3 h)
reflux temp (1 h)
318 (95) of 10a
194 (88) of 10b
261 (92) of 10c
346 (67) of 10d
187 (87) of 10e
171 (74) of 10 f
157 (50) of 12a
331 (75) of 12b
117 (53) of 12c
302 (58) of 12d
128 (55) of 12e
152 (54) of 12 f
125 (82) of 14a
316 (79) of 14b
43 (83) of 15a
321 (80) of 15b
3[a]
81 (0.55) of 9
161 (1.10) of 9
84 (0.55) of 9
140 (0.95) of 9
967 (0.66) of 11
146 (1.00) of 11
93 (0.64) of 11
161 (1.10) of 11
73 (0.50) of 11
140 (0.96) of 11
81 (0.55) of 9
162 (1.10) of 9
28 (0.2) of 11
162 (1.10) of 11
4[b]
5[b]
6[a]
7[a]
conducted
in
CD2Cl2,
CDCl3,
8[b]
[D6]acetone, and [D8]THF (locked to
Me4Si).[46] The assignments of quater-
nary C, CH, CH2, and CH3 have been
made by using distortionless enhance-
ment by polarization transfer (DEPT)
spectra. Elemental analyses were car-
ried out in the Microanalytical Labo-
ratories of the Organisch-Chemisches
Institut, Ruprecht-Karls-Universitꢁt,
Heidelberg, Germany, and of the Insti-
tut fꢀr Pharmazeutische Chemie,
Heinrich-Heine-Universitꢁt, Dꢀssel-
dorf, Germany.
9[a]
10[b]
11[c]
12[a]
13[a]
14[a]
15[d]
16[a]
[a] According to GP 1. [b] According to GP 2. [c] Reaction in toluene with T3P (175 mg, 0.55 mmol, 1.1 equiv;
50 wt% in DCE, 0.2 mL). [d] Reaction in acetic acid (0.4 mL) and ammonium acetate (13 mg).
solved (0.1m) in a mixture of methanol and toluene (2:1) and piperidine
Electrochemistry: Cyclic voltammetry
(5 equiv) was added (for experimental details, see Table 4). The color
changed immediately from yellow to red. After reaction at room temper-
ature or under heating to reflux temperature for the time indicated, the
precipitate was collected. After purification, merocyanines 10 and 12
were obtained as analytically pure orange to deep-red solids.
experiments were performed under argon in dry and degassed CH2Cl2 at
room temperature and at scan rates of 100, 250, 500, and 1000 mVsꢀ1
.
The electrolyte was Bu4NPF6 (0.1m). The working electrode was a 1 mm
platinum disk, the counterelectrode was a platinum wire, and the refer-
ence electrode was an Ag/AgCl electrode. The potentials were corrected
to the internal standard of Fc/Fc+ in CH2Cl2 (E00=þ1 =450 mV).[47]
(Z)-5-[(10-Hexyl-7-p-tolyl-10H-phenothiazine-3-yl)methylene]-3-methyl-
2-thioxothiazolidine-4-one (10a): According to GP 1, compound 10a was
obtained as a red solid after column chromatography on silica by using
hexane/acetone (15:1) as eluent. M.p. 2068C; 1H NMR (500 MHz,
CD2Cl2): d=0.85–0.94 (m, 3H), 1.27–1.38 (m, 4H), 1.41–1.51 (m, 2H),
1.82 (quint, J=7.5 Hz, 2H), 2.39 (s, 3H), 3.49 (s, 3H), 3.87–3.91 (m, 2H),
6.91 (d, J=8.6 Hz, 1H), 6.94 (d, J=8.5 Hz, 1H), 7.21–7.26 (m, 3H), 7.30–
7.34 (m, 2H), 7.39 (dd, J=2.2 Hz, J=8.5 Hz, 1H), 7.44 (d, J=8.2 Hz,
2H), 7.59 ppm (s, 1H); 13C NMR (125 MHz, CD2Cl2): d=14.1 (CH3),
21.1 (CH3), 23.0 (CH2), 26.8 (CH2), 27.0 (CH2), 31.4 (CH3), 31.8 (CH2),
48.3 (CH2), 115.0 (CH), 116.3 (CH), 120.4 (Cquat), 123.9 (Cquat), 125.1
(Cquat), 125.7 (CH), 126.2 (CH), 126.5 (2 CH), 127.7 (Cquat), 129.4 (CH),
129.9 (2 CH), 131.3 (CH), 132.5 (CH), 136.6 (Cquat), 136.9 (Cquat), 137.5
(Cquat), 142.8 (Cquat), 147.6 (Cquat), 168.0 (Cquat), 193.8 ppm (Cquat); IR
(KBr): n˜ =2956 (w), 1706 (s), 1595 (w), 1577 (m), 1470 (s), 1405 (m),
1290 (s), 1249 (m), 1128 (w), 1108 (w), 1050 (w), 9891 (w), 932 (w), 886
(w), 803 cmꢀ1 (w); UV/Vis (CH2Cl2): lmax (e)=269 (27000), 302 (25000),
360 (19000), 481 nm (22000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 532 (19),
531 (36), 530 (100) [M]+, 459 (20) [MꢀC5H11]+, 446 (18), 445 (55)
[MꢀC6H13]+, 345, (21), 344 (80), 326 (10), 58 (10), 44 (21), 43 (14); ele-
mental analysis calcd (%) for C30H30N2OS3 (530.8): C 67.89, H 5.70, N
5.28; found: C 67.65, H 5.70, N 5.23.
Electrochromism: The very small difference of absorbance of a dilute so-
lution in the presence (EF(n˜,f)) and in the absence (E(n˜)) of an external-
ly applied electric field F measured with linearly polarized light for two
different azimuth angles f=08 and f=908 towards F as a function of the
wavenumber n˜ represents the electro-optical absorption spectroscopy
(EOA) [Equation (4)]:
Â
Ã
F
ꢀ2
~
~
~
~
Lðn; fÞEðnÞ ¼ E ðn; fÞ ꢀ EðnÞ F
ð4Þ
The absorbance differences for these two azimuth angles correspond to a
linear dichroism of a solution in an electric field. Analysis of the wave-
number dependence of this absorption anisotropy [Eq. (4)] as a function
of the line shape of the corresponding UV band and its first and second
derivative yields the orientation of the electric dipole transition moment
meg(m=meg/jmeg j) with respect to the permanent dipole moment (mg) of
the electronic ground state of a molecule, the static dipole moment of
the ground state jmg j and the dipole moment difference jDmj=jmkeꢀmg j.
The parameter mke is the dipole moment of the kth excited electronic
state (for further details, see the Supporting Information). If not indicat-
ed otherwise, the absorption anisotropies have been measured in 1,4-di-
oxane. To increase the sensitivity of the absorption measurement, an AC
and DC electric field of each about 10 kV have been applied to cells pos-
sessing electrodes of about 30 mm in length which are about 3 mm apart.
(Z)-5-[(10-Hexyl-10H-phenothiazine-3-yl)methylene]-3-methyl-2-thioxo-
thiazolidine-4-one (10b): According to GP 2, compound 10b was ob-
tained as red crystals after crystallization and trituration with methanol.
M.p. 1598C; 1H NMR (300 MHz, CD2Cl2): d=0.84–0.90 (m, 3H), 1.26–
1.34 (m, 4H), 1.36–1.48 (m, 2H), 1.72–1.84 (m, 2H), 3.46 (s, 3H), 3.84 (t,
J =7.6 Hz, 2H), 6.85–6.90 (m, 2H), 6.90–6.97 (m, 1H), 7.06–7.19 (m,
3H), 7.28 (dd, J=8.6 Hz, J=2.2 Hz, 1H), 7.55 ppm (s, 1H); 13C NMR
(75 MHz, CD2Cl2): d=14.0 (CH3), 22.9 (CH2), 26.8 (CH2), 26.9 (CH2),
31.4 (CH3), 31.7 (CH2), 48.1 (CH2), 115.7 (CH), 116.1 (CH), 120.3 (Cquat),
123.6 (CH), 125.5 (Cquat) 127.6 (CH), 127.9 (CH), 129.3 (CH), 131.1
(CH), 132.4 (CH), 143.9 (Cquat) 147.8 (Cquat) 167.9 (Cquat) 193.9 ppm
(Cquat); IR (KBr): n˜ =2956 (w), 2925 (w), 2857 (w), 1710 (m), 1634 (w),
1589 (m), 1569 (m), 1495 (w), 1468 (s), 1443 (w), 1425 (w), 1405 (w),
1370 (m), 1354 (w), 1354 (w), 1292 (s), 1253 (m), 1224 (m), 1127 (m),
1107 (m), 749 (w), 738 cmꢀ1 (w); UV/Vis (CH2Cl2): lmax (e)=252
(28000), 304 (25000), 366 (25000), 474 nm (34000 Lmolꢀ1 cmꢀ1); HR-EI:
m/z calcd for C23H24N2OS3: 440.1051; found: 440.1041; EI-MS (70 eV):
Synthesis of merocyanines 10, 12, 14, and 15 by Knoevenagel condensa-
tions of the aldehydes 4–8 and 13 with N-methylrhodanine and indane-
1,3-dione (general procedure 1, GP 1):
A mixture of the aldehyde
(1.00 equiv) and N-methylrhodanine (9; 1.10 equiv) or indane-1,3-dione
(11; 1.10 equiv) was dissolved (0.1–0.5m) in a mixture of ethanol and tol-
uene (1:1) and piperidine (1–5 equiv) was added (for experimental de-
tails, see Table 4). The color changed immediately from yellow to red.
After heating to reflux temperature for the time indicated, the precipi-
tate was collected. After purification, merocyanines 10, 12, 14, and 15
were obtained as analytically pure orange to deep-red solids.
Synthesis of merocyanines 10 and 12 by Knoevenagel condensations of
aldehydes 3–5 with N-methylrhodanine and indane-1,3-dione (general
procedure 2, GP 2): A mixture of the aldehyde (1.00 equiv) and N-meth-
ylrhodanine (9; 1.10 equiv) or indane-1,3-dione (11; 1.10 equiv) was dis-
9994
www.chemeurj.org
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 9984 – 9998

Phenothiazinyl Merocyanine Dyes
FULL PAPER
m/z (%): 442 (18), 441 (28), 440 (100) [M]+, 369 (23) [MꢀC5H11]+, 355
(30) [MꢀC6H13]+, 254 (42); elemental analysis calcd (%) for
C23H24N2OS3 (440.7): C 62.69, H 5.49, N 6.36; found: C 62.56, H 5.50, N
6.35.
10 f was obtained as a red solid after column chromatography on silica by
using hexane/acetone (15:1) as eluent and after subsequent recrystalliza-
1
tion from dichloromethane and hexane. M.p. 2258C; H NMR (500 MHz,
CD2Cl2): d=0.88 (t, J=6.8 Hz, 3H), 1.28–1.34 (m, 4H), 1.39–1.48 (m,
2H), 1.74–1.83 (m, 2H), 3.49 (s, 3H), 3.86–3.92 (m, 2H), 6.90 (d, J=
8.6 Hz, 1H), 6.96 (d, J=8.6 Hz, 1H), 7.22 (d, J=1.9 Hz, 1H), 7.32–7.37
(m, 2H), 7.45 (dd, J=1.9, 8.5 Hz, 1H), 7.59 ppm (s, 1H); 13C NMR
(125 MHz, CD2Cl2): d=14.1 (CH3), 22.9 (CH2), 26.7 (CH2), 26.8 (CH2),
31.5 (CH3), 31.7 (CH2), 48.5 (CH2), 106.6 (Cquat), 115.0 (CH), 116.6 (CH),
118.7 (Cquat), 121.8 (Cquat), 124.6 (Cquat), 124.9 (Cquat), 129.1 (Cquat), 129.5
(CH), 130.7 (CH), 131.3 (CH), 131.8 (CH), 132.4 (CH), 146.1 (Cquat),
148.1 (Cquat), 168.0 (Cquat), 193.7 ppm (Cquat); IR (KBr): n˜ =2923 (w), 2854
(w), 2221 (m), 1704 (s), 1595 (w), 1575 (m), 1472 (s), 1400 (m), 1290 (s),
1253 (m), 1127 (m), 1108 (m), 915 (w), 801 cmꢀ1 (w); UV/Vis (CH2Cl2):
lmax (e)=294 (25000), 362 (17000), 458 nm (21000 Lmolꢀ1 cmꢀ1); EI-MS:
m/z (%): 467 (16), 466 (30) [M]+, 465 (100) [M]+, 394 (24) [MꢀC5H11]+,
381 (12), 380 (26) [MꢀC6H13]+, 364 (13), 293 (12), 280 (19), 279 (63), 261
(12), 247 (10), 43 (22); elemental analysis calcd (%) for C24H23N3OS3
(465.7): C 61.90, H 4.98, N 9.02; found: C 61.70, H 4.99, N 8.98.
(Z)-5-[(10-Hexyl-7-iodo-10H-phenothiazine-3-yl)methylene]-3-methyl-2-
thioxothiazolidine-4-one (10c): According to GP 1, compound 10c was
obtained as a red solid after column chromatography on silica by using
hexane/acetone (10:1) as eluent. M.p. 1908C; 1H NMR (500 MHz,
CD2Cl2): d=0.82 ꢀ0.94 (m, 3H), 1.24–1.37 (m, 4H), 1.38–1.47 (m, 2H),
1.77 (quint, J=7.5 Hz, 2H), 3.47 (s, 3H), 3.83 (t, J=7.3 Hz, 2H), 6.62 (d,
J=8.6 Hz, 1H), 6.90 (d, J=8.6 Hz, 1H), 7.20 (d, J=2.2 Hz, 1H), 7.31
(dd, J=2.2, 8.6 Hz, 1H), 7.39 (d, J=2.0 Hz, 1H), 7.44 (dd, J=2.0, 8.6 Hz,
1H), 7.58 ppm (s, 1H); 13C NMR (125 MHz, CD2Cl2): d=14.1 (CH3),
22.9 (CH2), 26.8 (CH2), 26.9 (CH2), 31.4 (CH3), 31.7 (CH2), 48.2 (CH2),
116.0 (CH), 117.8 (CH), 120.9 (Cquat), 125.0 (Cquat), 126.2 (Cquat), 128.1
(Cquat), 129.4 (CH), 131.2 (CH), 132.2 (CH), 135.6 (CH), 136.6 (CH),
144.0 (Cquat), 147.4 (Cquat), 168.2 (Cquat), 193.7 ppm (Cquat); IR (KBr): n˜ =
2954 (w), 2926 (w), 1709 (s), 1585 (s), 1560 (w), 1497 (w), 1461 (s), 1292
(s), 1245 (m), 1129 (m), 1108 (m), 988 (w), 931 (w), 797 cmꢀ1 (w);
MALDI MS: m/z (%): 569 (10), 568 (30), 567 (48), 566 (100) [M]+; UV/
Vis (CH2Cl2): lmax (e)=257 (26000), 299 (21000), 362 (20000), 467 nm
(25000 Lmolꢀ1 cmꢀ1); elemental analysis calcd (%) for C23H23IN2OS3
(566.5): C 48.76, H 4.09, N 4.94; found: C 49.00, H 4.26, N 4.86.
2-[(10-Hexyl-7-p-tolyl-10H-phenothiazine-3-yl)methylene]-1H-indene-
1,3(2H)-dione (12a): According to GP 1, compound 12a was obtained as
a red solid after column chromatography on silica by using hexane/ace-
tone (10:1) as eluent; 97.6 mg (0.24 mmol, 40%) starting material was
isolated. M.p. 1558C; 1H NMR (500 MHz, CD2Cl2): d=0.90 (t, J=
6.9 Hz, 3H), 1.28–1.40 (m, 4H), 1.44–1.52 (m, 2H), 1.81–1.90 (m, 2H),
2.37 (s, 3H), 3.93 (t, J=7.4 Hz, 2H), 6.90–6.99 (m, 2H), 7.24 (d, J=
8.1 Hz, 2H), 7.34 (d, J=2.0 Hz, 1H), 7.39 (dd, J=2.0, 8.5 Hz, 1H), 7.45
(d, J=8.1 Hz, 2H), 7.68 (s, 1H), 7.77–7.81 (m, 2H), 7.89–7.99 (m, 2H),
8.29 (dd, J=1.9, 8.7 Hz, 1H), 8.42 ppm (d, J=1.9 Hz, 1H); 13C NMR
(125 MHz, CD2Cl2): d=14.1 (CH3), 21.1 (CH3), 23.0 (CH2), 26.9 (CH2),
27.0 (CH2), 31.8 (CH2), 48.5 (CH2), 114.9 (CH), 116.4 (CH), 123.1 (CH),
123.2 (CH), 123.5 (Cquat), 124.1 (Cquat), 125.7 (CH), 126.1 (CH), 126.5 (2
CH),126.8 (Cquat), 128.1 (Cquat), 129.9 (2 CH), 133.0 (CH), 135.2 (CH),
135.4 (CH), 136.0 (CH), 136.81 (Cquat), 136.83 (Cquat), 137.6 (Cquat), 140.4
(Cquat), 142.2 (Cquat), 142.8 (Cquat), 145.3 (CH), 149.8 (Cquat), 190.0 (Cquat),
190.7 ppm (Cquat); IR (KBr): n˜ =2955 (w), 2927 (w), 2371 (w), 2346 (w),
1683 (m), 1597 (w), 1567 (m), 1469 (s), 1412 (w), 1248 (w), 1204 (m),
1154 (w), 1086 (w), 1051 (w), 998 (w), 802 (w), 735 cmꢀ1 (w); UV/Vis
(CH2Cl2): lmax (e)=268 (50000), 311 (24000), 340 (27000), 519 nm
(29000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 529 (10) [M]+, 444 (13)
[MꢀC6H13]+; elemental analysis calcd (%) for C35H31NO2S (529.7): C
79.36, H 5.90, N 2.64; found C 79.10, H 6.04, N 2.49.
(Z)-5-[(7-Bromo-10-hexyl-10H-phenothiazine-3-yl)methylene]-3-methyl-
2-thioxothiazolidin-4-one (10d): According to GP 2, compound 10d was
obtained as red crystals after purification by column chromatography on
1
silica by using hexane/ethyl acetate (4:1) as eluent. M.p. 1948C; H NMR
(500 MHz, CD2Cl2): d=0.85–0.90 (m, 3H), 1.28–1.33 (m, 4H), 1.39–1.46
(m, 2H), 1.73–1.81 (m, 2H), 3.48 (t, J=7.3 Hz, 2H), 6.75 (d, J=8.7 Hz,
1H), 6.91 (d, J=8.6 Hz, 1H), 7.20–7.24 (m, 2H), 7.27 (dd, J=2.2, 8.6 Hz,
1H), 7.33 (dd, J=2.1, 8.6 Hz, 1H), 7.59 ppm (s, 1H); 13C NMR
(125.5 MHz, CD2Cl2): d=14.1 (CH3), 22.9 (CH2), 26.8 (CH2), 26.9 (CH2),
31.5 (CH3), 31.7 (CH2), 48.3 (CH2), 115.6 (Cquat), 116.0 (CH), 117.4 (CH),
120.9 (Cquat), 124.9 (Cquat), 126.1 (Cquat), 128.1 (Cquat), 129.4 (CH), 129.9
(CH), 130.6 (CH), 131.3 (CH), 132.2 (CH), 143.3 (Cquat), 147.4 (Cquat),
168.0 (Cquat), 193.7 ppm (Cquat); IR (KBr): n˜ =2967 (w), 2927 (w), 2859
(w), 1709 (m), 1586 (s), 1562 (m), 1461 (s), 1405 (m), 1354 (m), 1290 (s),
1246 (m), 1128 (m), 1103 (m), 800 cmꢀ1 (w); UV/Vis (CH2Cl2): lmax (e)=
299 (16000), 361 (16000), 467 nm (21000 Lmolꢀ1 cmꢀ1); EI-MS (70 eV):
81
m/z (%): 522 (14), 521 (26), 520 (100) [Mꢀ Br]+, 519 (24), 518 (86)
79
[Mꢀ Br]+, 449 (22), 447 (19) [MꢀC5H11]+, 435 (40), 433 (38)
[MꢀC6H13]+, 335 (14), 334 (67), 333 (16), 332 (62), 267 (10), 253 (15); el-
emental analysis calcd (%) for C23H23N2OS3Br (519.5): C 53.17, H 4.46,
N 5.39; found: C 53.05, H 4.42, N 5.26.
2-[(10-Hexyl-10H-phenothiazine-3-yl)methylene]-2H-indan-1,3-dione
(12b): According to GP 2, compound 12b was obtained as red crystals
after purification by column chromatography on silica by using hexane/
ethyl acetate (4:1) as eluent. M.p. 1458C; 1H NMR (300 MHz, CD2Cl2):
d=0.84–0.90 (m, 3H), 1.28–1.36 (m, 4H), 1.46–1.56 (m, 2H), 1.80–1.92
(m, 2H), 4.07 (t, J=7.1 Hz, 2H), 7.02 (m, 1H), 7.09–7.27 (m, 4H), 7.68
(s, 1H), 7.89–8.00 (m, 3H), 8.35 (dd, J=8.8, 2.0 Hz, 1H), 8.63 ppm (d,
J=2.1 Hz, 1H); 13C NMR(75 MHz, CD2Cl2): d=14.1 (CH3), 23.0 (CH2),
26.9 (CH2), 27.1 (CH2), 31.8 (CH2), 48.4 (CH2), 115.0 (CH), 116.3 (CH),
123.1 (CH), 123.2 (CH), 123.8 (Cq), 124.0 (CH), 126.9 (Cquat), 127.7 (CH),
127.9 (CH), 128.1 (Cquat), 133.1 (CH), 135.2 (CH), 135.3 (CH), 135.9
(CH), 140.4 (Cquat), 142.8 (Cquat), 143.4 (Cquat), 145.4 (CH), 150.1 (Cquat),
189.7 (Cquat), 190.7 ppm (Cquat); EI-MS (70 eV): m/z (%): 440 (23)
[M+H]+, 439 (84) [M+], 369 (11), 368 (45) [MꢀC5H11]+, 355 (25), 354
(100) [MꢀC6H13]+, 336 (14), 43 (13), 28 (41); IR (KBr): n˜ =3060 (w),
2954 (m), 2926 (m), 2853 (m), 1679 (s), 1609 (m), 1584 (s), 1562 (s), 1496
(m), 1466 (s), 1442 (m), 1414 (s), 1351 (s), 1288 (m), 1251 (m), 1205 (s),
1176 (m), 1156 (m), 1090 (m), 998 (m), 737 cmꢀ1 (s); UV/Vis (CH2Cl2):
lmax (e)=254 (31000), 268 nm (20000 Lmolꢀ1 cmꢀ1); HR-EI: m/z calcd
for C28H25NO2S3: 439.1606, found: 439.1605; elemental analysis calcd (%)
for C28H25NO2S3 (439.6): C 76.51, H 5.73, N 3.19, S 7.29, O 7.28; found: C
76.26, H 6.03, N 3.08, S 7.17, O 7.46.
(Z)-10-Hexyl-7-[(3-methyl-4-oxo-2-thioxothiazolidine-5-ylidene)methyl]-
10H-phenothiazine-3-carbaldehyde (10e): According to GP 2, compound
10e was obtained as a red solid after crystallization and trituration with
methanol. M.p. 1968C; 1H NMR (500 MHz, CD2Cl2): d=0.83–0.93 (m,
3H), 1.27–1.37 (m, 4H), 1.39–1.50 (m, 2H), 1.78–1.85 (m, 2H), 3.48 (s,
3H), 3.91 (t, J =7.4 Hz, 2H), 6.95 (d, J=8.6 Hz, 1H), 6.97 (d, J=8.5 Hz,
1H), 7.21 (d, J=2.1 Hz, 1H), 7.33 (dd, J=2.1 Hz, 3J=8.7 Hz, 1H), 7.56
(d, J=1.9 Hz, 1H) 7.58 (s, 1H), 7.65 (dd, J=1.9, 8.5 Hz, 1H), 9.79 ppm
(s, 1H); 13C NMR (125 MHz, CD2Cl2): d=14.1 (CH3), 22.9 (CH2), 26.7
(CH2), 26.9 (CH2), 31.5 (CH3), 31.7 (CH2), 48.8 (CH2), 115.8 (CH), 116.5
(CH), 121.6 (Cquat), 124.3 (Cquat), 125.0 (Cquat), 128.3 (CH), 128.9 (Cquat),
129.4 (CH), 130.6 (CH), 131.2 (CH), 131.9 (CH), 132.2 (Cquat), 146.0
(Cquat), 149.3 (Cquat), 168.0 (Cquat), 190.0 (CH),193.7 ppm (Cquat); IR
(KBr): n˜ =2929 (w), 2855 (w), 1708 (s), 1687 (s), 1593 (m), 1572 (s), 1544
(w), 1473 (s), 1424 (m), 1402 (s), 1356 (m), 1289 (s), 1251 (s), 1223 (m),
1197 (m), 1128 (s), 1102 (s), 991 (w), 960 (w), 916 (w), 810 (w), 735 cmꢀ1
(w); UV/Vis (CH2Cl2): lmax (e)=300 (83000), 365 (60000), 466 nm
(71000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%)=470 (11), 469 (17), 468 (52)
[M]+, 397 (17) [MꢀC5H11]+, 383 (27) [MꢀC6H13]+, 296 (11), 284 (11),
283 (23), 282 (110), 264 (17), 254 (13), 43 (14), 28 (42); elemental analysis
calcd (%) for C24H24N2O2S3 (468.7): C 61.51, H 5.16, N 5.98; found: C
61.58, H 5.00, N 6.02.
2-[(10-Hexyl-7-iodo-10H-phenothiazine-3-yl)methylene]-1H-indene-
1,3(2H)-dione (12c): According to GP 1, compound 12c was obtained as
a red solid after column chromatography on silica by using hexane/ace-
(Z)-10-Hexyl-7-[(3-methyl-4-oxo-2-thioxothiazolidine-5-ylidene)methyl]-
10H-phenothiazine-3-carbonitrile (10 f): According to GP 1, compound
1
tone (10:1) as eluent. M.p. 1718C; H NMR (500 MHz, CD2Cl2): d=0.89
Chem. Eur. J. 2011, 17, 9984 – 9998
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9995

H.-G. Kuball, T. J. J. Mꢀller et al.
(t, J =6.9 Hz, 3H), 1.23–1.37 (m, 4H), 1.38–1.49 (m, 2H), 1.76–1.83 (m
2H), 3.86 (t, J=7.3 Hz, 2H), 6.64 (d, J=8.6 Hz, 1H), 6.92 (d, J=8.7 Hz,
1H), 7.40 (d, J=1.8 Hz, 1H), 7.44 (dd, J=1.8 Hz, J=1.8 Hz, 1H), 7.66
(s, 1H), 7.75–7.82 (m, 2H), 7.89–8.00 (m, 2H), 8.27 (dd, J=1.6 Hz, J=
8.7 Hz, 1H), 8.39 ppm (d, J=1.7 Hz, 1H); 13C NMR (125 MHz, CD2Cl2):
d = 14.1 (CH3), 23.0 (CH2), 26.8 (CH2), 26.9 (CH2), 31.7 (CH2), 48.4
(CH2), 85.8 (Cquat), 115.3 (CH), 117.9 (CH), 123.1 (CH), 123.3 (CH),
123.4 (Cquat), 126.4 (Cquat), 127.2 (Cquat), 128.4 (Cquat), 133.0 (CH), 135.3
(CH), 135.4 (CH), 135.6 (CH), 135.9 (CH), 136.5 (CH), 140.4 (Cquat),
142.8 (Cquat), 143.4 (Cquat), 145.1 (CH), 149.5 (Cquat), 189.7 (Cquat),
190.6 ppm (Cquat); IR (KBr): n˜ =2954 (w), 2924 (w), 2852 (w), 1673 (s),
1578 (s), 1553 (s), 1497 (w), 1468 (s), 1416 (s), 1388 (m), 1349 (m), 1205
(s), 1152 (w), 1091 (w), 1021 (w), 999 (w), 729 cmꢀ1 (m); UV/Vis
(CH2Cl2): lmax (e)=259 (42000), 312 (17000), 336 (21000), 499 nm
(26000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 565 (20) [M]+, 494 (6)
[Mꢀ(C5H11)]+, 480 (10) [Mꢀ(C6H13)]+, 438 (20) [MꢀI]+, 367 (9)
[MꢀIꢀ(C5H11)]+; elemental analysis calcd (%) for C28H24INO2S (565.5):
C 59.47, H 4.28, N 2.48; found: C 59.53, H 4.03, N 2.43.
tal analysis calcd (%) for C29H25NO3S (467.6) (+10% CH2Cl2): C 73.42,
H 5.34, N 2.94; found: C 73.66, H 5.54, N 3.03.
7-[(1,3-Dioxo-1H-indene-2(3H)-ylidene)methyl]-10-hexyl-10H-phenothia-
zine-3-carbonitrile (12 f): According to GP 1, compound 12 f was ob-
tained as a dark red solid after column chromatography on silica by using
hexane/acetone (10:1) as eluent. M.p. 168–1708C; 1H NMR (500 MHz,
CD2Cl2): d=0.89 (t, J=7.1 Hz, 3H), 1.28–1.38 (m, 4H), 1.41–1.51 (m,
2H), 1.75–1.88 (m, 2H), 3.90 (t, J=7.4 Hz, 2H), 6.90 (d, J=8.6 Hz, 1H),
6.96 (d, J=8.7 Hz, 1H), 7.33 (d, J=1.9 Hz, 1H), 7.44 (dd, J=2.0, 8.5 Hz,
1H), 7.66 (s, 1H), 7.78–7.83 (m, 2H), 7.91–7.95 (m, 1H), 7.95–8.00 (m,
1H), 8.26 (dd, J=2.1, 8.7 Hz, 1H), 8.39 ppm (d, J=2.0 Hz, 1H);
13C NMR (125 MHz, CD2Cl2): d=14.1 (CH3), 22.9 (CH2), 26.7 (CH2),
26.8 (CH2), 31.7 (CH2), 48.7 (CH2), 106.8 (Cquat), 115.8 (CH), 116.0 (CH),
118.7 (Cquat), 123.0 (Cquat), 123.2 (CH.), 123.3 (CH), 125.1 (Cquat), 127.9
(Cquat), 129.2 (Cquat), 130.6 (CH), 132.2 (CH), 132.9 (CH), 135.4 (CH),
135.6 (CH), 135.8 (CH), 140.4 (Cquat), 142.8 (Cquat), 144.7 (CH), 147.5
(Cquat), 148.1 (Cquat), 189.6 (Cquat), 190.4 ppm (Cquat); IR (KBr) n˜ =2928
(w), 2224 (w), 1720 (w), 1679 (m), 1567 (m), 1469 (s), 1415 (w), 1250 (w),
1204 (m), 1155 (w), 998 (w), 814 cmꢀ1 (w); UV/Vis (CH2Cl2): lmax (e)=
268 (27000), 301 (14000), 325 (13000), 350 (13000), 485 nm
(16000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 465 (34), 464 (100) [M]+, 394
(12), 393 (41) [MꢀC5H11]+, 380 (34), 379 (85) [MꢀC6H13]+, 362 (19), 322
(11), 44 (32), 43 (39), 41 (15); elemental analysis calcd (%) for
C29H24N2O2S (464.6): C 74.97, H 5.21 N 6.03; found: C 74.76, H 5.38 N
5.81.
2-[(7-Bromo-10-hexyl-10H-phenothiazine-3-yl)methylene]-2H-indan-1,3-
dione (12d): According to GP 2, compound 12d was obtained as red
crystals after crystallization and trituration with methanol. M.p. 1488C;
1H NMR (300 MHz, CD2Cl2): d = 0.85–0.92 (m, 3H), 1.28–1.37 (m, 4H),
1.38–1.50 (m, 2H), 1.73–1.86 (m, 2H), 3.46 (s, 3H), 3.83–3.89 (m, 3H),
6.75 (d, J =8.6 Hz, 1H), 6.91(d, J=8.7 Hz, 1H), 7.24 (d, J=2.2 Hz, 1H),
7.26 (dd, J=8.6 Hz, J=2.3 Hz, 1H) 7.66 (s, 1H), 7.75–7.82 (m, 2H),
7.90–7.99 (m, 2H), 8.26 (dd, J=8.7 Hz, J=2.1 Hz, 1H), 8.34 ppm (d, J=
2.1 Hz, 1H); 13C NMR (75 MHz, CD2Cl2): d = 14.1 (CH3), 23.0 (CH2),
26.8 (CH2), 27.0 (CH2), 31.8 (CH2), 48.6 (CH2), 115.3 (CH), 116.0 (CH),
117.5 (CH), 123.2 (CH), 123.3 (CH), 123.4 (Cquat), 126.3 (Cquat), 127.3
(Cquat), 128.4 (Cquat), 130.0 (CH), 130.5 (CH), 133.1 (CH), 135.3 (CH),
135.5 (CH), 136.0 (CH), 140.4 (Cquat), 142.76 (Cquat), 142.83 (Cquat), 145.2
(CH), 149.6 (Cquat), 189.7 (Cquat), 190.6 ppm (Cquat); EI-MS (70 eV): m/z
(Z)-5-[4-(Diethylamino)benzylidene]-3-methyl-2-thioxothiazolidine-4-
one (14a): According to GP 1, compound 14a was obtained as a red
solid after column chromatography on silica by using hexane/acetone
1
(10:1) as eluent. M.p. 1358C; H NMR (500 MHz, CD2Cl2): d=1.18–1.22
(m, 6H), 3.44 (quart, J=7.2 Hz, 4H), 3.47 (s, 3H), 6.72 (d, J=9.0 Hz,
2H), 7.39 (d, J=9.0 Hz, 2H), 7.64 ppm (s, 2H); 13C NMR (125.5 MHz,
CD2Cl2): d=12.7 (2CH3), 31.4 (CH3), 45.0 (2CH2), 112.0 (2CH), 115.3
(Cquat), 120.3 (Cquat), 133.9 (2CH), 134.9 (CH), 150.2 (Cquat), 168.3 (Cquat),
194.0 ppm (Cquat); IR (KBr) n˜ =2971 (m), 1702 (s), 1561 (s), 1513 (s),
1427 (m), 1406 (m), 1345 (m), 1271 (m), 1191 (m), 1124 (m), 1093 (m),
1077 (m), 949 (w), 809 (w), 750 (w), 717 (w), 673 (w), 531 cmꢀ1 (w); UV/
Vis (CH2Cl2): lmax (e)=254 (6000), 322 (11000), 486 nm
(45000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 306 (37) [M+], 291 (38)
[MꢀCH3+], 205 (57), 191 (14), 190 (100), 175 (15), 162 (37), 161 (84),
160 (40), 148 (12), 134 (29), 133 (34), 118 (11), 102 (11), 91 (11), 89 (52);
elemental analysis calcd (%) for C15H18N2OS2 (306.5): C 58.79, H 5.92, N
9.14; found: C 58.55, H 6.00, N 9.01.
81
79
(%): 520 (23), 519 (79) [Mꢀ Br]+, 518 (16), 517 (76) [Mꢀ Br]+, 448
(23), 446 (28), 435 (97), 434 (30), 433 (100), 432 (21), 367 (17), 353 (13),
352 (13), 296 (28), 264 (15), 220 (12), 104 (20), 76 (21), 43 (57), 41 (25),
32 (11), 29 (17), 28 (83); IR (KBr): n˜ =2967 (w), 2927 (w), 2859 (w), 1719
(w), 1677 (s), 1578 (s), 1558 (s), 1492 (m), 1461 (s), 1415 (m), 1393 (m),
1350 (m), 1251 (w), 1203 (s), 1154 (m), 1087 (w), 1020 (w), 998 (w),
734 cmꢀ1 (w); UV/Vis(CH2Cl2): lmax (e)=256 (35000), 334 (17000),
499 nm (21000 Lmolꢀ1 cmꢀ1); elemental analysis calcd (%) for
C28H24NO2SBr (518.5): C 64.86, H 4.67, N 2.70; found: C 64.76, H 4.69, N
2.60.
(Z)-5-[4-(Diphenylamino)benzylidene]-3-methyl-2-thioxothiazolidin-4-
one (14b): According to GP 1, compound 14b was obtained as an orange
solid after column chromatography on silica by using hexane/acetone
(5:1) as eluent. M.p. 1718C; 1H NMR (500 MHz, [D6]acetone): d=3.47
(s, 3H), 7.03 (d, J =8.8 Hz, 2H), 7.19–7.24 (m, 6H), 7.41 (t, J=7.9 Hz,
4H), 7.51 (d, J=8.8 Hz, 2H), 7.69 ppm (s, 1H); 13C NMR (125.5 MHz,
[D6]acetone): d=55.0 (CH3), 119.9 (Cquat), 121.0 (2CH), 126.1 (2CH),
126.4 (Cquat), 127.1 (4CH), 130.8 (4CH), 133.4 (2CH), 133.6 (CH), 147.3
(2Cquat), 151.4 (Cquat), 168.3 (Cquat), 194.6 ppm (Cquat); IR (KBr) n˜ =1695
(m), 1562 (s), 1489 (m), 1425 (m), 1284 (s), 1192 (m), 1124 (m), 1093 (m),
819 (w), 760 (w), 700 cmꢀ1 (w); UV/Vis (CH2Cl2): lmax (e)=302 (22000),
472 nm (47000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 402 (32) [M+], 301 (100),
191 (14), 167 (29), 77 (45), 43 (14); elemental analysis calcd (%) for
C23H18N2OS2 (402.5): C 68.63, H 4.51, N 6.96; found: C 68.57, H 4.47, N
6.93.
7-[(1,3-Dioxo-1H-indan-2(3H)-ylidene)methyl]-10-hexyl-10H-phenothia-
zine-3-carbaldehyde (12e): A mixture of 10-hexyl-10H-phenothiazine-
3,7-biscarbaldehyde (170 mg, 0.5 mmol) and 1,3-indandione (73 mg,
0.5 mmol) was dissolved in toluene (5 mL) and 2-propanephosphonic
acid anhydride (T3P; 175 mg, 0.55 mmol, 50 wt%) in 1,1-dichloroethene
(DCE; 0.2 mL) was added. The mixture was heated to reflux for 30 min,
and after cooling to RT, the residue was subjected to chromatography on
silica by using hexane/ethyl acetate (4:1) as eluent. The product (128 mg,
0.27 mmol, 55%) was isolated as a dark solid. M.p. >3008C; 1H NMR
(500 MHz, CD2Cl2): d=0.85–0.93 (m, 3H), 1.30–1.38 (m, 4H), 1.42–1.50
(m, 2H), 1.79–1.87 (m, 2H), 3.89–3.96 (m, 2H), 6.92–6.99 (m, 2H), 7.53–
7.57 (m, 1H), 7.61–7.67 (m, 2H), 7.75–7.82 (m, 2H), 7.89–7.94 (m, 1H),
7.94–7.99 (m, 1H), 8.26 (dd, J =8.6 Hz, J=2.0 Hz, 1H), 8.37 (d, J=
2.0 Hz, 1H), 9.78–9.81 ppm (m, 1H); 13C NMR (125.5 MHz, CD2Cl2): d
=
14.1 (CH3), 23.0 (CH2), 26.7 (CH2), 26.9 (CH2), 31.7 (CH2), 49.0
(CH2), 115.7 (CH), 115.8 (CH), 123.2 (CH), 123.3 (CH), 123.4 (Cquat),
124.4 (Cquat), 127.7 (Cquat), 128.3 (CH), 129.1 (CH), 130.4 (CH), 132.3
(Cquat), 132.9 (Cquat), 135.3 (CH), 135.5 (CH), 135.7 (CH), 140.4 (Cquat),
142.8 (Cquat), 144.8 (CH), 148.1 (Cquat), 148.7 (Cquat), 189.6 (Cquat), 190.0
(CH), 190.4 ppm (Cquat); IR (KBr) n˜ =2950 (m), 2924 (m), 2800 (m),
1669 (s), 1552 (s), 1478 (s), 1397 (s), 1177 (s), 1141 (s), 1081 (m), 994 (m),
910 (w), 877 (w), 809 (w), 731 (w), 578 cmꢀ1 (w); UV/Vis (CH2Cl2): lmax
(e)=271 (26000), 312 (21000), 326 (22000), 363 (19000), 493 nm
(23000 Lmolꢀ1 cmꢀ1); EI-MS (70 eV): m/z (%): 468 (29), 467 (94) [M]+,
397 (11), 396 (44) [MꢀC5H11]+, 383 (33), 382 (100) [MꢀC6H13]+, 364
(20), 297 (10), 296 (10), 76 (11), 43 (35), 41 (17), 29 (12), 28 (20); elemen-
2-[4-(Diethylamino)benzylidene]-1H-indane-1,3(2H)-dione (15a): N,N-
Diethyl aminobenzaldehyde (30 mg, 0.17 mmol) and 1,3-indandione
(27.7 mg, 0.19 mmol) were added to a mixture of acetic acid (0.4 mL)
and ammonium acetate (13.4 mg, 0.17 mmol) and heated to reflux for
3 h. After cooling to RT, the residue was chromatographed on silica by
using hexane/acetone (4:1) as eluent. Compound 15a (43 mg, 0.14 mmol,
83%) was isolated as a red solid. M.p. 1558C; 1H NMR (500 MHz,
CD2Cl2): d=1.24 (t, J=7.2 Hz, 6H), 3.49 (quart, J=7.1 Hz, 4H), 6.75 (d,
J=9.2 Hz, 2H), 7.70 (s, 1H), 7.71–7.76 (m, 2H), 7.83–7.92 (m, 2H),
8.51 ppm (d, J=8.3 Hz, 2H); 13C NMR (125.5 MHz, CD2Cl2): d=12.7
(2CH3), 45.3 (2CH2), 111.5 (2CH), 121.7 (Cquat), 122.4 (CH), 122.5 (CH),
9996
www.chemeurj.org
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 9984 – 9998

Phenothiazinyl Merocyanine Dyes
FULL PAPER
122.7 (Cquat), 134.3 (CH), 134.6 (CH), 138.5 (CH), 140.2 (Cquat), 142.6
(Cquat), 147.1 (CH), 152.6 (Cquat), 190.1 (Cquat), 191.7 ppm (Cquat); IR
(KBr) n˜ =2971 (m), 1665 (m), 1560 (s), 1509 (s), 1452 (m), 1411 (m),
1381 (m), 1346 (m), 1324 (m), 1280 (m), 1186 (s), 1151 (m), 1080 (m),
1019 (m), 993 (m), 820 (m), 786 (w), 735 (w), 666 (w), 589 (w), 519 cmꢀ1
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(w);
UV/Vis
(CH2Cl2):
lmax
(e)=275
(18000),
488 nm
(113000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 306 (15), 305 (45) [M+], 291
(23), 290 (100) [MꢀCH3+], 262 (14), 233 (16) [MꢀNEt2+], 177 (19), 176
(18), 162 (25), 130 (13), 105 (11), 104 (21), 101 (13), 77 (17), 76 (18); ele-
mental analysis calcd (%) for C20H19NO2 (305.37): C 78.66, H 6.27, N
4.62; found: C 78.63, H 6.45, N 4.62.
2-[4-(Diphenylamino)benzylidene]-1H-indane-1,3(2H)-dione (15b): Ac-
cording to GP 1, compound 15b was obtained as an orange solid after
column chromatography on silica by using hexane/acetone (4:1) as
eluent. M.p. 2128C; 1H NMR (500 MHz, CD2Cl2): d=6.99 (d, J=9.0 Hz,
2H), 7.18–7.27 (m, 6H), 7.39 (t, J=7.9 Hz, 4H), 7.74 (s, 1H), 7.76–7.80
(m, 2H), 7.88–7.97 (m, 2H), 8.41 ppm (d, J=2H); 13C NMR (125.5 MHz,
CD2Cl2): d=118.9 (2CH), 122.9 (CH), 123.0 (CH), 125.7 (Cquat), 125.9 (2
CH), 126.0 (Cquat), 127.0 (4 CH), 130.1 (4CH), 134.9 (CH), 135.1 (CH),
137.0 (2CH), 140.3 (Cquat), 142.7 (Cquat), 146.1 (2Cquat), 146.4 (CH), 153.0
(Cquat), 189.8 (Cquat), 191.1 ppm (Cquat); IR (KBr): n˜ =1681 (s), 1573 (s),
1489 (s), 1328 (m), 1285 (m), 1192 (m), 745 (w), 732 (w), 698 cmꢀ1 (m);
UV/Vis (CH2Cl2): lmax (e)=246 (33000), 293 (27000), 486 nm
(85000 Lmolꢀ1 cmꢀ1); EI-MS: m/z (%): 401 (80) [M+], 243 (10), 167 (30),
104 (22), 101 (17), 77 (100); elemental analysis calcd (%) for C28H19NO2
(401.46): C 83.77, H 4.77, N 3.49; found: C 83.71, H 4.71, N 3.53.
Acknowledgements
Financial support from the Fonds der Chemischen Industrie and the
Volkswagen Foundation is gratefully acknowledged. The authors also
thank BASF SE for the generous donation of chemicals.
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Received: February 22, 2011
Published online: July 21, 2011
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