Synthesis and photophysics of a red-light absorbing supramolecular chromophore system

Article abstract of DOI:10.1002/chem.201402398

In search of supramolecular antenna systems for light-harvesting applications, we report on a short and effective synthesis of a fused NDI-zinc-salphen-based chromophore (salphen = bis-salicylimide phenylene) and its photophysical properties. A supramolec

Full text of DOI:10.1002/chem.201402398

DOI: 10.1002/chem.201402398
Full Paper
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Chromophores
Synthesis and Photophysics of a Red Light Absorbing
Supramolecular Chromophore System
Jeroen A. Rombouts,[a] Janneke Ravensbergen,[b] Raoul N. Frese,[b] John T. M. Kennis,[b]
Andreas W. Ehlers,[a] J. Chris Slootweg,[a] Eelco Ruijter,[a] Koop Lammertsma,*[a] and
Romano V. A. Orru*[a]
Abstract: In search of supramolecular antenna systems for
light-harvesting applications, we report on a short and effec-
tive synthesis of a fused NDI–zinc–salphen-based chromo-
phore (salphen = bis-salicylimide phenylene) and its photo-
physical properties. A supramolecular recognition motif is
embedded into the chromophoric p-system of this com-
pound. The fused p-chromophore behaves as one pigment,
absorbs light between 600 and 750 nm and displays
a modest Stokes shift. Upon binding pyridines, the com-
pound (DATZnS) does not change its redox potentials, does
not undergo any internal excited state quenching and does
not appreciably alter its excited state lifetime. These notable
properties define DATZnS as an alternative to porphyrin-
based components used in supramolecular light-harvesting
architectures.
tectures.[5] The supramolecular coupling of components has
advantages over synthesizing covalent interconnections, but
requires precise control over the interaction stability and spe-
cificity.[6] Thus, units with predictable photophysical and elec-
trochemical properties, that are invariant when interacting
with other supramolecular components, are desirable; unfore-
seen property modulation will preclude sensible a priori
design of novel supramolecular light-harvesting systems.
These arguments considered, we present in this work a fully
synthetic chromophore DATZnS (see Scheme 1) as a new com-
ponent for rationally designed light-harvesting assemblies. This
DATZnS scaffold contains a core-expanded naphthalene di-
imide (cNDI) fused with a zinc bis-salicylimide phenylene (sal-
phen) moiety. The extensive use of rylenediimide dyes in light-
harvesting architectures[7] and the recent development of
cNDI-based (semi)-conductors for organic electronics inspired
us to the design and synthesis of DATZnS.[8] Moreover, pyri-
dine-coordinating zinc–salphen constructs are well-estab-
lished.[9] Orthogonal coordination of pyridine ligands to the
rigid p-electron skeleton of DATZnS is, therefore, expected to
limit electronic influence of supramolecular interactions on the
molecular orbitals involved in light absorption. By employing
sterically demanding tert-butyl substituents on the salphen
ring, this orthogonal coordination mode will be forced and dy-
namic excited-state processes leading to non-radiative losses
are likely to be suppressed. In this work we present the synthe-
sis of the chromophore and its pyridine complexes, a photo-
physical analysis using time-resolved spectroscopy and an in-
vestigation of the electronic influence of pyridine binding to
the chromophore.
Introduction
In natural photosynthesis, chlorophyll pigments absorb sun-
light by the extended conjugated p-system of their chlorin
rings. A Mg2+ cation is bound inside the macrocycle and inter-
acts with basic N-containing residues in the protein environ-
ment.[1] Metalated porphyrins and phthalocyanins, close ana-
logues to these natural chlorophylls, are used as chromophoric
building blocks in man-made artificial photosynthetic sys-
tems.[2] The redox-innocent 2p6 (Mg2+) or 3d10 (Zn2+) metal
support present inside the p-aromatic ring of these com-
pounds is ideally suited to provide structural support to the
chromophore without interfering with excited state energy
transfer or charge separation processes.[3] Notwithstanding the
synthesis of many porphyrin-related light-harvesting macrocy-
cles, only few alternative organic compounds with a ligand-
binding metal atom as integral part of its chromophore core
have been developed.[4] The integration of these and other
light-harvesting molecular components into artificial photosyn-
thetic assemblies has been carried out using various strategies
giving rise to polymeric, dendrimeric or supramolecular archi-
[a] J. A. Rombouts, Dr. A. W. Ehlers, Dr. J. C. Slootweg, Dr. E. Ruijter,
Prof. Dr. K. Lammertsma, Prof. Dr. R. V. A. Orru
Department of Chemistry and Pharmaceutical Sciences
VU University Amsterdam, De Boelelaan 1083
1081 HV Amsterdam (The Netherlands)
E-mail: K.Lammertsma@vu.nl
R.V.A.Orru@vu.nl
[b] J. Ravensbergen, Dr. R. N. Frese, Dr. J. T. M. Kennis
Department of Biophysics
VU University Amsterdam
De Boelelaan 1081, 1081 HV Amsterdam (The Netherlands)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402398.
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absorption features (see Supporting Information), which reach-
es its maximum value of about 20 nm after addition of one
equivalent of ligand. This concurs with literature reports on
monomeric ZnII–salphens, where ligand exchange of zinc-
bound water or alcohols takes place upon addition of one
equivalent of pyridine.[9a]
Excited-state photophysics
The photophysical properties of DATZnS, its pyridine com-
plexes and reference compounds DAT and ZnS (see Scheme 1)
were studied by steady-state and transient absorption spec-
troscopy (TAS), using toluene as a solvent.[15] Global analysis
was performed on the TAS data to extract interconverting evo-
lution associated difference spectra (EADS) and time con-
stants.[16]
Scheme 1. Structural formulas and synthesis of relevant compounds. R=n-
octyl. i) excess 1,2-diaminobenzene, DMF, 808C; ii) 2.5 equiv 1,2-diamino-4,5-
ditosylamidobenzene, DMF, 808C; iii) 98% H2SO4, RT; iv) 2.5 equiv aldehyde,
10 equiv ZnOAc2. H2O, DMF, 808C.
Zinc–salphen complex ZnS was characterized by broad ab-
sorption bands at 310 and 396 nm with onset of absorption at
500 nm in the steady-state experiments. Its fluorescence was
too weak to accurately record. The TAS data revealed 1.2 and
37 ps processes assigned to relaxation and one final excited
state decay process at a timescale beyond the 3.5 ns time limit
of our measurement apparatus. Steady-state absorption spec-
tra of core-expanded naphthalene diimide DAT shows four
bands between 450 and 600 nm, interpreted as a vibronic pro-
gression of the lowest excited state. The fluorescence spec-
trum of this molecule (Figure 8a, Supporting Information)
shows three bands of fluorescence from the lowest excited
state, again reflecting a vibronic structure, here due to vibra-
tional levels of the ground state. The Stokes shift observed be-
tween absorption and emission is 4 nm. TAS measurements on
DAT revealed relaxation processes with time constants of
621 fs and 46 ps, followed by excited state decay tentatively
fitted to 8.9 ns due to the aforementioned 3.5 ns time limit of
our experimental setup. The first lifetime of 621 fs refers to
a transition in which a small red-shift of the stimulated emis-
sion is observed. This is caused by structural relaxation of the
excited molecule or by solvation effects; as the molecule is ex-
cited to the lowest vibrational state, vibrational relaxation is
not expected. The second EADS has a lifetime of 46 ps, com-
prising a decrease of stimulated emission. This can be ex-
plained by a relaxation process of the molecule or the solvent
to a final state having less Franck-Condon overlap with the
ground state, leading to a decreasing probability for stimulat-
ed emission.
Results and Discussion
Synthesis
Our synthetic approach relies on the nucleophilic aromatic
substitution of tetrabrominated naphthalene diimide Br4NDI
with 1,2-diamino-4,5-ditosylamidobenzene to give the unsym-
metrical, core-expanded precursor DATTs (see Scheme 1). Ref-
erence material DAT was obtained using 1,2-diaminobenzene,
as described in the literature.[10] The dihydrodiazatetracene
polycycle thus afforded is much less prone to nucleophilic
attack on the remaining brominated positions and no double
nucleophilic aromatic substitution was observed under the re-
action conditions.[11] Whenever desired, palladium-catalyzed
cross-coupling may allow further derivatization of the diimide
core at a later stage.[12] Removal of the tosyl groups with con-
centrated sulfuric acid set the stage for a metal-templated con-
densation of the resulting diamine with 3,5-bis-(tert-butyl)sali-
cylaldehyde in the presence of zinc acetate.[13] This reaction
gave, after purification via repeated precipitation from CH2Cl2
and methanol, the target compound DATZnS (Scheme 1) as
a dark green solid in 54% overall yield from Br4NDI. We pro-
pose that the DATZnS-construct contains a zinc complex with
an adventitious water molecule in the fifth coordination site,
since no coordinated methanol (used during purification of the
material) or acetic acid (originating from the zinc acetate used)
1
could be identified by H NMR spectroscopy or high-resolution
The steady-state absorption and fluorescence spectra of the
cNDI/zinc–salphen dyad DATZnS are shown in the top of
Figure 1. The absorption spectrum contains the same features
as the reference compounds, but each band is substantially
red-shifted. Evidently this indicates that the two parts of the
dyad are electronically strongly coupled, and that the entire
diimide–salphen structure must be regarded as one chromo-
phore. This is confirmed by fluorescence excitation measure-
ments, which show full energy transfer between the two parts
of DATZnS. The dyad retains its fluorescence with an enlarged
Stokes shift of 20 nm compared to DAT.
FAB-MS. Such coordination of water is in agreement with
known sterically encumbered zinc–salphen complexes.[14]
In order to probe the influence of ligand binding to ZnII, pyr-
idine (P) and its more electronegative 4-tert-butyl (TP) and 4-
pyrrolidyl (PP) derivatives were added in CH2Cl2 to obtain the
corresponding Zn-coordinated DATZnS adducts in excellent
yields ranging from 97% to quantitative, as confirmed by FAB-
MS and multinuclear NMR analysis. Monitoring the titration of
DATZnS with up to four equivalents of 4-pyrrolidylpyridine
using UV/Vis spectroscopy led to a small bathochromic shift of
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observed time constants for ground-state decay t3 shows that
the ligand has only a small influence on the eventual fate of
the excited state. This indicates an insensitivity of the p-conju-
gated chromophore to changes in the fifth coordination site of
Zn, besides obvious but minor influences of the ligand to the
dielectric environment around the molecule.
Electronic structure
To probe the electronic structure of the compound and investi-
gate the effect of ligand coordination, we determined the oxi-
dation and reduction potential of DATZnS, its pyridine ad-
ducts, and the reference components DAT and ZnS by cyclic
voltammetry (Table 2). From the electrochemical investigation
it appears that the experimentally determined HOMO of the
dyads (ca. À5.6 eV) lies in between that of ZnS (À6.04 eV) and
DAT (À5.35 eV). Addition of the optical band gap of the mate-
Figure 1. Top: Normalized absorption (black) and fluorescence (red) spectra
of DATZnS. Bottom: EADS of DATZnS.
17]
rial allows calculation of experimental LUMO values.[7a,
The
dyads undergo a significant stabilization of ~0.8 eV from the
average constituent LUMO values of about À3.2 eV, giving
a LUMO energy of around À4 eV. Interestingly, across the in-
creasingly electron-rich series of pyridine ligands, no HOMO
destabilization is observed.
EADS data derived from global analysis of the TAS study on
DATZnS is presented on the bottom of Figure 1, spectra be-
longing to DATZnS-pyridine complexes can be found in the
Supporting Information. The data show ground-state bleaching
and stimulated emission corresponding with the bands in the
steady state spectra. The positive contribution in the EADS re-
sults from excited state absorption. In the steady-state meas-
urements no differences in absorption and emission band
structure were observed between DATZnS and its pyridine ad-
ducts. For each pyridine adduct three time constants of similar
order of magnitude are needed for a sufficient fit of the TAS-
derived EADS data, as summarized in Table 1. All four com-
pounds display excitation photophysics qualitatively similar to
that of parent NDI DAT. Hence, we assign time constants t1 to
structural relaxation or solvation of the dyads in the excited
state or a solvation process. The second process with t2 of all
dyads describes a decrease of stimulated emission, assigned to
a second structural relaxation of the excited state to a state
from which stimulated emission is less probable. The third
time constant t3 gives the lifetime of the excited state, which
is lowered by one order of magnitude compared to DAT. The
relaxation process t1 and excited state relaxation with t2 are af-
fected most by complexation of pyridines. The variation in the
The corresponding MO energy levels were calculated at the
B3LYP/LANL2DZ level of theory, whereas TD-DFT calculations
with the cam-B3LYP functional[18] were used to examine the
nature of the first two optical transitions (TS1 and TS2 in
Figure 2). The trends of reduced optical band gap in DATZnS
is reproduced by our TD-DFT calculations (Table 2, rightmost
column). The extensively delocalized HOMO and LUMO ob-
served in the DATZnS model demonstrate nicely that a strong
interaction exists between its components; the overlapping
electron density is caused by the flat geometry and unbroken
conjugation of the aromatic scaffold. It is evident that the elec-
tronic structure of the dye as assessed by the quantum-chemi-
Table 2. Experimental FMO energy levels from cyclic voltammetry and
steady-state absorption experiments, alongside TD-DFT calculated optical
band gap.
[a]
[b]
[c]
[d]
Compound EHOMO,exptl
ELUMO,
DEGap,
DEGap,TDDFT
exptl
exptl
[eV]
[eV]
[eV]
[eV]
ZnS
DAT
DATZnS
À6.04
À5.35[e]
À5.66
À3.22
2.82
2.07
1.56
1.56
1.56
1.56
3.07
2.40
2.10
2.09
2.09
2.08
À3.25[e]
À4.10
À4.05
À4.04
À4.04
DATZnS-P À5.61
Table 1. EADS-associated time constants obtained from transient absorp-
tion studies.
DATZnS-TP À5.60
DATZnS-
PP
À5.60
[b]
[b]
[b]
Compound[a]
t1
t2
t3
[a] From CV measurements, see Supporting Information for accompany-
ing CV plots. Experimental parameters: Anhydrous conditions, CHCl3 sol-
vent, 0.1m TBAP electrolyte, Pt counter electrode, Ag/Ag+ reference elec-
DAT
DATZnS
DATZnS-PP
DATZnS-TP
DATZnS-P
621 fs
6.5 ps
2.5 ps
0.5 ps
1.7 ps
46 ps
162 ps
54 ps
9.3 ps
14 ps
~9 ns[c]
770 ps
582 ps
709 ps
703 ps
trode, GC working electrode, scan rate 0.1 VsÀ1. Vacuum energy level cal-
[17]
culated via EHOMO,exptl =À4.9ÀEox,Ag/Ag+
EHOMO,
.
[b] Calculated via ELUMO,
=
exptl
+ DEGapexptl. [c] Calculated via DEGap,
=1240/lmaxonset; the
EXP
exptl
[a] Lifetime measurements determined in toluene as described in the
Supporting Information. [b] Time constants obtained by global transient
absorption analysis of TAS data. [c] Fitted on a timescale beyond the
3.5 ns measuring limit of our experimental setup.
onset wavelength is taken as the wavelength at 5% peak value intensity
of the main absorption feature. [d] Energy of the first optical transition
(TS1) as assessed by TD-DFT calculations, see text. [e] Values taken from
Q. Ye et al.[12]
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cal calculations is not a simple superposition of its constitu-
ents. This is in line with the observations reported by Vauthey
et al. on the photophysical properties of their cNDI/porphyrin
dyad.[10] Furthermore, inspection of the MO iso-contour plots
of, for example, the PP-adduct shows negligible electron densi-
ty on the pyridine ligand in the MOs involved in the optical
transition (Figure 2, right, other adducts show identical elec-
tronic structures), meaning that electronic interaction between
the ligand and the chromophore is precluded by the orthogo-
nal coordination of the pyridine derivatives to DATZnS. The
calculated configurations of orbitals involved in the optical
transitions are displayed in Table 3 and show that the electron-
ics of the photoexcitation process are not in any way per-
turbed upon coordination of pyridine or its more electron-rich
TP or PP congeners.
that of the parent DAT chromophore, because of its extended
conjugation. Compared to the widely utilized supramolecular
chromophore building block Zn–tetraphenylporphyrin, the
compound described herein shows a similar Stokes shift
(20 nm versus 17 nm for ZnTPP) and excited state lifetime
(0.6–0.7 ns versus 2 ns for ZnTPP).[20] The ability of this scaffold
to bind various pyridine ligands without modulating the pho-
tophysical properties of the chromophoric p-system is substan-
tiated by spectroscopic, voltammetric, and computational anal-
ysis. These results show the advantage of strategically incorpo-
rating metal-based supramolecular recognition sites inside
a chromophoric structure, and suggest that DATZnS or similar-
ly designed dyes may fulfill an important role in the future de-
velopment of organic supramolecular antenna systems.
Experimental Section
General: Details and results of the spectroscopic study are avail-
able online in the Supporting Information. Details of the DFT calcu-
lations and cyclic voltammetry experiments are available online in
the Supporting Information. Br4NDA was prepared according to lit-
erature procedures using 2.5 equivalents of dibromoisocyanuric
acid in H2SO4 with 20% dissolved SO3 as brominating reagent.[21]
ZnS was prepared according to literature procedures.[22] Unless
stated otherwise, all solvents and commercially available reagents
were used as purchased. Toluene and CH2Cl2 were distilled from
appropriate drying agents before use. Anhydrous N,N-dimethylfor-
mamide (DMF) was obtained from Sigma–Aldrich and used as re-
ceived. PBr3 was distilled before use and stored in a Schlenk vessel
under inert atmosphere. Melting points were measured using DT=
18CminÀ1 on a Stuart Scientific SMP3 melting point apparatus and
are uncorrected. Infrared (IR) spectra were recorded neat using
a Shimadzu FTIR-8400s spectrophotometer and wavelengths are
Figure 2. TD-DFT calculated energies and orbital configurations of optical
transitions TS1 and TS2; molecular orbital isocontour plots of involved orbi-
tals of DATZnS-PP adduct. Values for all DATZnS-compounds mentioned in
this work are similar (see Supporting Information).
1
reported in cmÀ1. H, HSQC, HMBC and 13C (Attached Proton Test)
NMR spectra were used to characterize prepared compounds, and
were recorded on a Bruker Avance 500 (125.78 MHz for 13C) using
the residual solvent as internal standard. Carbon atoms designated
with ‘C0’ denote a signal in the 13C APT spectrum which could not
be unambiguously assigned, but has a phase corresponding to
zero or two attached protons. All acquired spectra are available in
the Supporting Information. Mass spec (FAB): Fast Atom Bombard-
ment was carried out using a JEOL JMS SX/SX 102A four-sector
mass spectrometer, coupled to a JEOL MS-MP9021D/UPD system
program. Samples were loaded in a matrix solution (3-nitrobenzyl
alcohol) onto a stainless steel probe and bombarded with Xenon
atoms of 3 keV energy. During HRMS FAB-MS measurements, a re-
solving power of 10.000 (10% valley definition) was used. Electro-
spray Ionisation (ESI) mass spectrometry was carried out using
a Bruker micrOTOF-Q instrument in positive ion mode (capillary
potential of 4500 V). Flash chromatography was performed on
Sigma Aldrich basic Brockmann I aluminum oxide (particle size 150
mesh, pore diameter 58 ꢁ) using the described eluent systems.
Thin Layer Chromatography (TLC) was performed using TLC plates
from Merck (SiO2, Kieselgel 60 with F254 indicator on aluminium
backing) and compounds were visualized by visual inspection and
UV detection at 254/366 nm.
Table 3. Energies and configurations of optical transitions as calculated
by TD-DFT.
Compound
TS1[a]
Configuration[b]
TS2[a]
Configuration[b]
DATZnS
2.10 eV
591 nm
14%=H-2 to L
81%=H to L
2.80 eV
442 nm
34%=H-1 to L
43%=H to L+1
DATZnS-P
DATZnS-TP
DATZnS-PP
2.09 eV
593 nm
15%=H-2 to L
80%=H to L
2.78 eV
446 nm
40%=H-1 to L
38%=H to L+1
2.09 eV
593 nm
15%=H-2 to L
80%=H to L
2.78 eV
446 nm
42%=H-1 to L
37%=H to L+1
2.08 eV
596 nm
16%=H-2 to L
78%=H to L
2.76 eV
449 nm
47%=H-1 to L
33%=H to L+1
[a] Energy of the first two vertical singlet excitations from TD-DFT, in eV
and nm. [b] Orbital configuration for each transition. HOMO and LUMO
are indicated with parenthesized letters H and L, respectively.
4,5,9,10-Tetrabromonaphthalene di-n-octylimide (Br4NDI): To
a dry Schlenk flask kept under N2 atmosphere containing degassed
glacial acetic acid (50 mL) was added n-octylamine (4.26 mL,
20.4 mmol). The mixture was heated to 1208C using an oil bath.
Upon reaching reflux, Br4NDA (2.98 g, 5.1 mmol) was added as
Conclusion
We have synthesized a novel cNDI/zinc salphen hybrid with
major absorption features in the 600–750 nm range, beyond
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a solid. The initially turbid yellow suspension turned into a clear,
dark brown solution after 7 min of reflux, upon which the reaction
vessel was immediately cooled down in an ice bath. Immediate di-
lution with H2O (100 mL) at room temperature precipitated
a bright yellow solid, which was triturated with H2O (250 mL) and
pentane (100 mL) on a Buchner filter. Vacuum drying at room tem-
perature gave a bright yellow solid (3.40 g), which could not be an-
alyzed satisfactorily using NMR or mass spectrometry. The yellow
solid was dissolved in degassed, distilled toluene (50 mL) and
heated to reflux. After 10 min, PBr3 (3.35 g, 12.4 mmol) was added
dropwise via a syringe. 25 min after addition, the reaction mixture
was cooled down and diluted with H2O (150 mL). The organic
phase was extracted with satd. aqueous NaHCO3 (100 mL) and H2O
(3ꢂ100 mL). After drying over MgSO4 and concentration in vacuo,
column chromatography (60 g of neutral alumina; eluent system
1:1 pentane:CHCl3; 25 mL fractions, product in fraction 9–24) was
performed. From this was obtained an orange-yellow solid (1.16 g,
concentrated in vacuo and taken up in CH2Cl2 (200 mL). The organ-
ic phase was extracted with 1m aqueous HCl (200 mL) and H2O
(3ꢂ200 mL). After drying over MgSO4 and concentration in vacuo,
a pink powder was obtained (59.36 g, 97%). M.p.decomp 2408C;
1H NMR (500.2 MHz, [D6]DMSO, 296 K): d = 9.253 (brs, 2H, NHTos),
3
3
7.57 (d, J(H,H)=8.0 Hz, 4H, tosyl CH), 7.33 (d, J(H,H)=8.0 Hz, 4H,
tosyl CH), 6.98 (broad s, 4H, benzene CH’s), 2.35 (s, 6H, TosCH3);
13C{1H} NMR (125.8 MHz, [D6]DMSO, 296 K): d = 143.6, 136.1, 129.7,
129.6, 126.9, 125.8, 123.3, 21.0; IR: n˜ =3371, 3317, 3215, 1595,
1497, 1412, 1394, 1323, 1146, 1086, 912, 808, 744, 662, 544 cmÀ1
HR-MS (ESI): m/z: calcd for [M+Na]+: 439.0762 found: 439.0762.
;
1,2-Dinitro-4,5-ditosylamidobenzene: To a stirred solution of 1,2-
ditosylamidobenzene (4.10 g, 9.76 mmol) in glacial acetic acid
(250 mL) was added dropwise a solution of red fuming HNO3
(1.3 mL) in glacial acetic acid (5 mL) via a syringe. The reaction mix-
ture was stirred at 658C for 40 min. Upon cooling down to room
temperature, a yellow precipitate was recovered. The precipitate
was washed with cold ethanol to afford, after vacuum drying,
a faint yellow solid (4.70 g, 94%). M.p.decomp 220–2298C; 1H NMR
(500.2 MHz, [D6]DMSO, 296 K): d = 7.71 (s, 2H, benzene CH), 7.66
(d, 3J(H,H)=8.5 Hz, 4H, p-toluenesulfonyl o-CH), 7.34 (d, 3J(H,H)=
8.5 Hz, 4H, p-toluenesulfonyl m-CH), 2.36 (s, 6H, TosCH3); 13C{1H}
NMR (125.8 MHz, [D6]DMSO, 296 K): d = 144.34, 136.10, 135.05,
130.50 (p-toluenesulfonyl m-CH), 127.41 (p-toluenesulfonyl o-CH),
115.04 (benzene CH), 21.48 (p-toluenesulfonyl CH3); IR (ATR FTIR): n˜
= 3261, 1597, 1529, 1501, 1387, 1333, 1163, 1088, 1030, 918, 872,
1
28%). M.p.decomp 236–2448C; H NMR (500.2 MHz, C6D6, 296 K): d =
4.16 (t, 3J(H,H)=7.5 Hz, 4H, NCH2-C7H15), 1.82 (tt, 3J(H,H)=7.5,
8.0 Hz, 4H, NCH2CH2C6H13), 1.40–1.25 (m, 20H, NC2H4C5H10CH3), 0.88
(t, 3J(H,H)=8.0 Hz, 6H, NC7H14CH3); 13C{1H} NMR (125.8 MHz, C6D6,
296 K): d = 159.74 (C=O), 134.88, 126.54, 125.88, 42.57 (NCH2-),
32.18 (-CH2-), 29.68 (-CH2-), 29.61 (-CH2-), 28.44 (-CH2-), 27.45 (-CH2-),
23.05 (-CH2-), 14.41 (-CH3); IR (ATR FTIR): n˜ =2961, 2918, 2851, 1707,
1661, 1462, 1431, 1408, 1371, 1317, 1286, 1259, 1232, 1202, 1176,
1151, 1090, 1051, 1016, 908, 798 cmÀ1; MS (FAB, matrix) (%): m/z:
154.0 (100), 649.1 (2), 727.0 (3), 780.9 (3), 806.9 (3); HRMS (FAB):
m/z: calcd for [M+H]+: 806.9289, found: 806.9299.
860, 814, 665, 544 cmÀ1
.
1,2-Diamino-4,5-ditosylamidobenzene: To a stirred solution of
1,2-dinitro-4,5-ditosylamidobenzene (3.00 g, 6.75 mmol) in 1:1:1
H2O/MeOH/CH2Cl2 (250 mL) was added an excess of 85% technical
grade sodium dithionite (10.00 g, 48.82 mmol). The reaction mix-
ture was heated to reflux temperature for 25 min, after which it
was cooled down to room temperature. Filtration yields, after
vacuum drying, a faint yellow solid (1.40 g, 54%). M.p.decomp 2098C;
1H NMR (500.2 MHz, [D6]DMSO, 296 K): d = 8.51 (s, 2H, NHTos),
7.51 (d, 3J(H,H)=8.0 Hz, 4H, p-toluenesulfonyl o-CH), 7.32 (d,
3J(H,H)=8.0 Hz, 4H, p-toluenesulfonyl m-CH), 6.13 (s, 2H, benzene
CH), 4.50 (brs, 4H, NH2), 2.35 (s, 6H, TosCH3); 13C{1H} NMR
(125.8 MHz, [D6]DMSO, 296 K): d = 143.01, 136.27, 133.61, 129.45
(p-toluenesulfonyl m-CH), 126.94 (p-toluenesulfonyl o-CH), 120.00,
110.79 (benzene CH), 21.05 (p-toluenesulfonyl CH3); IR (ATR FTIR): n˜
= 3312, 3215, 1595, 1497, 1412, 1393, 1323, 1277, 1250, 1146,
8,9-Dibromo-5,12-dihydro-5,12-diazatetracene
di-n-octylimide
(DAT): To a stirred solution of Br4NDI (110 mg, 0.14 mmol) in dry
DMF (15 mL) kept under Ar atmosphere was added 1,2-phenylene-
diamine (285 mg, 2.6 mmol) as a solid. The solution was heated to
808C in the dark, reaction progress was monitored with TLC
(eluent system CHCl3). Upon completion, the reaction mixture was
concentrated in vacuo and taken up in CHCl3 (100 mL). The organic
layer was dried over MgSO4 after washing with 1m aqueous HCl
(100 mL), H2O (100 mL) and satd. aqueous NaCl (100 mL). The
volume of the solution was reduced to about 30 mL using the
rotary evaporator; overnight crystallization at À208C produced
a purple crystalline solid (40 mg, 39%). M.p.decomp 240–2468C;
1H NMR (500.2 MHz, C6D6, 296 K): d = 12.95 (s, 2H, NH), 6.40 (dd,
3J(H,H)=3.5, 2.5 Hz, 2H, protons in 4,5 position on 1,2-diamino-
phenyl moiety), 6.05 (dd, 3J(H,H)=3.5, 2.5 Hz, 2H, protons in 3,6
1086, 935, 914, 835, 808, 762, 662, 542, 527 cmÀ1
.
3
position on 1,2-diaminophenyl moiety), 4.28 (t, J(H,H)=8.0 Hz, 4H,
3
2,3-(p-Toluenesulfonamido)-8,9-dibromo-5,12-dihydro-5,12-
diazatetracene di-n-octylimide (DATTs): To a stirred solution of
Br4NDI (460 mg, 0.57 mmol) in dry DMF (20 mL) kept under Ar at-
mosphere was added 1,2-diamino-4,5-ditosylamidobenzene
(639 mg, 1.43 mmol) as a solid. The solution was heated to 808C in
the dark, reaction progress was monitored with TLC (eluent system
1:20 MeOH/CH2Cl2). Upon completion, the reaction mixture was
taken up in CHCl3 (150 mL). The organic layer was dried over
MgSO4 after washing with 1m HCl (100 mL), H2O (100 mL) and
satd. aqueous NaCl (100 mL). The volume of the solution was re-
duced to about 5 mL using the rotary evaporator and about dry
MeOH (100 mL) was added. Overnight recrystallization at À208C
NCH2-C7H15), 1.89 (tt, J(H,H)=7.5, 8.0 Hz, 4H, NCH2CH2C6H13), 1.47–
1.27 (m, 20H, NC2H4C5H10CH3), 0.89 (t, 3J(H,H)=8.0 Hz, 6H,
NC7H14CH3); 13C{1H} NMR (125.8 MHz, C6D6, 296 K): d = 164.81 (C=
O), 160.04 (C=O), 142.02, 125.82 (carbons in 4,5 position on 1,2-dia-
minophenyl moiety), 122.08, 116.25 (carbons in 3,6 position on 1,2-
diaminophenyl moiety), 95.66, 41.31 (NCH2C7H15), 32.24 (-CH2-),
29.78 (-CH2-), 29.74 (-CH2-), 28.34 (NC6H12CH2CH3), 27.68 (-CH2-),
23.08 (-CH2-), 14.37 (NC7H14CH3); IR (ATR FTIR): n˜ =3261, 2920, 2849,
2366, 1686, 1576, 1508, 1452, 1356, 1319, 1283, 1254, 1230, 791,
750, 667, 611, 536 cmÀ1; MS (FAB, matrix) (%): m/z: 154.0 (100),
594.3 (2), 752.1 (3); HR-MS (FAB): :m/z: calcd. for [M+H]+: 753.1474,
found: 753.1476.
1
produced a blue powder (436 mg, 70%). M.p.decomp 2188C; H NMR
1,2-Diamino-4,5-ditosylamidobenzene: This compound was pre-
pared by a three-step synthesis, starting from 1,2-diaminobenzene.
3
(400.2 MHz, CDCl3, 296 K): d = 12.92 (s, 2H, NH), 7.64 (d, J(H,H)=
3
8.0 Hz, 4H, p-toluenesulfonyl -CH), 7.31 (d, J(H,H)=10.0 Hz, 4H, p-
1,2-Ditosylamidobenzene: To a stirred solution of 1,2-diaminoben-
zene (15.77 g, 146 mmol) in pyridine (200 mL) cooled in an ice
bath was added p-toluenesulfonic acid chloride (57.50 g,
300 mmol) as a solid. The reaction mixture was allowed to warm
up to room temperature while stirring for 18 h. The mixture was
toluenesulfonyl -CH), 7.68 (s, 2H), 6.52 (s, 2H), 4.09 (t, 3J(H,H)=
7.5 Hz, 4H, NCH2C7H15), 2.44 (s, 6H, p-toluenesulfonyl CH3), 1.4–1.1
3
(m, 24H, NC2H4C5H10CH3)), 0.90 (t, J(H,H)=6.5 Hz, 6H, NC7H14CH3);
13C{1H} NMR (125.8 MHz, CDCl3, 296 K): d = 164.53 (C=O), 160.06
(C=O), 144.90, 141.51, 135.51, 130.10, 95.99, 41.59 (NCH2-), 31.95
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(-CH2-), 29.83 (-CH2-), 29.38 (-CH2-), 27.96 (-CH2-), 27.34 (-CH2-), 22.77
(-CH2-), 21.83 (p-toluenesulfonyl -CH3), 14.26 (NC7H14CH3); FTIR: n˜ =
2961, 2924, 2854, 1686, 1582, 1501, 1452, 1416, 1258, 1234, 1153,
1084, 1013, 874, 789, 667 cmÀ1; MS (FAB, matrix) (%): m/z: 154.1
(100), 781.2 (5), 935.2 (11), 1091.2 (7); HRMS (FAB): m/z: calcd for
[M+H]+: 1091.1869, found: 1091.1864.
(phenol CH), 127.31 (C0), 125.69 (C0), 121.75 (C0), 119.08 (C0), 107.26
(PP m-CH), 102.95 (bridging CH), 95.49 (C0), 46.49 (PP -NCH2-),
41.64 (NCH2C7H15), 36.38 (tBu -C(CH3)3), 34.33 (tBu -C(CH3)3), 32.39
(CH2), 31.89 (tBu -C(CH3)3 proximal to phenol oxygen), 30.31 (tBu
-C(CH3)3 distal to phenol oxygen), 30.01 (CH2), 29.91 (CH2), 28.44
(CH2), 27.71 (CH2), 24.95 (4-PyPyr -NCH2CH2-), 23.12 (CH2), 14.41
(NC7H14CH3); IR (ATR FTIR): n˜ =2955, 2924, 2851, 2365, 1595, 1531,
1518, 1458, 1400, 1223, 995, 800, 633, 530, 498 cmÀ1. The PP-
adduct was not observed in FAB MS, only the unbound tetra-coor-
dinated ZnII compound was found at m/z 1277.4.
DATZnS: In a round-bottomed flask, 98% H2SO4 (10 mL) was de-
gassed for 15 min using an N2 stream. DATTs was added as a solid
(430 mg, 0.39 mmol), the turquoise solution was stirred under N2
atmosphere for 5 d. The reaction mixture was poured into
a 1000 mL flask containing vigorously stirred H2O (500 mL) and
CHCl3 (100 mL). NaHCO3 was added as a solid until gas evolution
ceased. The biphasic mixture was diluted with CHCl3 (200 mL) and
extracted five times with H2O (500 mL). The organic phase was
concentrated at the rotavap. The resulting blue solid was washed
once with Et2O and freeze dried. A dark blue solid was obtained in
quantitative yield. The solid readily aggregates in solution, making
1H and 13C solution-state NMR impossible. FTIR: n˜ = 3456, 3416,
3362, 3339, 2953, 2914, 2849, 1678, 1570, 1489, 1452, 1425, 1286,
1234, 1134, 1094, 1013, 874, 812, 660 cmÀ1, indicating the presence
of aniline-like N–H stretching vibrations in this intermediate, typi-
cally located at 3500–3300 cmÀ1. The intermediate diamine com-
pound thus obtained was dissolved in dry, degassed DMF (25 mL)
kept under Ar atmosphere and heated to 808C. In a separate flask,
3,5-di-tert-butylsalicylaldehyde (232 mg, 0.99 mmol) and zinc ace-
tate monohydrate (865 mg, 3.94 mmol) were dissolved in dry, de-
gassed DMF (5 mL) kept under Ar. This mixture was stirred for
10 min, and added to the hot DMF solution via a syringe. The reac-
tion was followed using TLC (eluent system: 100% CH2Cl2). Upon
completion, the DMF reaction mixture was added to dry MeOH
(50 mL) and stored at À808C to induce precipitation of the prod-
uct. Cannula filtration of the DMF/MeOH suspension yielded
a green solid, which was washed on a filter first with H2O (100 mL)
and then with MeOH until no more discoloration of the MeOH was
observed. 398.7 mg of a dark green crystalline solid (0.30 mmol,
77% from DATTs) was obtained. The suspected monomeric water
adduct thus afforded is poorly soluble in common NMR solvents
(CDCl3, [D6]DMSO, C6D6), precluding multinuclear characterization
using 13C and 2D NMR spectroscopy. 1H NMR (400.1 MHz, C6D6,
293 K): d = 13.21 (s, 2H, NH), 8.26 (s, 2H), 7.86 (s, 2H), 7.20 (s, 2H),
6.29 (s, 2H), 5.47–5.45 (brs, 2H), 4.36 (brs, 4H, NCH2C7H15), 2.08 (m,
4H, CH2CH2C6H13), 1.91 (s, 18H, tBu -CH3), 1.51 (s, 18H, tBu -CH3),
1.4–1.3 (m, 24H, NCH2C6H12CH3), 0.92 (t, 3J(H,H)=7.2 Hz, 6H,
NC7H14CH3); IR (ATR FTIR): n˜ = 2951, 2922, 2853, 2363, 1684, 1570,
1450, 1315, 1281, 1248, 1229, 1163, 1130, 785, 658, 600 cmÀ1; MS
(FAB, matrix) (%): m/z: 136.1 (100), 154.1 (60), 781.2 (7), 998.3 (11),
1227.4 (16); HR-MS (FAB): m/z: calcd for [M+H]+: 1277.3862;
found: 1277.3834.
DATZnS-TP: Synthesized via similar procedure as described above
for the PP adduct. Green solid, yield quantitative. 1H NMR
(500.2 MHz, C6D6, 296 K): d = 13.11 (s, 2H, NH), 8.45 (s, 2H, N=CH),
8.21 (brs, 2H, ligand o-CH), 7.86 (s, 2H, salicylimine p-CH), 7.30
(brs, 2H, salicylimine o-CH), 6.56 (s, 2H, ligand m-CH), 6.37 (s, 2H,
3
bridging CH), 4.36 (t, J(H,H)=6.5 Hz, 4H, NCH2C7H15), 1.92 (s, 18H,
tBu -CH3 proximal to phenol oxygen), 1.53 (s, 18H, tBu -CH3 distal
to phenol oxygen), 1.4–1.3 (m, 24H, NCH2C6H12CH3), 0.91 (t,
3J(H,H)=7.5 Hz, 6H, NC7H14CH3), 0.89 (s, 9H, TP tBu); 13C{1H} NMR
(125.8 MHz, C6D6, 296 K): d = 173.38 (C0), 164.57 (C0), 162.00 (N=
CH), 160.63 (C0), 159.98 (C0), 149.53 (TP o-CH), 143.23 (C0), 140.58
(C0), 139.48 (C0), 135.23 (C0), 130.68 (phenol p-CH), 129.70 (phenol
o-CH), 127.48 (C0), 127.28 (C0), 125.67 (C0), 121.60 (C0), 121.15 (TP
m-CH)), 118.87 (C0), 102.92 (bridging CH), 95.45 (C0), 41.48
(NCH2C7H15), 36.31 (tBu -C(CH3)3), 34.37 (TP tBu -C(CH3)3), 34.28 (tBu
- C(CH3)3), 32.27 (CH2), 31.78 (tBu -C(CH3)3 distal to phenol oxygen),
30.22 (TP tBu -C(CH3)3), 29.83 (CH2), 29.78 (CH2), 28.39 (CH2), 27.81
(CH2), 23.06 (CH2), 14.33 (NC7H14CH3). IR (ATR FTIR): n˜ = 2951, 2924,
2854, 1682, 1612, 1574, 1519, 1250, 1227, 1022, 910, 845, 791, 744,
690, 570, 455 cmÀ1.The TP-adduct was not observed in FAB MS,
only the unbound tetra-coordinated ZnII compound was found at
m/z 1277.5.
DATZnS-P: Synthesized via similar procedure as described above
for the PP adduct. Green solid, yield quantitative. 1H NMR
(500.2 MHz, C6D6, 296 K): d = 13.04 (s, 2H, NH), 8.48 (s, 2H, N=CH),
8.28 (brs, 2H, ligand o-CH), 7.82 (s, 2H, salicylimine p-CH), 7.31 (s,
2H, salicylimine o-CH), 6.69 (brs, ligand p-CH, 1H), 6.36 (s, 2H,
bridging CH), 6.32 (m, 2H, ligand m-CH), 4.35 (t, 3J(H,H)=7.0 Hz,
4H), 1.87 (s, 18H, tBu -CH3 proximal to phenol oxygen), 1.50 (s,
18H, tBu -CH3 distal to phenol oxygen), 1.4–1.3 (m, 24H,
NCH2C6H12CH3), 0.91 (t, 6H). 13C{1H} NMR (125.8 MHz, C6D6, 296 K): d
= 172.81 (C0), 164.30 (C0), 162.10 (N=CH), 159.63 (C0), 148.11
(ligand o-CH), 142.84 (C0), 140.25 (C0), 139.10 (C0), 138.12 (ligand m-
CH), 135.03 (C0), 130.43 (salicylimine p-CH), 129.40 (salicylimine p-
CH), 126.83 (C0), 125.28 (C0), 124.27 (ligand p-CH), 121.38 (C0),
118.51 (C0), 102.60 (bridging CH), 95.18 (C0), 41.21 (NCH2C7H15),
35.94 (tBu -C(CH3)3), 33.93 (tBu -C(CH3)3), 31.90 (CH2), 31.43 (tBu
C(CH3)3), 29.87 (tBu C(CH3)3), 29.52 (CH2), 29.48 (CH2), 28.07 (CH2),
27.52 (CH2), 22.74 (CH2), 14.02 (NC7H14CH3). IR (ATR FTIR): n˜ =2955,
2920, 2854, 1682, 1574, 1497, 1380, 1315, 1250, 1226, 1018, 910,
871, 694, 613, 462 cmÀ1.The P-adduct was not observed in FAB MS,
only the unbound tetra-coordinated ZnII compound was found at
m/z 1277.4.
DATZnS-PP: In a round-bottomed flask, DATZnS (38.5 mg) was dis-
solved in dry CH2Cl2 (10 mL). 1 equiv PP was added as a 0.01m
CH2Cl2 solution. The flask was shaken for 30 s and evaporated at
the rotavap. This gave a green solid (41.4 mg, 97%). 1H NMR
(500.2 MHz, C6D6, 296 K): d = 13.17 (s, 2H, NH), 8.47 (s, 2H, N=CH),
8.00 (brs, 2H, ligand o-CH), 7.86 (s, 2H, salicylimine p-CH), 7.3–7.2
(s, overlapping with solvent peak, not integrated in spectrum, see
the Supporting Information p. 25), 6.41 (s, 2H, bridging CH), 5.53
(brs, 2H, ligand m-CH), 4.36 (brs, 4H, NCH2C7H15), 2.24 (brs, 4H,
ligand -NCH2-), 1.98 (s, 18H, tBu -CH3 proximal to phenol oxygen),
1.53 (s, 18H, tBu -CH3 distal to phenol oxygen), 1.4–1.3 (m, 24H,
NCH2C6H12CH3), 0.92 (t, 3J(H,H)=8.0 Hz, 6H, NC7H14CH3); 13C{1H}
NMR (125.8 MHz, C6D6, 296 K): d = 173.44 (C0), 164.63 (C0), 161.94
(N=CH), 160.13 (C0), 152.05 (C0), 149.16 (PP o-CH), 143.17 (C0),
140.52 (C0), 139.77 (C0), 134.91 (C0), 130.46 (phenol CH), 129.81
Acknowledgements
J.A.R. and J.R. were supported by the BioSolar Cells Programme
of the Dutch Ministry of Economic Affairs. J.T.M.K. was support-
ed by a VICI grant of the Chemical Sciences council of the
Netherlands Organization of Scientific Research (NWO-CW).
R.N.F. was supported by a VIDI grant of the Earth and Life Sci-
&
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[13] We also performed the condensation reaction with less sterically en-
cumbered salicylaldehyde and 4-dimethylaminosalicylaldehyde to
afford a dark blue material which could not be dissolved in any kind of
organic solvent. Preliminary ssNMR and electron microscopy experi-
ments performed on this microcrystalline solid suggest a structure con-
taining antiparallel stacks of the corresponding NDI-ZnSalphens con-
nected covalently through sharing of phenolic oxygens in a -O-Zn-O-
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ences council of the Netherlands Organization of Scientific Re-
search (NWO-ALW). This work was supported by a NWO-CW
equipment investment grant to J.T.M.K.
Keywords: naphthalene
diimides
·
porphyrinoids
·
supramolecular light harvesting · time-resolved spectroscopy ·
zinc–salphen complexes
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Received: February 27, 2014
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
Dye dyad design: The fusion of a naph-
thalene diimide dye to a zinc–bis-salicyl-
imide phenylene (salphen; see figure)
moiety creates an expanded red-light
absorbing chromophore with an em-
bedded metal atom for supramolecular
interaction with substituted pyridines. A
column-chromatography-free prepara-
tion of this novel scaffold is described
and its photophysical properties are an-
alyzed, which compare favorably with
the widely used supramolecular light-
harvester zinc tetraphenylporphyrin.
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Chromophores
J. A. Rombouts, J. Ravensbergen,
R. N. Frese, J. T. M. Kennis, A. W. Ehlers,
J. C. Slootweg, E. Ruijter, K. Lammertsma,*
R. V. A. Orru*
&& – &&
Synthesis and Photophysics of a Red
Light Absorbing Supramolecular
Chromophore System
The fusion of…
… a naphthalene diimide dye to
a zinc–bis-salicylimide phenylene
(salphen) moiety creates an
expanded red-light absorbing
chromophore with an embedded
metal atom for supramolecular
interaction with substituted
pyridines. A column-
chromatography-free preparation of
this novel scaffold is described and
its photophysical properties are
analyzed. For more details, see the
Full Paper by K. Lammertsma, R. V.
A. Orru et al. on page && ff.
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Chem. Eur. J. 2014, 20, 1 – 8
www.chemeurj.org
8
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!