Benzo[c][1,2,5]thiadiazole Donor-Acceptor Dyes: A Synthetic, Spectroscopic, and Computational Study

Article abstract of DOI:10.1021/acs.jpca.6b00447

The synthesis, optical characterization and computational modeling of seven benzo[c][1,2,5]thiadiazole (BTD) donor-acceptor dyes are reported. These dyes have been studied using electrochemical analysis, electronic absorption, emission, and Raman and resonance Raman spectroscopies coupled with various density functional theoretical approaches. Crystal structure geometries on a number of these compounds are also reported. The optical spectra are dominated by low energy charge-transfer states; this may be modulated by the coupling between donor and acceptor through variation in donor energy, variation of the donor-acceptor torsion angle, and incorporation of an insulating bridge. These modifications result in a perturbation of the excitation energy for this charge-transfer transition of up to ～2000 cm^-1. Emission spectra exhibit significant solvatochromisim, with Lippert-Mataga analysis yielding Δμ between 8 and 33 D. Predicted λ_max, ε, and Raman cross sections calculated by M06L, B3LYP, PBE0, M06, CAM-B3LYP, and ωB97XD DFT functionals were compared to experimental results and analyzed using multivariate analysis, which shows that hybrid functionals with 20-27% HF best predict ground state absorption, while long-range corrected functionals best predict molecular polarizabilities.

Full text of DOI:10.1021/acs.jpca.6b00447

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Article
Benzo[c][1,2,5]thiadiazole Donor-Acceptor Dyes: A
Synthetic, Spectroscopic and Computational Study
Jonathan E. Barnsley, Georgina E Shillito, Christopher Bryan Larsen,
Holly van der Salm, Lei E. Wang, Nigel T. Lucas, and Keith C Gordon
J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.6b00447 • Publication Date (Web): 26 Feb 2016
Downloaded from http://pubs.acs.org on March 1, 2016
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Benzo[c][1,2,5]thiadiazole Donor-Acceptor Dyes: A Synthetic, Spec-
troscopic and Computational Study
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Jonathan E. Barnsley‡, Georgina E. Shillito‡, Christopher B. Larsen‡, Holly van der Salm, Lei E.
Wang, Nigel T. Lucas*, Keith C. Gordon*
Department of Chemistry, University of Otago, P. O. Box 56, Dunedin, New Zealand
ABSTRACT: The synthesis, optical characterization and computational modelling of seven benzo[c][1,2,5]thiadiazole
(BTD) donor-acceptor dyes are reported. These dyes have been studied using electrochemical analysis, electronic absorp-
tion, emission, Raman and resonance Raman spectroscopies coupled with various density functional theoretical ap-
proaches. Crystal structure geometries on a number of these compounds are also reported. The optical spectra are domi-
nated by low energy charge-transfer states; this may be modulated by the coupling between donor and acceptor through
variation in donor energy, variation of the donor-acceptor torsion angle, and incorporation of an insulating bridge. These
modifications result in a perturbation of the excitation energy for this charge-transfer transition of up to ~2000 cm-1.
Emission spectra exhibit significant solvatochromisim, with Lippert-Mataga analysis yielding Δμ between 8 and 33 D.
Predicted λmax, ε and Raman cross-sections calculated by M06L, B3LYP, PBE0, M06, CAM-B3LYP and ωB97XD DFT func-
tionals were compared to experimental results and analyzed using multivariate analysis, which shows that hybrid func-
tionals with 20-27% HF best predict ground state absorption, whilst long-range corrected functionals best predict mo-
lecular polarizabilities.
INTRODUCTION
ies significantly depending on the chemical system
investigated or the target information.10,12-15
Organic donor-acceptor (D-A) dyes have been of
significant interest in recent years as a result of poten-
tial applications in organic photovoltaics, dye-
sensitized solar cells and non-linear optics.1-4 Specifi-
cally, D-A dyes incorporating benzo[c][1,2,5]thiadiazole
(BTD) have shown promise in these fields due to a low
band gap and highly tunable optical properties.5
Various computational approaches exist, including
‘pure’ functionals and hybrid methods (such as B3LYP).
‘Pure’ methods calculate exchange and correlation
terms by implementing electron density approxima-
tions (LDA/GGA), while hybrid methods combine
‘pure’ calculations with exact exchange energies calcu-
lated by Hartree-Fock theory (HF). These hybrid
methods fall into two categories (global and range sep-
arated) based on the evolution of HF exchange over
electron-electron distance.16 The fundamental differ-
ences in how these functionals predict geometries and
photophysical properties consequently afford func-
tional-dependent results, can compromise the under-
standing of these promising systems.
These tunable optical properties stem from charge-
transfer (CT) transitions, which are typical for D-A
dyes.6,7 CT transitions result in a shift of electron den-
sity from the donor to the acceptor moiety and modu-
lation of the coupling between the donor and acceptor
allows fine control of photophysical properties.8 Such
systems result in partially zwitterionic excited states
which can undergo solvent stabilization. Thus, varia-
tion of the solvent environment can also be utilized as
a tuning mechanism.9
There have been a number of studies investigating
computational predictions of photophysical properties
in donor acceptor-dye systems.17-27 In the case of this
study, particular attention is paid to the influence of
HF, and functionals are specifically picked based on
their common/wide use in donor-acceptor studies. The
inclusion of experimental and calculated Raman cross-
sections provides additional testing of the calculations
via experimental data.
In the pursuit of specialized photophysical proper-
ties, intense electronic absorption in the visible region,
for example, many predictive tools have been devel-
oped to identify promising synthetic targets.10,11 One
powerful and widely used approach is density func-
tional theory (DFT). DFT provides a computationally
efficient and reasonably accurate method to model
chemical systems.10,12 Despite its wide use, which DFT
approach is most effective is subject to debate and var-
Herein we report a series of seven D-A BTD dyes
with varying degrees of steric bulk so as to conforma-
tionally control the D-A torsion angle. Also included
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are several permutations of the D-A framework to in-
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vestigate linker and donor effects. The dependence of
optical properties on solvent is investigated both ex-
perimentally (with optical/vibrational spectroscopies)
and theoretically (with a DFT calculation library, using
six different functionals with different levels of HF ex-
change, M06L - 0%, B3LYP - 20%, PBE0 - 25%, M06 -
27%, CAM-B3LYP - 19-65% and ωB97XD - 22-100%,
with five different solvents). In order to identify possi-
ble correlation these data are subjected to principal
component analysis (PCA).
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RESULTS AND DISCUSSION
Compounds Investigated
For this study the compound series is based on a
benzothiadiazole-triphenylamine (BTD-TPA) frame-
work (Figure 1). Addition of substituents to either the
adjacent site to the TPA unit (as in BTDMe-TPA or
BTD-TPA2) or to the phenyl ring of the substituent (as
in BTD-(OMe)2TPA and BTD-(OMe)2Ph) should
cause an increase in the donor-acceptor torsion angle
due to steric factors. However, the methoxy group in
particular may also have electronic effects.28,29 BTD-
(OMe)2Ph lacks an amine donor, and is included as a
control for the influence of the methoxy-groups.
The other compounds investigated are altered in dif-
ferent ways; a ‘click’ triazolyl bridge is included (BTD-
TRZTPA), the donor group is changed from TPA to
Ph-NMe2 (BTD-NMe2) and an additional donor group
is added (BTD-TPA2) which alters both ϕD-A and the
electronic properties of the donor.
Figure 1. The compound series studied in this work, showing
D-A/bond length of the parent BTD-TPA in orange, and the
subsequent variations in blue.
ϕ
Synthesis and Characterization
The synthesis of the target compounds is presented
in Scheme 1. BTD-(OMe)2Ph, BTD-NMe2 and BTD-
TPA are prepared in one high-yielding step from 5-
bromobenzo[c][1,2,5]thiadiazole (BTD-Br) using Suzu-
ki-Miyaura couplings with the appropriate substituted
boronic acid. BTD-TPA2 is likewise prepared in one
high-yielding
step
from
5,6-
dibromobenzo[c][1,2,5]thiadiazole (BTD-Br2) using
Suzuki-Miyaura coupling.
Incorporation of methoxy groups on the TPA donor
was achieved by preparing an appropriately substituted
phenylboronic acid incorporating a masked halide in
the form of a trimethylsilyl group. This useful building
block was achieved in two high-yielding steps from
commercially
available
1-bromo-3,5-
dimethoxybenzene. The first step involves protecting
the bromo group site as a trimethylsilyl group through
lithiation and reaction with Me3SiCl. The second step
involves ortho-lithiation and subsequent borylation
selectively at the position flanked by the methoxy
groups. An X-ray crystal structure of the product
(Figure 2) shows intermolecular hydrogen-bonding
between the boronic acid protons and the methoxy
group oxygens. This is a rare case in which boronic
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acid protons are ‘tethered’ through intramolecular hy- using crystals obtained from EtOH recrystallizations.
drogen-bonding,30 permitting purification through
preparative column chromatography. Suzuki-Miyaura
coupling between this substituted phenylboronic acid
and BTD-Br proceeds in excellent yield. Deprotection
of the masked halide through iododesilylation pro-
ceeds in good yield at low temperatures, then Buch-
wald-Hartwig coupling N,N-diphenylamine affords
BTD-(OMe)2TPA in moderate yield.
BTD-NMe2 crystallized in the Pbca space group, BTD-
TPA in the P21/c space group, BTD-TPA2 in the Pbcn
space group and BTD-(OMe)2TPA in the P-1 space
group. In all cases the BTD unit is completely planar,
and the amine donor relatively planar, with N3 lying
0.10, 0.02, 0.02 and 0.00 Å, respectively, above a plane
defined by the ipso carbons (ipso carbon and methyl
groups for BTD-NMe2). The donor unit is rotated 9.7°,
26.7°, 53.4° and 47.9°, respectively, from the BTD ac-
ceptor. For BTD-TPA, BTD-TPA2 and BTD-(OMe)2-
TPA, terminal donor phenyl rings are rotated from the
donor phenylene with torsion angles of -31.8° and
128.4° for BTD-TPA, -49.4° and 74.1° for BTD-TPA2,
and -40.3° and 140.4° for BTD-(OMe)2TPA, which also
has the methoxy groups in plane with the donor phe-
nylene.
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Figure 2. X-ray crystal structure of 4-trimethylsilyl-2,6-
dimethoxyphenylboronic acid with ellipsoids depicted at the
50% probability level. Intermolecular hydrogen-bonding is
depicted with blue dashed lines.
Incorporation of a methyl group on the BTD accep-
tor was achieved through the preparation of an ana-
logue
of
BTD-Br,
namely
5-bromo-6-
methylbenzo[c][1,2,5]thiadiazole (BTDMe-Br). This
was accomplished in four steps from commercially
available 4-methyl-1,2-phenylenediamine. The first
step involves protection of the amines with TsCl in
near quantitative yield. The sterically bulky Ts groups
protect the 3- and 6- positions from substitution; bro-
mination occurs selectively at the 5-position. Depro-
tection of the amines with H2SO4, followed by NaOH
neutralization, affords the corresponding 1,2-
phenylenediamine in good yield and subsequent reac-
tion with SOCl2 affords the BTD in excellent yield. Su-
zuki-Miyaura
coupling
with
4-
diphenylaminophenylboronic acid affords BTDMe-
TPA in good yield.
BTD-TRZTPA was prepared in two steps from 5-
aminobenzo[c][1,2,5]thiadiazole. Diazotization of the
amino group and in situ conversion to the azide pro-
ceeds in average yields, followed by CuAAC “click” re-
action of the azide with 4-ethynyl-N,N-diphenylaniline
in excellent yield.
X-ray crystal structures were obtained for BTD-
NMe2, BTD-TPA, BTD-TPA2 and BTD-(OMe)2TPA,
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and an electron rich π system that favors planarity,
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while BTD-(OMe)2Ph possesses maximal steric bulk
with minimal ability to share π electrons due to the
absence of a donor group. In the case of the remaining
compounds, the trend in ϕD-A is consistent with steric
bulk; BTD-NMe2 < BTD-(OMe)2TPA < BTDMe-TPA <
BTD-TPA2. Whilst it might be expected that the meth-
oxy groups perturb the electronic nature of the TPA
donor,28,29 electrochemical studies show Eox of BTD-
(OMe)2TPA and BTD-TPA (Table S1) to be virtually
unchanged by methoxy substitution.
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Figure 4. DFT-calculated HOMO and LUMO orbitals for
BTD-TPA in acetonitrile using the B3LYP functional. Calcu-
lated orbitals for the remaining compounds can be found in
Figure S16.
The choice of functional has an effect on the abso-
lute calculated value which exemplifies the role that
functionals play in computational results. For M06L,
with no HF or orbital exchange contribution, the abso-
lute angle for all compounds is calculated to be the
smallest (-28.2o for BTD-TPA). As the contribution of
HF is increased from left to right across Table 1 (0%,
20%, 25%, 27%, 19-65% and 22-100%, respectively)
there is an increase of ϕD-A up to -38.8o for BTD-TPA
using ωB97XD. Typically, equilibrium geometries are
predicted much more effectively by pure or global hy-
brids with small HF contributions.31 A plausible expla-
nation for this is that the short range nature of cova-
lent bonds, where most of the stabilization results
from local electron interaction; this is observed, with
M06L most accurately and ωB97XD least accurately
replicating experimental results. Deviations between
calculated and experimental angles are attributed to
calculations not accounting for solid-state packing in-
teractions observed in the crystal.
Figure 3. X-ray crystal structures obtained for BTD-
OMe2Ph, BTD-TPA, BTD-TPA2, BTD-OMe2TPA. Ellipsoids
are shown at the 50% probability level.
Ground-State Geometries
Donor-acceptor torsion angles (ϕD-A) and bond
lengths (rD-A) obtained from DFT geometry optimiza-
tions and X-ray crystal structures are presented in Ta-
ble 1. DFT geometry optimizations yield partially
twisted structures around the D-A bond: BTD-
TRZTPA was predicted to possess the smallest calcu-
lated angle (-21.4o to -33.0o) through to BTD-
(OMe)2Ph with the largest (51.7o to 61.4o). The BTD-
TRZTPA structure results from minimal steric bulk
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Scheme 1. Synthesis of target compounds.
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(i) a. n-BuLi, THF, -78 °C, 2 h, b. Me3SiCl, rt, 15 h, 97%; (ii) a. n-BuLi, THF, 0 °C, 15 h, b. B(OMe)3, rt, 5 h, c. aq. NH4Cl (sat.), rt,
2 h, 69%; (iii) 2,6-dimethoxyphenylboronic acid, K2CO3, PdCl2(dppf), toluene, water, EtOH, reflux, 15 h, 87%; (iv) 4-
dimethylaminophenylboronic acid or 4-diphenylaminophenylboronic acid, K2CO3, PdCl2(dppf), toluene, water, EtOH, reflux, 15
h, 75% (R = Me), 94% (R = Ph); (v) 4-diphenylaminophenylboronic acid, K2CO3, PdCl2(dppf), toluene, water, EtOH, reflux, 15 h,
80%; (vi) K2CO3, PdCl2(dppf), toluene, water, EtOH, reflux, 15 h, 96%; (vii) ICl, CH2Cl2, -78 °C, 2 h, 80%; (viii) diphenylamine, t-
BuOK, [t-Bu3PH]BF4, Pd2(dba)3, toluene, reflux, 15 h, 50%; (ix) TsCl, py, CH2Cl2, rt, 3 h, 95%; (x) Br2, AcONa, AcOH, reflux, 3 h,
91%; (xi) a. conc. H2SO4, reflux,
3
h, b. NaOH, 87%; (xii) SOCl2, NEt3, CH2Cl2, reflux, 15 h, 90%;
(xiii) 4-diphenylaminophenylboronic acid, K2CO3, PdCl2(dppf), toluene, water, EtOH, reflux, 15 h, 80%; (xiv) TsOH, NaNO2,
NaN3, CH3CN, water, rt, 2 h, 20%; (xv) 4-ethynyl-N,N-diphenylaniline, L-ascorbic acid, CuSO4⋅5H2O, DMF, H2O, rt, 15 h, 91%
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Table 1. Calculated ϕD-A and bond lengths. Data shown are calculated with an acetonitrile solvent field.
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2
3
4
ϕ
D-A / ° (rD-A /Å)
M06L
B3LYP
PBE0
M06
CAM-B3LYP
36.0(1.48)
ωB97XD
Crystallography
26.7(1.49)
5
BTD-TPA
28.2(1.43)
34.0 (1.48) 34.3(1.48)
35.0 (1.47)
38.8(1.49)
6
7
8
9
BTD-
(OMe)2TP
A
47.9(1.49)
48.2(1.48)
43.4(1.47)
54.0(1.49)
55.8(1.49)
52.1(1.49)
55.3(1.48)
53.1 (1.48)
52.3 (1.48)
54.1 (1.48)
58.1(1.50)
57.4(1.49)
a
BTDMe-
TPA
-
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59.7(1.49)
56.1(1.49)
BTD-TPA2
46.9(1.49) 49.3(1.49)
48.0 (1.49)
31.5(1.47)
50.9 (1.48) 50.6(1.48)
53.4 (1.49)
BTD-NMe2 26.7(1.47)
31.0(1.48)
29.0(1.42)
31.8 (1.47)
25.9(1.42)
33.3(1.48)
30.5(1.42)
35.7 (1.48) 9.7(1.49)
a
BTD-
-
21.4(1.41)
TRZTPA
29.5 (1.41)
33.0(1.42)
a
BTD-
-
51.7(1.48)
(OMe)2Ph
57.5(1.49)
55.7(1.48)
55.4(1.48)
56.9(1.49)
61.4 (1.49)
a Dashes indicate compounds which failed to afford quality crystals for X-ray crystallography.
Ground-State Vibrational Spectroscopy
Figures S3-S10 detail significant variation in the
predicted Raman cross section values, which are af-
Mean absolute deviations (MADs) can be used to
understand how effectively an optimized geometry
models the compound in question. MADs for this
fected by both the functional used and the solvent
field. For example BTD-TPA has a considerable spre. In
acetonitrile, the absolute value for the cross section is
considerably overestimated by non-hybrid and global
hybrid functionals (400% for M06L, Table 3), while
long-range corrected functionals were more accurate (-
0.77% for ωB96XD). This result appears sensible in the
view that long-range corrected functionals (e. g.
ωB97XD), model long distance electron interactions
more effectively than non-hybrid and global hybrid
functionals, and would therefore be expected to more
effectively model the polarizability, a property which
depends on electron density across the whole mole-
cule.10 There appears to be no consistent error associ-
ated with TPA, BTD and mixed modes in these cases.
study were calculated as explained by Earles et al.32
A
MAD of around 10 cm-1 is considered satisfactory and
low HF functionals such as M06L and B3LYP overall
provide satisfactory MADs (13 and 10 cm-1 respectively,
Table 2) while range separated HF functionals CAM-
B3LYP and ωB97XD are considerably less accurate at
calculating vibrational frequencies for these com-
pounds (average MADs of 27 and 25 cm-1 respectively).
Vibrational frequencies are dependent on the ground-
state bonding networks, which as stated above, are
more accurately modelled in low HF hybrid function-
als.
Differential Raman cross-sections in acetonitrile and
toluene were evaluated for each compound. Raman
cross-sections probe the overall polarizability of a mol-
ecule, which is affected by conjugation.33 These are
presented in Table S4. In order to compare these
complex series the calculated normal modes were ex-
amined and it was possible to identify modes that are
BTD-based, TPA-based and delocalized. This is exem-
plified by the Raman spectrum of BTD-TPA (Figure 5).
Modes at 1179 cm-1 and 1278 cm-1 are TPA localized,
while 1217 cm-1 is a BTD band and the strongest bands
at 1597 and 1612 cm-1 are of mixed origin. The mixed
modes have the largest differential Raman cross sec-
tions, ranging from 2 to 40 cm2 sr-1 molecule-1 and are
typically 50 to 75% more intense than the localized
TPA and BTD modes.
Figure 5. FT-Raman spectra of neat BTD-TPA collected at
1064 cm-1.
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Table 2. Mean absolute deviations (MADs) for calculated Raman frequencies in acetonitrile.
Mean Absolute Deviation of Raman Modes / cm-1
4
5
6
7
8
9
M06L
17
B3LYP
10
PBE0
22
M06
13
CAM-B3LYP
32
ωB97XD
34
BTD-TPA
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25
39
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31
BTD-(OMe)2TPA
BTDMe-TPA
BTD-TPA2
13
10
8
23
17
16
18
8
BTD-NMe2
26
23
27
26
21
BTD-TRZTPA
12
10
BTD-(OMe)2Ph
Average
13
25
Table 3. Mean percentage errors for calculated Raman cross sections of BTD-TPA when compared to experi-
mental data.
Mean percentage error in calculated Raman cross section /%
M06L
400
B3LYP
298
PBE0
176
M06
148
CAM-B3LYP
4.14
ωB97XD
-0.770
-40.3
Acetonitrile
Toluene
195
49.2
46.5
77.0
-51.3
Electronic Absorption Spectroscopy
The inclusion of triazole results in a blue shift of the
low energy band by 2260 cm-1 and a decrease of nearly
30% in extinction coefficient when compared to BTD-
TPA. This indicates a decrease in communication be-
tween donor and acceptor similar to that due to an
increase in ϕD-A as for BTDMe-TPA, consistent with
the triazole acting as an electronically insulating
bridge. Computational chemistry supports these find-
ings with vast decreases in CT band intensity for all
functionals except ωB97XD.
Previously investigated D-A compounds using a BTD
acceptor show a series of optical transitions; the lowest
energy band is typically of CT character, while higher
energy transitions tend to be of π-π* character.34-36 Op-
tical data of this lowest energy transition for the inves-
tigated compounds are presented in Table 4. It ap-
pears that as ϕD-A is increased, the absorption band
energy increases and intensity decreases. This is exem-
plified by BTD-TPA, which has one of the smallest
calculated ϕD-A (-28.1o to -38.80o) and exhibits the low-
est energy (399 nm) and one of the most intense tran-
sitions (12600 M-1 cm-1) of the TPA-containing dyes.
Such results support the assignment of this low energy
band as CT, since ϕD-A affects conjugation or commu-
nication between donor and acceptor groups, which
consequently perturbs both the optical transition en-
ergy and allowedness of a transition. DFT results for
BTD-(OMe)2TPA and BTDMe-TPA correctly predict
decreases in λmax and ε as a result of an increased ϕD-A
.
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Table 4. Experimental and calculated absorption data for the lowest energy transition. All data were collected
or modelled in acetonitrile.
1
2
3
4
5
6
7
8
9
λmax /nm (ε /M-1 cm-1)
EXPERIMENTAL
Absorption Max λmax /nm (Oscillator Strength)
M06L B3LYP PBE0 M06
480(0.26) 469(0.27) 354(0.52)
CAM-B3LYP ωB97XD
BTD-TPA
399(12600)
382(9000)
686(0.19) 527(0.23)
680(0.12) 519(0.14)
335(0.56)
332(0.37)
BTD-
(OMe)2TPA
472(0.18)
459(0.18) 349(0.35)
330(0.27)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
BTDMe-
TPA
371(9330)
687(0.11)
515(0.09)
466(0.10) 455(0.13)
312(0.27)
BTD-TPA2
398(10300)
713(0.21)
621(0.21)
541(0.19)
510(0.25)
492(0.23) 479(0.24) 349(0.58)
472(0.27) 462(0.27) 362(0.40)
328(0.64)
345(0.40)
BTD-NMe2 408(16800)
BTD-
366(9100)
TRZTPA
886(0.03) 581(0.03)
512(0.04)
493(0.04) 329(0.30)
373(0.12) 316(0.15)
307(0.70)
309(0.12)
BTD-
315(10900)
(OMe)2Ph
457(0.11) 396(0.06) 371(0.12)
BTD-NMe2 provided the most intense (16800 M-1 cm-
1) and lowest energy (408 nm) band of all compounds.
This is a result of a small calculated ϕD-A and the donor
NMe2 group being a stronger donor than TPA, as evi-
denced by electrochemistry (Table S1).The addition of
a second TPA group in BTD-TPA2 resulted in a de-
crease in extinction coefficient but negligible change to
the λmax. The addition of the second TPA results in
both donor groups twisting out of plane relative to
BTD, changing ϕD-A significantly. The blue shift ex-
pected with an increased ϕD-A is offset by the presence
of a second donor. This results in an overall small net
change. The decrease of intensity resulting from a se-
cond TPA group is only predicted for functionals
B3LYP, PBE0 and M06, which also predict a small red-
shift for the transformation. In BTD-(OMe)2-Ph there
is an absence of the CT transition as a result of lacking
a strong donor group.
transition with an increase in HF contribution to the
calculation. For BTD-TPA there is an increase of
>15,000 cm-1 (51%) in transition energy and an increase
of >66% in oscillator strength when calculated with
wB97XD compared to M06L. This difference is a result
of the lack of sensitivity to long-range interactions in
low HF methods, resulting in an underestimation of
oscillator strength and excitation energy.31,39,40 A small
part of this change is likely to be a result of the in-
creased ϕD-A present in geometry optimization, but this
is minor compared to fundamental differences in the
nature of these functionals.
Long-range corrected functionals (CAM-B3LYP and
wB97XD) correctly predict the λmax experimental trend
within the compound series, while the functionals
B3LYP, PBE0 and M06 correctly predict the f trend.
The ability to predict these trends is powerful; DFT
calculated absolute values, however, are considerably
less meaningful. Figure S13 shows that high HF calcu-
lations (wB97XD) fail to account for any solvent effects
in these compounds, while M06L is much better and
predicts a stabilization of the ground state (HOMO) in
polar solvents like acetonitrile.
Resonance Raman spectra were collected at 351 nm,
which probes the lowest energy transition. Resonance
Raman spectra show selective enhancement of vibra-
tional modes associated with the active chromophore,
which helps elucidate the transition nature.37 More
specifically, modes that ‘mimic’ changes due to a exci-
tation to an excited state, such as CO stretching for
MLCT transitions, are typically enhanced on the order
of 104 to 105.38 In this case, spectra show the enhance-
ment of a number of BTD and TPA modes (Figure
S15), which would be expected for a shift of electron
density from TPA to BTD.
It is pertinent to not only investigate the predicted
energy and oscillator strengths of transitions but also
at the orbital contributions for said transitions. In
most cases the lowest energy transition is predicted to
be HOMO to LUMO in nature (Figure 4) which repre-
sents a CT transition since the HOMO is TPA-based
and the LUMO BTD-based. Long-range corrected
functionals (CAM-B3LYP and wB97XD) also predict
considerable orbital contribution from other donor
TD-DFT data (Table 4), shows a significant increase
in transition energy and oscillator strength for the CT
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orbitals (HOMO-1, HOMO-2 and HOMO-3). These
orbitals are significantly delocalized, causing the calcu-
lated transitions to become more π-π* in nature – ex-
plaining a higher predicted transition energy.
1
2
3
4
Figure 6 shows frontier molecular orbital (FMO) en-
ergies estimated from experimental techniques and
calculated using two different functionals. Experi-
mental HOMO and LUMO energies are estimated
from cyclic voltammetry data using previously estab-
lished methods (Table S1).41
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
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48
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53
54
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56
57
58
59
60
The agreement between values obtained from elec-
trochemistry and PBE0 calculations is within 20%. Us-
ing wB97XD the level of agreement becomes nearly
50%. The LUMO energies obtained electrochemically
and from PBE0 calculations show good agreement,
suggesting the LUMO is modelled well using this func-
tional. As the amount of orbital exchange in the func-
tional increases, the HOMO is predicted to be increas-
ingly stabilised, while the LUMO is increasingly desta-
bilized.
Figure 7. (a) Emission data for BTD-TPA in a number of
solvents and (b) a Lippert Mataga plot for BTD-TPA, BTD-
OMe2TPA and BTD-MeTPA.
Using the Lippert-Mataga equation, the relationship
between the Stokes shift and solvent polarity parame-
ter can be related to a change in dipole moment be-
tween the ground and emissive excited states (Δμ,
Figure 7b).9
Figure 6. Calculated frontier molecular orbital energies for
experimental and computational data. All data were collect-
ed or modelled in dichloromethane. A full FMO diagram can
be found in SI (Figure S14).
Emission Spectroscopy
For dyes with a similar rD-A, and therefore similar
Onsager radii, the Δμ value is around 21-22 D which
indicates significant charge transfer (Table 5). BTD-
NMe2 has a smaller Onsager radius, and a smaller cal-
culated Δμ of 15 D while BTD-TRZTPA which has a
larger Onsager radius is calculated to have a Δμ of 33
D, considerably more than the other compounds.
BTD-OMe2Ph shows emission from a π* state, not a
CT state as for the other compounds. The electron
density of the HOMO and LUMO orbitals can still be
localized, resulting in a net Δμ.
Emission spectra show solvatochromism (Figure 7a).
For BTD-TPA, the emission wavelength varies by
~5000 cm-1, from 502 nm in toluene to 673 nm in ace-
tonitrile. This behavior arises due to an excited state
which is more polarized than the ground state, and
therefore is more stabilized by more polar solvents.9
BTD-TPA shows dual emission in acetonitrile, with the
higher energy state likely to be of π,π* origin.
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Table 5. Lippert Mataga data for the compound se-
ries.
1
2
3
4
5
Compound
BTD-TPA
Δμ /D
22
BTD-OMe2TPA 22
6
7
8
9
BTD-MeTPA
BTD-TPA2
21
21
15
33
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
BTD-NMe2
BTD-TRZTPA
BTD-OMe2
Figure 8. Mean percentage errors for each functional when
compared to experimental data.
Mean Percentage Error (MPE) Analysis
Table 6. Overall mean percentage error for absorption
and Raman data; UV-Vis refers to a mean error associated
to both λmax and ε, where Raman refers to error in Raman
cross sections.
To investigate the effectiveness of the different func-
tionals to predict both structural and electronic prop-
erties of this compound series, MPEs have been calcu-
lated by comparing calculated DFT results to experi-
mental data. Parameters include λmax (cm-1), ε, and
cross sections for five Raman vibrations present in all
compounds, across solvent and functional.
UV-Vis /% Raman/ %
M06L
B3LYP
PBE0
M06
-43.1
-32.1
-27.5
-19.8
321
164
Figure 8 shows Raman cross sections are significant-
ly overestimated by nearly all functionals and the ex-
tent of error is considerably more than for the absorp-
tion max and extinction coefficient. As discussed pre-
viously, non-hybrid and global hybrid functionals con-
siderably overestimate the polarizability of this dye
series (over 320% for M06L, Table 6) whilst the long-
range corrected functionals are more accurate
(<±25%). The long-range corrected functionals overes-
timate the absorption energy and extinction co-
efficient for calculated transitions whilst the non-
hybrid and global hybrid functionals underestimate
these properties. In this case, M06 (27% HF) yields the
smallest error across solvent and compound (-19.77%).
Of particular note is the vast variation in error for the
five cross-sections. Figure S20 displays the predicted
origin for each vibration. Cross-sections 1 and 3 (TPA
based) are well predicted in terms of intensity, with
cross-sections 4 and 5 (delocalized) somewhat well
predicted, while cross-section 2 (BTD based) is vastly
over estimated. This result indicates complexity in vi-
brational predictions, such that vibrations of differing
nature result in differing degrees of overestimation. In
the case of the BTD unit and its associated vibrations,
most functionals performed poorly, especially that of
the low HF functionals (M06L, B3LPY, and PBE0).
133
69.7
5.96
-23.2
CAM-B3LYP 45.9
ωB97XD 95.5
Principle Component Analysis
Principal component analysis (PCA) factorizes varia-
tion within a data set into a series of principal compo-
nents. This technique is used to extract patterns from
the data set that may have gone unnoticed by other
analyses.42 For this analysis the optical properties (λmax
,
ε) were examined along with Raman cross-sections for
five bands from each sample; two TPA based, two
mixed and one BTD based. Analysis of the spectral and
Raman data results in two PCs describing 78% of all
data variance. The loadings plots give some insight
into the relationship between different parameters.
PC1 is positively correlated with ε and negatively cor-
related to λmax and all of the Raman cross sections as
seen in Figure 9b. The inverse relationship between ε
and λmax originates from computational trends where
increased energy of absorption is strongly associated
with an increased extinction co-efficient (ε). Function-
als that predicted a high energy transition also predict-
ed modest Raman cross-sections. Cross sections 1 and 3
appears to behave slightly differently from the remain-
ing cross sections as seen in PC1 and PC2 (Figure S21).
This is believed to result from a nearly exclusive TPA
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The Journal of Physical Chemistry
contribution to these stretches. In compounds such as experimental data with an overall slight underestima-
1
2
3
4
5
6
7
8
BTD-NMe2, BTD-OMe2Ph and BTD-TPA2 the pre-
dicted intensity for these bands is lower than for BTD-
TPA, this especially so for cross section 1.
tion of ε and an overestimation of both λmax and α. This
finding provides evidence that functionals with HF
contributions close to 27% are suited for investigating
the photo-physical properties of donor-acceptor dyes
of similar nature to those studied here. At this point is
in unclear how general these findings are. Although
valid for these systems, further investigation is war-
ranted to ascertain if our conclusions are appropriate
for different donor-acceptor compounds and how ap-
plicable these strategies may be to other types of com-
pounds.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CONCLUSIONS
The synthesis and characterization of seven ben-
zo[c][1,2,5]thiadiazole donor-acceptor dyes has been
reported. A broad absorption band is observed be-
tween 350 and 410 nm, and shown to be charge-
transfer in nature from the TPA group to BTD using
resonance Raman spectroscopy; DFT calculations us-
ing any of the functionals discussed herein are con-
sistent with this. The energy and intensity of this tran-
sition is decreased by an increase in the torsion angle
between donor and acceptor units or with the inclu-
sion of an insulating linker group. Emission spectra
show significant solvatochromism, with large values
calculated using Lippert-Mataga analysis.
DFT calculations using a number of functionals with
different HF exchanges were investigated in terms of
their ability to accurately predict experimental proper-
ties. Data suggests that absorption properties (energy
and ε) were predicted best using M06, while the mo-
lecular polarizability and therefore Raman cross-
section were predicted best using hybrid functionals
with long-range corrected Hartree-Fock exchange.
EXPERIMENTAL
General Experimental
Figure 9. a) PCA scores plot for all compounds and solvents,
distinguished by functional and b) PC1 loadings plot which
describes 65% of variation within the data set.
5-bromobenzo[c][1,2,5]thiadiazole,
dibromobenzo[c][1,2,5]thiadiazole,
5,6-
5-
aminobenzo[c][1,2,5]thiadiazole and 4-ethynyl-N,N-
diphenylaniline were prepared using literature proce-
dures.43-45 Commercially available reagents and sol-
vents were used as received. Sigma-Aldrich spectro-
scopic or HPLC grade solvents were used for all spec-
troscopic measurements. Spectral data were analyzed
using GRAMS A/I (ThermoScientific) and OriginPro
v9.0 (Origin Lab Corporation). Numbering schemes for
NMR assignments are presented in Figure S23.
Figure 9a presents PC1 (65% variation) and PC2 (13%
variation) with an identical parameter set used for
MPE analysis. The dispersed nature of data points is a
visual reminder of the variability of computational
chemistry. Experimental data clusters close to the
origin, the closer functionals group to experimental
data, the more effective the prediction. Whist there is
mixing between clusters, M06L and B3LYP functionals
can be separated from long-range corrected function-
als (ωB97XD and CAM-B3LYP) as the former have
negative PC1 scores and latter positive PC1 scores.
What is powerful about PCA is the ability to ‘see’ how
closely the functionals mimic the experimental data
and where calculations fail. M06 best approximates
Computational Methods
Geometry and vibrational calculations were generat-
ed using the Gaussian 09W program package which
implemented M06L, B3LYP, PBE0, M06, CAM-B3LYP
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Page 12 of 20
and wB97XD functionals employing the basis set 6-
90.00°, β = 103.162(9)°, γ = 90.00°, V = 1353.4(4) Å3,
31G(d).46 Calculated gas phase vibrational spectra were
generated using Gaussum v2.2.5 software, and scaled
to give the lowest value for the mean absolute devia-
tion for band position from experimental data with
scale factors typically around 0.975.47 TD-DFT calcula-
tions were also implemented, using the same function-
als and basis set. molecular orbitals were visualized
using Gauss View 5.0 W (Gaussian Inc.) while vibra-
tions were visualized using Molden.48
space group P21/c (#14), Z = 4, μ(Mo Kα) = 0.173 mm–1,
2θmax = 56.52°, 25387 reflections measured, 3267 inde-
pendent reflections (Rint = 0.0365). The final R1(F) =
0.0384 (I > 2σ(I)); 0.0469 (all data). The final wR2(F2) =
0.0965 (I > 2σ(I)); 0.1024 (all data). GoF = 1.048.
1
2
3
4
5
6
7
8
Crystal data for BTD-NMe2: C14H13N3S, M = 255.33,
yellow needle, 0.23 × 0.08 × 0.04 mm3, orthorhombic, a
= 6.48560(10) Å, b = 16.0610(4) Å, c = 22.6793(6) Å,
α = 90.00°, β = 90.00°, γ = 90.00°, V = 2362.39(9) Å3,
space group Pbca (#61), Z = 8, μ(Cu-Kα) = 2.288 mm–1,
2θmax = 147.56°, 31297 reflections measured, 2349 inde-
pendent reflections (Rint = 0.1128). The final R1(F) =
0.0791 (I > 2σ(I)); 0.0888 (all data). The final
wR2(F2) = 0.1247 (I > 2σ(I)); 0.1289 (all data). GoF =
1.082. CCDC 1446716
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Physical Measurements
1H NMR spectra were recorded at 500 MHz and 13C at
126 MHz on a Varian 500AR spectrometer. All samples
were recorded at 25 °C in 55 mm diameter tubes.
Chemical shifts were referenced internally to residual
non-perdeuterated solvent using δ values as reported
by Gottlieb et al..49 Chemical shifts are rounded to the
nearest 0.1 Hz. Assignment of signals is assisted
through the use of 2D NMR techniques (COSY,
NOESY, 1H-13C HSQC and 1H-13C HMBC), recorded on a
Varian 500AR spectrometer using standard pulse se-
quences. HR-ESI-MS was performed on a Bruker Mi-
crOTOF-Q mass spectrometer operating in positive
mode. Values are quoted as m/z ratio, with an instru-
mental uncertainty of m/z ±0.003. Analysis of ele-
mental composition was made by the Campbell Micro-
analytical Laboratory at the University of Otago, using
a Carlo Erba 1108 CHNS combustion analyzer. The es-
timated error is the measurements in ±0.4%.
Crystal data for BTD-TPA: C24H17N3S, M = 379.47,
yellow plate, 0.44 × 0.22 × 0.02 mm3, monoclinic, a =
19.4003(4) Å, b = 9.4082(2) Å, c = 21.1126(5) Å,
α = 90.00°, β = 105.654(2)°, γ = 90.00°, V = 3710.58(14)
Å3, space group P21/c (#14), Z = 8, μ(Cu-Kα) = 1.651 mm–
1, 2θmax = 153.42°, 23852 reflections measured, 7724 in-
dependent reflections (Rint = 0.0395). The final R1(F) =
0.0394 (I > 2σ(I)); 0.0459 (all data). The final wR2(F2) =
0.1018 (I > 2σ(I)); 0.1080 (all data). GoF = 1.041. CCDC
1446717
Crystal data for BTD-TPA2: C42H30N4S, M = 622.76,
orange hexagonal prism, 0.51 × 0.17 × 0.13 mm3, ortho-
rhombic, a = 6.8534(2) Å, b = 18.7576(4) Å, c =
24.5481(5) Å, α = 90.00°, β = 90.00°, γ = 90.00°, V =
3155.74(13) Å3, space group Pbcn(#60), Z = 4,
μ(Cu-Kα) = 2.288 mm–1, 2θmax = 147.04°, 12262 reflec-
tions measured, 3122 independent reflections
(Rint = 0.0304). The final R1(F) = 0.0449 (I > 2σ(I));
0.0462 (all data). The final wR2(F2) = 0.1252 (I > 2σ(I));
0.1268 (all data). GoF = 1.043. CCDC 1446718
For X-ray crystallography, single crystals were at-
tached with Paratone N to a fibre loop supported in a
copper mounting pin, and then quenched in a cold
nitrogen stream. Data were collected at 100 K using
Cu-Kα radiation (micro-source, mirror monochromat-
ed) using an Agilent Supernova, Dual, Cu at zero dif-
fractometer with an Atlas detector. Data processing
was undertaken with CrysAlisPro.50 A multiscan ab-
sorption correction was applied to the data. Structures
were solved by direct methods with SHELXS-97, and
extended and refined with SHELXL-97 using the X-
Seed interface.51,52 The non-hydrogen atoms in the
asymmetric unit were modelled with anisotropic dis-
placement parameters and a riding atom model with
group displacement parameters used for the hydrogen
atoms. X-ray crystallographic data is available in CIF
format (supporting information). CCDC 1446715-
1446719 contain the supplementary crystallographic
data for this Article. These data can be obtained free of
charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Crystal data for BTD-(OMe)2TPA: C26H21N3O2S, M =
439.52, yellow needle, 0.62 × 0.11 × 0.03 mm3, triclinic,
a = 11.2770(5) Å, b = 11.7982(5) Å, c = 17.6321(4) Å,
α = 93.230(3)°, β = 90.383(3)°, γ = 113.527(4)°, V =
2146.40(14) Å3, space group P-1(#2), Z = 4,
μ(Cu-Kα) = 2.288 mm–1, 2θmax = 149.14°, 19921 reflections
measured, 8458 independent reflections (Rint = 0.0336).
The final R1(F) = 0.0408 (I > 2σ(I)); 0.0475 (all data).
The final wR2(F2) = 0.1073 (I > 2σ(I)); 0.1136 (all data).
GoF = 1.029. CCDC1446719
FT-Raman spectra were recorded using a Bruker
MultiRAM spectrometer implementing a 1064 nm exci-
tation at 600 mW power, a resolution of 4 cm-1 and 500
co-added scans. Differential Raman cross sections were
calculated using Origin Pro 7.5 peak integration on
strong peaks at ~1176, ~1215, ~1295, ~1595 and ~1613 cm-1
which represent peaks 1 through 5 (respectively) used
Crystal
data
for
4-trimethylsilyl-2,6-
dimethoxyphenylboronic acid: C11H19BO4Si, M = 254.16,
colourless block, 0.41 × 0.24 × 0.21 mm3, monoclinic, a
= 7.7685(12) Å, b = 12.973(2) Å, c = 13.791(2) Å, α =
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for cross section analysis. Differential Raman cross- into CH2Cl2 and washed with NH4Cl solution (sat.),
1
2
3
4
5
6
7
8
sections are obtained by comparison of the peak areas
with reported differential Raman cross-sections of sol-
vent as described in the literature.53 In short, solute
differential Raman cross-sections were obtained rela-
tive to solvent cross-sections using the following equa-
tion:
then water. The organic extract was dried over MgSO4,
and the solvent removed under reduced pressure. The
residue was purified using preparative column chroma-
tography (SiO2, CH2Cl2) to afford 1-trimethylsilyl-3,5-
dimethoxybenzene (3.00 g, 97%) as a colorless oil.
1H NMR (400 MHz, CDCl3):57 δ 6.65 (d, J = 2.3 Hz, 2H,
H2), 6.46 (t, J = 2.3 Hz, 1H, H4), 3.81 (s, 6H, OMe), 0.26
(s, 9H, SiMe3) ppm.
ꢁꢂꢃ
ꢁꢄ
ꢇꢆ ꢉꢈ ꢁꢂꢃ
ꢀ
ꢀ
ꢅ =
ꢅ
ꢊꢋꢌꢍꢎꢏꢐꢑ 1.
ꢇꢈ ꢉꢆ ꢁꢄ
9
ꢆ
ꢈ
4-Trimethylsilyl-2,6-dimethoxyphenylboronic acid
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ꢒ
ꢓ
Where ꢁꢂꢃ/ꢁꢄ is the is the differential Raman
ꢆ
A
solution
of
trimethylsilyl-3,5-
cross-section of the solute band of interest, Iu and Iv
are the fully corrected observed intensities for the so-
lute and solvent, respectively, cu and cv are the concen-
trations of solute and solvent and ꢁꢂꢃ/ꢁꢄ ꢈv is the
differential Raman cross-section of a solvent band. Sol-
vent Raman cross sections were retrieved from the lit-
erature including acetonitrile and toluene.54,55
dimethoxybenzene (2.87 g, 13.7 mmol) in anhydrous
THF (20 mL) was cooled to 0 °C using an ice bath, and
n-BuLi (11.0 mL, 2.0 M in hexane) added dropwise un-
der an argon atmosphere. The reaction mixture was
stirred at 0 °C for 15 h under an argon atmosphere.
B(OMe)3 (3.5 mL, 31.4 mmol) was added dropwise and
the reaction mixture stirred at rt for 5 h. NH4Cl solu-
tion (sat.) was then added and the reaction mixture
stirred at rt for 2 h. The product was extracted into
CH2Cl2 and washed with NH4Cl solution (sat.), then
water. The organic extract was dried over MgSO4, and
the solvent removed under reduced pressure. The
product was recrystallized from hexane to afford 4-
ꢒ
ꢓ
Electronic absorption spectra were measured on
1 × 10-5 M solutions implementing an OceanOptics
USB2000 spectrometer.
Emission spectra were recorded using the same set-
up as resonance Raman, with light instead dispersed
in the horizontal plane by a 300 grooves mm−1 diffrac-
tion grating. Spectra were measured on 1 × 10-5 M solu-
tions. Onsager radii used for Lippert Mataga analysis is
taken as half the distance of the molecular long axis.
trimethylsilyl-2,6-dimethoxyphenylboronic
acid
(2.39 g, 69%) as a white crystalline solid. An alternative
purification using preparative column chromatography
(SiO2, 1:3 ethyl acetate/hexane) affords the product in
The electrochemical cell for cyclic voltammetry was
made up of a 1 mm diameter platinum rod working
electrode embedded in a KeL-F cylinder with a plati-
num auxiliary electrode and a Ag/AgCl reference elec-
trode. The potential of the cell was controlled by an
ADI Powerlab 4SP potentiostat. Solutions were typical-
ly about 10-3 M in CH2Cl2 with 0.1 M tetrabutylammo-
nium hexafluorophosphate (n-Bu4PF6) as a supporting
electrolyte, and were purged with argon for approxi-
mately 5 min prior to measurement. The scanning
speed was 100 mV s-1, and the cyclic voltammograms
were calibrated against the decamethylferroceni-
um/decamethylferrocene (Fc*+/Fc*) couple (-0.012 V in
CH2Cl2) and are reported relative to the saturated cal-
omel electrode (SCE) for comparison with other data
by subtracting 0.045 V.56
1
63% yield. H NMR (500 MHz, CDCl3): δ 7.24 (s, 2H,
B(OH)2), 6.75 (s, 2H, H3), 3.94 (s, 6H, OMe),
13
0.30 (s, 9H, SiMe3) ppm. C NMR (126 MHz, CDCl3): δ
165.01 (C2), 147.37 (C4), 108.85 (C3), 56.27 (OMe), -1.05
(SiMe3) ppm.
5-(2,6-Dimethoxyphenyl)benzo[c][1,25]thiadiazole
(BTD-(OMe)2Ph)
A mixture of 5-bromobenzo[c][1,2,5]thiadiazole(0.541
g, 2.51 mmol), 2,6-dimethoxyphenylboronic ac-
id (0.719 g, 2.95 mmol) and K2CO3 (2.41 g, 17.4 mmol)
in toluene (20 mL), H2O (10 mL) and EtOH (5 mL) was
bubbled with argon for 15 min. PdCl2(dppf) (0.212 g,
0.290 mmol) was added and the reaction mixture heat-
ed at reflux for 15 h under an argon atmosphere. The
reaction mixture was allowed to cool, and the product
extracted into CHCl3, and washed with NH4Cl solution
(sat.), then water. The organic extract was dried over
MgSO4, and the solvent removed under reduced pres-
sure. The residue was purified using preparative col-
umn chromatography (SiO2, CH2Cl2) to afford BTD-
Materials
1-Trimethylsilyl-3,5-dimethoxybenzene
A solution of 1-bromo-3,5-dimethoxybenzene (3.18 g,
14.7 mmol) in anhydrous THF (30 mL) was cooled to -
78 °C using a dry ice bath, and n-BuLi (11.0 mL, 2.0 M
in hexane) added dropwise under an argon atmos-
phere. The reaction mixture was stirred at -78 °C for
2 h under an argon atmosphere. Me3SiCl (4.5 mL,
35.5 mmol) was added dropwise and the reaction mix-
ture stirred at rt for 15 h. The product was extracted
1
(OMe)2Ph (0.596 g, 87%) as a white solid. H NMR
(500 MHz, CDCl3): δ 8.00 (s, 1H, H4), 7.99 (d, J = 9.0
Hz, 1H, H7), 7.60 (dd, J = 9.0, 1.4 Hz, 1H, H6), 7.36 (t, J =
8.4 Hz, 1H, H4′), 6.71 (d, J = 8.4 Hz, 2H, H3′),
3.77 (s, 6H, OMe) ppm. 13C NMR (126 MHz, CDCl3): δ
157.70 (C2′), 155.19 (C3a), 154.19 (C7a), 136.05 (C5),
13
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134.06 (C6), 129.75 (C4′), 123.14 (C4), 119.98 (C7), 117.83 (dd, J = 8.5, 7.4 Hz, 4H, H3″), 7.18 (d, J = 8.7 Hz, 2H,
1
2
3
4
5
6
7
8
(C1′), 104.30 (C3′), 56.00 (OMe) ppm. MS (MALDI-TOF)
calcd for C14H12N2O2S ([M]+): m/z 272.06. Found: m/z
272.03. Elemental analysis calcd for C14H12N2O2S: C,
61.75; H, 4.44; N, 10.29. Found: C, 61.51; H, 4.72;
N, 10.29.
H3′), 7.17 (dd, J = 8.5, 1.0 Hz, 4H, H2″), 7.08 (tt, J = 7.4, 1.1
Hz, 2H, H4″) ppm. C NMR (126 MHz, CDCl3): δ 155.72
13
(C3a), 154.20 (C7a), 148.47 (C4′), 147.49 (C1″), 142.05 (C5),
132.79 (C1′), 130.10 (C6), 129.55 (C3″), 128.29 (C2′), 125.02
(C2″), 123.60 (C4″), 123.35 (C3′), 121.49 (C7), 117.50 (C4)
ppm. HRMS (ESI) calcd for C24H18N3S ([M+H]+): m/z
380.122. Found: m/z 380.121. Elemental analysis calcd
for C24H17N3S: C, 75.69; H, 4.52; N, 11.07. Found: C,
75.66; H, 4.37; N, 11.02.
5-(4-
Dimethylaminophenyl)benzo[c][1,2,5]thiadiazole
(BTD-NMe2)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
A
mixture of 5-bromobenzo[c][1,2,5]thiadiazole
5,6-Di(4-
(0.508 g, 2.36 mmol), 4-dimethylaminophenylboronic
acid (0.539 g, 3.27 mmol) and K2CO3 (1.72 g, 12.4 mmol)
in toluene (20 mL), water (10 mL) and EtOH (5 mL)
diphenylaminophenyl)benzo[c][1,2,5]thiadiazole
(BTD-TPA2)
was
bubbled
with
argon
for
15 min.
A mixture of 5,6-dibromobenzo[c][1,2,5]thiadiazole
(0.132 g, 0.449 mmol), 4-diphenylaminophenylboronic
acid (0.420 g, 1.45 mmol) and K2CO3 (0.500 g, 3.62
mmol) in toluene (20 mL), H2O (10 mL) and EtOH
(5 mL) was bubbled with argon for 15 min. PdCl2(dppf)
(0.062 g, 0.076 mmol) was added and the reaction mix-
ture heated at reflux for 15 h under an argon atmos-
phere. The reaction mixture was allowed to cool, and
the product extracted into CHCl3, and washed with
NH4Cl solution (sat.), then water. The organic extract
was dried over MgSO4, and the solvent removed under
reduced pressure. The residue was purified using pre-
parative column chromatography (SiO2, CH2Cl2) to
PdCl2(dppf) (0.112 g, 0.153 mmol) was added and the
reaction mixture heated at reflux for 15 h under an ar-
gon atmosphere. The reaction mixture was allowed to
cool to rt, and the product extracted into CH2Cl2, and
washed with NH4Cl solution (sat.), then water. The
organic extract was dried over MgSO4, and the solvent
removed under reduced pressure. The residue was pu-
rified using preparative column chromatography (SiO2,
CH2Cl2) to afford BTD-NMe2 (0.453 g, 75%) as a yellow
1
crystalline solid. H NMR (500 MHz, CDCl3): δ 8.09 (d,
J = 1.7 Hz, 1H, H4), 8.00 (d, J = 9.2 Hz, 1H, H7),
7.90 (dd, J = 9.2, 1.8 Hz, 1H, H6), 7.64 (d, J = 8.9 Hz, 2H,
H2′), 6.85 (d, J = 7.0 Hz, 2H, H3′), 3.04 (s, 6H, NMe2)
1
afford BTD-TPA2 (0.203 g, 72%) as a yellow solid. H
13
ppm. C NMR (126 MHz, CDCl3): δ 155.96 (C3a), 155.22
NMR (500 MHz, CDCl3): δ 8.02 (s, 2H, H4,7), 7.26 (t, J =
7.3 Hz, 8H, H3″), 7.11 (dd, J = 8.5, 1.1 Hz, 8H, H2″), 7.06
(d, J = 8.7 Hz, 4H, H2′), 7.04 (t, J = 7.3 Hz, 4H, H4″),
6.99 (d, J = 8.6 Hz, 4H, H3′) ppm. 13C NMR (126 MHz,
CDCl3): δ 154.55 (C3a,7a), 147.66 (C1″), 147.32 (C4′), 143.84
(C5,6), 134.22 (C1′), 130.80 (C2′), 129.49 (C3″), 124.75 (C2″),
123.29 (C4″), 122.68 (C3′), 121.29 (C4,7) ppm. MS (MALDI-
TOF) calcd for C42H30N4S ([M]+): m/z 622.22. Found:
m/z 622.21. Elemental analysis calcd for C42H30N4S: C,
81.00; H, 4.86; N, 9.00. Found: C, 81.28; H, 5.06; N,
8.87.
(C1′), 154.05 (C7a), 150.70 (C4′), 142.56 (C5), 130.24 (C6),
128.35 (C2′), 121.28 (C7), 116.41 (C4), 112.89 (C3′),
40.62 (NMe2) ppm. HRMS (ESI) calcd for C14H14N3S
([M+H]+): m/z 256.090. Found: m/z 256.092. Elemental
analysis calcd for C14H13N3S: C, 65.86; H, 5.13; N, 16.46.
Found: C, 66.10; H, 5.32; N, 16.52.
5-(4-
Diphenylaminophenyl)benzo[c][1,2,5]thiadiazole
(BTD-TPA)
A
mixture of 5-bromobenzo[c][1,2,5]thiadiazole
5-(4-Trimethylsilyl-2,6-
(0.516 g, 2.40 mmol), 4-diphenylaminophenylboronic
acid (0.890 g, 3.08 mmol) and K2CO3 (1.84 g, 13.3
mmol) in toluene (15 mL), H2O (10 mL) and EtOH
(5 mL) was bubbled with argon for 15 min. PdCl2(dppf)
(0.100 g, 0.122 mmol) was added and the reaction mix-
ture heated at reflux for 15 h under an argon atmos-
phere. The reaction mixture was allowed to cool, and
the product extracted into CHCl3, and washed with
NH4Cl solution (sat.), then water. The organic extract
was dried over MgSO4, and the solvent removed under
reduced pressure. The residue was purified using pre-
parative column chromatography (SiO2, CH2Cl2) to
afford BTD-TPA (0.856 g, 94%) as a yellow crystalline
solid. 1H NMR (500 MHz, CDCl3): δ 8.13 (dd, J = 1.7, 0.7
Hz, 1H, H4), 8.03 (dd, J = 9.2, 0.7 Hz, 1H, H7), 7.89 (dd, J
= 9.2, 1.8 Hz, 1H, H6), 7.59 (d, J = 8.7 Hz, 2H, H2′), 7.30
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole
A
(0.358
mixture of 5-bromobenzo[c][1,2,5]thiadiazole
g, 1.67 mmol), 4-trimethylsilyl-
2,6-dimethoxyphenylboronic acid (0.510 g, 2.01 mmol)
and K2CO3 (1.22 g, 8.82 mmol) in toluene (20 mL),
H2O (10 mL) and EtOH (5 mL) was bubbled with argon
for 15 min. PdCl2(dppf) (0.130 g, 0.159 mmol) was added
and the reaction mixture heated at reflux for 15 h un-
der an argon atmosphere. The reaction mixture was
allowed to cool, and the product extracted into CHCl3,
and washed with NH4Cl solution (sat.), then water.
The organic extract was dried over MgSO4, and the
solvent removed under reduced pressure. The residue
was purified using preparative column chromatog-
raphy (SiO2, CH2Cl2) to afford 5-(4-trimethylsilyl-2,6-
14
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The Journal of Physical Chemistry
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole (0.549 g,
then water. The organic extract was dried over MgSO4,
and the solvent removed under reduced pressure. The
residue was purified using preparative column chroma-
1
1
2
3
4
5
6
7
8
96%) as a white solid. H NMR (500 MHz, CDCl3): δ
8.00 (dd, 1.5, 0.8 Hz, 1H, H4),
J
=
7.98 (dd, J = 9.0, 0.8 Hz, 1H, H7), 7.61 (dd, J = 9.0, 1.6
Hz, 1H, H6), 6.84 (s, 2H, H3′), 3.80 (s, 6H, OMe),
tography
(SiO2,
CH2Cl2)
to
afford
BTD-
(OMe)2TPA (0.367 g, 50%) as a yellow crystalline solid.
1H NMR (500 MHz, CDCl3): δ 8.02 (dd, J = 1.4, 0.7 Hz,
1H, H4), 7.96 (dd, J = 9.1, 0.7 Hz, 1H, H7), 7.64 (dd, J =
9.1, 1.5 Hz, 1H, H6), 7.31 (dd, J = 8.4, 7.4 Hz, 4H, H3″),
13
0.36 (s, 9H, SiMe3) ppm. C NMR (126 MHz, CDCl3): δ
157.12 (C2′), 155.20 (C3a), 154.22 (C7a), 142.95 (C4′),
136.12 (C5), 134.03 (C6), 123.14 (C4), 119.97 (C7), 118.57
(C1′), 108.74 (C3′), 56.05 (OMe), 0.92 (SiMe3) ppm.
MS (MALDI-TOF) calcd for C17H20N2O2SSi ([M]+): m/z
344.10. Found: m/z 344.08. Elemental analysis calcd for
C17H20N2O2SSi: C, 59.27; H, 5.85; N, 8.13.
Found: C, 59.10; H, 5.92; N, 8.02.
7.21 (dd,
J
=
8.6,
1.0
Hz,
4H,
H2″),
9
7.08 (tt, J = 7.3, 1.0 Hz, 2H, H4″), 6.38 (s, 2H, H3′), 3.58
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
(OMe) ppm. C NMR (126 MHz, CDCl3): δ 158.15 (C2′),
155.30 (C3a), 154.11 (C7a), 149.55 (C4′), 147.51 (C1″), 136.07
(C5), 134.48 (C6), 129.43 (C3″), 125.04 (C2″), 123.51 (C4″),
123.18 (C4), 119.76 (C7), 112.11 (C1′), 99.87 (C3′), 55.97
(OMe) ppm. HRMS (ESI) calcd for C26H22N3O2S
([M+H]+): m/z 440.143. Found: m/z 440.143. Elemental
analysis calcd for C26H21N3O2S: C, 71.05; H, 4.82; N,
9.56. Found: C, 71.05; H, 4.86; N, 9.62.
5-(4-Iodo-2,6-
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole
A
solution
of
5-(4-trimethylsilyl-2,6-
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole (0.549 g,
1.59 mmol) in CH2Cl2 (100 mL) was cooled to -78 °C
using a dry ice/acetone bath under an argon atmos-
phere. ICl (2.5 mL, 1 M in CH2Cl2) was added dropwise
and the resultant mixture stirred at -78 °C under an
argon atmosphere for 2 h. The dry ice/acetone bath
was removed, excess ICl quenched by dropwise addi-
tion of aqueous Na2S2O4 (sat., 20 mL), and the mixture
allowed to warm to rt. The product was extracted into
CH2Cl2 and washed with aqueous NH4Cl (sat.), then
water. The organic extract was dried over MgSO4, and
the solvent removed under reduced pressure. The resi-
due was purified using preparative column chromatog-
raphy (SiO2, CH2Cl2) to afford 5-(4-Iodo-2,6-
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole (0.505 g,
4-Methyl-1,2-di(tosylamino)benzene
A mixture of 4-methyl-1,2-phenylenediamine (8.01 g,
65.5 mmol) and pyridine (20 mL, 250 mmol) in CH2Cl2
(150 mL) was cooled to 0 °C using an ice bath.
TsCl (30.0 g, 157 mmol) was added in small portions,
the reaction mixture warmed to rt, and stirred for 3 h
at rt. The product was extracted into CH2Cl2, and
washed with NH4Cl solution (sat.), then water. The
organic extract was dried over MgSO4, and the solvent
removed under reduced pressure. The residue was re-
crystallised from EtOH to afford 4-methyl-1,2-
di(tosylamino)benzene (26.8 g, 95%) as a white solid.
1H NMR (500 MHz, CDCl3): δ 7.60 (d, J = 8.3 Hz, 2H,
1
80%) as a white solid. H NMR (500 MHz, CDCl3): δ
H2′/2″), 7.53 (d, J = 8.3 Hz, 2H, H2′/2″), 7.22 (dd, J = 8.6,
7.97 (d, J = 9.1 Hz, 1H, H7), 7.94 (s, 1H, H4),
7.53 (d, J = 9.0, 1.4 Hz, 1H, H6), 7.03 (s, 2H, H3′), 3.75 (s,
6H, OMe) ppm. 13C NMR (126 MHz, CDCl3): δ 157.92
(C2′), 155.07 (C3a), 154.22 (C7a), 135.13 (C5), 133.58 (C6),
0.6 Hz, 2H, H3′/3″), 7.21 (dd, J = 8.6, 0.6 Hz, 2H, H3′/3″),
7.02 (s, 1H, NH), 6.93 (d, J = 1.4 Hz, 1H, H3), 6.79 (ddd,
J = 8.1, 2.0, 0.7 Hz, 1H, H5), 6.67 (d, J = 8.1 Hz, 1H, H6),
6.43 (s, 1H, NH), 2.39 (s, 6H, Ts-Me), 2.19 (s, 3H, Me)
ppm. 13C NMR (126 MHz, CDCl3): δ 144.31 (C4′/4″),
144.16 (C4′/4″), 138.45 (C4), 135.97 (C1′/1″), 135.44 (C1′/1″),
131.97 (C2), 129.75 (C3′/3″), 129.69 (C3′/3″), 127.80 (C5),
127.70 (C2′/2″), 127.64 (C2′/2″), 127.20 (C1), 127.08 (C6),
126.41 (C3), 21.75 (Ts-Me), 21.73 (Ts-Me), 21.16 (Me)
ppm. HRMS (ESI) calcd for C21H22N2NaO4S2 ([M+Na]+):
m/z 453.091. Found: m/z 453.093. Elemental analysis
calcd for C21H22N2O4S2: C, 58.58; H, 5.15; N, 6.51.
Found: C, 58.48; H, 5.14; N, 6.66.
123.16 (C4),
120.17 (C7),
117.81 (C1′),
114.23 (C3′),
93.92 (C4′), 56.30 (OMe) ppm. MS (MALDI-TOF) calcd
for C14H11IN2O2S ([M]+): m/z 397.96. Found: m/z 397.92.
Elemental analysis calcd for C14H11IN2O2S: C, 42.23; H,
2.78; N, 7.03. Found: C, 42.35; H, 2.76; N, 7.11.
5-(4-Diphenylamino-2,6-
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole
(BTD-
(OMe)2TPA)
A
mixture
of
5-(4-iodo-2,6-
4-Bromo-5-methyl-1,2-di(tosylamino)benzene
dimethoxyphenyl)benzo[c][1,2,5]thiadiazole (0.292 g,
0.733 mmol), diphenylamine (0.229 g, 1.35 mmol) and
t-BuOK (0.264 g, 2.35 mmol) in toluene (20 mL) was
bubbled with argon for 15 min. [t-Bu3PH]BF4 (0.032 g,
0.112 mmol) and Pd2(dba)3 (0.060 g, 0.065 mmol) were
added and the reaction mixture heated at reflux for 15
h under an argon atmosphere. The reaction mixture
was allowed to cool to rt, and the product extracted
into CHCl3, and washed with NH4Cl solution (sat.),
A mixture of 4-methyl-1,2-di(tosylamino)benzene
(23.0 g) and AcONa (8.00 g, 98.0 mmol) in
AcOH (200 mL) was cooled to 0 °C using an ice bath.
Br2 (3.5 mL, 68.0 mmol) was added dropwise, and the
reaction mixture heated at reflux for 3 h. Water was
added, and the precipitate filtered and washed with
water. The residue was recrystallised from EtOH to
afford
4-bromo-5-methyl-1,2-
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di(tosylamino)benzene (24.8 g, 91%) as a white solid.
1H NMR (500 MHz, CDCl3): δ 7.59 (d, J = 8.3 Hz, 2H,
2′/2″), 7.56 (d, J = 8.3 Hz, 2H, H2′/2″), 7.26 (d, J = 7.8 Hz,
2H, H3′/3″), 7.25 (d, J = 7.9 Hz, 2H, H3′/3″), 7.01 (s, 1H, H3),
6.93 (s, 1H, H6), 6.91 (s, 1H, NH), 6.56 (s, 1H, NH), 2.41
5-(4-Diphenylaminophenyl)-6-
methylbenzo[c][1,2,5]thiadiazole (BTDMe-TPA)
1
2
3
4
5
6
7
8
H
A
mixture
methylbenzo[c][1,2,5]thiadiazole (0.532 g, 2.32 mmol),
4-diphenylaminophenylboronic acid (0.928 g, 3.21
of
5-bromo-6-
(s,
3H,
Ts-Me),
2.40 (s,
3H,
Ts-Me),
mmol) and K2CO3 (1.71 g, 12.4 mmol) in toluene (20
mL), H2O (10 mL) and EtOH (5 mL) was bubbled with
argon for 15 min. PdCl2(dppf) (0.131 g, 0.179 mmol) was
added and the reaction mixture heated at reflux for 15
h under an argon atmosphere. The reaction mixture
was allowed to cool, and the product extracted into
CHCl3, and washed with NH4Cl solution (sat.), then
water. The organic extract was dried over MgSO4, and
the solvent removed under reduced pressure. The resi-
due was purified using preparative column chromatog-
raphy (SiO2, CH2Cl2) to afford BTDMe-TPA (0.735 g,
2.21 (s, 3H, Me) ppm. 13C NMR (126 MHz, CDCl3): δ
144.69 (C4′/4″), 144.49 (C4′/4″), 137.95 (C5), 135.62 (C1′/1″),
135.16 (C1′/1″), 130.69 (C1), 130.11 (C3), 129.90 (C3′/3″),
129.84 (C3′/3″), 128.98 (C2), 127.69 (C2′/2″), 126.67 (C6),
126.64 (C2′/2″), 122.30 (C4), 22.66 (Me), 21.77 (Ts-Me),
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21.76 (Ts-Me)
ppm. HRMS (ESI)
calcd for
C21H21BrN2NaO4S2 ([M+Na]+): m/z 531.002. Found: m/z
530.999. Elemental analysis calcd for C21H21BrN2O4S2:
C, 49.51; H, 4.15; N, 5.50. Found: C, 49.62; H, 4.01; N,
5.57.
1
4-Bromo-5-methyl-1,2-phenylenediamine
80%) as a yellow solid. H NMR (500 MHz, CDCl3): δ
7.86 (s, 1H, H7), 7.85 (s, 1H, H4), 7.30 (t, J = 7.5 Hz, 4H,
H3″), 7.24 (d, J = 8.5 Hz, 2H, H2′), 7.18 (d, J = 7.7 Hz, 4H,
H2″), 7.15 (d, J = 8.5 Hz, 2H, H3′), 7.07 (t, J = 7.3 Hz, 2H,
H4″), 2.45 (s, 3H, Me) ppm. 13C NMR (126 MHz, CDCl3):
δ 154.57 (C7a), 154.11 (C3a), 147.66 (C1″), 147.62 (C4′),
145.22 (C5), 139.53 (C6), 134.03 (C1′), 129.92 (C2′), 129.49
(C3″), 124.87 (C2″), 123.37 (C4″), 122.80 (C3′), 120.83 (C4),
120.75 (C7), 22.19 (Me) ppm. MS (MALDI-TOF) calcd
for C25H20N3S ([M+H]+): m/z 393.14. Found: m/z 393.12.
Elemental analysis calcd for C25H19N3S: C, 76.31; H,
4.87; N, 10.68. Found: C, 76.71; H, 5.09; N, 10.59.
A
mixture
of
4-bromo-5-methyl-1,2-
di(tosylamino)benzene (4.14 g, 8.13 mmol) and conc.
H2SO4 (12 mL) was heated at reflux for 3 h. The reac-
tion mixture was cooled to 0 °C, and water added.
Aqueous NaOH (2 M) was added dropwise to achieve
pH 5. The product was extracted into CHCl3 to afford
4-bromo-5-methyl-1,2-phenylenediamine (1.42 g, 87%)
1
as an off-white solid. H NMR (500 MHz, (CD3)2SO): δ
6.66 (s, 1H, H3), 6.43 (s, 1H, H6), 4.51 (s, 4H, NH2),
13
2.08 (s, 3H, Me) ppm. C NMR (126 MHz, (CD3)2SO): δ
134.77 (C1), 134.69 (C2), 124.04 (C5), 116.90 (C3),
116.24 (C6), 109.90 (C4), 21.32 (Me) ppm. HRMS (ESI)
calcd for C7H10BrN2 ([M+H]+): m/z 201.002. Found: m/z
201.002. Elemental analysis calcd for C7H9BrN2·H2O: C,
38.38; H, 5.06; N, 12.79. Found: C, 38.49; H, 4.98; N,
12.82.
5-Azidobenzo[c][1,2,5]thiadiazole
A
mixture of 5-aminobenzo[c][1,2,5]thiadiazole
(1.50 g, 9.89 mmol) and TsOH (6.34 g, 33.3 mmol) in
CH3CN (100 mL) was cooled to 0 °C using an ice bath.
A solution of NaNO2 (1.78 g, 25.8 mmol) in water
(10 mL) was added dropwise, and the reaction mixture
stirred at 0 °C for 30 min. A solution of NaN3 (3.30 g,
50.8 mmol) in water (10 mL) was added dropwise, and
the reaction mixture stirred at rt for 2 h. Aq. Na2S2O3
(sat.) was added, and the product extracted into
EtOAc. The organic extract was dried over MgSO4, and
the solvent removed under reduced pressure. The resi-
due was purified using flash chromatography
(SiO2, CH2Cl2) to afford 5-azobenzo[c][1,2,5]thiadiazole
(0.353 g, 20%) as an off-white solid. The product was
5-Bromo-6-methylbenzo[c][1,2,5]thiadiazole
Thionyl chloride (0.8 mL, 11.0 mmol) was added
dropwise to
a mixture of 4-bromo-5-methyl-1,2-
phenylenediamine (1.02 g, 5.08 mmol) and NEt3 (5 mL,
35.9 mmol) in CH2Cl2 (50 mL). The reaction mixture
was heated at reflux for 15 h, then allowed to cool to rt.
HCl (100 mL, 5 M) was added and the reaction mixture
stirred for 1 h. The product was extracted into CH2Cl2
and washed with NH4Cl solution (sat.), then water.
The organic extract was dried over MgSO4, and the
solvent removed under reduced pressure. The residue
was purified using flash chromatography (SiO2,
CH2Cl2) to afford BTDMe-Br (1.05 g, 90%) as an off-
1
reacted without further characterisation. H NMR (400
MHz, CDCl3): δ 7.97 (d, J = 9.3 Hz, 1H, H7),
7.64 (d, J = 2.2 Hz, 1H, H4), 7.27 (dd, J = 9.3, 2.2 Hz, 1H,
H6) ppm.
1
white solid. H NMR (500 MHz, CDCl3): δ 8.25 (s, 1H,
H4), 7.83 (s, 1H, H7), 2.58 (s, 3H, Me) ppm. 13C NMR
(126 MHz, CDCl3): δ 154.13 (C7a), 154.02 (C3a), 139.69
(C6), 128.95 (C5), 124.08 (C4), 120.70 (C7), 24.09 (Me)
ppm. MS (MALDI-TOF) calcd for C7H5BrN2S ([M]+):
m/z 227.94. Found: m/z 227.92. Elemental analysis
calcd for C7H5BrN2S: C, 36.70; H, 2.20; N, 12.23.
Found: C, 36.51; H, 1.86; N, 11.93.
5-(4-(4-Diphenylaminophenyl)-1,2,3-triazol-1-yl)-
benzo[c][1,2,5]thiadiazole (BTD-TRZTPA)
A
mixture of 5-azidobenzo[c][1,2,5]thiadiazole
(0.353 g, 1.99 mmol), 4-ethynyl-N,N-diphenylaniline
(0.487 g, 1.81 mmol), L-ascorbic acid
(0.453 g, 2.57 mmol), Na2CO3 (0.297 g, 2.80 mmol) and
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The Journal of Physical Chemistry
Support from the University of Otago and MacDiarmid Insti-
CuSO4·5H2O (0.253 g, 1.01 mmol) in DMF (20 mL) and
1
2
3
4
5
6
7
8
tute for Advanced Materials and Nanotechnology is grateful-
ly acknowledged. Greg S. Huff from the University of Otago
is recognized for an intellectual contribution towards this
publication.
water (5 mL) was stirred at rt for 15 h. Aq. EDTA (0.1
M) and NH4OH (0.1 M) was added, and the resulting
precipitate filtered. The residue was purified using
preparative column chromatography (SiO2, 20% EtOAc
in CHCl3) to afford BTD-TRZ-DPAB (0.735 g, 91%) as a
yellow solid. 1H NMR (500 MHz, CDCl3): δ 8.33 (dd, J =
1.8, 0.4 Hz, 1H, H4), 8.31 (dd, J = 9.3, 2.1 Hz, 1H, H6),
8.27 (s, 1H, H5′), 8.20 (dd, J = 9.3, 0.4 Hz, 1H, H7),
7.80 (d, J = 8.6 Hz, 2H, H2″), 7.29 (dd, J = 8.2, 7.5 Hz,
4H, H3‴), 7.17 (d, J = 8.7 Hz, 2H, H3″), 7.15 (d, J = 8.5 Hz,
4H, H2‴), 7.07 (tt, J = 7.4, 0.8 Hz, 2H, H4‴) ppm. 13C
NMR (126 MHz, CDCl3): δ 154.53 (C3a), 154.11 (C7a),
149.10 (C4′), 148.59 (C4″), 147.55 (C1‴), 137.95 (C5), 129.53
(C3‴), 127.01 (C2″), 124.92 (C2‴), 123.62 (C6), 123.50 (C4‴,1″),
123.49 (C3″), 123.22 (C7), 116.81 (C5′), 110.85 (C4) ppm.
HRMS (ESI) calcd for C26H19N6S ([M+H]+): m/z 447.139.
Found: 447.137. Elemental analysis calcd for C26H18N6S:
C, 69.94; H, 4.06; N, 18.82. Found: C, 69.80; H, 4.12; N,
18.84.
ABBREVIATIONS
DFT, Density Functional Theory; DA, Donor-Acceptor; CT,
Charge Transfer; LDA, Local Density Approximations; GGA,
Generalized Gradient Approximations; B3LYP, Becke, three-
parameter, Lee-Yang-Parr; HF Hartree Fock; BTD, ben-
zo[c][1,2,5]thiadiazole; MAD, Mean Absolute Deviation;
HOMO, Highest Occupied Molecular Orbital; LUMO, Low-
est Unoccupied Molecular Orbital; FMO, Frontier Molecular
Orbital; TPA, Triphenylamine; MPE, Mean Percentage Error;
PCA, Principal Component Analysis; PC, Principal Compo-
nent.
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ASSOCIATED CONTENT
Supporting Information. Electrochemical data; mean abso-
lute deviations between FT and calculated Raman spectra in
toluene and vacuo; experimental Raman spectra in acetoni-
trile, toluene and vacuo; experimental Raman cross-sections;
electronic absorption data; calculated electronic absorption
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and LUMOs); emission data; Lippert-Mataga plots; scores
plot for principle component 2 from principle component
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AUTHOR INFORMATION
Corresponding Author
From D-π-A to D-A-π-A: Effect of the Internal
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Soc. Rev., 2013, 42, 2039-2058.
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3 479 7908.
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ACKNOWLEDGMENT
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Predicting donor-acceptor properties: a systematic study of a series of donor-acceptor compounds in
differing solvents reveal that electronic absorption properties are well modeled by the MO6 functional but
Raman cross sections require range-separated functionals (CAM-B3LYP) for most accurate prediction.
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