Terphenyl backbone-based donor-π-acceptor dyads: Geometric isomer effects on intramolecular charge transfer

Article abstract of DOI:10.1039/c9cp06466d

The molecular geometry effects of ortho, meta, and para-terphenyl based donor-π-acceptor (D-π-A) dyads on intramolecular charge transfer (ICT) were studied to investigate structure-ICT relationships. Terphenyl based D-π-A dyads were prepared by two-step palladium catalyzed, Suzuki-Miyaura coupling reactions, in which triphenylamine (TPA) was used as the electron donor and 1,2-diphenyl-benzimidazole (IMI) as the electron acceptor. The photophysical and electrochemical properties of terphenyl backbone-based ortho (O), meta (M), and para (P) dyads were compared. In steady state absorption spectra, a red-shift of CT band was observed in the order O < M < P, which was attributed to terphenyl isomer conjugation effects and agreed well with density functional theory (DFT) based calculations. In particular, the emission spectra of the three terphenyl D-π-A dyads produced showed similar emission maxima at ～475 nm and a bathochromic shift property was observed in order to increase the solvent polarity, indicating the ICT process. From Lippert-Mataga plots, excited-state dipole moment changes (Δμ) were estimated to be 31.5 Debye (D) for O, 62.9 D for M, and 51.5 D for P. For M isomer, a large Δμ and the markedly reduced quantum yield was shown, as well as photo-induced electron transfer (PET) was expected in the excited state, but no radical species were observed by femtosecond transient absorption (TA) measurements. Based on experimental results, we conclude that all three terphenyl based D-π-A dyads, including non-conjugated ortho- and meta-terphenyl dyads, exhibit partial charge transfer rather than unit-electron transfer.

Full text of DOI:10.1039/c9cp06466d

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DOI: 10.1039/C9CP06466D
ARTICLE
Terphenyl Backbone-Based Donor--Acceptor Dyads: Geometric
Isomer Effects on Intramolecular Charge Transfer
Received 00th January 20xx,
Accepted 00th January 20xx
Min-Ji Kim, Mina Ahn, Jun Ho Shim,* and Kyung-Ryang Wee*
The molecular geometry effects of ortho, meta, and para-terphenyl based donor--acceptor (D--A) dyads on intramolecular
charge transfer (ICT) were studied to investigate structure-ICT relationships. Terphenyl based D--A dyads were prepared
by two-step palladium catalyzed, Suzuki-Miyaura coupling reactions, in which triphenylamine (TPA) was used as the electron
donor and 1,2-diphenyl-benzimidazole (IMI) as the electron acceptor. The photophysical and electrochemical properties of
terphenyl backbone-based ortho (O), meta (M), and para (P) dyads were compared. In steady state absorption spectra, a
red-shift of CT band was observed in the order O < M < P, which was attributed to terphenyl isomer conjugation effects and
agreed well with density functional theory (DFT) based calculations. In particular, the emission spectra of the three terphenyl
D--A dyads produced showed similar emission maxima at ~475 nm and bathochromic shift property was observed in order
to increasing the solvent polarity, indicating the ICT process. From Lippert–Mataga plots, excited-state dipole moment
changes (Δμ) were estimated to be 31.5 Debye (D) for O, 62.9 D for M, and 51.5 D for P. For M isomer, a large Δμ and the
markedly reduced quantum yield was shown, as well as photo-induced electron transfer (PET) was expected in the excited
state, but no radical species were observed by femtosecond transient absorption (TA) measurements. Based on
experimental results, we conclude that all three terphenyl based D--A dyads, including non-conjugated ortho- and meta-
terphenyl dyads, exhibit partial charge transfer rather than unit-electron transfer.
DOI: 10.1039/x0xx00000x
is highly polarized, photoinduced electron transfer (PET) occurs
whereby an electron is transferred from the donor to the
acceptor in the excited state. In D--A dyads, PET and ICT
Introduction
Dipolar organic chromophores, in which a -linker is end-
capped by an electron-donor (D) and an electron-acceptor (A),
are actively investigated because of their photophysical
properties and potential applications. The properties of
donor-π-acceptor dyads (D--A dyads) can be easily controlled
by changing donor, acceptor, and -linker moieties. Adequate
D-π-A molecular systems are thus suitable tools for a wide range
2
2
appear similar but are completely different phenomena and
2
3
both are used in research. Unlike ICT, PET generates a radical
cation and a radical anion from donor and acceptor moieties,
respectively. In addition, since radicals are usually non-emissive
species, PET is associated with significantly lower quantum
1
-8
2
4
25
yields. Recently, Cho et al. reported on the dependences of
ICT and PET on molecular geometry and demonstrated the non-
conjugated D-π-A dyad system exhibits PET and that the
conjugated system exhibits ICT. Herein, the quantum yield of
non-conjugated D-π-A dyad indicative of PET is 0.03 for exciplex
9
,10
of applications such as nonlinear optical materials,
1
1,12
fluorescence sensors,
organic light-emitting diodes
3-15
dye-sensitized solar cells (DSSCs),16 and
(
OLEDs),1
1
7, 18
photoeletrochemical cells (PECs).
-3
emission, <10 for monomer emission.
The most important property of D--A dyads is
intramolecular charge transfer (ICT) in the excited state. D--A
dyads tend to have large electronic dipoles in the excited state,
which can result in effective ICT emission. ICT characters of D-
The high polarization characteristics of D-π-A dyads renders
their excited states susceptible to isomer effects. Positional
isomers often endow distinctive photophysical properties due
to their different effects on electron distributions, conjugation,
molecular packing and planarity. Recently, various studies have
taken advantage of position-dependent substituent effects in

-A dyads in the excited state are key in terms of determining
1
9, 20
optical and electronic properties.
nature of ICT is attributed to the natures of donor, acceptor, -
linker units, and to molecular geometry. When a D--A dyad
Moreover, the electronic
2
6
the contexts of aggregation-induced emission (AIE) and
2
1
2
7, 28
mechanofluorochromic (MFC) phenomena.
Therefore, in
this work, we investigated optical properties of positional
isomers (ortho/meta/para), particularly focusing on ICT and/or
PET dynamics.
Department of Chemistry, Daegu University, Gyeongsan 38453, Republic of Korea.
E-mail: krwee@daegu.ac.kr; junhoshim@daegu.ac.kr
†
Electronic Supplementary Information (ESI) available: X-ray crystallographic data
In order to understand the effect of geometric isomerism of
backbone-based donor--acceptor (D--A) dyads, emission lifetime profiles, D-π-A dyads, three isomer D-π-A dyads with ortho-, meta-, and
1
13
1
of dyad M (CCDC code 1968408). H and C{ H} NMR spectra of the three terphenyl
absorption and emission spectra in various solvents and in the solid state, Lippert-
Mataga plots, spectroelectrochemical results, and DFT/TD-DFT calculation results.
See DOI: 10.1039/x0xx00000x
para-terphenyl backbones were prepared. We selected ortho-,
meta-, and para-terphenyl isomers as -linkers because the
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Ph yP sl ei c aa sl eC hd eo mni os ttr ya dC jhu es mt mi c aa lr Pg hi ny ss ics
Page 2 of 9
ARTICLE
Journal Name
terphenyl entity is a simple conjugated aryl unit. In addition, an Information (SI) provide details of synthetic procedures and
View Article Online
DOI: 10.1039/C9CP06466D
electron-deficient hetero aromatic unit of 1-phenyl-1H- characterization data.
benzimidazole (IMI) is widely used as a functional group to
facilitate electron acceptor and/or electron transport
properties.2
9,
30
Furthermore, the electron-rich aromatic
triphenylamine (TPA) unit has excellent electron donor and/or
3
1, 32
hole transport properties,
and thus, in the present study,
IMI was used as the electron acceptor and TPA as the electron
donor moiety as shown in Chart 1. In D-π-A dyads, geometric
isomerism of the terphenyl linker affects conjugation between
the IMI and TPA moieties. Basically, the ortho-terphenyl
structure has a non-conjugated system for each of the phenyl
unit due to the steric hindrance. Likewise, the meta-terphenyl
structure is well known as a non-conjugated system.
Specifically, only two phenyl units are conjugated due to the
electronically nodal site at meta-position. The para-terphenyl
structure is well conjugated over all of three phenyl units.
In this study, we investigated the ortho-, meta-, and para
isomer effects of the terphenyl group on photophysical and
electrochemical properties, including ICT and/or PET
properties, of terphenyl backbone-based D-π-A dyads, and
performed density functional theory (DFT) calculations. The
photophysical and electrochemical properties of the three
terphenyl backbone-based isomers were compared, and to
clarify the distinction between ICT and PET occurring in the
three isomeric D-π-A dyads, spectroelectrochemical (SEC) and
femtosecond transient absorption (fs-TA) measurements were
conducted.
Figure 1. ORTEP drawings of M. Hydrogen atoms are omitted for clarity.
For X-ray crystallographic analysis, a single crystal of M was
grown by slow evaporation in a CH
temperature. Dyad M crystallized in the triclinic space group P-
; crystal data and collection parameters are summarized in
2 2
Cl /MeOH mixture at room
1
Tables S1 and S2. Fig. 1 shows the X-ray structure and packing
of M. In the packing diagram (Figure S4), the molecules of M
were packed in a step-wise manner. Degree of -conjugation of
M in the solid state was determined from terphenyl torsion
angles. The angle between the central benzene and the phenyl
bound to the IMI moiety was ca. 26.6 (C15C14C49C57),
and that between the central benzene and the phenyl bound to
the TPA moiety was ca. 36.1 (C15C7C17C18), indicating a
slightly twisted structure. As shown in Fig. 6, the DFT calculated
structure of M (B3LYP/6-31G (d,p)) was in accord with its
observed X-ray structure. The intramolecular distance between
the N atom of TPA and the C atom including double bond with
the N atom of IMI was 12.0 Å, which agreed with the DFT
calculated value (12.5 Å). Based on the results obtained for M,
we assumed that the molecular structures of the O and P
isomers were reliably predicted by DFT calculation.
N
N
N
N
N
N
N
N
N
Electrochemical properties
Ortho (O)
Meta (M)
Para (P)
Cyclic voltammetry (CV) was used to evaluate the redox
properties of O, M, and P in CH Cl containing tetrabutyl
2 2
Chart 1. Molecular structures of terphenyl isomer-based D-π-A dyads.
ammonium perchlorate (0.1 M) as the supporting electrolyte,
using a three-electrode cell system, a platinum wire working
electrode, a glassy carbon counter electrode, and an SCE
reference electrode (Fig. S5). All three dyads showed reversible
oxidation peaks with oxidation onsets at 0.89, 0.91, and 0.88 V
for O, M, and P, respectively.
Results and discussion
Synthesis and structure characterization
Scheme S1 shows the synthetic procedures used to produce
the terphenyl backbone-based D--A dyads produced. The
starting materials, (4-(diphenylamino)phenyl)bronic acid (TPA-
BA), 1-phenyl-2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)phenyl)-1H-benzo[d]imidazole (IMI-PB), were prepared as
previously described. Terphenyl based D-π-A dyads were then
prepared using two-step palladium catalyzed Suzuki-Miyaura
coupling reactions and triphenylamine (TPA) as an electron
donor and 1,2-diphenyl-benzimidazole (IMI) as an electron
acceptor at yields of 74-83 %. All three compounds were
purified by silica gel column chromatograph using ethyl
acetate/n-hexane mixtures. Molecular structures of all products
Experimental and calculated HOMOLUMO energy levels of
the three dyads are compared and optical and calculated energy
band gaps (퐸
) are summarized in Table 1. Experimental HOMO
푔
energy levels were estimated from oxidation onset potentials
and fell in the range -5.69 ± 0.02 eV. Because no cathodic
reduction processes were measured using optical band gaps
calculated from the edges of the absorption spectra,
experimental LUMO energy levels were estimated using optical
band gaps and HOMO energy levels. In contrast with HOMO
energy levels, LUMO energy levels were relatively constant at -
2.35 (O), -2.41 (M), and -2.64 (P) eV. Calculated HOMO energy
levels fell in the range -4.92 ± 0.14 eV, and calculated LUMO
energy levels in the range -1.29 ± 0.09 eV; calculated values
were higher than experimental values for all dyads, but
tendencies were similar. These results show the more gradually
increased terphenyl isomer conjugation lower the LUMO,
1
13
1
were determined by H- and C{ H}-NMR, elemental analysis,
and mass spectrometry. Finally, the structural identity of
compound M was authenticated by single-crystal X-ray
crystallography. The experimental section and Supporting
2
| J. Name., 2012, 00, 1-3
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ARTICLE
thereby narrowing the band gap, and producing a red-shift in slightly lower emission intensity, as was observed for
View Article Online
DOI: 10.1039/C9CP06466D
the absorption spectrum from O to M and from M to P.
absorption spectra. The emission intensity of M is markedly
lower than those of O and P, and the emission quantum yields
of the D--A dyads followed the order P > O >> M. Generally,
PET generates a radical cation and/or anion from donor and
acceptor moieties, respectively, and the radicals produced are
Table 1. Energy band gap properties of O, M, and P.
HOMO푎
eV)
LUMO푏
opt
HOMO푐
LUMO푐
퐸푔
퐸푔
(
(eV)
(eV)
(eV)
(eV)
(eV)
O
M
P
-5.69
-5.71
-5.68
-2.35
-2.41
-2.64
3.34
3.30
3.04
-4.78
-4.98
-4.92
-1.24
-1.29
-1.38
3.54
3.69
3.54
2
4
non-emissive. Therefore, we assumed that the markedly
reduced quantum yield such as M is generally attributed to the
PET process.
Fluorescence lifetime measurements performed on O and P
exhibited single exponential fluorescence decays, in contrast M
exhibited biexponential fluorescence decay (Fig. S8). For M, we
ox
퐸LUMO (eV) = ―푒(퐸HOMO + 퐸 go pt
a
퐸HOMO (eV) = ― 푒
(
퐸onset + 4.8).
b . c Obtained by DFT calculation.
)
Photophysical properties
Fig. 2 shows the steady state UV-visible absorption and assumed that the slow process of the biexponential
emission spectra of O, M, and P. In UV-visible absorption fluorescence decay is attributed to the charge transfer from TPA
spectra, all D--A dyads showed bands at ~300 nm, which were to IMI moieties, and the fast process of the biexponential
ascribed to locally excited (LE) transitions of the TPA and IMI fluorescence decay is attributed to the charge transfer centered
moieties. P produced a strong absorption band at ~354 nm, on and around TPA. Also, the longer emission lifetime of M
which was attributed to intramolecular charge transfer (ICT) indicated the decay rate of the excited state was slower than
transition due to strong electron coupling between donor (TPA) those of O or P. These results are mainly explained by radiative
and acceptor (IMI) caused by the well-conjugated nature of the and nonradiative decay rate constants. We accessed the
para-terphenyl. In addition, a weak absorption shoulder at ~346 relationship between Φ푓 and τF values using radiative and
nm in the absorption spectrum of O was attributed to ICT nonradiative decay rate constants (Table 2). Although 푘nr of P
between TPA and IMI. Likewise, for M, a weak shoulder hidden
in broad absorption band was observed in the range of 340-370
nm, which was attributed to ICT. Notably, a red-shift of CT band
in absorption spectra was observed in the order O < M < P,
which was well explained by the ground state geometries of the
three terphenyls. i) The ortho-terphenyl structure is a non-
conjugated system at each phenyl unit due to steric hindrance,
and showed high energy absorption. ii) The meta-terphenyl
structure is conjugated at only two phenyl units due to the
electronic nodes at meta-position, and showed lower energy
absorption. iii) The para-terphenyl structure is conjugated over
all phenyl units, and showed least energy absorption. To
investigate inter-molecular interactions, thin-film absorption
and emission spectra were also recorded (Fig. S7). The thin film
absorption and emission spectra of O, M, and P were found to
exhibit red shifts as compared with corresponding spectra in
hexane solution, suggesting the terphenyl D--A dyads formed
J-aggregates.33
The emission spectra of the three D--A dyads exhibited
2 2
similar emission maxima at ~475 nm in CH Cl (Fig. 2 (bottom)),
Figure 2. UV-vis absorption (top) and emission (bottom) spectra of O, M, and P in
CH Cl at a concentration of 4.
indicating the dyads had a similar lowest excited state. In
addition, emission spectra were slightly red-shifted in the order
O < M < P, due to increased conjugation. As was expected, P
showed the largest emission intensity due to good electronic
coupling between TPA and IMI, and the O isomer showed
2
2
Table 2. Photophysical properties of O, M, and P.
휆푎푏푠 [nm]
휆푒푚 [nm]
푐
τF푑 (ns)
푒
8
―1
푒
8 ―1
Φ푓
푘rad × 10 푠
푘nr × 10 푠
푘rad/푘nr
sol푎
305
314
film푏
315
sol푎
film푏
439
414
451
O
M
P
472
478
479
0.45
0.069
0.62
7.92
0.56
0.37, 0.05
3.05
0.70
4.92, 0.67
1.88
0.80
0.08, 0.07
1.62
332
1.89, 13.83
2.03
309, 354
313,358
a
at room temperature (RT). b Measured in thin films. Fluorescence quantum yields, with 9,10-diphenylanthracene (ФPL = 0.95, ethanol) as
c
Measured in CH
2
Cl
2
d
). Values of rad and nr were calculated using, 푘rad
e
푘
푘
= Φ /휏
F and nr F) rad.
푘 = (1/휏 ― 푘
the standard, in CH
2
Cl
2
at RT. Fluorescence lifetimes at 500 nm (in CH
2
Cl
2
푓
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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2
2
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=
× (∆휇) ∆푓
(1)
DOI: 10.1039/C9CP06466D
(ℎ푐푎
3
)
0
where, μ
e
− μ
g
(Δμ) is the difference between the dipole
moments of excited and ground states, c is the speed of light, h
is Planck’s constant, and a is the radius of the Onsager cavity
0
around the fluorophore. Solvent dielectric constant (ε) and
refractive index (n) are included in the term Δf, known as the
solvent polarity parameter. Onsager radii were determined by
ab initio calculation and were considered to be half of the
average molecular sizes of O, M, and P (18.1, 22.8, and 23.6 Å,
respectively). Fig. 4 shows Stokes shift in different solvents for
Figure 3. Emission spectra of (a) O, (b) M, and (c) P measured in various solvents: 1, n-
hexane; 2, cyclohexane; 3, toluene; 4, ethyl ether; 5, THF; 6, CH
2
Cl
2
; 7, CH
3
CN; 8, MeOH. ICT was linearly related to Δf. Using eq (1), dipole moment
changes (Δμ) for O, M, and P were estimated to be 31.5, 62.9,
and 51.5 Debye (D), respectively. Table S4 of the SI shows the
ground state dipole moments (휇
structures (obtained by DFT) were > zero due to the asymmetry
of the three dyads. Using ground state dipole moments (휇
and dipole moment changes (Δμ), excited state dipole moments
휇푒) of O, M, and P were calculated to be 35.2, 67.1, and 55.4
) for energy minimized
푔
)
푔
(
D, respectively. Red-shifts and slopes of Lippert-Mataga plots
are related to Stokes shift and large Stokes shifts in polar
solvents are attributable to ICT. As was expected, P had a large
Δμ value due to -electron conjugation, which allows the charge
to be easily transferred from donor to acceptor. Interestingly, O
had a lower Δμ value than P, and P had a lower Δμ value than
M, which was presumed to be due to charge bias to one side in
M, which attributed to electronic nodal site and far distance
between the donor-acceptor by meta-terphenyl. O also had the
smallest Δμ value, because conjugation was disrupted and
because of closer donor/acceptor proximity. In a previous
report, an Si-atom containing donor/acceptor molecular system
Figure 4. Lippert-Mataga plots for O, M, and P in different solvents: 1, n-hexane; 2,
cyclohexane; 3, toluene; 4, ethyl ether; 5, THF; 6, CH Cl ; 7, CH CN; 8, MeOH.
2
2
3
is not smallest of the three dyads, 푘rad is significantly larger than
푘nr, indicating that the conjugated structure of P favors
radiative decay. Notably, O had a larger 푘rad than M because
the donor and acceptor were closer in O. Also, O has a smaller
푘nr than M due to the lower reorganization energy by the rigid
ortho-terphenyl with sterically hindered. These experimental
results show O and M favor radiative and nonradiative decay,
respectively.
In addition, we investigated the solvent-dependence of the
emission spectra of the three D--A dyads. The absorption
maxima of O, M, and P were showed weak polarity-dependent
solvent effects (Table S3). In contrast, the emission spectra of
the dyads were markedly red-shifted in a polarity-dependent
manner, indicating the presence of ICT state in the excited state
25
with a large Δμ (67.8 D) was found to exhibit PET process.
Therefore, we assumed that the M isomer, which has a similarly
large Δμ (62.9 D), exhibits PET in the excited state.
Spectroelectrochemistry (SEC) and transient absorption (TA)
To confirm radical species of three D--A dyads, SEC
measurements were performed under constant voltage (1.2 V)
in CH CN, that is, the potential corresponding to one-electron
3
oxidation (Fig. S11). When the three dyads were oxidized, a new
absorption band appeared in the energy band above 500 nm.
All dyads showed weak increases in broad absorption bands
between 600 and 700 nm, which was attributed to TPA radical
(Fig. 3). Especially, the emission spectra in hexane show vibronic
structure for M and P, but not for O. This indicates occurring
active molecular motion of O in the excited state even in non-
polar solvent. Based on these observed interactions between
solvents and dyads, solvatochromic analysis was performed to
investigate changes in the dipole moments of O, M, and P in
ground and excited states. It was found larger dipole moment
changes caused larger Stokes shifts in the emission spectra.
Stokes shift between maximum absorption and emission
35
cations. In addition, the peaks of the dyads appeared under
keeping the spectral shape after prolonged electrolysis at 766
(
O), 773 (M), and 855 (P) nm. These peaks were assigned to
+•
+•
+•
radical cations of O , M , and P . In particular, the red-shift
property of the absorption bands of the radical cation species
followed the order O < M < P, due to the terphenyl conjugation
effect.
3
4
wavelengths, in wavenumbers (Δν), is given by Eq. (1):
To distinguish between ICT and PET for the three dyads,
femtosecond transient absorption (fs-TA) measurements were
conducted. The fs-TA spectra of O, M, and P in CH Cl were
2
휀 ― 1
(2휀 + 1 2푛 + 1)
푛 ― 1
푣 ― 푣 =
×
―
×
(
휇푒 ― 휇푔)2
푎
푓
(ℎ푐푎
3
)
2
2
0
obtained by laser excitation at 320 nm (Fig. 5 and Fig. S12). All
dyads exhibited a negative transient absorption band at ~400
nm, which was attributed to bleaching. As was expected, no
4
| J. Name., 2012, 00, 1-3
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Ph yP sl ei c aa sl eC hd eo mni os ttr ya dC jhu es mt mi c aa lr Pg hi ny ss ics
Journal Name
radical anion or cation species was observed in the fs-TA
ARTICLE
Fig. S14 and Table S6 of the SI show the time-deVpieewnAdrteicnletODnlFinTe
spectrum of P, but broad peaks were observed at ~552, 641 and (TD-DFT) with the same functional and DbOasI:i1s0s.1e0t39c/oCn9fiCrPm06s46th6De
origin of the * transitions and the ICT transitions of O, M,
and P with the spectral shift showing. TD-DFT calculations on O
and P exhibited absorption bands that did not perfectively
match experimental data. In particular, O had an absorption
band of ~357 nm in the TD-DFT calculated absorption spectrum,
but this band was not observed experimentally. These
differences were presumed to be due to strong spectral shifts
in ICT transition. However, for M, TD-DFT calculation and
experimental results agreed well, indicting weak ICT transition
in the ground state. For all three dyads, the lowest-energy
singlet transition involves charge transfer from the HOMO to
the LUMO, which corresponds to ICT from TPA to IMI. These
transition shifts followed the order M (367 nm), O (372 nm), and
Figure 5. Transient absorption spectra of M in CH
Inset: decay profiles were monitored at selected wavelengths.
2 2
Cl
. Excitation wavelength was 320 nm. P (387 nm), and the oscillator strengths of these transitions
increased in the order M < O << P. In the case of the P isomer,
this transition was the major transition, but was a minor
7
46 nm, which decayed with time constants of 0.58  0.02, 0.64 transition for the O and M isomers. For O and P, the transition

0.01, and 0.63  0.1 ns, respectively. These peaks were from HOMO to L+1 involved charge transfer from TPA to the
1
attributed to the ICT state of (dyad P)*. For O, broad peaks diphenyl and IMI phenyl moieties. However, in the case of M,
were observed at ~499, 636, and 723 nm with decay time this transition was centered on and around TPA. These results
constants of 1.86  0.03, 1.76  0.02, and 1.85  0.03 ns, showed the two types of charge transfer from HOMO to L+1
respectively. These peaks were attributed to the ICT state of were due to different distances between TPA donor and IMI. In
1
(dyad O)*. No radical anion or cation species was observed, as the case of the O isomer, transitions based on orbital
was the case for the P isomer. Although M was expected to distribution are similar to P, because IMI and TPA are relatively
exhibit PET, as mentioned above, no radical cation or anion was close to each other. However, in M, this distance is far greater,
generated based on transient absorption measurements. Peaks and thus, charge transfer from TPA to IMI is inefficient, as
were observed at ~ 501 and 567 nm in the TA spectrum of M, evidenced by transition around the TPA boundary mentioned
which decayed with time constants of 0.86  0.01 and 0.89  above.
0
.01 ns, respectively, and both were attributed to the ICT state
1
of (dyad M)*. In particular, the TA spectra at ~501 and 567 nm
had similar decay profiles, though the 501 nm peak decayed
slightly less rapidly than the 567 nm peak on the 4.91 ns
timescale. Thus, the 501 nm peak was attributed to the slow
process of the biexponential fluorescence decay for M.
Resultantly, TA spectra of the three dyads showed that ICT
states were red-shifted in the order O < M < P.
DFT Calculations
Fig. 6 shows the HOMO and LUMO orbitals of terphenyl
backbone-based D--A dyads (O, M, and P), which were
obtained using Gaussian 16 and visualized using Chem3D and
GaussView programs. Geometries were optimized by DFT
Figure 6. Frontier orbital distributions (HOMO-1, HOMO, LUMO, LUMO+1) of O, M, and
method using the B3LYP correlation function employing the 6- P calculated by DFT with the B3LYP function and the 6-31G (d,p) basis.
3
1G (d,p) level in the vacuum state. H-1 orbitals of O, M, and P
were largely centered on the IMI moiety, while HOMO orbitals
were largely centered on the TPA moiety. With the exception of
the O isomer, the HOMOs of the TPA moiety of M and P were
slightly extended to the triphenyl linker. In contrast, the LUMOs
of O, M, and P were largely centered on the IMI moiety and
extended to the terphenyl linker in the order O < M < P. These
changes in the orbital distributions of HOMOs and LUMOs
showed charge transfer occurs from TPA to IMI in the excited
state. In addition, as mentioned above, the conjugation system
affected by the terphenyl geometry isomer were confirmed by
the DFT calculation as well.
Conclusions
Three geometric isomers, that is, ortho-, meta-, and para-,
terphenyl backbone-based D--A dyads containing TPA as an
electron donor and IMI as an electron acceptor, were prepared
and compared their photophysical and electrochemical
properties. In absorption spectra, a red-shift of CT band was
observed in the order P > M > O, which was attributed to
increased conjugation within the terphenyl moiety, and agreed
well with DFT calculations. In particular, the emission spectra of
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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Ph yP sl ei c aa sl eC hd eo mni os ttr ya dC jhu es mt mi c aa lr Pg hi ny ss ics
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Journal Name
the three dyads showed similar emission maxima at ~475 nm in comparative method for samples of five different
View Article Online
DOI: 10.1039/C9CP06466D
2 2
CH Cl , and these maxima were bathochromically shifted as concentrations of (1 – 5) μM, using 9,10-diphenylanthracene
3
8
solvent polarity increased, which was attributed to ICT. Lippert– (ФPL = 0.95, ethanol) as a reference standard. A CH
Mataga plost showed excited-state dipole moment changes Instruments 701D potentiostat was used for electrochemical
(Δμ) for O, M, and P were ~31.5 D, 62.9 D, and 51.5 D, measurements, and cyclic voltammetry (CV) was performed in
respectively. Generally, non-conjugation between donor and an electrolytic solution prepared using 1 mM of electroactive
acceptor moieties exhibit large Δμ value and PET. Of the three compounds and 0.1 M tetrabutyl ammonium perchlorate
isomers, M had the markedly reduced quantum yield and (Bu NClO ) at RT under argon atmosphere. A three-electrode
4 4
largest Δμ, indicating PET in the excited state, but no radical configuration, platinum wire, glassy carbon, and SCE were used
species were observed by fs-transient absorption (TA). Based on as working, counter, and reference electrodes, respectively.
the experimental results obtained, we confirmed all terphenyl
2
'-Bromo-N,N-diphenyl-[1,1'biphenyl]-4-amine (TPAB-Br-O)
isomer-based D--A dyads exhibit partial charge transfer. Thus,
we concluded non-conjugation of O and M does not necessarily A mixture of 1,2-dibromobenzene (0.97 g, 4.11 mmol), (4-
induce unit-electron transfer. Further studies on conjugated (diphenylamino)phenyl)bronic acid (0.7 g, 2.42 mmol),
and non-conjugated -linkers between donors and acceptors Pd(PPh
3
)
4
(10 mol%), and K
O (40 mL/10 mL) was refluxed under argon at 110 ℃
overnight. After cooling to room temperature, deionized water
50 ml) was added and the organic layer was collected. The
2 3
CO (1.67 g, 12.1 mmol) in
are under investigation.
toluene/H
2
(
Experimental
water layer was washed using methylene chloride (×3) to
extract remaining organics. After combining organic extracts,
the organic layer was dried over anhydrous MgSO and filtered.
4
General information
On the basis of standard Schlenk techniques, all of the synthesis Solvent was removed under reduced pressure, and the residue
experimental procedures were performed under a dry argon was purified by silica gel column chromatography using
condition. All of the reagents and solvents were obtained from CH Cl /n-hexane (v/v = 1:5) as eluent to obtain TPAB-Br-O as an
2
2
Sigma-Aldrich, Duksan and Chemical Oriental Chemical oil. Yield: 0.61 g, 87 %.
1
H-NMR (500 MHz, CDCl , ppm) δ 7.55
3
Industries, and used without purification. Deuterated solvent (d, J = 8.0 Hz, 1H), 7.23-7.22 (m, 2H), 7.19-7.15 (m, 6H), 7.06-
for NMR experiments was obtained from Merck or Cambridge 7.02 (m, 5H), 7.01 (d, J = 8.0 Hz, 2H), 6.95 (t, J = 7.0 Hz, 2H).
Isotope Lab. Inc. All reactions were monitored with thin layer 13C{
1
H} (125 MHz, CDCl , ppm) δ 147.69, 147.30, 142.26, 133.27,
3
chromatography (TLC) using commercial TLC plates (Merck Co.). 131.38, 130.28, 129.39, 129.35, 128.46, 127.45, 124.78, 124.49,
Silica gel column chromatography was carried out on silica gel 123.17, 122.48. GC-MS Calcd for [C H BrN]: 399.2 m/z, Found:
2
4 18
6
0 G (230–400 mesh ASTM, Merck Co.). The synthesized 399.06 m/z. Anal. Calcd for C H BrN: C, 72.05; H, 4.71; N, 3.71.
24 18
1
13
1
compounds were characterized by H-NMR or C{ H}-NMR, and Found: C, 72.01; H, 4.53; N, 3.50.
1
13
elemental analysis. The H and proton-decoupled C spectra
were recorded on a Bruker500 spectrometer operating at 500
and 125 MHz, respectively, and all proton and carbon chemical
N,N-diphenyl-4"-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1':2',1"-
terphenyl]-4-amine (O)
shifts were measured relative to internal residual chloroform A mixture of 2'-bromo-N,N-diphenyl-[1,1'biphenyl]-4-amine
99.5 % CDCl ) from the lock solvent. The elemental analyses (C, (0.61 g, 1.52 mmol), 1-phenyl-2-(4-(4,4,5,5-tetramethyl-1,3,2-
(
3
H, N) were performed using Thermo Fisher Scientific Flash 2000 dioxaborolan-2-yl)phenyl)-1H-benzo[d]imidazole (1 g, 2.58
series analyzer. The GC-MS analysis was performed using a mmol), Pd(PPh ) (5 mol%), and K CO (1.1 g, 7.6 mmol) in
3
4
2
3
highly sensitive Gas Chromatograph /Mass Selective Detector toluene/H O (v/v = 40 mL/10 mL) was refluxed under argon at
2
spectrometer (Agilent, 7890B-5977B GC/MSD). The (4- 110℃ overnight. After cooling to room temperature, deionized
3
6
(
(
diphenylamino)phenyl)bronic acid (TPA-BA) and 1-phenyl-2- water (50 ml) was added and the organic layer was removed.
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-1H-
The water layer was washed using methylene chloride (×3) to
3
7
benzo[d]imidazole (IMI-PB) were prepared based on the extract remaining organics, and after combining organic
previously published method. The UV/Vis absorption spectra extracts, the organic layer was dried over anhydrous MgSO4,
were recorded with photodiode array spectrophotometry by filtered, and solvent was removed under reduced pressure. The
Sinco Mega-2100, and the fluorescence emission residue was purified by silica gel column chromatography using
measurements were carried out using Shimadzu fluorometer ethyl acetate/n-hexane (v/v = 1:5) as eluent, and evaporation
(
RF-6000) with a wavelength resolution of ~1 nm. Fluorescence yielded O as a white powder. Yield: 0.45 g, 74 %.
H NMR (500
1
lifetimes were measured by PicoQuant FluoTime 200 that takes MHz, CDCl , ppm) δ 7.85 (d, J = 7.5 Hz, 1H), 7.40-7.31 (m, 10H),
3
advantage of the time-correlated single photon counting 7.23 (d, J = 7.5 Hz, 3H), 7.19-7.15 (m, 5H), 7.07 (d, J = 8.5 Hz, 2H),
method. A pulsed diode laser operated at 20 MHz repetition 7.01 (d, J = 9.0 Hz, 4H), 6.93 (t, J = 7.5 Hz, 2H), 6.87 (d, J = 9.0 Hz,
rate was used as the excitation source. The full width at half 2H), 6.82 (d, J = 8.5 Hz, 2H). 13C{
1
H} (125 MHz, CDCl , ppm) δ
3
maximum (FWHM) of a laser pulse was typically 45 ps, and the 147.60, 146.43, 140.24, 139.52, 134.93, 130.60, 130.42, 130.38,
instrument response function was ~190 ps when the 129.88, 129.84, 129.27, 129.06, 127.90, 127.38, 127.25, 124.54,
Hamamatzu photomultiplier tube (H5783-01) was used. The 122.95, 122.66, 110.48. GC-MS Calcd for [C H N ]: 589.4 m/z,
4
3 31 3
emission quantum yields (ΦPL) were calculated using William’s
6
| J. Name., 2012, 00, 1-3
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Page 7 of 9
Ph yP sl ei c aa sl eC hd eo mni os ttr ya dC jhu es mt mi c aa lr Pg hi ny ss ics
Journal Name
ARTICLE
Found: 589.25 m/z. Anal. Calcd for C43
N, 7.15. Found: C, 87.58; H, 5.30; N, 7.13.
H
31
N
3
: C, 87.60; H, 5.33; 110 ℃ overnight. After cooling to room temperature, deionized
View Article Online
DOI: 10.1039/C9CP06466D
water (50 ml) was added and the organic layer was removed.
The water layer was then washed using methylene chloride (×3)
3
'-Bromo-N,N-diphenyl-[1,1'biphenyl]-4-amine (TPAB-Br-M)
to extract remaining organics, and after combining organic
A mixture of 1,3-dibromobenzene (0.97 g, 4.11 mmol), (4- extracts, the organic layer was dried over anhydrous MgSO and
diphenylamino)phenyl)bronic acid (0.7 g, 2.42 mmol), filtered. Solvent was then removed under reduced pressure,
Pd(PPh (10 mol%), and K CO (1.67 g, 12.1 mmol) in and the residue was purified by silica gel column
toluene/H O (v/v = 40 mL/10 mL) was refluxed under argon at chromatography using CH Cl /n-hexane (v/v = 1:5) as eluent to
10 ℃ overnight. After cooling to room temperature, deionized obtain TPAB-Br-P as a light-yellow powder. Yield: 0.65 g, 93 %.
4
(
)
3 4
2
3
2
2
2
1
1
water (50 ml) was added and the organic layer was removed.
3
H NMR (500 MHz, CDCl , ppm) δ 7.57-7.54 (m, 2H), 7.47 (dd, J
The water layer was then washed using methylene chloride (×3) = 8.5 Hz, 2H), 7.32-7.28 (m, 6H), 7.18-7.15 (m, 6H), 7.09-7.06 (m,
1
3
1
to extract remaining organics. After combining organic extracts, 2H). C{ H} (125 MHz, CDCl
the organic layer was dried over anhydrous MgSO and filtered. 133.66, 133.17, 131.84, 129.35, 129.31, 128.21, 127.58, 124.58,
Solvent was then removed under reduced pressure, and the 124.47, 123.72, 123.14. GC-MS Calcd for [C24 18BrN]: 399.2 m/z,
residue was purified by silica gel column chromatography using Found: 399.06 m/z. Anal. Calcd for C24 18BrN: C, 72.05; H, 4.71;
CH Cl /n-hexane (v/v = 1:5) as eluent and TPAB-Br-M was N, 3.71. Found: C, 72.01; H, 4.53; N, 3.50.
obtained as a light-yellow powder. Yield: 0.6 g, 86 %. H NMR
500 MHz, CDCl , ppm) δ 7.83 (s, 1H), 7.58 (d, J = 8.0 Hz, 1H),
.53 (d, J = 9.0 Hz, 3H), 7.39-7.33 (m, 6H), 7.26-7.24 (m, 5H),
3
, ppm) δ 147.59, 147.58, 139.60,
4
H
H
2
2
1
N,N-diphenyl-4"-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1':4',1"-
(
3
terphenyl]-4-amine (P)
7
7
1
1
1
3
1
3
.17 (t, J = 7.5 Hz, 2H). C{ H} (125 MHz, CDCl , ppm) δ 147.91, A mixture of 4'-bromo-N,N-diphenyl-[1,1'biphenyl]-4-amine
47.66, 142.94, 133.41, 130.40, 129.80, 129.52, 129.38, 127.92, (0.6 g, 1.5 mmol), 1-phenyl-2-(4-(4,4,5,5-tetramethyl-1,3,2-
25.32, 124.75, 123.75, 123.34, 123.11. GC-MS Calcd for dioxaborolan-2-yl)phenyl)-1H-benzo[d]imidazole (1 g, 2.55
[
24
C H18BrN]: 399.2 m/z, Found: 399.06 m/z. Anal. Calcd for mmol), Pd(PPh
3 4 2 3
) (5 mol%), and K CO (1 g, 7.5 mmol) in
C
24
H
18BrN: C, 72.05; H, 4.71; N, 3.71. Found: C, 72.01; H, 4.53; toluene/H O (v/v = 40 mL/10 mL) was refluxed under argon at
2
N, 3.50.
110 ℃ overnight. After cooling to room temperature, deionized
water (50 ml) was added and the organic layer was removed.
The water layer was washed using methylene chloride (×3) to
extract remaining organics, and after combining extracts, the
N,N-diphenyl-4"-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1':3',1"-
terphenyl]-4-amine (M)
A mixture of 3'-bromo-N,N-diphenyl-[1,1'biphenyl]-4-amine organic layer was dried over anhydrous MgSO
0.6 g, 1.5 mmol), 1-phenyl-2-(4-(4,4,5,5-tetramethyl-1,3,2- solvent was removed under reduced pressure, and the residue
dioxaborolan-2-yl)phenyl)-1H-benzo[d]imidazole (1 g, 2.55 obtained was purified by silica gel column chromatography
4
and filtered. The
(
mmol), Pd(PPh
toluene/H
3
)
4
(5 mol%), and K
2
CO
3
(1 g, 7.5 mmol) in using ethyl acetate/n-hexane (v/v = 1:5) as eluent to obtain P as
1
2
O (v/v = 40 mL/10 mL) was refluxed under argon at a white powder. Yield: 0.5 g, 83 %. H NMR (500 MHz, CDCl
3
,
1
10℃ overnight. After cooling to room temperature, deionized ppm) δ 7.86 (d, J = 8.0 Hz, 1H), 7.61-7.57 (m, 7H), 7.53 (d, J = 8.5
water (50 ml) was added and the organic layer was removed. Hz, 2H), 7.48-7.43 (m, 6H), 7.32-7.29 (m, 3H), 7.22-7.20 (m, 4H),
1
3
1
The water layer was then washed using methylene chloride (×3) 7.08 (d, J = 8.5 Hz, 6H), 6.99 (t, J = 7.5 Hz, 2H). C{ H} (125 MHz,
to extracted remaining organics. Combined organic extracts CDCl , ppm) δ 147.64, 147.43, 140.10, 138.35, 134.25, 130.01,
were then dried over anhydrous MgSO and filtered. Solvent 129.91, 129.32, 129.76, 127.65, 127.52, 127.37, 127.01, 126.75,
was removed under reduced pressure, and the residue was 124.52, 123.81, 123.05, 119.72, 110.51. GC-MS Calcd for
purified by silica gel column chromatography using ethyl [C43 ]: 589.4 m/z, Found: 589.25 m/z. Anal. Calcd for
: C, 87.60; H, 5.33; N, 7.15. Found: C, 87.58; H, 5.30; N,
3
4
H N
31 3
acetate/n-hexane (v/v = 1:5) as eluent to provide M as a white
C
43
H
N
31 3
1
3
powder. Yield: 0.48 g, 79 %. H NMR (500 MHz, CDCl , ppm) δ 7.13.
7
.98 (d, J = 8.0 Hz, 1H), 7.79 (s, 1H), 7.72 (d, J = 8.5 Hz, 2H), 7.64
X-ray crystal structure analysis
(d, J = 8.5 Hz, 2H), 7.58-7.50 (m, 9H), 7.41 (dd, J = 7.0 Hz, 3H),
7
.32-7.28 (m, 5H), 7.18-7.16 (m, 6H), 7.08 (t, J = 7.0 Hz, 2H). The preliminary examination and data collection were
1
3
1
3
C{ H} (125 MHz, CDCl , ppm) δ 147.66, 147.43, 141.43, 140.50, performed using a Bruker SMART CCD detector system single-
1
1
34.84, 130.07, 129.95, 129.31, 129.28, 127.90, 127.51, 127.11, crystal X-ray diffractometer equipped with a sealed-tube X-ray
26.22, 125.58, 125.55, 124.48, 123.87, 123.02, 110.59. GC-MS source (50 kV × 30 mA) using graphite-monochromated Mo Kα
31 3
Calcd for [C43H N ]: 589.4 m/z, Found: 589.25 m/z. Anal. Calcd radiation (λ = 0.71073 Å). Preliminary unit cell constants were
for C43
N, 7.13.
H
31
N
3
: C, 87.60; H, 5.33; N, 7.15. Found: C, 87.58; H, 5.30; determined using a set of 45 narrow-frame (0.3° in ω) scans. The
double pass method of scanning was used to exclude noise.
Collected frames were integrated using an orientation matrix
4
'-Bromo-N,N-diphenyl-[1,1'biphenyl]-4-amine (TPAB-Br-P)
determined from narrow-frame scans. The SMART software
A mixture of 1,4-dibromobenzene (0.97 g, 4.11 mmol), (4- package was used for data collection, and SAINT was used for
3
9
(
diphenylamino)phenyl)bronic acid (0.7 g, 2.42 mmol), frame integration. Final cell constants were determined by
Pd(PPh (10 mol%), and K CO (1.67 g, 12.1 mmol) in global refinement of xyz centroids of reflections harvested from
toluene/H O (v/v = 40 mL/10 mL) was refluxed under argon at the entire data set. Structure solution and refinement were
)
3 4
2
3
2
This journal is © The Royal Society of Chemistry 20xx
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Ph yP sl ei c aa sl eC hd eo mni os ttr ya dC jhu es mt mi c aa lr Pg hi ny ss ics
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Journal Name
carried out using the SHELXTL-PLUS software package.40 The This research was supported by the Basic ScienVcieew ARrteicsleeOanrlcinhe
crystallographic information has been deposited with Program through the National ResearchDOFoI:u10n.1d0a3t9io/Cn9CoPf0K64o6r6eDa
Cambridge Crystallographic Data Centre and signed to CCDC (NRF), funded by the Ministry of Education (NRF-
code 1968408 for M.
2017R1C1B1010736).
Spectroelectrochemical (SEC) measurements
Notes and references
Measurements were carried out using a custom-made, optically
transparent, thin-layer electrochemical cell (light pass length =
1
mm) equipped with a platinum mesh working electrode and a
1
2
M. R. Wasielewski, Chem. Rev., 1992, 92, 435-461.
D. Gust, T. A. Moore and A. L. Moore, Acc. Chem. Res., 1993,
platinum coil counter electrode, and an SCE was used as the
reference electrode. Potentials were applied using
commercial electrochemical analyzer.
2
6, 198-205.
a
3
4
5
6
7
8
9
D. W. Cho, M. Fujitsuka, A. Sugimoto, U. C. Yoon, P. S. Mariano
and T. Majima, J. Phys. Chem. B, 2006, 110, 11062-11068.
M. Ito, E. Ito, M. Hirai and S. Yamaguchi, J. Org. Chem., 2018,
Femtosecond transient absorption (fs-TA) measurements
8
3, 8449-8456.
H. Liu, Q. Bai, L. Yao, H. Zhang, H. Xu, S. Zhang, W. Li, Y. Gao,
J. Li and P. Lu, Chem. Sci., 2015, 6, 3797-3804.
M. Ahn, M.-J. Kim and K.-R. Wee, J. Org. Chem., 2019, 84,
Sub-picosecond time-resolved absorption spectra were
collected using pump–probe transient absorption
a
spectroscopy system (Ultrafast Systems, Helios). The pump light
was generated using a regenerative, amplified titanium
sapphire laser system (Spectra Physics, Spitfire Ace, 1 kHz)
pumped by a diode-pumped Q-switched laser (Spectra Physics,
Empower). Seed pulse was generated using a titanium sapphire
laser (Spectra Physics, MaiTai SP). The pulses (290 and 340 nm)
generated by an optical parametric amplifier (Spectra Physics,
1
2050-12057.
S. K. Panja, N. Dwivedi and S. Saha, RSC Adv., 2016, 6, 105786-
105794.
R. Kurata, A. Ito, M. Gon, K. Tanaka and Y. Chujo, J. Org. Chem.,
2
017, 82, 5111-5121.
H. S. Nalwa, in Handbook of Organic Conductive Molecules
and Polymers, ed. H. S. Nalwa, Wiley, Chichester, U.K., 1997,
vol. 4, pp. 261-363.
TOPAS prime) were used as excitation pulse. A white light 10 D. Jiang, S. Chen, Z. Xue, Y. Li, H. Liu, W. Yang and Y. Li, Dyes
Pigm., 2016, 125, 100-105.
continuum pulse, (generated by focusing the residual of the
1
1
1 K. A. Willets, P. R. Callis and W. Moerner, J. Phys. Chem. B,
fundamental light to a thin Sapphire crystal after the controlled
optical delay) was used as a probe beam and directed at the
sample cell with 2.0 mm of the optical path and detected using
2
004, 108, 10465-10473.
2 B. Qiu, Y. Zeng, L. Cao, R. Hu, X. Zhang, T. Yu, J. Chen, G. Yang
and Y. Li, RSC Adv., 2016, 6, 49158-49163.
a CCD detector installed in the absorption spectroscope. The 13 K. Suzuki, S. Kubo, K. Shizu, T. Fukushima, A. Wakamiya, Y.
Murata, C. Adachi and H. Kaji, Angew. Chem. Int. Ed., 2015,
pump pulse was chopped by
synchronized to one-half of the laser repetition rate, so as to
produce a pair of spectra (i.e., with and without the pump),
a mechanical chopper
5
4, 15231-15235.
1
4 K.-R. Wee, H.-C. Ahn, H.-J. Son, W.-S. Han, J.-E. Kim, D. W. Cho
and S. O. Kang, J. Org. Chem., 2009, 74, 8472-8475.
from which absorption change induced by the pump pulse was 15 Z. Ge, T. Hayakawa, S. Ando, M. Ueda, T. Akiike, H. Miyamoto,
estimated.
T. Kajita and M. a. Kakimoto, Adv. Funct. Mater., 2008, 18,
84-590.
6 Y. Ooyama, Y. Hagiwara, Y. Oda, T. Mizumo, Y. Harima and J.
Ohshita, New J. Chem., 2013, 37, 2336-2340.
7 K.-R. Wee, B. D. Sherman, M. K. Brennaman, M. V. Sheridan,
A. Nayak, L. Alibabaei and T. J. Meyer, J. Mater. Chem. A, 2016,
4, 2969-2975.
8 B. D. Sherman, M. V. Sheridan, K.-R. Wee, S. L. Marquard, D.
Wang, L. Alibabaei, D. L. Ashford and T. J. Meyer, J. Am. Chem.
Soc., 2016, 138, 16745-16753.
5
Density functional theory (DFT) calculations
1
1
DFT calculations were performed by using Gaussian’16 software
package. Full geometry optimizations in ground states were
performed using the B3LYP functional and the 6-31G (d,p) basis
set for all atoms. Excitation energies and oscillator strengths for
the lowest 100 singlet–singlet transitions for optimized
geometries in the ground state were obtained using time-
dependent DFT (TD-DFT) calculations using the same basis set
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Conflicts of interest
There are no conflicts to declare.
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