Carbazole-perylenebisimide electron donor/acceptor dyads showing efficient spin orbit charge transfer intersystem crossing (SOCT-ISC) and photo-driven intermolecular electron transfer

Article abstract of DOI:10.1039/c9tc06429j

Perylenebisimide-carbazole (PBI-Cz) dyads were prepared to study charge-recombination (CR) induced intersystem crossing (ISC) in electron donor/acceptor dyads. The distance and the mutual orientation of the perylenebisimide (PBI) and carbazole (Cz) moieties were varied to study their effect on photophysical properties. Steady state and time-resolved optical spectroscopies show that electronic coupling between the electron donor and acceptor is negligible at the ground state. The fluorescence of the PBI moiety is strongly quenched in the dyads, and a larger separation between the donor and the acceptor results in less fluorescence quenching. The Gibbs free energy changes of the electron transfer and the energy level of the charge transfer state were studied using the electrochemical and optical spectra data. The singlet oxygen quantum yields (Φ_Δ) are up to 72% for dyads with the shortest separation between the donor and the acceptor. Nanosecond transient absorption spectra confirmed the formation of the PBI-localized long lived triplet state (the lifetime is up to 190 μs). Notably non-orthogonal dyads show efficient spin orbit charge transfer (SOCT-ISC), which is different from the previously proposed orthogonal molecular structure for SOCT-ISC. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy shows that all three dyads give the same electron spin polarization of eae/aea, and thus the radical pair ISC (RP ISC) mechanism is excluded, which is different from the previously reported PBI-phenothiazine analogues. Efficient and reversible transformation of dyads to their radical anion was observed in the presence of sacrificial electron donor triethanolamine in an inert atmosphere with photo-irradiation.

Full text of DOI:10.1039/c9tc06429j

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DOI: 10.1039/C9TC06429J
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Carbazole-Perylenebisimide Electron Donor/Acceptor Dyads
Showing Efficient Spin Orbit Charge Transfer Intersystem Crossing
(SOCT-ISC) and Photo-Driven Intermolecular Electron Transfer
Received 00th January 20xx,
Noreen Rehmat,a Antonio Toffoletti,b Zafar Mahmood,c Xue Zhang,a Jianzhang Zhao*a and Antonio
Barbon*b
Perylenebisimide-Carbazole (PBI-Cz) dyads were prepared to study the charge-recombination (CR) induced intersystem
crossing (ISC) in these electron donor-acceptor dyads. The distance and the mutual orientation of the perylenebisimide (PBI)
and carbazole (Cz) moieties were varied to study its effect on the photophysical properties. Steady state and time-resolved
optical spectroscopies show that the electronic coupling between the electron donor and acceptor is negligible at ground
state. The fluorescence of the PBI moiety is strongly quenched in the dyads, larger separation between the donor and
acceptor results in the less fluorescence quenching. The Gibbs free energy changes of the electron transfer and the energy
level of the charge transfer state were studied by electrochemical and optical spectra data. Singlet oxygen quantum yields
(∆) of the dyads are up to 72% for the dyad with shortest separation between the donor and acceptor. Nanosecond
transient absorption spectra confirmed the formation of the PBI-localized long lived triplet state (the lifetime is up to 190
µs). Notably these non-orthogonal dyads show efficient spin orbit charge transfer (SOCT-ISC), which is different from the
previously proposed orthogonal molecular structure for SOCT-ISC. Time-resolved electron paramagnetic resonance (TREPR)
spectroscopy show that all three dyads give the same electron spin polarization of eae/aea, thus radical pair ISC (RP ISC)
mechanism is excluded, which is different from the previously reported PBI-phenothiazine analogues. Efficient and
reversible transformation of dyads to their radical anion was observed in the presence of sacrificial electron donor
triethanolamine under inert atmosphere with photo-irradiation.
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
fundamentally interesting in photochemistry studies. Various
ISC mechanisms have been studied, for instance the above
mentioned heavy atom effect, n-*  -* transitions,33
Introduction
Triplet photosensitizers (PSs) are versatile materials for
applications in
photocatalysis,14 photovoltaics,57
photodynamic therapy (PDT),8−15 and triplet-triplet annihilation
(TTA) upconversion.16−23 Intersystem crossing (ISC) is the crucial
property for the triplet PSs.24 Heavy atom effect is the typical
method to enhance the ISC such as by using Ir, Ru, Pt, I or Br
atoms.25−31 However, concerning some applications, dark
toxicity and the high cost of these heavy atom containing
compounds are the disadvantages,24,32 thus it is highly desired
to develop heavy atom free triplet PSs, which are also
exciton coupling,34−36 systems based on spin converters37−40 and
the energy level matching of Sn/Tn states.24,41 In comparison, the
charge recombination (CR) induced ISC was less investigated. It
is known that the CR in electron donor/acceptor dyads, with
long separation between the donor and acceptor, may induce
ISC, given the electron exchange integral is extremely small (J ˂
0.1 cm−1).42 Under this circumstance, the radical pair ISC (RP-ISC)
may occur by the magnetic coupling between the electron and
the magnetic nuclei, i.e. ISC of 1CT to 3CT. The subsequent
electron spin-selective CR would produce a locally excited
triplet state (3LE), given the 3LE state is with lower energy level
than the CT state.
a. State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian
University of Technology, E-208 West Campus, 2 Ling–Gong Road, Dalian 116024, P.
R. China. E-mail: zhaojzh@dlut.edu.cn (J. Z.)
It is worthy to mention that the charge separation (CS) and
CR are electron spin selective, which means 1LE  S0, 1CT  S0
are bound to prevail than the 1LE  3LE and 1CT  3CT,
respectively. Therefore prerequisites are required for 1CT  3CT
(RP-ISC). In order to facilitate the states mixing of 1CT and 3CT
states, the energy gap of these two states should be very small
(J value should be on the scale of Zeeman effect, ˂ 0.1 cm‒1),
which requires decoupling between the donor and acceptor,
achieved by large separation of the donor and acceptor, which
makes the synthesis difficult.43−45 Moreover, due to the coupling
b. Dipartimento di Scienze Chimiche, Università degli Studi di Padova, Via Marzolo 1,
34921 Padova, Italy. E-mail: antonio.barbon@unipd.it (A. B.)
c
Light Industry and Chemical Engineering College, Guangdong University of
Technology, Guangzhou 510006, P. R. China
Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC06429J
O
O
O
O
N
N
O
4
5
O
O
N
O
O
O
O
O
O
O
O
3
2
3-Aminopentane,
imidazole
140oC, 4 h, N2
6
3-Aminopentane,
aniline, imidazole
1
KOH, t-BuOH
140oC, 3 h, N2
140oC, 4 h, N2
12
11
7
8
O
N
O
10
9
O
O
N
NH2
3
2
PBI-Ph
N
N
N
Br
N
OH
HO
OH
HO
B
N
B
N
O
N
O
O
N
O
O
N
N
O
O
N
O
O
K2CO3, Pd(PPh3)4
90oC, 8 h, N2
K2CO3, Pd(PPh3)4
90oC, 8 h, N2
O
N
O
O
N
O
O
O
O
N
1
PBI-Cz-1
PBI-Cz-3
PBI-Cz-2
Scheme 1. Synthetic routes to perylenebisimide-carbazole Dyads and reference compound.
of electron magnetic dipole and the nuclear magnetic dipole, perylenebisimide (PBI)-carbazole (Cz) derived electron
the 1CT  3CT is usually slow, thus the ISC yield is not expected donor/acceptor dyads to study the above issues (Scheme 1). PBI
1
to be high, due to the competing CT  S0 process. Normally, is used as electron acceptor in the dyads, and Cz moiety was
the ISC yields and the triplet state properties (the lifetimes and used as electron donor. To the best of our knowledge, PBI was
the application in electron transfer) were not studied in detail not used for SOCT-ISC dyads. Moreover, the molecular structure
for molecular systems showing RP-ISC.42
(geometry) is different from the recently reported SOCT-ISC
Recently, compact electron donor/acceptor dyads were dyads, which usually show orthogonal geometry, as a result of
reported to show ISC, in this case, the -conjugation planes of large conformation restriction. The PBI-Cz dyads studied herein
the donor and acceptor take orthogonal geometry, thus the are with medium separation distance between the electron
electron spin angular momentum change during ISC is donor and acceptor, and the orientation of the electron donor
compensated by the molecular orbital angular momentum and acceptor is not orthogonal. The photophysical properties of
change of the CR process, and it is the so-called spin orbit charge the PBI-Cz dyads were studied with steady-state and time-
transfer ISC (SOCT-ISC).46−51 For these molecules, RP-ISC can be resolved optical spectroscopies, as well as time-resolved
excluded, because of the significant J values (large 1CT/3CT electron paramagnetic resonance (TREPR) spectroscopy.
energy gaps) caused by the strong coupling of the electron Interestingly, we found satisfactory SOCT-ISC yields for the PBI-
donor/acceptor.52 Anthracene, acridinium, bodipy and perylene Cz dyads, and TREPR spectroscopy excluded the RP-ISC
moieties have been used for construction of the compact mechanism. Although some of the current PBI-Cz dyads are with
electron donor/acceptor dyads showing SOCT-ISC.46,47,53−55 similar structure to that of previously reported PBI-
These dyads share a common feature, i.e. the electron donor Phenothiazine (PTZ) dyads, which show RP-ISC.42
and acceptor are directly connected, and the -conjugation
planes of the electron donor/acceptor adopt close-to-
orthogonal geometry. It will be interesting to explore the
Results and discussion
application of other chromophores and molecular structures for
the construction of such SOCT-ISC dyads. Herein we prepared
Molecular design and synthesis
Previously bay-substituted carbazole-perylenebisimide donor-
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acceptor system has been investigated, which show strong ground length, structured emission peak appears at 535 nm with a
View Article Online
state electronic coupling, but no ISC was observed.56 Considering pronounced vibrational shoulder at 575 nm. The emission of PBI-Cz
DOI: 10.1039/C9TC06429J
that the chemical modification at imide position will result in weak dyads is quenched even in low polar solvent toluene as compared to
to moderate electronic coupling between donor and acceptor reference compound PBI-Ph, which is highly fluorescent (optically
moieties. It is of scientific interest to investigate the ISC ability of matched solution was used). The fluorescence quantum yield (F) of
imide substituted PBI-Cz donor/acceptor system. For this study, PBI-Cz-2 is 0.44 (in toluene), which is lower than that of reference
three PBI-Cz dyads were designed by attaching carbazole donor at compound PBI-Ph (F = 0.90). Although the linker between the PBI
the imide position of PBI acceptor. The linker length between the PBI and the Cz moieties in PBI-Cz-1 and PBI-Cz-2 are one and two phenyl
and the carbazole moiety was varied from one phenyl moiety (PBI- rings respectively, yet we observed the different fluorescence
Cz-1 and PBI-Cz-3) to two phenyl moieties (PBI-Cz-2). The orientation quantum yield in these two dyads.
of the PBI and the carbazole moieties was also varied, to study the
It should be noted that fluorescence is strongly quenched in case
relationship between the molecular structure and the SOCT-ISC of PBI-Cz-1 (F = 0.02) and PBI-Cz-3 (F = 0.01) in toluene (Table 1),
efficiency.
the photo-induced charge separation (CS) is possible reason for
fluorescence quenching (Cz moiety as electron donor). We proposed
this different fluorescence quenching in PBI-Cz dyads is due to
different length of spacer which controls the electronic interaction
between Cz and PBI moieties. As the length of spacer increases, the
electronic interaction between two moieties decreases which results
in less fluorescence quantum yield in PBI-Cz-2 as compared to other
two dyads. The solvent-dependent fluorescence of dyads was also
studied (see ESI†, Fig. S16). In all solvents only structured emission
band were observed in case of PBI-Cz dyads, no CT emission band
was observed. Although with increasing polarity the quenching of
fluorescence becomes more pronounced which confirms the PET
process in the PBI-Cz dyads.
Fluorescence emission spectra of these imide substituted PBI
derivatives are different from the previously reported bay
substituted PBI-carbazole derivatives (1,6- and 1,7-substitution).
Those derivatives showed the red shifted structureless emission
band due to strong electronic coupling.56 Moreover, in case of bay
substituted PBI-PTZ dyads, structureless red shifted emission band
UV-Vis absorption and emission
The UVVis absorption spectra of the compounds were studied (Fig.
1a). All the three PBI-Cz dyads and reference compound PBI-Ph
display very similar absorption feature. The structured absorption
bands between 400 and 550 nm are assigned to the S0  S1 transition
of the PBI core. The spectral features indicate that substitution of
carbazole on imide position of PBI has little influence on the
electronic structure of the PBI core. In other words, no electronic
coupling between carbazole and PBI moiety was observed at ground
state. However, in case of previously reported bay-substituted PBI-
phenothiazine (PBI-PTZ) dyads in which PTZ is attached to PBI
through different orientation, different absorption spectra were
observed. For the dyad with orthogonal geometry, the PBI and PTZ
are completely electronically decoupled, the absorption spectrum
was similar to un-substituted PBI but for the dyad with non-
orthogonal geometry, the absorption spectrum was broad and
structureless and strong electronic coupling between PBI and PTZ
moieties was observed.57 Moreover, in case of previously reported
bay substituted PBI-carbazole derivatives, red shifted and broad
structureless absorption spectra was observed, which indicate that
strong ground state electronic coupling is present in bay substituted
PBI-carbazole derivatives due to -conjugation,56 while imide
substituted PBI-Cz dyads (Scheme 1) inherit photophysical
characteristics from the PBI.
104
103
102
101
100
104
103
102
101
a
b
 = 0.1 ns (82.3 %)
 = 3.6 ns (18.6 %)
 = 0.6 ns (12.7 %)
 = 3.9 ns (87.3 %)
The fluorescence of PBI-Cz dyads and reference compound were
studied (Fig. 1b). All the compounds shows similar emission wave-
0
10 20 30 40 50
Time / ns
0
10 20 30 40 50
Time / ns
PBI-Cz-1
PBI-Cz-2
PBI-Cz-3
PBI-Ph
PBI-Cz-1
PBI-Cz-2
PBI-Cz-3
PBI-Ph
a
b
45
30
15
0
104
103
102
101
100
104
103
102
101
0.6
0.4
0.2
0.0
c
d
0.30
0.15
0.00
 = 0.6 ns (83.9 %)
 = 4.3 ns (16.1 %)
 = 4.3 ns
500
600
700
Wavelength / nm
300
450
600
750
500
600
700
800
Wavelength / nm
Wavelength / nm
0
10 20 30 40 50
Time / ns
0
10 20 30 40 50
Time / ns
Fig. 1 (a) spectra UVVis absorption spectra of PBI-Cz dyads, c = 1.0 × 10–5 M in toluene;
(b) Fluorescence emission spectra of PBI-Cz dyads in toluene (ex = 475 nm). Optically
matched solutions were used (all the compounds have same absorbance at the
excitation wavelength c ≈ 1.0 × 10–5 M, absorbance A = 0.23), 20 °C. Inset: enlarged
emission spectra of PBI-Cz-1 and PBI-Cz-2.
Fig. 2 Fluorescence decay traces of PBI-Cz dyads; (a) PBI-Cz-1 (em = 535 nm); (b) PBI-Cz-2
(em = 535 nm); (c) PBI-Cz-3 (em = 535 nm); (d) PBI-Ph (em = 535 nm), ex = 510 nm c =
1.0 × 10–5 M in toluene, 20 C.
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DOI: 10.1039/C9TC06429J
Table 1. Photophysical parameters of the compounds.
a
e
f
abs
b
em
Fc
Fd

T
PBI-Cz-1
PBI-Cz-2
PBI-Cz-3
PBI-Ph
526
526
526
526
0.65
0.62
0.66
0.65
535
535
535
535
0.02
0.44
0.01
0.90
1.85
3.87
1.02
4.29
0.45
0.38
0.72
179.6
188.8
109.7
g
g
─
─
a In toluene (1.0 × 10−5 M) and in nm. b Molar absorption coefficient (105 M−1cm−1). c Fluorescence quantum yield with Bodipy as a standard (F = 72% in tetrahydrofuran).
d Fluorescence lifetimes (ns) in toluene, λex = 510 nm (EPL picosecond pulsed laser), e Singlet oxygen quantum yield in toluene with 2,6-diiodobodipy as a standard ( =
0.83 in DCM) and excited at 531 nm. f Triplet state lifetime (µs) in toluene, determined with nanosecond transient absorption spectroscopy. g Not applicable.
around 780 nm, along with structured emission (locally excited)
band at 524 nm was observed, which indicates the existence of
strong electronic coupling between donor PTZ and PBI
+
+
Fc / Fc
-1.06
Fc / Fc
-1.09
moieties.57
-1.25
a
b
-1.24
The fluorescence lifetime of PBI-Cz dyads was also studied
(Fig. 2). In all dyads the fluorescence emission decays faster as
compared to reference compound and exhibits biexponential
feature, which confirm the PET process in these dyads. For PBI-
Ph, the decay of fluorescence at 520 nm (LE emission) is with
lifetime of 4.3 ns, similar to that of unsubstituted PBI moiety
which has fluorescence lifetime of 4.4 ns (see ESI†, Fig. S18)
For PBI-Cz-2 (Fig. 2b), the fluorescence decay is with minor
biexponential feature of 0.6 ns (population ratio 13%) and 3.9
ns (87%), respectively. For the dyads, PBI-Cz-1 and PBI-Cz-3,
showing weak fluorescence, the biexponential decay feature is
more significant. In case of PBI-Cz-1 fluorescence lifetime is 0.1
ns (population ratio 82%) and 3.6 ns (18%); while for PBI-Cz-3,
the fluorescence lifetime is 0.6 ns (population ratio 84%) and
4.3 ns (16%). The fast decaying components of PBI-Cz-1 and PBI-
Cz-3, generally indicate the quenching channel of the 1LE state,
e.g. photo-induced CS.58 Fluorescence decay of PBI-Cz dyads
were also studied in polar solvent such as dichloromethane (see
ESI†, Fig. S17). In polar solvent the fluorescence also decays
faster and exhibit biexponential feature which support above
results.
The singlet oxygen quantum yields (∆) of the PBI-Cz dyads were
studied (Table 1), as a preliminary evolution of the triplet state
production ability of the compounds. The detailed method for
measurement of ∆ values is given in ESI†. PBI-Cz dyads show very
high singlet oxygen quantum yields in toluene (∆ = 0.72 for PBI-Cz-
3). Since PBI moiety is devoid of ISC ability, the ISC is attributed to
the charge transfer mediated triplet state population in these dyads.
It was found that by increasing the ‘effective’ spacer length in the
dyads, the ∆ decreases. Moreover, in polar solvents, the ∆
decreases sharply as well. In toluene, the ∆ values are in the range
of 38% ~ 72%, in dichloromethane, the PBI-Cz dyads showed ∆ of
only 4−10 %, whereas no singlet oxygen generation was observed in
acetonitrile. The solvent polarity dependency of ∆indicates that CT
state is involved the ISC, which is character of SOCT-ISC mechanism.
It is interesting that the Cz and the PBI -conjugation planes do not
adopt orthogonal geometry, but the ISC is efficient. This result is
different from the previously proposed orthogonal molecular
geometries for electron donor-acceptor dyads showing efficient
SOCT-ISC.46−48
+0.81
+0.87
1
0
-1
1
0
-1
Potential / V
Potential / V
+
+
Fc / Fc
-1.25
-1.25
Fc / Fc
d
-1.07
c
-1.06
+0.84
1
0
-1
1
0
-1
Potential / V
Potential / V
Fig. 3 Cyclic voltammogram of (a) PBI-Cz-1; (b) PBI-Cz-2; (c) PBI-Cz-3 and (c) PBI-Ph. In
deaerated dichloromethane containing 0.10 M Bu4NPF6 as supporting electrolyte,
Ferrocene (Fc) was used as the internal reference. Scan rates: 50 mV/s. c = 5.0 × 10−4 M,
20 C.
Electrochemical studies
In order to study the Gibbs free energy changes of electron transfer
and to determine the energy levels of charge transfer (CT) states of
the PBI-Cz dyads, electrochemical measurements were carried out
(Fig. 3). For PBI-Cz-1, two reversible reduction potential waves at
1.25 and 1.06 V were observed which can be attributed to PBI
moiety (Table 2). One reversible oxidation potential wave at +0.81 V
was also recorded, which can be assigned to Cz moiety. In case of
PBI-Cz-2, one reversible oxidation wave potential at +0.87 V was
observed which can be assigned to Cz moiety. Two reversible
reduction potential waves similar to that of PBI moiety at 1.09 V and
1.24 V were also observed. In case of PBI-Cz-3, one reversible
oxidation wave at +0.84 V was observed, this can be assigned to the
Cz moiety. Two reversible reduction waves similar to that of PBI
moiety at 1.07 V and 1.24 V were also observed. For the reference
compound PBI-Ph only two reversible reduction waves at 1.11 V
and 1.33 V were observed and no oxidation potential wave was
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observed within potential range used in the electrochemical Nanosecond transient absorption spectroscopy: triplet state
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DOI: 10.1039/C9TC06429J
measurements, which indicates that the PBI moiety is an electron properties
acceptor rather than electron donor (Fig. 3d).
The Weller equation is used to calculate the free energy changes
of PET process (Equation 13):59,60
Perylenebisimide (PBI) chromophore devoid ISC ability and is highly
fluorescent.61 However, PBI-Cz dyads show significant singlet oxygen
production (Table 1), which indicates efficient ISC ability. For
instance, the singlet oxygen quantum yield (∆) of PBI-Cz-3 is 72% in
toluene, for PBI-Cz-1 and PBI-Cz-2, the singlet oxygen quantum yields
in toluene are 45% and 38%, respectively. To study the triplet excited
states of the PBI-Cz dyads, nanosecond transient absorption spectra
were studied (Fig. 4). Upon 532 nm pulsed laser excitation, a
prominent excited state absorption (ESA) band was observed in the
range of 400−650 nm that is similar to typical T1Tn absorption
profile of PBI moiety.62
G0  e[EOX  ERED ] E 00 GS
(1)
cs
e2
e2
1
1
1
1









GS  



(2)
(3)
4s0RCC 80 RD RA REF S



GCR  

GCS E00

For PBI-Cz-1, PBI-Cz-2 and PBI-Cz-3, ground state bleach bands
(GSB) were observed at 528 nm. To monitor the lifetime of triplet
excited state, the decay traces at 470 nm were studied. Interestingly,
longer lifetime (110−189 µs) was observed in the case of PBI-Cz dyads.
The lifetime of transient species detected in case of PBI-Cz dyads are
greatly quenched in the presence of air, which confirms the
formation of triplet species. The PBI-localized triplet state is much
longer-lived than that observed with heavy atom effect in a Pt(II)
complex (246 ns  1.0 µs).63,64 The triplet state lifetimes are also
much longer than that observed with the S1/Tn (n > 1) energy level
matching approach (30  60 µs).65 However, in a PBI derivative with
phenyl acetylides substituents at 2, 5, 8, 11-position of the PBI core,
a much longer triplet state lifetime was observed (505 µs).66
where GS is the static Coulombic energy, which is described by
equation 2, e = electronic charge, EOX = half-wave potential for one-
electron oxidation of the electron-donor unit, ERED = half-wave
potential for one-electron reduction of the electron-acceptor unit;
E00 = energy level approximated with the crossing point of UV−Vis
absorption and fluorescence emission after normalization at the
singlet excited state, S = static dielectric constant of the solvent, RCC
= center-to-center separation distance between the electron donor
(carbazole) and electron acceptor (perylenebisimide), determined by
DFT optimization of the geometry, RCC (PBI-Cz-1) = 13.57 Å, RCC (PBI-
Cz-2) = 13.57 Å, RCC (PBI-Cz-3) = 10.69 Å, RD is the radius of the
electron donor, RA is the radius of the electron acceptor, REF is the
static dielectric constant of the solvent used for the electrochemical
studies, 0 is permittivity of free space. The solvents used in the
calculation of free energy of the electron transfer is Toluene (S = 2.4),
CH2Cl2 (S = 8.9) and acetonitrile (S = 37.5).
Time-resolved EPR spectral study
In order to study the triplet state property and the ISC mechanisms
of the dyads, time-resolved electron paramagnetic resonance (TR-
EPR) spectra of the dyads were recorded. Based on the UVVis
absorption spectrum (Fig. 1a), we acquired the TR-EPR spectra of the
compounds (Fig. 5) upon photoexcitation at 355 and 530−536 nm,
where the Cz (355 nm) and/or the PBI (at 530 ca and 355 nm)
moieties show absorption maxima, respectively.
The free energy changes of intermolecular electron transfer and
charge recombination process are listed in Table 3. Both PBI-Cz-1 and
PBI-Cz-2 show the comparable ΔG0 value in low polar solvent
CS
toluene i.e. ‒0.06 eV and ‒0.07 eV respectively and also have similar
CSS energy level of 2.27 eV. However, in polar solvent the ECSS of PBI-
Cz-1 becomes lower as compared to PBI-Cz-2. For PBI-Cz-3, in which
Cz is linked with PBI moiety using a spacer of short length, the ECSS is
Upon pulsed photoexcitation at 530−536 nm, all the dyads show
similar TREPR spectra, with eae/aea electron spin polarization (ESP,
a and e refer to enhanced absorption or emission, respectively) . On
the base of the ZFS parameters, D = 469 MHz and E = 44 MHz (Table
4), the triplet state is localized on the PBI moiety for all three dyads.
The polarization is not typical triplet state accessed with a regular
SO-ISC,42 for its polarization would be eee/aaa (see the spectrum
labeled PBI-ISC in Fig. 5a, simulated with the parameters taken from
reference,42 and presented in Table 4). The spectral features are,
instead, rather similar to those for a compact PBI-PTZ dyads, where
the triplet was obtained by SOCT-ISC.42 Moreover, similar ESP pattern
was observed in case of Julolidine−Anthracene (DMJ-AN) dyads
exhibiting SOCT-ISC.46 For this type of ISC process, we still have a
population of the ZFS states, but the population rates of the sublevels
of the triplet state is different from that obtained from a regular SO-
ISC. The population of the ZFS states (molecular frame) will be carried
over to the high-field energy levels (laboratory frame), thus highly
polarized TREPR spectra of the triplet state were observed. It should
be pointed out that the typical ESP of the triplet state accessed with
RP ISC (either aee/aae or eaa/eea42) was not observed, and we didn’t
observe any narrow bands relative to spin correlated radical pair (SC
2.20 eV which is lower compared to other two dyads and ΔG0 is
CS
‒0.14 eV in toluene. These results indicate the strong PET process in
the PBI-Cz-3 which also support the low fluorescence quantum yield
(∆= 0.01) and high singlet oxygen quantum yield (∆ = 0.72).
The ΔG0 values also indicate that the CS is thermodynamically
CS
allowed for all PBI-Cz dyads even in non-polar solvent such as toluene
which is in agreement with experimental observations (Fig. 1b, Table
3). This prediction was also confirmed by the fluorescence quenching
of compounds in non-polar solvent. Moreover, we found that the CT
state energy levels decrease in polar solvents (Table 3).
Table 2. Electrochemical redox potentials of the compounds a
Compounds
PBI-Cz-1
PBI-Cz-2
PBI-Cz-3
PBI-Ph
E(ox) (V)
+0.81
+0.87
E(red) (V)
1.25, 1.06
1.24, 1.09
1.25, 1.07
1.11, 1.33
+0.84
b
−
a
Cyclic voltammetry in N2-saturated DCM containing a 0.10 M Bu4NPF6. Counter
electrode is Pt electrode and working electrode is glassy carbon electrode,
Ag/AgNO3 couple as the reference electrode. b Not observed.
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Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C9TC06429J
Table 3. Driving forces of charge recombination (G0CR) and charge separation (G0CS) and the energy of charge separated state (CSS) for dyads in different solvents a
ΔG0CS (eV)
DCM
0.57
0.49
0.57
ΔG0CR (eV)
DCM
1.76
1.85
1.77
ECSS (eV)
DCM
1.76
1.85
1.77
TOL
ACN
TOL
ACN
TOL
2.27
2.27
2.20
ACN
1.62
1.70
1.65
PBI-Cz-1
PBI-Cz-2
PBI-Cz-3
0.06
0.07
0.14
0.71
0.64
0.69
2.27
2.27
2.20
1.62
1.70
1.65
aE00 = 2.34 eV was used for all PBI-Cz dyads. E00 is the approximated energy level with the cross point of UV−Vis absorption and fluorescence emission after normalization.
The calculation of ΔG0CS, ΔG0CR and ECSS values are based on electrochemical and optical measurements.
0.08
a
0.02
0.00
b
c
0.02
0.00
0.04
0.00
1763.8 s
1763.8 s
1727.8 s
-------------
35.8 s
773.2 s
746.5 s
-------------
26.6 s
0 s
1727.8 s
-------------
35.8 s
0 s
-0.02
-0.04
-0.06
-0.04
-0.08
-0.02
-0.04
0 s
300 400 500 600 700 800
Wavelength / nm
300 400 500 600 700 800
Wavelength / nm
300 400 500 600 700 800
Wavelength / nm
f
d
e
0.04
0.02
0.00
0.04
0.02
0.00
0.06

T = 179.6 s

T = 188.8 s
0.04
0.02
0.00
T = 109.7 s
0
500 1000 1500 2000
0
500 1000 1500 2000
0
500 1000 1500 2000
Time / s
Time / s
Time / s
Fig. 4 Nanosecond transient absorption spectra of (a) PBI-Cz-1, (b) PBI-Cz-2, (c) PBI-Cz-3, decay curves of (d) f PBI-Cz-1 ( 470 nm), (e) PBI-Cz-2 (470 nm) and (f) PBI-Cz-3 (470 nm).
ex = 525 nm (nanosecond pulsed laser), c = 1.0 × 10−5 M in deaerated toluene. 20 °C.

RP) species, thus, the ISC of the dyads discussed in this manuscript is
not due to RP ISC.67 The TR-EPR spectra of the dyads were also
recorded upon excitation at 355 nm (Fig. 5b). PBI-Cz-1 and PBI-Cz-3
gave similar spectra (Fig. 5b), both show the formation of two triplet
states, localized on the PBI and the Cz moiety, respectively. Instead,
PBI-Cz-2 leads to a spectrum in which only the Cz triplet is present.
Also for this species, the polarization is different from that obtained
from a regular SO-ISC of carbazole (Table 4).68 This result indicate
that the intramolecular triplet energy transfer is retarded at low
temperature.69 Notably, PBI-Cz-2 is with two intervening phenyl
moieties between the PBI and the Cz moieties, yet no RP ISC was
observed for this dyad, based on the ESP of the triplet state TREPR
spectrum. Interestingly, for the previously reported PBI-Ph2-PTZ
Y' X' Z
Z' X Y
Y' X' Z
PBI-Cz-1
Z' X Y
a
b
PBI-Cz-1
PBI-Cz-2
A
E
PBI-Cz-2
PBI-Cz-3
Cz-ISC
PBI-Cz-3
PBI-ISC
300
350
400
250 300 350 400 450
/ mT
B
/ mT
B
0
0
dyad, RP-ISC contributes significantly above 150
K (at low
Fig. 5 TR-EPR spectra with excitation at (a) 530 nm and (b) 355 nm in frozen solutions (T
80  130 K) of PBI-Cz-1, PBI-Cz-2, PBI-Cz-3 in toluene/MTHF (3: 1, v/v). The
temperature, the SO-ISC contributes more, accordingly the ESP
changed from aee/aae to eee/aaa with decreasing temperature).42
Another interesting result is that the tilting of the ZFS principal axes
of the PBI and the Cz moieties in the three dyads are different, yet
the ESP of the triplet state of the PBI moiety formed via the SOCT-ISC
are the same for the three dyads. This result is different from the
=
concentration was 3.0 × 105 M, but for PBI-Cz-2, the concentration was doubled because
of the poor signal intensity. The spectra in red are the simulations of the experimental
curves. Curve with PBI-ISC label in (a) refers to a simulation of a PBI triplet.42 and Cz-ISC
in (b) refers to a simulation of a Cz triplet state,68 both populated by a regular SO-ISC
mechanism, taken as reference.
6 | J. Mater. Chem. C, 2020, 00, 1-11
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ARTICLE
Table 5. Zero-field splitting parameters (D and E) and relative population rates PX,Y,Z of
previous report that the ESP is sensitive to the mutual orientation of
the electron donor and acceptor in SOCT-ISC electron
donor/acceptor dyads.53,69 Although SO-ISC was expected for all PBI-
Phn-PTZ (n = 1  5) at low temperature, yet the population ratio of
the three sublevels are different, for PBI-Phn-PTZ (n = 2  5), the X
and Y sublevels are almost equally populated. For PBI-Ph1-PTZ,
however, only one of the sublevels is overwhelmingly populated. Our
results for the three dyads are similar to the compact dyad PBI-Ph1-
PTZ.42 In other words, the ESP of the 3PBI triplet state of PBI-Phn-PTZ
( n = 1  5) accessed with the SO ISC can be either eee/aaa (PBI-Phn-
PTZ, n = 2  5), or eae/aea (PBI-Ph1-PTZ).42 In case of previously
reported PBI-PTZ derivatives, E value is negative (E < 0).42 But its sign
depends on the labelling of the components (see Fig. 5). Given D > 0
and E > 0 (Table 4), the alignment of the three sublevels of the T1
state is in the order of Y > X > Z (Y, X > 0, Z ˂ 0).46
View Article Online
the zero-field spin states of the dyads PBI-Cz-1, PBI-Cz-2 and PBI-Cz-3.a The spectra are
DOI: 10.1039/C9TC06429J
obtained as a different combination of the triplet spectra labeled as PBI and Cz, which
refer to triplets localized on either the PBI or the Cz moieties. The relative weight is
presented in the parenthesis. The excitation wavelength (ex. In nm) used for recording
the spectra was presented
ex
530
D (mT)
46.5 (100%)
E (mT)
4.2
Pz
1
Pz
0.18
Pz
0
PBI-Cz-1
PBI-Cz-2
PBI-Cz-3
530
530
355
46.8 (100%)
46.5 (100%)
4.4
4.3
1
1
0.15
0.25
0
0
PBI-Cz-1
(two triplet
states)
47.1 (20%)
118.8 (80%)
4.4
30.1
1
0
0.2
1
0
0.8
PBI-Cz-2
355
355
47.1 (100%)
4.4
1
0.2
0
Photochemical studies: reversible formation of radical anion in the
presence of sacrificial electron donor TEOA
PBI-Cz-3
(two triplet
states)
47.1 (70%)
118.8 (30%)
4.4
30.1
1
0
0.2
1
0
0.8
Photoreduction experiments were conducted in order to confirm the
potential application of the dyads in photocatalysis (Fig. 6). The PBI-
Cz dyads show efficient ISC, thus these compounds can be potentially
used as photocatalysts, to derive electron transfer.41 The UV-Vis
absorption changes of the dyads were monitored upon photo-
irradiation by xenon lamp in the presence of TEOA in acetonitrile.
Upon photo-irradiation, PBI-Cz-1 and PBI-Cz-3 show the formation of
PBI radical anion (PBI−•) absorption bands at 698 nm, 794 nm and 953
nm, in the presence of sacrificial electron donor triethanolamine
(TEOA).70−72 Emergence of of new absorption bands at 698 nm, 794
nm and 953nm, indicate the characteristic D0⟶Dn absorption of PBI
radical anion (PBI−•).70−72
For dyad PBI-Cz-3, the absorption band at 519 nm gradually
decreased in intensity under deaerated conditions in the presence of
TEOA upon photoirradiation. New absorption bands at 698 nm, 794
nm and 953 nm appeared and gradually increase in intensity with
time of irradiation (Fig. 6a). These gradually intensifying new NIR
bands indicates the formation of PBI radical anion (PBI−•). These new
NIR absorption bands attains maximum intensity upon 15 minutes of
photoirradiation under N2 environment and absorbance band at 519
nm was reduced to about 66% of the original signal intensity. When
the photoirradiated solution was exposed to air, the absorption
peaks in the near IR region disappeared, due to the oxidation of
radical anion (PBI−•). Reversibility of the persistent radical anion
formation was examined by photoirradiating the solution until 3
cycles (see ESI†, Fig. S20). The orange color of PBI-Cz-3 changed to
light blue upon radical anion formation and original color of
a
Obtained from simulations of the triplet-state TREPR spectra of the indicated
molecules in a frozen toluene matrix at 80 K upon excitation at 530 nm and 355
nm.
compound was restored upon exposure of the photoirradiated
solution to air (Fig. 6b). Similar phenomenon was observed in the
case another dyad PBI-Cz-1 (see ESI † , Fig. S19). For PBI-Cz-2, no
radical anion formation was observed as it aggregates in acetonitrile.
1.0
2, 4
(hv , N2)
b
a
1, 3, 5 (no light , air)
1
2
3
4
5
0.5
0.0
400 600 800 1000
Wavelength / nm
Fig.
6 (a) UVVis absorption spectra changes of PBI-Cz-3 upon continuous
photoirradiation in the presence of TEOA in the deaerated ACN and reversibility of the
formation of PBI radical anion upon photoirradiation; (b) Photos showing the reversible
color change of the PBI-Cz-3/TEOA mixed solution upon photoirradiation and re-
exposure to air: c [PBI-Cz-3] = 1.0  105 M, c [TEOA] = 1.0  104 M. The light source is a
xenon lamp, power density is 180 mW/cm2, photoirradiation time: 15 min. 20 C.
Table 4. Simulation parameters of the TR-EPR spectra of the PBI and Cz references in
Figure 5. The population rates of the different sublevels (PX, PY and PZ) and the calculated
ZFS principle values are also presented, together with the selected experimental values
from literatures.
DFT calculations
In order to rationalize the photophysical properties, the ground state
geometries of the perylenebisimide-carbazole (PBI-Cz) dyads were
optimized with DFT method by using CAM-B3LYP/6-31G (d) basis set.
The frontier molecular orbitals of the dyads were presented
(Scheme 2). For all the three dyads, the HOMO is mainly localized on
the Cz moiety, the LUMO is localized on the PBI moiety. This result
indicates the possibility of the electron transfer from Cz to PBI moiety
in the dyads upon photoexcitation. Moreover, the electron density
D (mT)
39.9
51.1
107.1
131.7
E (mT)
7.7
5.1
12.9
0.6
Px
0.8
─
1.0
─
Py
1.0
─
1.0
─
Pz
0.0
─
0.0
─
PBI-ISC a
PBI (calc)
Cz-ISC b
Cz (calc)
a From compound 3 in ref.42 Two electron-donating groups slightly reduce the ZFS-
values of the triplet state of PBI moiety. b Literature value.68
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC06429J
PBI-Cz-1
PBI-Cz-3
PBI-Cz-2
0.54
LUMO+1
LUMO
0.58
0.59
2.39
2.34
6.64
2.38
6.70
HOMO
6.76
7.07
7.02
HOMO–1
7.06
Scheme 2. Selected frontier molecular orbitals of PBI-Cz-1, PBI-Cz-2, and PBI-Cz-3 calculated at DFT (CAM-B3LYP/6-31G (d)) level with Guassian 09W. The energy levels of the
orbitals are presented (in eV).
of HOMO orbital also spread to the intervening phenyl moieties in all This geometry indicates the conformation restriction of the two
the dyads, but to a slightly less extent in PBI-Cz-2 compared to other carbonyl moieties. On the other hand the dihedral angle between the
dyads. In principle the separation of the HOMO/LUMO molecular intervening phenyl ring and the Cz moiety is 37.3°, indicating the
orbitals is prerequisite for the SOCT-ISC. Fully overlapped conformation restriction is weak.
HOMO/LUMO orbits usually do not facilitate ISC.73
The dihedral angle between the planes of carbazole and PBI in
The ground state geometries of the dyads were optimized (Fig. 7). PBI-Cz dyads was also determined (see ESI†, Fig S21). For PBI-Cz-1
For PBI-CZ-1 and PBI-CZ-3, the dihedral angle between the PBI and and PBI-Cz-3, the dihedral angle between carbazole and PBI planes is
the intervening phenyl moiety is 85.5°, almost orthogonal (Fig. 7).
ca. 49.2° and 24.7° respectively. It should be pointed out that the Cz
and the PBI moiety are not in orthogonal geometry, yet the ISC is
efficient. This result is different from previously reported electron
PBI-Cz-1
PBI-Cz-3
PBI-Cz-2
Fig. 7 Optimized conformations and the dihedral angles (degree) of the PBI and Cz units
in the dyads calculated by DFT (B3LYP/6-31G (d)) with Gaussian 09W.
Fig. 8 Spin density distribution of the triplet states of the PBI-Cz dyads obtained by
computation with DFT theory at (CAM-B3LYP/6-31G (d)) level using Gaussian 09W.
8 | J. Mater. Chem. C, 2020, 00, 1-11
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View Article Online
DOI: 10.1039/C9TC06429J
PBI-Cz-3
PBI-Cz-2
PBI-Cz-1
Anion
Cation
Fig. 9 Spin Density distribution of the PBI-Cz dyads anions and cations, obtained by computation with DFT theory at (UB3LYP/6-31G (d)) level using Gaussian 09W.
donor/acceptor dyads showing SOCT-ISC, in which orthogonal population in high polar solvent can be the fast CR process which
geometry was desired.46−48,52
competes strongly with SOCT-ISC. The Jablonski diagrams
The electron spin density surfaces of the T1 states of the dyads demonstrating photophysical process involved in other two dyads
were studied (Fig. 8). For all the three dyads, the triplet states are all (PBI-Cz-1 and PBI-Cz-2, see ESI†)
confined on the PBI moieties; there is no spin leakage to the
intervening phenyl moieties. These results are in agreement with the
TREPR results (D and E parameters, Table 4). The electron spin
Conclusions
density surfaces of the radical anion and radical cations of the dyads
were also studied (Fig. 9). This characterization shows the
localization of the hole and electron of the CT states. The results
show the hole is confined on the electron donor carbazole moiety
and the intervening phenyl rings. The electron is localized on the
electron acceptor PBI units.
The photophysical processes of the dyads upon photoexcitation
are summarized in Scheme 3. PBI is a visible light-harvesting
chromophore, upon photoexcitation, ultrafast CS occurs (supported
by the quenched fluorescence of the PBI moiety and fast decay of the
LE emission), CT state is formed. The subsequent CR will lead to
formation of 3LE states. Since the CT state energy level will decrease
in polar solvents, the matching of the 1CT state and the Tn state may
change, as a result, the ISC efficiency is highly solvent polarity-
dependent. The singlet oxygen quantum yields are high in toluene
(Table 1), but the singlet oxygen quantum yields in polar solvents are
much lower. Another possible reason for inefficient triplet
In summary, we prepared a series perylenebisimide (PBI)-carbazole
(Cz) electron donor/acceptor dyads to study the spin orbital charge
transfer (SOCT-ISC) induced intersystem crossing in these dyads. The
molecular conformation was varied by changing the mutual
orientation and distance between perylenebisimide donor and
carbazole acceptor. Negligible ground state electronic coupling
between the PBI and Cz moiety was observed in all the dyads. High
singlet oxygen quantum yields ( = 38 ~ 72%) were observed,
especially in case of PBI-Cz-3 in which the donor and acceptor are
separated by smallest distance. All the dyads shows the long-lived
PBI localized triplet state (T is up to 190 s), confirmed by
nanosecond transient absorption spectroscopy. It should be noted
that dyads (PBI-Cz-1 and PBI-Cz-3) with one phenyl spacer between
donor and acceptor adopts non-orthogonal geometry, but the ISC is
still efficient, which is different from the previously reported
molecular structural profiles which require orthogonal geometry for
efficient SOCT-ISC. Time-resolved electron paramagnetic resonance
(TREPR) spectroscopy reveals that all three dyads have same electron
spin polarization of eae/aea, which is different from the SO-ISC
(eee/aaa), thus confirming the SOCT–ISC mechanism. Moreover,
upon photoirradiation, PBI-Cz-1 and PBI-Cz-3 show the formation of
near-IR absorbing PBI radical anion (PBI−•) in the presence of
sacrificial electron donor (TEOA). These results are useful for future
design of heavy atom-free triplet photosensitizers and for study of
the charge recombination in the electron donor/acceptor dyads.
Experimental section
Materials and methods
All chemical used in the study are of analytical grade and used as
received. UVVis absorption spectra were recorded on a UV-2550
UVVis spectrophotometer (Shimadzu Ltd., Japan). Fluorescence
Scheme 3. Jablonski diagram demonstrating the photophysical processes involved in PBI-
Cz-3 upon photoexcitation. The energy levels of the excited state are derived from the
spectroscopic data and energy level of charge separated (CS) state are determined from
electrochemical data. The triplet energy levels are estimated by TD-DFT method (in
toluene). The numbers in superscripts indicates the spin multiplicity.
spectra were obtained with
a RF-5301PC spectrofluorometer
(Shimadzu Ltd., Japan). Fluorescence lifetimes were measured by
OB920 luminescence lifetime spectrometer (Edinburgh Instruments
Ltd, U.K.).
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Synthesis
Journal of Materials Chemistry C
Nanosecond transient absorption spectroscopy
View Article Online
DOI: 10.1039/C9TC06429J
The detail of the synthesis and characterization of compounds 1, 2, 3
and PBI-Ph are given in the ESI†.
LP980 laser flash photolysis spectrometer (Edinburg
Instruments, U.K.) equipped with Tektronix TDS 3012B
oscilloscope was used to study the nano- and microsecond
dynamics. The samples were deaerated with N2 for 15 min prior
to investigations. The data was processed by L900 software.
Synthesis of PBI-Cz-1: Under N2 atmosphere, compound 1 (100 mg,
0.16 mmol), 9-phenyl-9H-carbazol-3-ylboronic acid (92 mg, 0.32
mmol) and K2CO3 (100 mg, 0.72 mmol) were dissolved in 25 mL mixed
solvent of PhCH3/EtOH/H2O (4/2/1, v/v). The reaction mixture was
deoxygenated by using vacuum pump and N2 purging for 20 minutes.
Then Pd(PPh3)4 (20 mg, 5 mol%) was added and reaction mixture was
refluxed for 8 h under nitrogen atmosphere. After completion of
reaction, the reaction mixture was cooled to room temperature,
extracted with CH2Cl2 (30 mL), washed with water (2 × 100 mL) and
dried over anhydrous sodium sulfate. After evaporation of solvent
under reduced pressure, the crude product was further purified with
column chromatography (Silica gel, CH2Cl2/petroleum ether, 2/1, v/v)
Time-resolved electron paramagnetic resonance (TREPR)
spectroscopy
The solutions containing the compounds PBI-Cz-1, PBI-Cz-2, PBI-Cz-
3 (Scheme 1) in toluene/MTHF (3:1, v/v) 3  105 M were prepared,
the solutions were transferred into 3 mm (i.d.) quartz tubes and
sealed under vacuum after removing dissolved gas by a few freeze-
pump-thaw cycles. TR-EPR spectra were recorded with an Elexsys
Bruker EPR spectrometer, equipped with a dielectric cavity placed
inside an Oxford CF595 cryostat with an optical access for irradiation
of the sample by a pulsed laser. A Quantel Nd:YAG laser provided
pulsed light (6 ns duration) for the photoexcitation of the sample in
the visible range with an OPO pumped by 355 nm pulses (also
available for irradiation of the sample).
1
to give red solid (75 mg, yield: 60 %). mp  250 C. H NMR (CDCl3,
400 MHz);  8.79 (d, 2H, J = 8.0 Hz), 8.72–8.67 (m, 6H), 8.43 (s, 1H),
8.22 (d, 1H, J = 4.0 Hz), 7.92 (d, 2H, J = 8.0 Hz), 7.73 (dd, 1H, J = 8.0
Hz), 7.67–7.61 (m, 4H), 7.52–7.44 (m, 6H), 7.36–7.30 (m, 1H), 5.12–
5.05 (m, 1H), 2.32–2.23 (m, 2H), 2.02–1.91 (m, 2H), 0.94 (t, 6H, J =
8.1 Hz). TOF MALDIHRMS (C53H35N3O4‒) Calcd: m/z = 777.2628.
Found: m/z = 777.2606.
Acknowledgements
Synthesis of PBI-Cz-2: Under N2 atmosphere, compound 1 (100 mg,
0.16 mmol), (4-(9-carbazolyl)benzeneboronic acid (92 mg, 0.32 mmol)
and K2CO3 (100 mg, 0.72 mmol) were dissolved in 25 mL mixture of
PhCH3/EtOH/H2O (4/2/1, v/v). The reaction mixture was
deoxygenated by N2 purging for 20 minutes. Then Pd(PPh3)4 (20 mg,
5 mol%) was added and reaction mixture was refluxed for 8 h under
N2 atmosphere. After completion of reaction, the reaction mixture
was cooled to room temperature, extracted with CH2Cl2 (30 mL),
washed with water (2 × 100 mL) and dried over anhydrous sodium
sulfate. After evaporation of solvent under reduced pressure, the
crude product was further purified with column chromatography
(silica gel, CH2Cl2/petroleum ether, 2/1, v/v) to give red solid (60 mg,
yield: 48 %). mp  250 C. 1H NMR (CDCl3, 500 MHz);  8.81 (d, 2H, J
= 10.0 Hz), 8.73–8.72 (m, 6H), 8.18 (d, 2H, J = 5.0 Hz), 7.90–7.89 (m,
4H), 7.70 (d, 2H, J = 10.0 Hz), 7.53–7.50 (m, 4H), 7.47–7.44 (m, 4H),
5.13–5.06 (m, 1H), 2.33–2.25 (m, 2H), 1.99–1.93 (m, 2H), 0.94 (t, 6H,
J = 8.0 Hz). TOF MALDIHRMS (C53H35N3O4‒) Calcd: m/z = 777.2628.
Found: m/z = 777.2637.
J. Z. thanks the NSFC (21673031, 21761142005, 219911530095 and
21421005), the State Key Laboratory of Fine Chemicals
(ZYTS201901), the Fundamental Research Funds for the Central
Universities (DUT2019TA06) and Department of Chemical Science,
University of Padua, Italy (Visiting Scientist) for support.
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Journal of Materials Chemistry C
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Journal of Materials Chemistry C
Page 12 of 12
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DOI: 10.1039/C9TC06429J
Table of Contents Entry:
Carbazole-Perylenebisimide Electron Donor/Acceptor Dyads Showing
Efficient Spin Orbit Charge Transfer Intersystem Crossing (SOCT-ISC) and
Photo-Driven Intermolecular Electron Transfer
Noreen Rehmat,a Antonio Toffoletti,b Zafar Mahmood,c Xue Zhang,a Jianzhang Zhao*a and
Antonio Barbon b
Efficient spin orbit charge transfer intersystem crossing (SOCT-ISC) was demonstrated in non-
orthogonal compact carbazole-perylenebisimide electron donor/acceptor dyads.