Corrole-phenothiazine and porphyrin-phenothiazine dyads connected at β-position: Synthesis and photophysical properties

Article abstract of DOI:10.1016/j.dyepig.2017.04.062

Two novel donor-acceptor dyads, in which phenothiazine (PTZ) connected at β-pyrrolic position of either freebase corrole (TPC) or freebase porphyrin (TPP) via vinylic spacer have been synthesized. Both the dyads were characterized by ESI-MS, IR, ¹H NMR (1D and 2D ¹H-¹H COSY and J-Resolved), UV–Vis, Study state Fluorescence, Time-resolved fluorescence (Time-correlated single photon counting (TCSPC), Streak Camera) as well as electrochemical methods. In the absorption spectra of the dyads, both Soret and Q-bands were red shifted by 8–20?nm indicating weak electronic communication between the two chromophores. However, the fluorescence emission from the PTZ of the dyad was efficiently quenched (96–99%) as compared to pristine PTZ where the dyad was excited at 310?nm, which is attributed to singlet-singlet excited energy transfer. Fluorescence emission from porphyrin part of the TPP-PTZ dyad also quenched when excite the dyad at 420?nm, which is ascribed to photoinduced electron transfer from ground state of PTZ to excited state of porphyrin. In contrast, when excite the corrole at 420?nm in TPC-PTZ dyad, we found there are no significant changes in photophysical properties. In both the cases the solvent dependence of the rate of energy and electron transfer was observed.

Full text of DOI:10.1016/j.dyepig.2017.04.062

Accepted Manuscript
Corrole-phenothiazine and porphyrin-phenothiazine dyads connected at β-position:
Synthesis and photophysical properties
Jaipal Kandhadi, Fan Cheng, Hua-Hua Wang, Atif Ali, Li-Li Wang, Hui Wang, Hai-
Yang Liu
PII:
S0143-7208(17)30560-0
10.1016/j.dyepig.2017.04.062
DYPI 5959
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 19 March 2017
Revised Date: 28 April 2017
Accepted Date: 28 April 2017
Please cite this article as: Kandhadi J, Cheng F, Wang H-H, Ali A, Wang L-L, Wang H, Liu H-Y, Corrole-
phenothiazine and porphyrin-phenothiazine dyads connected at β-position: Synthesis and photophysical
properties, Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.04.062.
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Graphical Abstract

ACCEPTED MANUSCRIPT
Corrole-phenothiazine and porphyrin-phenothiazine dyads connected at β-
position: synthesis and photophysical properties
a
b
b
b
a
a,
b,
Jaipal Kandhadi , Fan Cheng , Hua-Hua Wang , Atif ali , Li-Li Wang , Hui Wang *, Hai-Yang Liu *
a
State Key Laboratory of Optoelectronics Materials and Technologies, Sun Yat-Sen University, Guangzhou 510275, China.
b
Department of Chemistry, Laboratory of Functional Molecular Engineering of Guangdong Province, South China University of Technology,Guangzhou,510641, China.
Keywords: Donor-Acceptor, Porphyrin, Corrole, Energy-transfer, Electron-transfer, Phenothiazine.
A B S T R A C T
Two novel donor-acceptor dyads, in which phenothiazine (PTZ) connected at β-pyrrolic position of either freebase
corrole (TPC) or freebase porphyrin (TPP) via vinylic spacer have been synthesized. Both the dyads were
1
1
1
characterized by ESI-MS, IR, H-NMR (1D and 2D H- H COSY and J-Resolved), UV-Vis, Study state
Fluorescence, Time-resolved fluorescence (Time-correlated single photon counting (TCSPC), Streak Camera) as
well as electrochemical methods. In the absorption spectra of the dyads, both Soret and Q-bands were red shifted by
8
-20 nm indicating weak electronic communication between the two chromophores. However, the fluorescence
emission from the PTZ of the dyad was efficiently quenched (96-99%) as compared to pristine PTZ where the dyad
was excited at 310 nm, which is attributed to singlet-singlet excited energy transfer. Fluorescence emission from
porphyrin part of the TPP-PTZ dyad also quenched when excite the dyad at 420 nm, which is ascribed to
photoinduced electron transfer from ground state of PTZ to excited state of porphyrin. In contrast, when excite the
corrole at 420 nm in TPC-PTZ dyad, we found there are no significant changes in photophysical properties. In both
the cases the solvent dependence of the rate of energy and electron transfer was observed.
1
. Introduction
Photosynthesis is the one of most important processes driven by nature, in which the energy in sunlight is introduced
into the biosphere. Chlorophyll is the centerpiece of photosynthesis, it performs core functions of the process that is
the cascade of photoinduced energy and electron transfers between different donors and acceptors in the antenna
complexes and the reaction center. For example, the photosynthetic unit of purple bacteria has several hundreds of
bacteriochlorophylls (BChls) and carotenoids (Car’s) to absorb the light, these multichromophoric systems transport
the absorbed energy via singlet-singlet photoinduced energy transfer (PEnT) and subsequently, an electrostatic
potential [1]. Interestingly most of the BChls serve as antennae, collecting sunlight and transferring its energy, only
a few BChls participate in the electron transfer reaction, termed the photosynthetic reaction center, where the
excitation energy converts to chemical energy in the form of transmembrane charge separation and achieves a long
lived charge separated state via a series of photoinduced electron transfer reactions [2, 3]. Carotenoids in the antenna
systems not only transfer their singlet energy but also act as photoprotective pigments by transferring triplet energy
out of the chlorophyll system, thereby preventing chlorophyll-sensitized singlet oxygen formation which is harmful
to the organism [4-6]. In order to elucidate the complex events in primary process and the mechanism of the charge
separation process to achieve the long lived charge separated (CS) state, much effort has been devoted to the
construction of artificial photosynthetic model systems [7-18]. Although significant progress has been achieved in
this area, research towards exploring for new systems that differ from existing systems in photosensitizer,
geometrical arrangement, spacer and position of substitution of donor to acceptor etc..., are in great demand because
of their applications in constructing optoelectronic devices [19-22] and DSSC applications [23-26].
Owing to its close resemblance to the natural tetrapyrrolic pigment and relatively easy synthetic manipulations to
attain the desired photophysical properties as well as its rich redox chemistry, the porphyrin chromophore served as
the primary photoactive molecule has dominated this area of research [27–32]. Additionally, many other tetra
pyrrolic analogs were also used as photosensitizers to construct donor-acceptor systems, to achieve the long lived
charge transfer state [13, 33-35], corroles are contracted analogues (direct pyrrole-pyrrole bond) of porphyrin and
are particularly important due to their remarkable electrochemical and photophysical properties such as high
fluorescence quantum yields, larger Stokes shifts, high molar extinction coefficients, stabilization of higher
oxidation states of transition metal ions and lower oxidation potentials [16]. Corrole has pulled out from the
backwater after the synthetic breakthroughs by Gross and Paolesse [36, 37], which have opened the door to more
1

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extensive research. It is important to mention that, the role of either an energy/electron donor or acceptor depends on
the nature of counter molecular entity of the porphyrin/corrole (vide infra), by utilizing this, many donor-acceptor
(
D-A) systems have been constructed with different energy/electron donors such as ferrocene [38], anthracene [39],
carbazole [40], coumarin [41], triphenylamine [42], fluorene [15], pyrene [15], BODIPY [43], carotenyls [5],
tetrathiafulvalenes [44], oligothiophenes [45], xanthenes [46] and azulene [47] connected either with porpyrin and/or
corrole have been studied. On the other hand the efficient electron acceptors such as C , anthraquinone [8],
60
naphthalenediimide (NDI) were also reported [27, 28]. However, the majority of these dyads, triads or tetrads are
connected at either a meso or axial position of porphyrin/corrole but D-A systems connected at β-position are
relatively scarce in the literature.
Apart from the aforementioned donors, a tricyclic heteroaromatic chromophores such as phenothiazines (PTZ) have
gained much attention due to their interesting structural, photophysical and electrochemical properties such as low
oxidation potential and a high propensity to form stable radical cations [48]. One of the important structural features
of the PTZ ring is that, it is non-planar in the ground state with a butterfly conformation, which can impede the
molecular aggregation and the formation of intermolecular excimer [49]. These promising electronic and optical
properties of PTZ make them as good candidates in dye sensitized solar cells [25, 26] and organic light emitting
diodes [50, 51].
Many D-A systems containing PTZ have been constructed, for example Meyer et al. reported intramolecular
II
2+
photoinduced electron transfer in Ru-Bipyridine-Quinone complex ([Ru (bpy-AQ) (bpy-PTZ)] ) in which PTZ is
2
electron donor, quinone is electron acceptor [52]. D’Souza et al. reported the solvent effect and substitution effect
on the photoinduced charge separation and recombination in PTZ-BODIPY-fullerene triads [53]. Other D-A systems
such as PTZ-C60 dyads [54], PTZ-pyrene dyads [55], D-bridge-A motif containing PTZ and bis (dicarboximide)
[
56], PTZ- benzothiazole dyads [57] and PTZ-BODIPY dyads [49] have been reported. Very few reports are
available with the combination of PTZ and either corrole or porphyrin chromophores. For example, Liu et. al.
reported corrole-PTZ dyads in which PTZ connected via ester linkage at the meso-position of corrole [58], Ran Lu
et. al. reported PTZ appended porphyrin [59].
An analysis of the results of the D-A systems, in which donor subunits directly connected to corrole/porphyrin,
suggests that neither the directly attached donor entity nor the corrole/porphyrin itself retains its individual
characteristics in these systems (vide infra). It is important to mention that, to modulate the electronic properties of
corrole/porphyrin, β-substitution is of great interest because it directly affects the 18π-electron system. Bearing these
features in mind, here we report the synthesis and photophysical properties of corrole-phenothiaziene (TPC-PTZ)
and porphyrin-phenothiazine (TPP-PTZ) dyads, connected via vinylic spacer at β-position of the macrocycle. In
these systems, PTZ is an energy/electron donor and porphyrin/corrole as energy acceptor. Both the dyads were
systematically investigated by spectroscopic and electrochemical methods and computational studies. All of the
energy/electron transfer studies were studied in four different solvents and the effect of solvent polarity on rates of
energy and electron transfer were described.
2
. Materials and methods
2
.1. General
All chemicals were used as received unless otherwise noted. Spectroscopic grade solvents (CH Cl , DMF, MeCN,
2
2
and PhMe) were used to measure absorption, emission and electrochemical properties. Thin-layer chromatography
TLC) was performed on silica gel 60 F254 (pre-coated aluminum sheets) from Merck. Column chromatography was
performed on silica (200 400 mesh). In all cases dual solvent system was used and the major band was collected.
(
̴
All the reactions were carried out under nitrogen or argon atmosphere using degassed solvents and the apparatus was
shielded from ambient light.
2
.2. Instrumentation
1
H NMR spectra were recorded on Avance- 400 MHz and Bruker 600 MHz spectrometers in CDCl and TMS as an
3
internal standard. ESI-MS spectra were recorded on an Esquire HCT PLUS. Study-state absorption and emission
spectra of the samples were measured using a PerkinElmer Lambda 850 UV-Visible Spectrophotometer and Perkin
Elmer LS55 luminescence Spectrophotometer (PE Company, USA) respectively. Fluorescence spectra were
2

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o
recorded at 25 C in a 1 cm quartz fluorescence cuvette. The cyclic voltammograms (CV) were performed using
CHI-660E electrochemical analyzer. The electrochemical experiments were performed on 1mM sample solution in
dichloromethane solvent using 0.1 M tetrabutyl ammonium hexafluorophosphate (TBAPF ) as supporting
6
electrolyte. The working electrode is glassy carbon, (Ag/AgCl) is the reference electrode and plantinum wire is an
auxillary electrode. The time-resolved fluorescence decays of all samples were measured by using time-resolved
fluorescence spectroscopic technology. A Nd:YAG laser (EKSPLA PL2143) and an PG401SH/DFG2 10 ps laser
(
EKSPLA Co., Lithuania) were employed to generate the excitation pulses with 10 Hz repetition, a full width at
half-maximum (fwhm) of 25 ps. For picoseconds resolution the fluorescence emitted from sample was collected
with a set of lenses with big caliber and recorded by a streak camera (Hammatsu C1587) and a CCD (C4742-95)
after passing through a monochromator.
3
. Experimental
3
.1. Synthesis of precursors
The compounds 5,10,15,20-tetraphenyl porphyrin, triphenyl[[(5,10,15,20-tetraphenyl porphyrin-2-yl]methyl]
phosphonium chloride(TPP-PPh Cl) [60], 5,10,15-Triphenyl corrole (TPC), Triphenyl[[5,10,15-triphenylcorrole-3-
3
3
yl]methyl]phosphonium bromide (TPC-PPh ·Br) [15] and organic precursor, 10-Methyl-10H-phenothiazine (PTZ)
and 10-Methyl-10H-phenothiazine-3-carbaldehyde (PTZ-CHO) [61] were prepared according to reported
procedures.
3
.2. Synthesis of dyads
3
.2.1. Synthesis of 5,10,15,20-tetraphenyl-2-(10-methyl-3-phenothazine-1-yl-vinyl)porphyrin (TPP-PTZ): Wittig–
Horner reaction was successfully employed in the synthesis of this dyad. Phosphonium salf of porpyrin TPP-PPh
3
Cl
(
100 mg, 0.108 mmol), PTZ-CHO (30 mg, 0.124 mmol) were dissolved of CH Cl (15 mL) and DBU (95 mg, 0.625
2
2
mmol) was added, immediately color change was observed, continued stirring for 5 min at RT. The reaction
mixture was subjected to flash chromatography using CH Cl /Hexane 1:1 as eluant, and collected first two spots,
2
2
2 2 ,
evaporated to dryness under vaccuo. The obtained solid was redissolved in CH Cl (20 mL) to this catalytic amount
of I (0.0018 g) was added for cis–trans isomerization and the reaction mixture was stirred at RT for 16 h under inert
2
atmosphere. The reaction mixture was washed with 1M Na S O solution in water and extracted with CH Cl , dried
2
2
3
2
2
over sodium sulfate, solvent was evoparated and the obtained solid material was further purified by silica gel
column chromatography using CH Cl /Hexane (1:1) as eluant to get the desired trans isomer as a purple solid with
2
2
o
-1
8
7
7
6
1
1
1
2% yield; mp > 300 C ; IR (KBr, ν, cm ): 3300, 3055, 2920, 2859, 1563, 1465, 1336, 1253, 1147, 1069, 960, 795,
1
44, 701. H NMR (CDCl , 600 MHz) δH: 8.91 (s,1H), 8.79 - 8.66 (m, 6H), 8.22-8.12 (m, 8H), 7.78-7.65 (m, 12H),
3
.18 (d, 1H, J = 16 Hz), 7.14 -7.09 (q, 2H), 6.99 - 6.95 (t, 2H, J = 6.97 Hz), 6.92- 6.87 (t, 1H, J = 6.89 Hz), 6.80 –
13
.71 (q, 2H), 6.66 – 6.63 (d, 1H, J = 6.64 Hz), 3.43(s, 3H), -2.57(s, 2H). C NMR (CDCl , 600 MHz) δC: 145.46,
3
45.04, 142.72, 142.34, 142.32, 141.99, 134.61, 134.58, 134.53, 134.32, 132.50, 129.55, 128.69, 127.77, 127.74,
27.48, 127.34, 127.23, 126.78, 126.74, 126.71, 126.68, 124.65, 123.61, 123.20, 122.98, 122.55, 120.55, 120.04,
19.94, 119.58, 114.13, 113.82, 35.41.Anal. Calcd. For C H N S, % (852.06): C, 83.15; H, 4.80; N, 8.24; S, 3.71.
59
41
5
Found C, 83.13; H, 4.76; N, 8.20; S, 3.69. ESI-MS ((m/z): C59
41 5
H N S [852]: 852.55(100%).
3
.2.2. Synthesis of 5,10,15 triphenyl-3-(10-methyl-3-phenothazine-1-yl-vinyl)corrole (TPC-PTZ): The dyad was
synthesized by slightly modifying the literature procedure [15]. 10-Methyl-10H-phenothiazine-3-carbaldehyde (12
mg, 0.049 mmol), 18-crown-6 (10 mg, 0.04 mmol), anhydrous potassium carbonate (15 mg, 0.1 mmol) and corrole
+
-
phosphonium salt TPC-CH -PPh Br (50 mg, 0.055 mmol) were dissolved in dry DMF (6 mL). The reaction mixture
2
3
o
was stirred at 0 C for 4 h under nitrogen atmosphere. The reaction mixture was poured into water and green
compound extracted with CH Cl2 (a mixture of cis-trans isomers), which was then subjected to column
2
chromatography in silica gel by CH Cl /Hexane (1:1), the solvent was evaporated in vacuo and the resulting solid
2
2
was dissolved in 30 mL dry THF followed by reflux in the presence of catalytic amount iodine for 8 h. The mixture
was poured into aqueous NaOH solution (0.5 M) to remove excess iodine. The organic layer was extracted with
2 2 2 4 2 2
CH Cl , dried over Na SO . Then, the CH Cl was evaporated and the resulting residue was purified by silica gel
column chromatography using dichloromethane-hexane (1:2) as eluent to give the trans-isomer as greenish solid
o
-1
with 65% yield; mp > 300 C; IR (KBr, ν, cm ): 3450, 3070, 2933, 1596, 1465, 1289, 1256, 1125, 1041, 960, 793,
1
7
7
49, 701. H NMR (CDCl , 600 MHz) δH: 8.98- 8.54 (m, 4H), 8.39 (s, 2H), 8.32-7.95 (m, 6H), 7.92-7.41 (m, 10H),
3
.34 (d, 1H, J = 16 Hz), 7.16 (d, 2H, J = 7.14 Hz), 7.02 – 6.80 (m, 4H), 6.79 - 6.57 (m, 2H), 3.31 (s, 3H), -2.37 (s,
3

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1
3
3
1
1
8
H). C NMR (CDCl , 600 MHz) δC: 166.71, 165.40, 165.31, 136.58, 135.88, 131.49, 129.83, 129.30, 129.24,
3
28.01, 127.79, 127.71, 127.67, 127.47, 127.27, 127.20, 126.82, 126.75, 126.53, 126.52, 126.19, 125.18, 121.73,
13.16, 112.74, 112.06, 36.10. Anal. Calcd. For C H N S, (763.95): C, 81.70; H, 4.82; N, 9.10; S, 4.22. Found C,
1.69; H, 4.80; N, 9.08; S, 4.20. ESI-MS ((m/z): C H N S [764]: 764.40 (100%).
52
37
5
52
37
5
4
. Results and discussion
4
.1. Synthesis and structure characterization
Fig. 1 illustrates the synthesis of both the dyads including PTZ formylation. The preparation of both the dyads
TPC-PTZ and TPP-PTZ) was started with formylation of TPP/TPC at β-position by Vilsmeier–Haack reaction
using DMF and POCl as reagents, according to reported procedures [60, 15]. The formyl derivatives (TPC-
(
3
CHO/TPP-CHO) were reduced by using NaBH
4
in ethanol at room temperature to afford their corresponding
reduced products (TPC-CH OH/TPP-CH OH). The preparation of wittig salt of both macrocycles are slightly
2
2
+
-
different, corrole wittig salt (TPC-CH
2 3 2
PPh Br ) was obtained by treating TPC-CH OH with
triphenylphosphoniumhydro bromide (PPh ·HBr), whereas for the porphyrin, an extra step is needed. The reduced
3
product (TPP-CH
2 2
OH) was firstly converted to its halo derivative (TPP-CH -Cl) by treating with pyridine and
SOCl according to literature [60], followed by treating with triphenylphosphine (PPh ) results the porphyrin wittig
2
3
+
-
salt (TPP-CH PPh Cl ). Wittig-Horner reaction holds good for the synthesis of double bond between macrocycle
2
3
and PTZ, reagents and conditions see Fig.1. In both cases, an additional step was necessary (cis-trans isomerization
by catalytic amount of I see experimental section) to obtain trans isomer predominantly.
2
,
Preliminary characterizations of both the dyads were carried out by ESI-MS and UV–Vis spectroscopic methods.
+
The ESI mass spectrum of both the dyads TPC-PTZ and TPP-PTZ showed peaks at m/z = 764 ([M] ,C52H N S) and
8
37 5
+
1 13
52 ([M] ,C H N S), are ascribable to the molecular-ion peak (supporting information, Fig. S1and S2). H and C
59 41 5
NMR spectra of both the dyads including PTZ (10-Methyl-10H-phenothiazine) are presented in the ESI (Fig. S3-
S10). In both the dyads the presence of the singlet corresponds to N-methyl group of PTZ at 3.43 ppm in TPP-PTZ
and 3.31 ppm in TPC-PTZ indicating the incorporation of PTZ unit with porphyrin/corrole. Moreover, the formation
of two doublets corresponding to vinylic protons at 7.18 and 6.87 ppm in TPP-PTZ and 7.34 and 6.85 ppm in TPC-
1
1
PTZ dyad are the diagnostic protons for the formation of the dyads, additionally H- H COSY spectrum
unumbiguisoly confirms their connectivity in both the dyads (supporting information Fig. S11 and S12). In both
dyads the aforementioned doublets appears as 16 Hz coupling constants in two Dimensional-J-Resolved spectra
(
supporting information, Fig.S13) unequivocally confirms the presence of exclusive E-isomer. In addition to this the
trans nature of the double bond further conformed by IR spectra (supporting information, Fig. S14 and S15) the
-1
presence of 960 cm band in both the dyads corresponding to wagging vibration of trans-double bond (vide infra)
clearly evidencing the presence of E-isomer in both the dyads.
Fig. 1. Synthetic scheme of the dyads.
4

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4
.2. Optical Absorption Spectra
The absorption spectra of the dyads along with their constituent monomers in CH
Wavelength of maximum absorption and molar extinction coefficients are summarized in Table 1. The pristine PTZ
shows two peaks at 253 and 310 nm in CH Cl arising from localized aromatic π-π* transitions [49].The absorption
spectra of both the dyads are mere superposition of the absorption spectra of monomers in which the PTZ transitions
dominated by transitions of corrole/porphyrin, that is S →S (Q-band) and S →S (Soret band), due to their high
2 2
Cl solvent are shown in Fig.2.
2
2
0
1
0
2
molar extinction coefficients. The incorporation of the PTZ at the β-position of the porphyrin/corrole results in the
following changes in the absorption spectra in both the dyads: (i) red shift (8-10 nm) and broadening of the Soret
bands; (ii) red shift (11-20 nm) and broadening of Q-bands. The red shift might be due to presence of donor-
acceptor type of molecular arrangement which promotes extending electron delocalization thus leads to ground state
stabilization. In contrast, broadening can also be due to many conformers at different orientations of
corrole/porphyrin around the two (-C=C-) double bonds. In addition to this, a split in the Soret band of corrole in
TPC-PTZ was also observed; this is probably due to bulky substitutions at the β-position of corrole, which lowers
the symmetry. These observations of broadening, red-shift and split in the Soret band suggests that weak electronic
interaction between the PTZ either with porphyrin or corrole [38]. The absorption spectra of both dyads along with
their monomers in different solvents (MeCN, DMF and PhMe) have shown in (Supporting info. Fig. S16), from
these spectra, we observed that the solvent effect on absorption spectra of all the tested samples, in solvents with
varying polarity is more or less similar except TPC and its dyad in DMF, it is important to mention that, corroles
exhibit significant solvent-dependent absorption than its analogues porphyrin, our results also in line with the earlier
reports [62].
Fig. 2. Optical absorption spectra of the dyads along with their monomers in CH
.3. Electrochemical properties
2 2
Cl .
4
To evaluate the redox potentials which are useful for the understanding of the site of electron transfer of the
individual redox units, we have carried out differential pulse voltammetry (DPV) and cyclic voltammerty (CV)
experiments. Fig. 3 depicts the differential pulse voltammograms of both the dyads along with their monomers. Both
the dyads were investigated under the same experimental conditions (CH Cl , 0.1 M TBAPF ) and the redox data
2
2
6
are summarized in Table 1. From Fig. 3 it is evident that both the dyads exhibits four oxidations and two reduction
peaks. Wave analysis suggested that the first two oxidation steps are reversible (ipc/ipa 1 and ∆E = 65±3 mV)
̴
p
reactions, and two reductions are quasi reversible (E -E = 95-160 mV). The pristine PTZ shows one reversible
pc pa
+
oxidation at E1/2 = 0.76 fallowed by one quasi-reversible oxidation at 1.46 V vs Ag/Ag , during the cathodic
scanning we did not find any reduction corresponding to PTZ within the experimental window (0 to -2 V vs
+
Ag/Ag ), our results are in agreement with the literature [63]. In order to understand the charge transfer states (ECT),
the first oxidation/ reduction only necessary. In TPP-PTZ first one-electron oxidation was found at 0.67 V vs
Ag/Ag+ corresponding to PTZ oxidation and second oxidation at 0.98 V corresponding to porphyrin, in contrast to
this, first oxidation at 0.51 V corresponding to corrole core and second oxidation at 0.79 V corresponding to PTZ in
TPC-PTZ. PTZ oxidation was found to be easier by 100 mV in TPP-PTZ whereas in TPC-PTZ harder to oxidize by
1
3
0 mV, the similar anodic and cathodic shifts were also reported in the literature [53]. Collectively, H-NMR, UV-
Vis and electrochemical data indicate that there is no significant electronic interactions between the hetero
chromophores in these dyads, giving an opportunity to excite the selective chromophores to enquire photophysical
properties at different wavelengths.
5

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Fig. 3. Differential pulse voltammograms of the dyads along with their monomers in CH
2
Cl
2
containing 0.1M
-1
TBAPF , with scan rate 100 m Vs .
6
Table 1
UV−Visible and Electrochemical Data of TPC, TPP, PTZ, TPC-PTZ and TPP-PTZ.
-1
-1
a
+b
Absorption, λmax, nm (log ε, M cm )
Potential V vs Ag/Ag
Compound
TPC
Corrole/ Porphyrin bands
PTZ- bands
Oxidation
Reduction
416(4.83), 573(4.14), 616(4.02), 650(3.95)
-
0.58, 1.49
-0.98, -1.91
-1.23, -1.56
4
18(6.05),515(4.53),551(4.15)
TPP
-
0.98,1.32, 1.84
592(3.99), 647(3.85)
PTZ
-
255(4.92), 310(3.5)
285(3.5), 310(3.49)
277 (4.16), 310
(4.10)
0.76,1.46
0.51, 0.79, 1.26, 1.78
0.66, 0.97
-
TPC-PTZ
429(4.93), 453(4.86), 608(4.34), 642(4.38) 671(4.11).
24(5.38),526(4.34),571(4.19),
05(3.95),658 (3.28)
-1.03, -.81
4
TPP-PTZ
-1.07, -.51
6
1.35, 1.44,1.89
a
b
Solvent CH
2 2 2 2 6
Cl . Error limits: λmax, ±1 nm; logε, ±10%. CH Cl , 0.1 M TBAPF Glassy carbon working electrode; standard Ag/AgCl is reference
electrode, Pt electrode is auxiliary electrode. Error limits, E1/2 ± 0.03 V.
4
.4. Theoretical calculations
The computational studies involving DFT and TD-DFT calculations using B3LYP/6-31G (d, p) level were
performed to visualize the geometry, electronic structure and optical properties of the dyads. Both the dyads were
optimized on the Born-Oppenheimer potential energy surface. Optimized structures, molecular electrostatic potential
maps (ESP) and location of frontier molecular orbitals (HOMO and LUMO) are shown in Table 2. From ESP maps
of both the dyads it is evident that, the positive potential was located on PTZ and negative potential was located on
corrole/porphyrin. Interestingly, From Table 2 it is clear that, though both the dyads are not co-planar but when we
carefully examine the co-planarity with respect to the vinyl linker, the TPP-PTZ has slightly higher co-planar than
the TPC-PTZ. By careful examination of frontier molecular orbitals (FMO’s) of both dyads, the HOMO-1 and
HOMO distributed among the donor subunit (PTZ) and porphyrin/corrole, whereas LUMO and LUMO+1
completely located on the acceptor unit (porphyrin/corrole). The gas phase HOMO-LUMO gap, edge-to-edge
distance (R ), center-to center distance (R ) between PTZ and corrole/porphyrin units in the dyads were
e-e
c-c
summarized in Table 3.
On the basis of the experimental observations, to elaborate the electronic structure and furnish the bands assignment
of UV-Vis bands, TD-DFT calculations were also performed by using the same basis set within the framework of
the polarizable continuum model (PCM) in CH Cl as the solvent. The computed wavelength positions are in good
2
2
agreement with the experimental values. Table S1. (Supporting information) shows wavelength of absorption
maximum (λmax), excited state energy (E), oscillator strength (f) and percentage contribution of molecular orbital of
both dyads by means of absorption spectra. Theoretical absorption spectra of dyads have been computed by using
the GaussSum-2.1.6 software and plotted (Supporting information, Fig. S17).
6

ACCEPTED MANUSCRIPT
Table 2
Geometrically optimized structures, FMO’s and Electrostatic potential maps (ESP) of TPC-PTZ and TPP-PTZ
dyads.
TPC-PTZ
TPP-PTZ
Optimized structure
Electrostatic potential
map (ESP)
LUMO+1
LUMO
HOMO
HOMO-1
Table 3
Optimized distances between PTZ and porphyrin/corrole moieties and related orbital energy’s (eV) in the TPC-PTZ
and TPP-PTZ dyads.
o
o
Compound
E, K.cal/mol
R
e-e, A
R
c-c, A
HOMO-1
HOMO (H)
LUMO (L)
LUMO+1
H-L gap
TPC-PTZ
TPP-PTZ
-1678600
-1847400
4.96
4.67
11.69
11.85
-5.16
-5.23
-4.74
-5.03
-2.48
-2.52
-1.89
-2.43
2.26
2.51
7

ACCEPTED MANUSCRIPT
4
4
.5. Study-State Emission Spectra
.5.1. Single-singlet energy transfer from PTZ to porphyrin/corrole
Unlike the ground state properties, we observed major differences in singlet state properties of the dyads when
-6
compared to their monomeric units. Equimolar (
selectively excited at 310 nm in dichloromethane (where the PTZ moiety absorbs predominantly) emission maxima
em: 450 nm) corresponding to PTZ was completely quenched in case of both the dyads when compare to pristine
̴ 10 M) solution of the dyads and their constituent monomers when
(
λ
PTZ, see Fig. 4. Emission maxima and fluorescence quantum yields were collected in Table 4. By careful
examination of Fig. 2 and 4, it is observed that there exist a strong overlap between PTZ emission and
corrole/porphyrin (Macrocycle) absorption, clearly suggesting that the quenching of fluorescence emission of PTZ
in these dyads can be due to intramolecular photoinduced energy transfer from excited singlet state of PTZ to
1
1
Macrocycle ( PTZ*-Macrocycle →PTZ- Macrocycle*). Similar results were also observed when we performed the
same experiment in different solvents (PhMe, MeCN and DMF) with varying polarity. From these experiments the
interesting results are summarized as: (i) the quenching corresponding to PTZ was more pronounced by decreasing
polarity of the solvent; (ii) a new emission band corresponding to porphyrin (red shifted, around 660 nm) in TPP-
PTZ and corresponding to corrole (red shifted, around 680 nm) in TPC-PTZ was more sensitized by decreasing the
polarity of the solvent (Supporting information Fig. S18) is clearly evidenced that, intramolecular energy transfer
from PTZ to porphyrin/corrole in these dyads. It is important to mention that when the dyads excited at 310 nm in
non-polar toluene, we did not find emission band corresponding to PTZ, at the same time, maximum sensitization of
corrole/ porphyrin indicated the exclusive presence of energy transfer. (Fig. S18). The efficiency of energy transfer
decreases with increasing solvent polarity is consistent with earlier reports [64].
Fig. 4. Emission spectra of PTZ, TPP-PTZ, TPC-PTZ, Corrole and Porphyrin at (λ = 310 nm and λ = 420 nm) in
ex
ex
CH Cl equi-absorbing solutions (O.D. λ = 0.05), the sharp peaks labelled with asterisk (*) is due to instrument
2
2
ex
response.
In order to verify the nature of the energy transfer, we have performed similar experiments with 1:1 mixture of PTZ
either with porphyrin or corrole. These controlled experiments did not show any emission quenching corresponding
to PTZ and there is no new emission band in longer wavelengths corresponding to porphyrin/corrole, providing
strong evidence for the intramolecular energy transfer. Furthermore the excitation spectrum of TPC-PTZ recorded at
8

ACCEPTED MANUSCRIPT
6
80 nm is well matched with absorption spectrum of the dyad, giving further evidence for the intramolecular energy
transfer. Similar results from TPP-PTZ were also observed (Fig. 5).
Fig. 5. Overlay of excitation spectra with absorption spectra of (a) TPC-PTZ (λ = 680 nm) (b) TPP-PTZ (λ = 660
em
em
nm) in dichloromethane, the excitation spectra were normalized with respect to the absorption spectra. The sharp
peaks labelled with asterisk (*) is due to instrument response.
Table 4
Emission properties of the dyads along with their monomers.
a
λ
em nm(Φ, %Q)
λ
ex= 310 nm
λ
ex= 420 nm
PhMe
Compound
TPC
CH
2
Cl
2
PhMe
MeCN
DMF
CH
2
Cl
2
MeCN
DMF
-
-
-
-
660(0.234)
649, 712 (0.13)
-
662(0.21)
645(0.257)
649(0.67)
648, 710
TPP
PTZ
-
-
-
-
651,713 (0.11)
-
649,713 (0.20)
-
(
0.22)
445(0.092)
446(0.094)
No peak
448(0.168)
449(0.238)
476(0.015,94)
-
420(0.005,96),
510(sh)
TPC-PTZ
440(0.004,95)
680(0.136, 42)
681(0.075,66)
679(0.16,37)
647(0.019,91)
685(0.298, 56)
(
100)
No peak
100)
661,723
(0.026, 80)
661,725
(0.034,68)
649(0.0115,
95)
TPP-PTZ
441(0.0019,98)
438(0.0025,98)
441(0.01, 95)
(
a
Spectra were measured at RT, Error limits λem ±1nm, Φ±10%. The quantum yields of the dyads were estimated by a comparative method using
TPP (Φ = 0.13) in CH Cl and TPC (Φ = 0.21) in toluene as a standards [38, 40]. The PTZ quantum yields were determined against quinine
sulfate in 0.1 N H SO (Φ = 0.546) as the standard (λex = 365 nm) [65].
f
2
2
f
2
4
The E0-0 (0-0 spectroscopic transition energy) values of the PTZ (3.20 eV), corrole (1.96 eV) and porphyrin (2.02
eV) moieties in the dyads were estimated from an overlap of their absorption and emission spectra. From the
magnitude of the fluorescence quantum yields, the quenching efficiency (Q) can be estimated from eq. (1) and rate
of fluorescence quenching kobs estimated from eq. (2) [64] in all the investigated solvents and data are listed in
(
Table 4 and 5).
Q = Φ(ref)- Φ(dyad)/Φ(ref)
kobs = [Q/(1-Q)]/τ(ref)
(1)
(2)
In equation (1) and (2) Φ(ref) and Φ(dyad) refer to the fluorescence quantum yields of PTZ and dyad. τ(ref) is the
excited singlet state life time of pristine PTZ (Table 6). From Table 4, the quenching efficiency of the TPP-PTZ
dyad was more efficient in all the solvents ̴ 99% than TPC-PTZ dyad (95-98%), this might be due to higher co-
planarity in TPP-PTZ dyad [40], because due to substitution at the β-position of corrole leads to a bent shape which
lowers the symmetry (loss of co-planarity) in addition to this, high electron density at corrole core than its analogues
porphyrin also might be the reason for the low efficiency of energy transfer [40] in TPC-PTZ dyad.
9

ACCEPTED MANUSCRIPT
Singlet-singlet energy transfer in these bichromophoric D-A systems can occur by two mechanisms: (i) the Forster
mechanism (dipole-dipole interaction) [66] and (ii) Dexter mechanism (electron-exchange mechanism) [67]. In case
10
11 -1
of a higher rate of energy transfer (10 -10 s ) or where a singlet state possesses high quantum yields, in general
the dipole-dipole mechanism prevails, whereas in case of poorly emitting state or donor-acceptor orbitals are in
close proximity, Dexter mediated energy transfer prevails. Importantly, in both mechanisms the rate of energy
transfers is proportional to extent of spectral overlap (J) of the donor emission with acceptor absorption. The rate of
energy transfer (kForster) from PTZ to corrole/porphyrin can be calculated by means of eq. (3).
2
3
2
-4 -1
Forster η τ
-6
DA
k
Forster = (8.8x10 )K Φ
D
J
D
R
(3)
Where Φ and τ are the emission quantum yield and lifetime of the pristine donor (PTZ) in various solvents (see
D
D
Table 4 and Table 6), RDA is the donor−acceptor center-to-center distance (Table 3), η is the refractive index of the
2
employed solvent and JForster is the overlap integral, K the orientation factor (2/3) for the randomly oriented donor-
acceptors (vide infra). The spectral overlap integral, JForster for the emission of the donor and absorption of the
acceptor can be evaluated according to eq. (4).
4
J
Forster = ∫ F
D
(λ)Ɛ
A
(λ) λ dλ/ ∫ F
D
(λ)dλ
(4)
Where F (λ) is the fluorescence intensity of the donor, Ɛ (λ) molar extinction coefficient of the acceptor expressed
D
A
−1
−1
in units of M cm and wavelength in nm. In the present study JForster values for TPC-PTZ and TPP-PTZ in four
different solvents were calculated by “PhotochemCAD” software [68] and the data were summarized in Table 5. In
-
14
6
-1
case of TPP-PTZ the calculated J
0
vales are 2.1-3.9 x 10 cm mmol and TPC-PTZ they were in the range of
Forster
-14
6
-1
.93-2 x 10 cm mmol ranging from non-polar toluene to polar DMF. By using these JForster vales, the Forster rate
10 -1 10 -1
of energy transfer (kForster) values are in the range of 5 – 22 x 10 s in TPP-PTZ and 2.3-12 x10 s in TPC-PTZ,
from Table 5, it is observed that the rate of energy transfer in TPP-PTZ is approximately two orders of magnitude
higher than TPC-PTZ in all the investigated solvents.
Table 5
a
Energy transfer data of both the dyads in all the investigated solvents .
Compound
9
-1
b
6
-1
c
b
10 -1
S
Forster (10 )
Solvent
%Q
%T(obs)
K
obs(10 s )
J
forster (cm mmol )
k
-
14
TPP-PTZ
PhMe
99
98
98
95
99
95
96
85
82
69
70
68
80
85
65
58.8
33.6
27.8
9.13
56.2
13.1
14.2
7.6
2.182 X 10
4.723 X 10
5.07
d
d
d
(
η
=1.496,
CH Cl
=1.424,
MeCN
=1.344,
DMF
=1.43,
PhMe
=1.496,
CH Cl
=1.424,
MeCN
=1.344,
DMF
=1.43,
Ɛ
Ɛ
Ɛ
=2.38)
=8.93)
-13
2
2
15.26
10.76
16.40
2.35
(
η
-
14
1.761X 10
3.947 X 10
9.304 X 10
1.158 X 10
2.175 X 10
2.048 X 10
(
η
=37.5)
-14
d
(
η
Ɛ =36.7)
-15
TPC-PTZ
d
d
d
(
η
Ɛ
=2.38)
=8.93)
-13
2
2
8.63
(
η
Ɛ
Ɛ
-14
14.42
10.58
(
η
=37.5)
-14
94
d
(
η
Ɛ =36.7)
a
b
2
c
Error limits: %Q, Kobs ±8, %T(obs) ± 15%,
calculated from photochemCAD software.
K
= 0.66 in all the cases, and Rc-c = 11.85 Å (TPP-PTZ) and 11.69 (TPC-PTZ). Spectral overlap term
and refer to refractive index and dielectric constant of the solvents, energy transfer efficiency
d
η
Ɛ
(
%T(obs)) was calculated from overlap of the excitation and absorption spectra.
4
.5.2. Photoinduced electron transfer from PTZ to porphyrin/corrole
The quenching of the excited states of the dyads takes place by various radiative and non-radiative processes, among
them the energy transfer and photoinduced electron transfer (ET) is particularly important. From Fig 2 and 4 it is
obvious that the emission of corrole/porphyrin does not overlap with PTZ absorption, thus the porphyrin/corrole
emission quenching cannot be ascribed to the energy transfer from excited state of porphyrin/corrole to PTZ. An
alternative pathway for the emission quenching is the intramolecular photoinduced electron transfer from ground
state of PTZ to excited state of porphyrin/corrole. The free energy change for the electron transfer from PTZ to
porphyrin, when selective excitation of porphyrin unit (λex = 420 nm) in TPP-PTZ can be calculated by the Rehm-
Weller approach [30] eq. (5).
1
ox
red
∆
G (PTZ → por) = E [(E (PTZ)-E (por)] - E (por)
(5)
CT
0-0
1
0

ACCEPTED MANUSCRIPT
∆
G of TPP-PTZ was found to be - 0.33 eV, the negative value of free energy clearly indicating that possibility of the
electron transfer from PTZ to porphyrin. Moreover from Table 4, the decrease in fluorescence quantum yields (
̴ 95
%) of the dyad by increasing the polarity of the solvent (spectra provided in Supporting information, Fig. S13),
evidenced that occurrence of electron transfer, the more acceleration of electron transfer in polar solvents than the
non-polar solvents also consistent with the earlier reports [64]. In contrast to this, when excite the corrole unit (λ =
ex
4
20 nm) in TPC-PTZ, very slight quenching in its fluorescence emission intensity (̴ 40%) was observed but did not
fallow the solvent trend (Fig. S19). From previous knowledge in energy and electron transfer studies, it is important
to mention that, the fluorescence quenching due to singlet-singlet energy transfer may or may not depends on the
solvent polarity but the fluorescence quenching due to photoinduced electron transfer must depends on solvent
polarity (vide infra). Moreover, in case of TPC-PTZ the thermal free energy for electron transfer (∆G = - 0.14 eV)
was probably insufficient to separate the charges [16a]. The emission intensity of dyads with respect to their
monomers I(dyad) / I(ref) in equi-absorbing solutions when excited at 420 nm have shown in (Supporting info.
Table S2), from this values, in case of TPP-PTZ the dyad emission was quenched effectively with respect to its
monomer and fallowed solvent trend, whereas, in case of TPC-PTZ the dyad emission was not quenched more and
also does not fallowed solvent trend. All these results corroborate, the decrease in fluorescence intensity cannot be
attributed to electron transfer in TPC-PTZ dyad. Hence this decrease may be due to excited state and ground state
interactions between the two chromophore units in the dyad, leading to lower the quantum yields [64].
4
.6. Time resolved emission spectra
The excited-state decay curves of the dyads provides further evidence for the intramolecular energy transfer (PEnT)
when selectively exciting the donor unit in the dyad. The decay curves of pristine PTZ shown in Fig. 6 and data
were summarized in Table 6.
Fig. 6. Fluorescence decay of the pristine PTZ in four different solvents (λ = 310 nm and λem = 450 nm).
ex
The decay of the dyads with picoseconds resolution have been achieved by Streak Camera technique with excitation
at 310 nm and emission monitored at 450 nm in all four solvents with varying polarity shown in Fig. 7. The decay
parameters collected in Table 6. From the data it is clear that the fluorescence emission lifetime of the PTZ unit
decreased in both the dyads and fallowed the solvent trend similar to study-state emission. Decay curves are fitted
with a biexponential expression in which the major component has a shorter lifetime (ps) attributed to energy
transfer from PTZ to acceptor (porphyrin/corrole), the other longer lifetime (ns) component either unquenched or
different orientation of dyad which will not participate in energy transfer, because different conformers are possible
around the flexible linker in solution state [69]. The fluorescence decay of the dyads when excited at acceptor unit of
the dyad (420 nm), giving additional support for photoinduced electron transfer. The decay curves of the dyads
investigated in four solvents were shown in Fig. 7 and the data were summarized in Table 6, along with their
monomer units. Decay cures of monomeric porphyrin/corrole shown in (Supporting information, Fig. S20).
1
1

ACCEPTED MANUSCRIPT
Fig. 7. Fluorescence decay of the dyads (a) TPC-PTZ (
presented. (c) TPC-PTZ ( ex = 420 nm) and (d) TPP-PTZ (
wavelengths according to Table 4.
λ
ex = 310 nm), (b) TPP-PTZ (
λex = 310 nm) in both cases, the decay from toluene was not
λ
λ
ex = 420 nm). All the decay curves were monitored at their respective emission
From the data, in case of TPP-PTZ the decay curves are fitted with biexponential decay; the major component has a
shorter and is attributed to photoinduced electron transfer from ground state of PTZ to excited state of porphyrin, the
other longer lifetime component may be the unquenched or no suitable orientation of the dyad which does not
participate in electron transfer. The rate constant for the charge transfer from PTZ to TPP in TPP-PTZ is calculated
by eq. (6).
kET =1/τ(dyad)-1/τ(por)
(6)
Where τ(
is lifetime of the dyad and τ
is the pristine porphyrin lifetime, the rates of charge transfer in toluene
dyad)
-1
(por)
-1
9
9
9
-1
9 -1
(
0.52x10 s ), dicholoromethane (2.42x10 s ), aceonitrile (2.51x10 s ) and in dimethyl formamide (19.9x10 s ).
Table 6
Fluorescence decay parameters of dyads alongwith their monomers.
a
Compound
λ
ex, nm
τ, ps (A%)
PhMe
CH
2
Cl
2
MeCN
DMF
T
TPC
406(660)
4570
3980
8480
1455
3830
4270
10380
2101
T
TPP
406(650)
310 (450)
9670
9190
PTZ
1682
1761
b
TPC-PTZ
TPC-PTZ
TPP-PTZ
TPP-PTZ
a
310
52(55), 2965(45)
5218
125(70), 1937(24)
4545
251(49),1559(52)
2392
347(79), 3536(12)
4728
b
420
b
c
310
Weak Flu.
10(90), 1429(10)
392(47),11903(50)
12(96), 1449(6)
384(75),9091(15)
45(60),1434(40)
50(71),7065(18)
b
420
1602(41),8142(55)
All lifetimes are in picoseconds (ps), error limits of
corresponding decay component. Emission monitored at corresponding emission wavelength in different solvents according to their respective
emission values. Lifetime measured by TCSPC technique, and dyads and pristine PTZ by Streak Camera technique. Due to infant emission we
unable to fit the data.
τ
̴
10%. Values in parenthesis are relative amplitudes, values remaing is 100% of
b
T
c
The solvent dependent rate of electron transfer (kET) values increasing with increasing polarity of the solvent (PhMe
<
CH Cl < MeCN < DMF) indicating the participation of charge-transfer state in the excited state deactivation of
2 2
porphyrin in the TPP-PTZ dyad. On the other hand when we excite the corrole unit (420 nm) in TPC-PTZ dyad, the
decay curves are fitted with single exponential (Fig. 6) and the lifetimes are in the nanosecond range similar to the
monomeric corrole, furthermore we did not observed any solvent dependence on the decay clearly indicating that the
absence of charge transfer in TPC-PTZ dyad, which is consistent with the study-state emission data. The energy
levels of singlet excited states which are participates in energy transfer as well as charge transfer states associated
with electron transfer in both the dyads have shown in supporting information (Fig. S21).
1
2

ACCEPTED MANUSCRIPT
5
. Conclusions
In conclusion, we have synthesized and characterized two dyads in which phenothiazine was also connected at the
β-pyrrolic position of either porphyrin or corrole. Absorption and electrochemical properties indicate that there are
no significant interactions between these subunits. Fluorescence emission of the dyad was completely quenched
when the dyad was excited at 310 nm is attributed to excited energy transfer from PTZ to either porphyrin/ corrole,
and we found that the rate of energy transfer is higher in TPP-PTZ due to high co-planarity than TPC-PTZ dyad.
Furthermore photoinduced electron transfer from the ground state of PTZ to excited state of porphyrin was observed
when excite the dyad at 420 nm. In contest to TPP-PTZ, there are no significant changes in photophysical properties
of TPC-PTZ when excited at 420 nm. Interestingly due to lack of one methine (=CH-) bridge in the corrole unit,
noticeable differences were observed in photoinduced process. The theoretical data also supported the experimental
results. These results collectively, encourage us to prepare new hybrid materials based on these chromophores for
various light harvesting applications.
This work was financially supported by National Natural Science Foundation of China (Nos. 61178037, 81273549,
2
1371059,
81400023,
21671068),
National Basic
Research Program (973 Program)
of China under Grant 2013CB922403 and the Open Fund of State Key Laboratory of Optoelectronic Materials and
Technologies, Sun Yat-sen University (No. OEMT-2015-KF-05).
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Research Highlights:
•
•
•
•
Two novel donor-acceptor systems, in which PTZ connected at β-pyrrolic position of either free base porphyrin/corrole
via vinylic spacer have been synthesized and characterized.
Photoinduced singlet-singlet energy transfer from PTZ to corrole/porphyrin was observed when selective excitation of
the dyad at 310 nm.
Due to high co-planarity, the energy transfer is more efficient in TPP-PTZ dyad (99%) than the TPC-PTZ dyad (96-
9
8%).
Fluorescence emission from porphyrin part of the TPP-PTZ dyad also quenched due to Photoinduced electron transfer
λex = 420nm), under similar experimental conditions there are no significant changes in photophysical properties of the
(
TPC-PTZ dyad.
•
Solvent dependence of the energy and electron transfer was discussed.