Molecular engineering of pyrene carbazole dyes with a single bond and double bond as the mode of linkage

Article abstract of DOI:10.1039/d0nj03228j

Both carbazole and pyrene are electron-rich aromatic systems and are expected to be potential donors when used in a push-pull dye architecture in the field of DSSC technology. Herein, two novel pyrene-carbazole dyes bearing single bond (PC1) and double bond (PC2) linkers and cyano-acrylic acid as an acceptor were synthesized. The dye with a double bond spacer (PC2) in the presence of CDCA achieved an improved power conversion efficiency of 6.30% with a short circuit current of 11.59 mA cm-2, open circuit potential (VOC) of 0.80 V, and a fill factor of 0.68 under standard global AM 1.5G solar conditions. Cyclic voltammetry and density functional theory studies indicate that the incorporation of two donors improved the ease of oxidation of the dyes, which resulted in a high VOC. Despite having a rigid single bond, the charge transfer of the PC1 dye is found to be poor, which affected the photovoltaic performance. The dihedral angle measured at each joint of the optimized dye indicated that PC2 exhibits excellent intramolecular charge transfer due to the near planarity in the structure. Besides, the high electron lifetime in the excited state of PC2 makes it the best performer among the three dyes studied.

Full text of DOI:10.1039/d0nj03228j

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: D. Unny, G. R.
Kandregula, J. Sivanadanam and K. Ramanujam, New J. Chem., 2020, DOI: 10.1039/D0NJ03228J.
Volume 42
Number
March 2018
Pages 3963-4776
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
6
21
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
Molecular engineering of pyrene carbazole dyes with a single bond and double
bond as the mode of linkage
1
#
1#
1,2
Divya Unny , Ganapathi Rao Kandregula , Jagadeeswari Sivanadanam * and Kothandaraman
1
,2
Ramanujam *
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1Department of Chemistry, Indian Institute of Technology Madras, Chennai, India, 600 036
2DST-IITM Solar Energy Harnessing Centre, Indian Institute of Technology Madras, Chennai,
India, 600 036
#
Contributed equally
*Corresponding author’s email: rkraman@iitm.ac.in; jagadhi333@gmail.com
Abstract
Both carbazole and pyrene are electron-rich aromatic systems and are expected to be potential
donors when used in push-pull dye architecture in the field of DSSC. Herein, two novel pyrene-
carbazole dyes bearing single bond (PC1) and double bond (PC2) linkers and cyano-acrylic acid
as acceptor were synthesized. The dye with double bond spacer (PC2) in the presence of CDCA
achieved an improved power conversion efficiency of 6.30 % with short circuit current of 11.59
-2
mA cm , open circuit potential (푉 ) of 0.80 V, and a fill factor of 0.68 under standard global AM
푂퐶
1
.5G solar condition. Cyclic voltammogram studies and density functional theory indicate that the
incorporation of two donors improved the ease of oxidation of the dyes, which resulted in the high
푉푂퐶. Despite having rigid single bond, the charge transfer of PC1 dye is found to be poor which
affected the photovoltaic performance. The dihedral angle measured at each joint of the optimized
dye indicated that PC2 to exhibit excellent intramolecular charge transfer due to the near planarity
in the structure. Besides, the high electron lifetime in the excited state of PC2 makes it best
performing among the three dyes studied.
1

New Journal of Chemistry
Page 2 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Keywords
Pyrene – carbazole dyes, π-spacer, dihedral angle, open-circuit voltage, reorganization energy
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2

Page 3 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
. Introduction
Dye sensitized solar cells (DSSC) comprise one of the most promising third-generation
photovoltaic (PV) technologies, and they have remained an important field of research for more
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1, 2
than two decades, beginning with Gratzel's invention of DSSC in 1991 . Presently, DSSCs have
outperformed most other long-established PV technologies under ambient light conditions and the
best power conversion efficiency (PCE) has reached up to 14.3 % on the laboratory scale3, 4
.
Researchers in the field of DSSCs focuses mainly on the four core components of the device:
dye/sensitizer, semiconductor metal oxide, counter electrode and the redox electrolyte. Despite
many years of research, considerable efforts are still being made to find appropriate alternative
materials for each of these components. Among the various components, visible light-responsive
sensitizers are attractive candidates to realize DSSC, as they are required to inject electrons into the
wide bandgap semiconductor metal oxide. With a history of over thirty years of development, a
large number of sensitizers have been synthesized and they are classified into three main
categories: (i) Ruthenium polypyridyl complexes 5-7, (ii) Porphyrin complexes , and (iii) Metal-
8
9
free organic dyes , with the best-reported PCE of these being 11.5 %, 13 %, and 14.3 %,
respectively. Compared to the first two categories of dyes, which are tedious to prepare, affected
by precious metal scarcity and low-throughput synthesis pathway, the latter is easy to synthesize
with ample of molecular engineering strategies 10-12. The traditional design of a sensitizer is the
simple rod-like donor-π-acceptor (D-π-A) configuration, and a recent report shows that it remains
1
3
more promising than complex donor-acceptor structures . It has been observed in the literature
that the design strategy for metal-free organic dyes are based on highly fused and heterocyclic
aromatic moieties as donors 14 , 15, rigid and planar π-spacers 16 and strong electron-accepting units
3

New Journal of Chemistry
Page 4 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
17, 18.
It is clear that the donor group of the organic dye has a pivotal role in enhancing the PCE as
1
9
it improves the light-harvesting properties and adjusts the energy levels of the dyes .
Among the aryl amine heterocyclic chromophores, carbazole is considered as a strong electron-
donor system due to its unique rigid and planar configuration, excellent structural and thermal
stability, and electron-richness which allow it to be part of the materials for optoelectronic
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
applications and organic photovoltaic cells , such as DSSCs 22, 23. Wang et al., have studied the
2
0
21
2
4
hexylthiophene-functionalized carbazole dyes and obtained a PCE of 8.3 % . El-shafei et al.,
reported a PCE of 9.37 % for two heteroleptic Ru(Ⅱ) isomers with carbazole antenna, which has
2
5
outperformed the standard N719 (8.17 %) dye . Recently, Qian et al., reported indolo [3,2-b]
2
6
carbazole-based dye with 8.09 % efficiency . Maddala et al. employed carbazole-based small
27
molecules as hole transport materials for perovskite solar cells . Furthermore, a large number of
carbazole-based dyes show good PCE in DSSCs, a notable one being ADEKA-1 with PCE of 10.4
2
8
% .
Pyrene is another popular polycyclic aromatic hydrocarbon and its derivatives have been studied
29
extensively as emissive materials in the organic light-emitting diodes (OLED) , hole-transport
materials in the perovskite solar cells (HTM) 30 and DSSCs, because of their extensive electron
delocalization, high fluorescence quantum yield, long-lived excited-state, good thermal stability and
31
multiple substitution sites . The first report on a pyrene based dye (N,N – dialkyl amine linked pyrene
with thiophene linker and cyano-acrylic acid acceptor) exhibited a short circuit photocurrent density (퐽푆퐶
2
)
of 12.1 mA/cm , an open-circuit voltage (푉 ) of 0.71 V, and a fill factor (FF) of 0.71, corresponding
푂퐶
32
to an overall PCE of 6.1 % under AM 1.5 conditions . Later, Lu et al., reported the best efficient
33
pyrene-conjugated porphyrin dye with an overall PCE of 8.7% . A recent report on pyrene by
4

Page 5 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
Khamrang et al., who studied two π-linkers, furan and ethynyl furan, with a pyrene core, showed a PCE
3
4
of 1.89 % and 2.47 % respectively .
As far as we know, there are no studies on the pyrene-carbazole combo-based dye for DSSCs.
Therefore, the motive of this study is to gain a better understanding of the structure-property
relationships of pyrene–carbazole systems. To this end, we have developed two new pyrene–
carbazole based organic dyes, wherein they are connected by a single bond (PC1) or double bond
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(PC2) linkage (π-spacer), with cyano-acrylic acid as the acceptor. Pyrene cyano-acrylic acid dye
3
5
was used as a reference (PC0) for comparison . The incorporation of the double bond spacer
(PC2), between the pyrene and carbazole moieties, would extend the conjugation while
maintaining planarity with pyrene as well as carbazole. It is expected that these two donors will
extend the conjugation and adjust the energy levels so that both 퐽 and 푉 can be improved. Our
푆퐶
푂퐶
previous work had shown that the planar and rigid geometric donors exhibit a much better PCE than the
36
flexible moieties due to reduced energy loss during vibrational relaxation . Recently, Zhang et al.,
have reported two triazatruxene-based sensitizers, with one containing double bond spacer, and
another a rigid single bond one, and found that the latter provided a rapid electron injection and
3
7
small vibrational relaxation resulted in enhancement of PCE .
The main aspiration of this study with PC1 and PC2 is to understand the effect of mode of linkage
(single vs. double bond), between the pyrene and carbazole donors, on the PCE of dye (Fig. 1). An octyl
group is attached at the carbazole nitrogen to impart a hydrophobic environment around the donor,
improve the dye-solubility, and reduce the dye aggregation on the TiO surface. Theoretical studies
2
were carried out to explore the intra-molecular charge transport (ICT) process involved in these
dyes. Time-dependent density functional theory (TDDFT) calculations were also carried out to
comprehend the electronic structure of these dyes.
5

New Journal of Chemistry
Page 6 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fig. 1 Structures of pyrene-carbazole dyes (PC0, PC1, PC2).
2. Experimental Section
2
.1. Materials
The chemical and reagents used in this work (pyrene, TiCl , dichloromethylmethyl ether,
4
potassium tertiary butoxide (tBuOK), methyltriphenylphosphonium iodide (CH PPh I), carbazole,
3
3
pyrene1-boronic acid, Tris(dibenzylideneacetone) dipalladium(0) [Pd (dba) ], Xphos, palladium
2
3
acetate, dimethyl sulfoxide-d (DMSO-d ), deuterated chloroform (CDCl ), tetrabutylammonium
6
6
3
hexafluorophosphate (TBAPF ), 4-tert butyl pyridine (TBP), iodine (I ) and lithium iodide (LiI))
6
2
were purchased from Sigma Aldrich. 1-bromooctane, sodium hydroxide, phosphorous
oxychloride, potassium iodide, potassium iodate, potassium phosphate, triethylamine, ammonium
acetate, cyano-acetic acid, and chenodeoxy cholic acid (CDCA) were purchased from Alfa Aesar.
1,2-dimethyl-3-propylimidazolium iodide was purchased from TCI Chemicals, India. The solvents
used for photophysical studies were HPLC grade. Laboratory grade solvents were purchased from
Rankem chemicals and used without further purification. Dimethylformamide (DMF) and
dichloromethane (DCM) were distilled with calcium hydride, whereas tetrahydrofuran (THF) and
toluene were distilled in the presence of sodium and benzophenone under nitrogen atmosphere
immediately prior to use. All reactions were monitored by thin-layer chromatography (TLC) using
silica gel plates. Titania (TiO ) paste (18NR-T), Fluorine-doped SnO (FTO) with a sheet
2
2
2
resistance of 15 Ω/cm , and thickness of 2.2 mm (MS001695-10), and hot-melt sealing agent
6

Page 7 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
(
MS004610-10, 60 µm thick thermoplastic film) were purchased from Dyesol Ltd., Australia.
Silica gel (Rankem, spherical, 100 - 200 mesh) was used as a stationary phase for column
chromatography.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
.2. Characterizations
1
13
All H NMR (500, 400 MHz) and C NMR (125, 100 MHz) spectra were recorded on a Bruker
Avance NMR spectrometer in either CDCl or DMSO-d with tetramethyl silane as an internal
3
6
1
standard. H NMR spectra were referenced to CDCl (7.26 ppm) and DMSO – d (2.5 ppm) central
3
6
1
3
lines, while C NMR was referenced to CDCl (77.16 ppm) and DMSO – d (39.5 ppm) central
3
6
lines. The multiplicity is given as, s = singlet, d = doublet, t = triplet, dd = doublet of doublet, qui
quintet, m = multiplet while coupling constant, J is reported in Hz. The melting point of the dye
=
was measured by packing dye in an open capillary tube on a melting point apparatus and was
uncorrected. Fourier-transform infrared (FTIR) spectra were taken by JASCO FTIR–4100
spectrometers using KBr cell. High-resolution mass spectra (HRMS) were obtained by
micromass-quad time of flight (MICRO-Q TOF) mass spectrometer by using the electron spray
ionization (ESI) technique at 10 eV. The solution state absorption spectra of dyes were recorded in
a 1 cm path length quartz cell on a JASCO V-650 UV-visible spectrophotometer. Emission spectra
of dyes were measured using a JASCO FP-6300 spectrofluorimeter. Cyclic voltammetric studies
and electrochemical impedance spectroscopy (EIS) were carried out in Metrohm Autolab 302N
potentiostat/galvanostat having FRA32M module controlled by NOVA 2.1.3 software. The EIS
analysis has carried out at 푉푂퐶 over the frequency range of 100 kHz to 0.1 Hz with 10mV
perturbation under 1 sun illumination and the fitting was performed using the ZSimWin 3.6
software. The electrochemical experiments were performed in a three-electrode set up with a 5
7

New Journal of Chemistry
Page 8 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
mm diameter glassy carbon disc electrode (GCE) (working electrode), Pt mesh counter electrode,
and Ag/AgNO (0.01 M) in 0.1 M TBAPF in acetonitrile (ACN) solventreference electrode. GCE
3
6
was polished using alumina powder (0.05 μ) before use. The dye was dissolved in dry DCM
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
solvent, and 0.1 M TBAPF was added as supporting electrolyte. The solution was then purged
6
with nitrogen gas for 5 min to eliminate dissolved oxygen. The cyclic voltammogram (CV) was
-1
recorded at room temperature at a scan rate of 50 mV s . The photovoltaic performance (current
density vs. voltage, J-V) of the prepared DSSCs were measured under one sun condition using
LOT technologies solar simulator fitted with 150 W Xenon lamp and air mass (AM) 1.5 global
-2
filter providing a light power of 100 mW cm . Silicon solar cell (type RC2-1010, SN:
0520160006, SPD laboratory) was used to calibrate the spectral intensity of the solar simulator.
Except for the active area of the cell, the remaining portion was covered with a black mask to avoid
reflected light entering the system.
2
.3. Molecular design and synthesis
The synthetic approach used to prepare the pyrene-carbazole dyes (named as PC0, PC1, and PC2)
is outlined in Scheme 1. The reference PC0 dye has been synthesized by single-step Knoevenagel
condensation of pyrene aldehyde (2) with cyano-acetic acid (Scheme S1). Compound (6) was the
common building block for PC1 and PC2 dye, which was synthesized by a nucleophilic
substitution reaction of 1-bromooctane, followed by Vilsmeier-Haack formylation reaction and
iodination reaction. 1-vinyl pyrene (3), which is another building block used in the formation of
PC2 dye and is obtained by a two-step process: First step is the formation of pyrene aldehyde (2)
followed by its reaction with methyltriphenyl phosphonium iodide (CH PPh I) to yield 1-vinyl
3
3
pyrene. The compound (6) and (7) are combined via the Suzuki coupling reaction to get the
compound (8), whereas the compound (6) and (3) were combined by Heck coupling reaction to
8

Page 9 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
afford the compound (9). Finally, Knoevenagel condensation is carried out to the corresponding
aldehydes (8) and (9) for obtaining the target dyes (PC1 and PC2). The desired final products (PC0,
PC1, PC2) were obtained in good yields and well-characterized by NMR, FT-IR, HRMS
techniques (Fig. S1-S6).
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
CN
B(OH)2
CHO
COOH
Cyanoacetic acid
NH4OAc, 80 °C,
7
N
Pd2(dba)3, XPhos
K3PO4, dry toluene
glacial CH3COOH
85 %
N
C8H17
C8H17
8
PC1
80 %,
I
CHO
N
CN
COO
C8H17
CHO
Cyanoacetic acid
NH4OAc, 80 °C
H
6
3
N
NEt3, Pd(OAc)2
N
glacial CH3COOH
C8H17
85 %
MeCN, 90 °C, 24 h
8 17
C H
79 %
PC2
9
Scheme 1: Synthetic route of pyrene-carbazole dyes.
2
6
.4. Synthesis of intermediates
-iodo-9-octyl-9H-carbazole-3-carbaldehyde (6)
38
The three-step reaction was followed to obtain the building block (6) . Similarly, the building
3
9
block (3) is prepared by following the procedure . The detailed scheme was shown in the
supplementary information (Scheme S1).
Pyrene-1-carbaldehyde (2)
Pyrene (3 g, 4.8 mmol, 1 equiv.) and dichloromethyl methyl ether (1.74 ml, 19.3 mmol, 1.3 equiv.)
in CH Cl (70 mL) was cooled to 0 °C. A solution of TiCl (3 ml, 26.6 mmol, 1.8 equiv.) in CH Cl
2
2
2
4
2
(6 mL) was added slowly. The mixture was stirred for 1 h at 0°C and 1.5 h at room temperature.
After the completion of reaction, the reaction mixture was poured into ice-water and extracted with
9

New Journal of Chemistry
Page 10 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
CH Cl . The organic layer was washed with water, dried over Na SO . The organic layer was
2
2
2
4
evaporated to get the crude product. The product was purified by column chromatography with 5
% ethyl acetate and hexane mixture.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
Yield = 88 % (3.00 g); yellow solid; H-NMR (500 MHz, CDCl ) δ: 10.72 (s, 1H), 9.32 (d, 1H, J
3
=
9.32 Hz), 8.34 (d, 1H, J = 7.92 Hz), 8.25- 8.21(m, 3H), 8.15 (d, 1H, J = 8.32 Hz), 8.06-7.98 (m,
1
3
3
1
H). C-NMR (125 MHz, CDCl ) δ: 192.9, 135.4, 131.2, 130.9, 130.8, 130.7, 130.6, 130.3, 127.3,
3
27.1, 126.9, 126.7, 126.5, 125.8, 124.9, 124.4, 122.9. HRMS (ESI): Calculated for C H O
17 10
+
[
M+H] 230.0730; found 230.0732.
1-Vinylpyrene (3)
A round bottom flask was charged with Methyltriphenylphosphonium iodide (2 g, 4.95 mmol, 1
equiv), which is dissolved in 20 mL freshly distilled THF and is stirred at 0 °C under nitrogen
atmosphere. Potassium tert-butoxide (0.83 g, 7.42 mmol, 1.5 equiv) was then added and stirred for
3
0 minutes. Compound 2 (0.8 g, 3.46 mmol, 0.7 equiv) was then added, and the mixture was stirred
at room temperature for 4 h. TLC was used to monitor the progress of the reaction. Finally, a
yellow solution was obtained and the mixture was neutralized by dilute HCl and then extracted by
chloroform. The crude product was purified by silica column chromatography eluting with hexane.
1
Yield = 70 % (0.56 g); pale yellow solid; H-NMR (400 MHz, CDCl ) δ: 8.28 (d, 1H, J = 9.28 Hz
3
), 8.11 - 7.99 (m, 5H), 7.94 – 7.88(m, 3H), 7.69 (dd, 1H, J = 11 Hz, J = 6.32 Hz), 5.89 (d, 1H, J
1
3
= 17 Hz), 5.52(d, 1H, J = 11 Hz); C-NMR (100 MHz, CDCl ) δ: 134.2, 132.4, 131.5, 130.9,
3
1
30.9, 128.1, 127.6, 127.4, 127.3, 125.9, 125.3, 125.0, 124.9, 124.9, 123.7, 123.0, 117.2.
+
HRMS (ESI): Calcd. For C H [M+H] ; 228.0930 found 228.0939.
1
8
12
9
-octyl-6-(pyren-1-yl)-9H-carbazole-3-carbaldehyde (8)
10

Page 11 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
A mixture of compound 6 (0.7 g, 1.61 mmol, 1 equiv), pyrene 1- boronic acid (7) (0.48 g, 1.93
mmol, 1.2 equiv), and K PO ( 1.03 g, 4.84 mmol, 3 equiv) were dissolved in a mixture of solvents:
3
4
toluene (80 V, 56 ml), tertiary butyl alcohol (14 V, 9.8 ml) and water (7 V, 4.9 ml). The solution
was purged under N atmosphere for 30 minutes and then Pd (dba) (163 mg, 0.18 mmol, 0.11
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
3
equiv) and XPhos (323 mg, 0.68 mmol, 0.42 equiv) was added simultaneously. The reaction was
set at 90˚C for 12 h. After completion of the reaction, the mixture was concentrated by evaporation
and purified by column chromatography using 10 % ethyl acetate and hexane mixture as an eluent
to give the desired compound (8).
1
Yield = 80 % (0.66 g); white solid; H-NMR (400 MHz, CDCl ) δ: 10.08 (s, 1H), 8.63 (d, 1H, J =
3
2
.7 Hz), 8.40 (s, 1H), 8.26-8.24 (m, 2H), 8.21-8.16 (m, 2H), 8.13-8.00 (m, 6H), 7.80 (d, 1H, J =
8.25 Hz ), 7.63 – 7.60 (m, 1H), 7.54-7.51(m, 1H), 4.41(q, 2H, J = 7.4 Hz, J = 7.25 Hz), 1.97 (m,
1
2
13
2
1
H), 1.57- 1.27 (m, 12H), 0.88 (t, 3H, J = 6.35 Hz); C-NMR (100 MHz, CDCl ) δ: 191.7, 144.5,
3
40.4, 138.0, 133.4, 131.5, 131.0, 130.4, 129.5, 128.8, 128.6, 128.1, 127.5, 127.4, 127.3, 127.1,
126.0, 125.4, 124.9, 124.8, 124.4, 123.2, 109.3, 109.2, 43.7, 31.8, 29.4, 29.2, 29.0, 27.3, 22.6, 14.1;
+
HRMS (ESI): Calcd. For C H NO [M+H] 507.2573; found 507.2562.
3
7
33
(E)-9-octyl-6-(2-(pyren-1-yl)vinyl)-9H-carbazole-3-carbaldehyde (9)
A Dried 50 mL round bottom flask was charged with compound (6) (0.75 g, 2.43 mmol, 1 equiv),
compound (3) (0.84 g, 3.6 mmol, 1.5 equiv), palladium acetate ( 0.027 g, 0.12 mmol, 0.05 equiv),
triethylamine (0.68 ml, 4.88 mmol, 2 equiv) and 10 ml of ACN solvent. The tube was evacuated
and backfilled with nitrogen. The reaction mixture was heated in an oil bath at 90 °C for 24 h. The
progress of the reaction was monitored by TLC. After completion of the reaction, it was allowed
to cool to room temperature and extracted with ethyl acetate. The organic phase was dried with
anhydrous Na SO . The organic layer was then evaporated and the crude product was adsorbed on
2
4
11

New Journal of Chemistry
Page 12 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
silica and purified by column chromatography, using (95:5; hexane: ethyl acetate) mixture as
eluent.
1
Yield = 79 % (0.725 g); yellow solid; H-NMR (500 MHz, CDCl ) δ: 10.11 (s, 1H), 8.66 (s, 1H),
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
8
.55 (d, 1H, J = 9.32 Hz), 8.42 (s, 1H), 8.37 (d, 1H, J = 8.0 Hz ), 8.24 (d, 1H, J = 16.0 Hz), 8.18-
8.12(m, 4H), 8.04 – 7.98 (m, 4H), 7.86 (d, 1H, J = 8.40 Hz), 7.54 (d, 1H, J = 16 Hz), 7.47-7.44
13
(
m, 2H), 4.30 (t, 2H, J = 7.16 Hz), 1.91-1.88 (m, 2H), 1.41- 1.25 (m, 10H), 0.87 (t, 3H); C-NMR
(
125 MHz, CDCl ) δ: 191.8, 144.5, 140.9, 132.2, 132.0, 131.6, 131.0, 130.5, 128.7, 128.3, 127.5,
3
127.3, 127.1, 126.0, 125.8, 125.2, 125.0, 124.9, 124.2, 123.9, 123.5, 123.5, 123.1, 118.9, 109.7,
+
1
09.2, 43.6, 31.8, 29.3, 29.2, 29.0, 27.3, 22.6, 14.1; HRMS (ESI): Calcd. For C H NO [M+H]
39 35
5
33.2692; found 533.2719
2
.5. Synthesis of final compounds
(Z)-2-cyano-3-(9-octyl-6-(pyren-1-yl)-9H-carbazol-3-yl)acrylic acid (PC1)
Compound (8) (0.3 g, 0.6 mmol, 1 equiv), cyano-acetic acid (0.0753 g, 0.89 mmol, 1.5 equiv), and
ammonium acetate (0.089 g, 1.15 mmol, 1.95 equiv) were dissolved in 10 mL glacial acetic acid.
The solution was refluxed at 80 °C in an oil bath under the N atmosphere for 12 h. After
2
completion of the reaction, the reaction mixture was poured into water, the resulting precipitate
was filtered and washed several times with water and dried. The final yellow colored PC1 dye was
obtained by purification through column chromatography (silica gel, dichloromethane/methanol,
9
7:5).
Yield = 85 % (0.289 g); yellow solid; mp = 215 ˚C; H-NMR (500 MHz, DMSO) δ: 8.92 (s, 1H),
.44 (s, 1H), 8.41-8.33 (m, 4H), 8.29-8.27 (m, 1H), 8.25 (d, 1H, J = 4.3 Hz ), 8.22-8.14 (m, 3H),
1
8
8.13-8.08 (m, 2H), 7.90 (t, 2H), 7.80-7.79 (m, 1H), 4.55 (d, 2H, J = 6.9 Hz), 1.89-1.84 (m, 2H),
12

Page 13 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
13
1
.37-1.32 (m, 2H), 1.30-1.27 (m, 2H), 1.24- 1.19 (m, 6H), 0.82 (t, 3H, J = 6.7 Hz); C-NMR (125
MHz, CDCl ) δ 164.6, 155.7, 143.7, 140.5, 138.0, 133.0, 131.5, 130.9, 130.4, 129.8, 128.7, 128.4,
3
128.1, 127.9, 127.8, 126.9, 126.8, 125.8, 125.4, 124.7, 124.6, 122.9, 122.8, 122.7, 117.7, 111.0,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
1
10.8, 43.2, 31.6, 29.2, 29.0, 26.9, 22.5, 14.4; IR (KBr): 3721, 2994, 2352, 1759, 1574, 1592,
-1
+
371, 1240, 1055 cm ; HRMS (ESI): Calcd. For C H N O [M+H] 574.2592; found 574.2620
4
0
34
2
2
(
E)-2-cyano-3-(9-octyl-6-((E)-2-(pyren-1-yl)vinyl)-9H-carbazol-3-yl)acrylicacid (PC2)
PC2 dye was prepared from compound (9) (0.7 g, 1.31 mmol, 1 equiv), cyano-acetic acid (0.17 g,
.96 mmol, 1.5 equiv), ammonium acetate (0.197 g, 2.56 mmol, 1.95 equiv), and glacial acetic
1
acid (10 ml) by following a procedure described above for PC1 dye. The precipitate obtained was
then purified by column chromatography, using (95:5; dichloromethane: methanol).
1
Yield = 85 % (0.67 g); dark yellow solid; mp = 220 ˚C; H-NMR (500 MHz, CDCl ) δ: 8.91 (s,
3
1
1
H), 8.83 (d, 1H, J = 9.3 Hz ), 8.64 (s, 1H), 8.59 (d, 1H, J = 8.05 Hz), 8.48-8.47 (m, 1H), 8.43 (s,
H), 8.33-8.18 (m, 7H), 8.14 –8.02 (m, 2H), 7.85 (d, 1H, J = 8.35 Hz), 7.80-7.77 (m, 2H), 4.52-
4.49 (t, J = 5.9 Hz, 6.4 Hz, 2H), 1.84-1.82 (m, 2H), 1.28-1.18 (m, 10H) 0.82 (t, J =6.7 Hz ,7.0 Hz,
13
3
1
1
3
H); C-NMR (125 MHz, CDCl ) δ: 164.6, 143.5, 141.1, 132.8, 132.5, 131.6, 131.0, 130.7, 130.5,
3
28.2, 128.0, 127.9, 127.8, 127.5, 126.8, 126.7, 126.2, 125.9, 125.6, 125.5, 124.9, 124.7, 123.9,
23.7, 123.3, 123.2, 122.9, 119.8, 117.9, 111.0, 43.2, 31.6, 29.2, 29.0, 26.8, 22.5, 14.3; IR (KBr):
-1
724, 2920, 2845, 2364, 1691, 1684, 1563, 1476, 1388, 1234, 1143, cm ; HRMS (ESI): Calcd.
+
For C H N O [M+H] 600.2825; found 600.2777
4
2
36
2
2
2.6. DSSC Fabrication
FTO conducting plates were cleaned with a soap solution and water to remove the organic
impurities on the surface, followed by sonication for 10 minutes in Millipore water, acetone, and
13

New Journal of Chemistry
Page 14 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
isopropanol. After drying these plates over N flow, they were immersed in a 40 mM aqueous
2
solution of TiCl , washed with water and ethanol, and subsequently sintered at 500 ˚C for 30
4
2
minutes. A 11.4 ± 0.85 μm thick (Fig. S7), 0.196 cm active area nanocrystalline transparent TiO
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
layer was coated by the doctor blade technique, and these TiO coated electrodes were heated at
2
5
0˚C for 15 min, followed by sintering at 450 ˚C for half an hour. After cooling to room
temperature, a scattering layer of TiO colloid was coated on the top of the transparent layer and
2
dried for 20 minutes at 50 ˚C followed by sintering at 400 ˚C for 20 minutes (FTO/TiO ). Finally,
2
FTO/TiO was immersed in a 5 ml of 0.5 mM PC0, PC1 or PC2 dye bath containing different
2
solvents such as tertiary butyl alcohol and acetonitrile (1:1 ratio; TACN), ACN, DCM, Acetone
(ACE), ethyl acetate (EtOAc), chloroform (CHCl ) and chlorobenzene (C H Cl) and kept at room
3
6
5
temperature for 24 h. To understand the effect of dye aggregation on TiO , 5 mM of CDCA has
2
been added to the dye solution. Finally, the stained electrodes (Photoanodes) were rinsed with the
respective solvent to remove unadsorbed dye. The iodine/iodide electrolyte [0.1 M LiI, 0.05 M, I2,
and 0.5 M TBP, 1-butyl-3-methyl imidazolium iodide (0.6 M) in 1 ml of ACN (85 %) and Valero
nitrile (15 %)] was used to soak the dye-coated FTO/TiO film and sandwiched against a platinum-
2
coated FTO electrode. To prevent short circuit and electrolyte leak, the two electrodes were
separated by a 60 m hot-melt Surlyn gasket film.
2
.7. Computational details
40
All the theoretical calculations on the dyes were performed with the help of Gaussian 09 . To
gain insights about the molecular structure, Kohn-Sham density functional theory (DFT)
calculations at B3LYP/ 6-31G(d,p) level was performed 41, 42. TD-DFT calculations were carried
out on the optimized ground state geometries to obtain oscillator strengths (f) and excitation
14

Page 15 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
energies using CAM-B3LYP 43 and PBE1PBE 44 functional and 6-31G(d,p) method. The effect of
solvent (DCM) was included by an integral equation formalism polarizable continuum model
4
5
(IEF-PCM) (dielectric constant, ε = 8.93) .
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
To understand the dye and TiO interactions, we had calculated the adsorption of dye molecules
2
46, 47
onto the semiconductor anatase TiO surface (1 0 1) by VASP
(Vienna ab initio simulation
2
package), using generalized gradient approximation (GGA) together with the Perdew–Burke–
Ernzerhof (PBE) functional 48, 49. The pseudopotential was used based on the projector-augmented
wave (PAW) method that explicitly includes the valence electrons. An energy cutoff of 520 eV
was employed. Moreover, the total densities of states (TDOS) of the dye@TiO complex systems
2
and the projected density of states (PDOS) of the TiO supercell were also calculated at the similar
2
level to analyze the adsorption properties 50-53
.
3
. Results and discussion
3.1. Absorption spectra
UV-visible absorption experiments have been performed to investigate the light-harvesting
potential and the molar extinction coefficient () of the dyes (PC0, PC1, and PC2). A DCM stock
−3
solution of 0.5 × 10 M dye was prepared, and the absorbance was measured in dilute concentration,
and the  was calculated for the ICT bands. Fig. 2a shows the absorption spectrum of the dyes in the
DCM solvent. The dyes displayed prominent absorption bands in the range of 200 – 500 nm. The
bands in the higher energy region are attributed to π-π* transition of the pyrene- carbazole
fluorophores, whereas the lower energy band is because of intramolecular charge transfer (ICT)
from donor to acceptor. The λmax values for PC0, PC1, and PC2 were 430 nm, 410 nm, and 387
4
-1
-1
nm, respectively. The calculated  for the ICT of dyes were PC0: 1.03 × 10 M cm , PC1: 3.59 ×
15

New Journal of Chemistry
Page 16 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4
-1
-1
4
-1
-1
1
0 M cm , PC2: 4.19 × 10 M cm respectively, which are higher than that of Ru–complex
4
-1
-1
4
-1
-1 54
sensitizers N3 (1.39  10 M cm ) and N719 (1.40  10 M cm ) .
TD-DFT calculations were carried out using PBE1PBE/6-31G(d,p) for PC0 and PC1 dyes, and
CAM-B3LYP functional was used for PC2 dye, to understand the electronic transitions from the
occupied to virtual orbitals. Fig. 2b displays the theoretical UV-Vis absorption spectra of dyes
obtained by considering the 20 lowest singlet-singlet transitions in the DCM solvent. The
simulated absorption spectra show reasonable agreement (in terms of the qualitative order of the
maximum wavelength (λcom) of ICT peak; PC0(449 nm) > PC1(421 nm) > PC2 (386 nm)) with
the experimental UV-Vis spectra of the dyes in DCM solvent. The calculated absorption spectrum
of the dyes deviates from the experimental absorption spectrum within the 20 nm limit which is
acceptable. The details of calculated oscillator strength (f), λcom, triplet state energy and the
percentage of the major transitions are presented in Table 1.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Generally, short conjugation leads to high triplet energy to the dye. Still, carbazole, although
5
5
having three fused rings, is characterized with high triplet energy . Especially carbazole whose
3 and 6 positions substituted possess high triplet energy than carbazole itself. The reason behind
is the five-membered heterocyclic aromatic ring in carbazole has reduced aromaticity resulting in
a reduced conjugation effect between the five-membered heterocyclic aromatic ring and the
neighbouring benzene rings. We have calculated the triplet energy of the dyes, and it is 1.44, 1.73,
1
.38 eV for PC0, PC1, and PC2, respectively. PC1 is higher than PC0, as the presence of a single
bond between the chromophores (pyrene and carbazole) reduces the conjugation of the molecule.
As shown in Table 1, the % of HOMO-LUMO transition is low for PC2 in comparison to the PC1
and PC0; therefore, PC2 shows the lowest solution-phase λmax among the dyes studied here.
Furthermore, the λcom of ICT is in good agreement with the f and percentage of major transitions.
16

Page 17 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
2
0
7
6
5
4
3
2
1
0
PC0
PC1
PC2
PC0
PC1
PC2
16
1
2
8
4
0
(a)
(b)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
00
250
300
350
400
450
500
200 250 300 350 400 450 500 550 600
Wavelength (nm)
Wavelength (nm)
Fig. 2 UV-Vis absorption spectra of the dyes in dichloromethane solvent (a) experimental and
b) computational.
(
Table 1 Computed absorption wavelengths (λcom, in nm), electronic transitions, triplet state energy
and oscillator strengths (f) for the singlet–singlet transitions for metal-free organic dyes in DCM
solvent medium.
Triplet state
훌퐜퐨퐦
Oscillator
nm) strength (f)
Major Transition
(%)
energy
Dyes
PC0
Functional
(
HOMO->LUMO
(97%);
4
49
0.4841
0.2453
0.5192
PBE1PBE/6-
31G(d,p)
258
H-1->L+1 (70%);
H-6->L (25%), H-1-
1.44
2
27
21
>
L+2 (43%)
HOMO->LUMO
(96%);
4
0.3355
0.9096
0.3887
0.2975
PBE1PBE/6-
375
356
264
PC1
PC2
H-1->L (85%);
H->L+1 (84%);
H-2->L+2 (62%)
HOMO->LUMO
(37%), H->L+1
(42%); H-1->L (37%),
H->L+1 (42%);
H->L+2 (36%);
H-1->L+1 (39%)
1.73
1.38
3
1G(d,p)
3
86
2.1541
0.2707
0.3125
0.4287
CAM-
347
B3LYP/6-
1G(d,p)
2
2
99
85
3
17

New Journal of Chemistry
Page 18 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Solid State absorption studies (Fig. 3) were analyzed together with the solution state to understand
the type of aggregation of three dyes (PC0, PC1, and PC2) on TiO film. H-type and J-type
2
aggregations are because of the relative alignment of transition dipole moments on the adjacent
molecules and predicting upfront the type of aggregation molecule will adopt in a solid-state is a
challenging task. To best of our knowledge, there is no universal guideline developed on this
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
5
6
topic . It has been reported in the literature that H-and J-type aggregation will lead to poor and
better photovoltaic performance, respectively57-58. In general, dye-aggregation might lead to
quenching. At the same time, the formation of such aggregates has significant consequences for
the energies of the excited states and the oscillator strengths of the transitions to these states from
the ground state. In the literature, J-aggregation is credited with collective excitation of dye, which
59
in turn improves the Jsc, thereby benefiting the DSSC . It can be seen that PC2 dyes on TiO film
2
showed a broadened and red-shifted absorption compared to the solution state absorption spectrum
and is due to J-aggregation (head-to-tail arrangement of dye molecules) which is beneficial for
60
enhancing PCE of DSSC . Whereas when compared to the solution state, a blue shift is observed
for PC0 dye on TiO film and is because of H- type aggregation. The aggregation of the H-type
2
6
1
usually results in poor photovoltaic performance . On TiO film, PC0 and PC2 dyes, along with
2
CDCA, show a slight broadening in their absorption spectra compared to their CDCA free solid-
state spectrum, whereas for PC1+ CDCA, a significant blue shift was observed. While we do not
know the exact reason for this H-type aggregation of PC1 dye, we assume it is due to its
comparatively rigid structure compared to PC2. The percentage decrease in the dye loading due to
incorporation of CDCA is 31 %, 44 %, and 35% for dye PC0, PC1, and PC2, respectively.
18

Page 19 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fig. 3 Normalized UV–Visible absorption spectra of the dyes adsorbed onto TiO film (a) PC0
2
(b) PC1 (c) PC2.
3
.2. Electrochemical properties
The electrochemical properties of the dyes (PC0, PC1, and PC2) such as redox potential, energy level
-
-
alignment with respect to TiO and I /I redox couple were examined by cyclic voltammetry and
2
3
computational methods. The benchmark analysis was done using different meta-hybrid functionals
such as B3LYP, CAM-B3LYP, M06, M06-2X, PBE1PBE, and WB97XD with basis set 6-
3
1G(d,p). A close match to the experimental data was seen with the B3LYP/6-31G(d,p), as shown
in Table S1.
The representative CV of PC0 (Fig. 4) shows one oxidation and one reduction event, whereas PC1 and
PC2 exhibit a pair of peaks for oxidation and a pair of peaks for reduction. The first oxidation peak
(lower potential) may come from the aromatic core of the pyrene and the second one from the carbazole
19

New Journal of Chemistry
Page 20 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
donor moiety. The HOMO-LUMO (E , eV) gaps were calculated using equation (1) from λ (nm)
H-L
onset
+
of absorption spectra. Following calibration with Fc / Fc couple (Fc=Ferrocene), the energy level of
HOMO (EHOMO) was determined using equation (2), and from EH-L and EHOMO, the energy of LUMO
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
ELUMO) was calculated. The dyes exhibited a quasi-reversible redox behavior, and the calculated EHOMO
were -5.30 eV, -5.07 eV, -5.05 eV vs. vacuum and the corresponding ELUMO values were -2.80 eV, -
.40 eV, -2.48 eV for the PC0, PC1 and PC2 dye, respectively. The experimental EH-L for PC0, PC1
2
and PC2 were 2.50 eV, 2.67 eV and 2.57 eV, respectively. EHOMO values indicate incorporation of
carbazole makes PC1 and PC2 more electropositive than PC0, which is a requested property for easy
oxidation of the dye while shining light. But, the increase in E , upon the introduction of carbazole,
H-L
indicates the poor light-harvesting ability of PC1 and PC2 at higher wavelengths compared to PC0,
which is in line with the observation of solution UV-Vis spectra, wherein higher max was observed for
PC0. At the same time, it should be noted that  value of PC1 and PC2 are higher than PC0; therefore,
the introduction of carbazole may not be a bad choice as it enhances the probability of light
absorption. PC1 having higher EH-L may indicate orthogonal positioning of pyrene with respect to
carbazole donor moieties via a single bond spacer.
0.15
PC0
PC1
PC2
0
0
.10
.05
0.00
0.05
0.10
-
-
-0.15
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
+
Potential applied (V) vs. Ag/Ag
20

Page 21 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
Fig. 4 Cyclic voltammogram of the dyes in 0.1 M TBAPF in dry DCM solvent recorded at a
6
-1
scan rate of 50 mVs .
The experimental energy level diagram in Fig. 5, shows both EHOMO and ELUMO are favorably aligned
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
with the conduction band (CB) of semiconductor metal oxide (TiO ; -4.0 eV) and the redox energy level
2
of the iodine/triiodide electrolyte (-4.8 eV), respectively, to complete the electrical circuit. The dye
regeneration energy is found to be 0.5 eV, 0.27 eV and 0.25 eV for PC0, PC1 and PC2, respectively.
According to the literature, the optimum driving force for dye regeneration lies in the range of 0.2–
0
.25 V to achieve a theoretical regeneration yield of 99.9 %. As the driving force is further
6
2
increased, the regeneration reaction becomes diffusion controlled , leading to a reduction in the
photocurrent. Therefore, PC1 and PC2 are expected to perform better than PC0. The driving force
for the electron injection (G ), that is, the energy difference of LUMO of the dye and CB of
inj
semiconducting oxide, is found to be 1.20 eV, 1.60 eV, 1.52 eV, for PC0, PC1, and PC2,
respectively.
1
240
퐸퐻 ― 퐿(푒푉) =
(1)
(2)
(3)
휆표푛푠푒푡
퐸퐻푂푀푂(푒푉) = ― 퐸1 ― 퐸1 2 (퐹푐 퐹푐 +
표푥
)
+ 5.1 푣푠. 푣푎푐푢푢푚
[
]
2
퐸퐿푈푀푂 (푒푉) = 퐸퐻푂푀푂 + 퐸0 ― 0
21

New Journal of Chemistry
Page 22 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
-2
-
2.40
-
2.48
LUMO
-2.80
-
3
-4.0
E0-0 gap
-
2.50 -2.67 -2.57
-4
CB
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-4.8
-
-
5
6
-
-
I /I HOMO
3
PC0 PC1
5.3
-5.07
PC2
-5.05
-
-
7.2
-7
VB
TiO2
-
8
Fig. 5 Experimental energy level diagram of the dyes with calculated EHOMO, ELUMO and E0-0 gap
-
-
values along with the redox energy of I /I redox couple and CB of TiO .
3
2
3
.3. Frontier molecular orbital diagram
The optimized geometries and electron distribution of dyes have been shown in the frontier
molecular orbital diagram (FMO, Fig. 6a – 6c), which depicts the push-pull nature of ICT for the
dyes. For PC0 dye, HOMO is delocalized on the entire pyrene cyano-acrylic acid. In contrast,
LUMO is shifted to the cyano-acrylic acid unit, with small retention of electron density on pyrene
donor which is due to the electron-accepting nature of the pyrene. In the case of PC1 and PC2,
HOMO covers both pyrene and carbazole donors along with π-spacer, and LUMO shifted to
carbazole cyano-acrylic acid unit, as both the dyes are having same donors and acceptors. It is
evident from the above results that the spatial separation of ICT is high for PC1 and PC2 dye
compared to PC0, which increases the efficiency of electron injection due to the maximum charge
density on the cyano-acrylic acid acceptor. Further, it is confirmed by larger dipole moment
observed for PC2 (9.92 D) than PC0 (9.75 D) and PC1 (7.92 D) dye. The higher value for the
dipole moment shows that the distance between the centroid of the hole and the electron is longer
22

Page 23 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
and thus shows a strong separation of the charge. PDOS was calculated using the B3LYP/6-31G
d,p) method, and the relevant data is shown in Table S2. For the dyes PC0, PC1, and PC2, the
(
electron density is delocalized to a larger extent in the donor part for HOMO and in the acceptor
part for LUMO.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Optimized geometry
HOMO
LUMO
(a)
(b)
(c)
Fig. 6 The optimized geometries and the frontier orbital diagram (isovalue for the surfaces = 0.02)
of (a) PC0, (b) PC1, and (c) PC2.
3
.4. Dihedral angle
The geometry (twist vs. planar) of dyes is one of the most critical factors determining the efficiency of
ICT, which, in turn, results in light-harvesting ability and photovoltaic properties of DSSCs. Fig. 7 &
23

New Journal of Chemistry
Page 24 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
38.26 
44.66 
PC0
PC1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
179.84 
0.02 
0.58 
1
79.58 
PC2
Fig. 7 The dihedral angle of dyes (PC0, PC1 and PC2) with respect to acceptor.
Fig. 8 show the geometry-optimized ground-state molecular structures of dyes with the dihedral angles
measured at the interface of pyrene/carbazole (via single and double bond) and carbazole/cyano-acrylic
acid. The role of carbazole is apparent while comparing the dihedral angles measured between donor
and acceptor. For PC0, the dihedral angle between the unit of pyrene and cyano-acrylic acid is 138.26 ˚
(trans configuration). In contrast, for PC1 and PC2 (between carbazole and cyano-acrylic acid, trans
24

Page 25 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
˚
˚
configuration) the angles are 179.84 and 179.58 respectively, suggesting the introduction of carbazole
enables achieving planarity between donor and acceptor, which could be the reason for the high 
˚
values of PC1 and PC2. For PC1, the dihedral angle between pyrene and carbazole is 123.23 , and for
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
˚
PC2, the dihedral angle between pyrene and the double bond is 153.48 , and double bond and carbazole
˚
is 169.11 . Therefore, ICT from the pyrene end to the acceptor is expected to be effective in PC2 than
PC1 due to the near planarity in the overall dye structure.
Fig. 8 The dihedral angle in between pyrene and carbazole donors of dyes (PC1 and PC2) with
respect to π-spacer.
25

New Journal of Chemistry
Page 26 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
.5. Reorganization energy calculation
Reorganization energy is the energy penalty caused by the conformational change in the molecule
during photooxidation and regeneration. According to Marcus electron transfer theory, it could
affect the kinetics of electron injection. Customarily, reorganization energy can have two parts:
internal reorganization energy (Λ ) and external reorganization energy (Λ ). Λ embodies the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
int
ext
ext
effect of charge transfer due to solvent medium, and Λ due to the structural transformation
int
between neutral and ionic states. We had ignoring the effect of the solvent and considered the Λint
of isolated organic molecule DFT calculation to speculate the mobility of the charge carriers. The
sum of the electron (Λ ) and hole (Λ ) reorganization energies is the total reorganization energy
e
h
(Λtotal). The smaller the Λtotal, better would be the electron injection ability to achieve higher 퐽푆퐶.
The calculated Λ , Λ , and Λ of three dyes are given in Table 2. The Λtotal value of PC1 and PC2
e
h
total
is nearly equal and smaller than that of PC0. This indicates that PC0 will have a lower electron
injection ability, therefore expected to show low PCE in DSSC. PC1 and PC2 exhibited the lowest
Λtotal, which would enhance the rate of electron transfer to the CB of TiO from the excited state of
2
dye, which is expected to manifest in their PCE as well.
Table 2 The calculated electron reorganization energy (Λ ), hole reorganization energy (Λ ), total
e
h
reorganization energy (Λtotal) obtained using B3LYP/6–31G (d,p) method.
Dyes Λ (eV) Λ (eV)
Λtotal (eV)
0.732
e
h
PC0
PC1
PC2
0.559
0.173
0.254
0.221
0.246
0.289
0.500
0.510
3
.6. Adsorption and density of states of dye@TiO (101) surface
2
The adsorption energies (E ) for PC1 and PC2 are calculated on the anatase TiO (1 0 1) surface
ads
2
using DFT after attaching dye molecule. The geometries optimization was done on dye anchored
26

Page 27 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
TiO using bidentate bridging mode, which are shown in Fig. 9. The calculated distance between
2
Ti and O (from the acceptor), and adsorption energy for dyes have been tabulated in Table 3. The
negative adsorption energy (E ) implies the formation of chemical bond between the dye and
ads
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
TiO surface, hence there will be better electron injection ability from the LUMO of dye to the CB
2
of the TiO . The E values are estimated by using equation 4, and the values are listed in the
2
ads
Table 3.
퐸푎푑푠 = 퐸
(
)
―
(
퐸푑푦푒 + 퐸푇푖푂2
)
(4)
푑푦푒 + 푇푖푂2
Where 퐸(푑푦푒 + 푇푖푂 is the total energy for the dye anchored onto the TiO surface, and 퐸
and
푇푖푂2
2)
2
Edye refer to the total energy of the TiO semiconductor and isolated dye, respectively. Both PC1
2
and PC2 had shown a sufficiently negative adsorption energy value. Furthermore, DOS
calculations were performed to understand the nature of bonding interaction of the dye molecules
with the TiO surface. The PDOS profiles of the TiO slab, the DOS of dye, and dye@TiO (in the
2
2
2
case of dye absorbed onto the TiO surface) are displayed in Fig. 10. It is clear from the DOS of
2
TiO (101) oriented slab, that the surface does not lead to any defect states in the bandgap. PDOS
2
of dye adsorbed TiO surface confirms the absence of any defect state/trap states in the bandgap
2
of TiO which helps in the smooth transfer of electrons from dye to TiO .
2
2
Table 3 Calculated adsorption energies (Eads in eV) and bond lengths (in Å) of the optimized dye
structures.
Dye
Name
Eads (eV) Ti -O / Å Ti -O / Å d / Å O -H / Å
1
1
2
2
3
PC1
PC2
-0.379
-0.465
2.099
2.062
1.994
1.946
2.047
2.004
0.966
0.969
27

New Journal of Chemistry
Page 28 of 41
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Fig. 9 Ground state optimized geometries of dyes@TiO with an expanded view of the interface
2
between the dyes and the TiO surface displaying the bidentate bridging binding of the dye onto
2
the TiO surface shown at the center of the figure.
2
Fig. 10 Partial density of states of TiO and total density of states of the dye@TiO .
2
2
28

Page 29 of 41
New Journal of Chemistry
View Article Online
DOI: 10.1039/D0NJ03228J
1
2
3
4
5
6
7
8
9
3
.7. Photovoltaic performance
Fig. 11 illustrates the J-V diagram for the dyes (PC0, PC1, and PC2), and the corresponding
photovoltaic parameters such as 푉 , 퐽 , FF, and PCE are summarized in Table 4. The
푂퐶
푆퐶
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
photovoltaic performance of the fabricated DSSCs in different solvents (TACN, ACN, ACE,
DCM, CHCl , EtOAc, and C H Cl) was assessed under simulated AM 1.5G irradiation (100 mW
3
6
5
−
2
cm ) (Fig. S8, Table S3-S5). Standard N719 dye also measured under the same experimental
conditions. It can be inferred that the sensitizing solvent greatly affects the PCE of DSSC, and the
best PCE is observed with a 1:1 mixture of TACN for the dyes (PC0, PC1, and PC2). The FF and
the PCE of the DSSC were calculated by following the equations (5) and (6)
푉푂퐶  퐽푆퐶 퐹퐹
푃퐶퐸 (%) =
× 100
(5)
(6)
푃푖푛
푃푚푎푥
퐽푚푎푥 × 푉푚푎푥
where 퐹퐹 = 퐽푆퐶 × 푉푂퐶 = 퐽푆퐶 × 푉푂퐶
–2
Pin is the incident light power, Jmax (mA cm ) and V (V) are the current density and voltage at
max
the maximum power point in the J-V curves, respectively.
The 푉푂퐶 was in the range of 0.71- 0.81 V for the dyes in the chosen solvents, whereas the 퐽 and
푆퐶
FF have varied for the dyes in different solvents. The solvent effect on DSSC performance is
complicated. It may be attributed to the various properties such as solubility, dielectric constant,
polarity, viscosity, etc. and this decides the optimum amount of dye adsorbed on the TiO electrode
2
63, 64. It is thus found that TACN is the best solvent for the dyes. As expected, the open circuit
potential for PC1 and PC2 is slightly higher compared to PC0, which is consistent with the
oxidation ability of the two donors in the dyes. The photovoltaic parameters (푉 , 퐽 , PCE) are
푂퐶 푆퐶
found to be in the following order: PC2 > PC1 > PC0. The DSSC of PC2 showed the best PCE at
29