Highly effective thieno[2,3-b]indole-diketopyrrolopyrrole near-infrared photosensitizer for photodynamic/photothermal dual mode therapy

Article abstract of DOI:10.1016/j.dyepig.2017.08.023

Synthesis of photodynamic and photothermal agents with absorption in the near-infrared (NIR) region and featuring excellent photostability, high singlet oxygen generation efficiency, good photothermal conversion efficiency, and good biocompatibility is ne

Full text of DOI:10.1016/j.dyepig.2017.08.023

Accepted Manuscript
Highly effective thieno[2,3-b]indole-diketopyrrolopyrrole near-infrared photosensitizer
for photodynamic/photothermal dual mode therapy
Jing Yang, Yu Cai, Yanxiang Zhou, Caixia Zhang, Pingping Liang, Baomin Zhao,
Jinjun Shao, Nina Fu, Wei Huang, Xiaochen Dong
PII:
S0143-7208(17)31277-9
10.1016/j.dyepig.2017.08.023
DYPI 6185
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 2 June 2017
Revised Date: 7 August 2017
Accepted Date: 14 August 2017
Please cite this article as: Yang J, Cai Y, Zhou Y, Zhang C, Liang P, Zhao B, Shao J, Fu N, Huang
W, Dong X, Highly effective thieno[2,3-b]indole-diketopyrrolopyrrole near-infrared photosensitizer
for photodynamic/photothermal dual mode therapy, Dyes and Pigments (2017), doi: 10.1016/
j.dyepig.2017.08.023.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract
Highly Effective Thieno[2,3-b]indole-Diketopyrrolopyrrole
Near-Infrared Photosensitizer for
Photodynamic/Photothermal Dual Mode Therapy
§
a
§a
a
b
a
Jing Yang, Yu Cai, , Yanxiang Zhou, Caixia Zhang, Pingping Liang, Baomin
b
a
b
a
a
Zhao , Jinjun Shao , Nina Fu,* Wei Huang,* Xiaochen Dong*
a
Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM),
Jiangsu National Synergistic Innovation Center for Advanced Materials (SICAM), Nanjing
Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, P.R. China
b
Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced
Materials, National Jiangsu Synergetic Innovation Center for Advanced Materials (SICAM),
Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023, China
X.C.Dong: iamxcdong@njtech.edu.cn.
§
These authors contributed equally to this work.
Three NIR absorption compounds based on thieno[2,3-b]indole (TI) and diketopyrrolopyrrole
(DPP) were designed and synthesized. Their UV-vis-NIR absorption, photoluminescence,
electronic distribution, energy levels and thermally induced phase transitions have been carefully
determined. As structural analogues, only DPP-TI possesses excellent singlet oxygen quantum
1
yield ( O , Φ = 48.5%), which displays effective photothermal conversion efficiency (η = 15.8%)
2
ꢀ
as nanoparticles in water. The potential of DPP-TI nanoparticles as fluorescence imaging
therapeutic agent for synergetic PDT and PTT in vitro were explored preliminarily.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Highly Effective Thieno[2,3-b]indole-Diketopyrrolopyrrole
Near-Infrared Photosensitizer for
Photodynamic/Photothermal Dual Mode Therapy
§
a
§a
a
b
a
Jing Yang, Yu Cai, Yanxiang Zhou, Caixia Zhang, Pingping Liang, Baomin
b
a
b
a
a
Zhao, Jinjun Shao, Nina Fu,* Wei Huang,* Xiaochen Dong*
a
Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM),
Jiangsu National Synergistic Innovation Center for Advanced Materials (SICAM), Nanjing
Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, P.R. China
b
Key Laboratory for Organic Electronics and Information Displays & Institute of Advanced
Materials, National Jiangsu Synergetic Innovation Center for Advanced Materials (SICAM),
Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023, China
N.N.FU: iamnnfu@njupt.edu.cn
§
These authors contributed equally to this work.

ACCEPTED MANUSCRIPT
Abstract: Synthesis of photodynamic and photothermal agents with absorption in the
near-infrared (NIR) region and featuring excellent photostability, high singlet oxygen
generation efficiency, good photothermal conversion efficiency, and good
biocompatibility is necessary for the application of photodynamic therapy (PDT) and
phtothermal therapy (PTT). Three NIR absorption compounds based on
thieno[2,3-b]indole (TI) and diketopyrrolopyrrole (DPP) were designed and
synthesized. Their UV-vis-NIR absorption, photoluminescence, electronic
distribution, energy levels and thermally induced phase transitions have been
carefully determined. As structural analogues, only DPP-TI possesses excellent
1
singlet oxygen quantum yield ( O , Φ = 48.5%), which displays effective
2
ꢀ
photothermal conversion efficiency (η = 15.8%) as nanoparticles in water. The
potential of DPP-TI nanoparticles as fluorescence imaging therapeutic agent for
synergetic PDT and PTT in vitro using only one wavelength light were explored
preliminarily.
Keywords: photodynamic therapy; photothermal therapy; diketopyrrolopyrrole;
thieno[2,3-b]indole.

ACCEPTED MANUSCRIPT
1
. Introduction
Since its first use in clinic trials in 1980s,[1] photodynamic therapy (PDT) has
been an approved photo-activated and non-invasive medical technique widely used
for cancer therapy and has been demonstrated to be effectives as a both a curative and
palliative treatment.[2,3] PDT is often used to treat solid tumors which cannot be
easily surgically removed and which may not respond well to radiation therapy and
chemotherapy. Principally, PDT involves the administration of a non-toxic
photosensitizer[3,4] and tissue oxygen under harmless visible light to generate
cytotoxic reactive oxygen species (ROS) such as singlet oxygen (Type II). As one of
the primary toxic ROS, the singlet oxygen is generated by energy transfer between the
triplet excited state of photosensitizers and the ground state of O , which are directly
2
toxic to cells by apoptosis and/or necrosis.[2-4] In addition to direct tumor cell killing,
PDT also causes vascular damage and blood flow stasis which deprives the nutrients
to tumor cells and PDT has also been shown to stimulate anti-tumor immune
responses.[5,6] Compared to conventional treatments (surgery, radiation and
chemotherapy), PDT has certain advantages, including minimal normal tissue
toxicity, no long-term systemic toxicity such as spatial selectivity,
immunosuppression, lack of drug resistance mechanisms, and favourable cosmetic
outcomes.[7]Note that prolonged PDT treatment time would cause severe local
hypoxia by depletion of tissue oxygen and lead to the decrease of therapeutic effect,
for example, the O content is reported to be about 4% in various tumor tissues.[8] To
2

ACCEPTED MANUSCRIPT
address this issue, it is smart to combine PDT with other anti-cancer
techniques/agents. As well known that photothermal therapy has unique feature and
induce cell injury as a systemic effect, resulting in protein denaturation, mechanical
membrane damage, and even cell fragmentation.[9] Thus, the use of nanomaterials in
medicine by combining PDT and PTT into a single platform holds great potential to
revolutionize the future of cancer therapy.[10]
However, the requirement of outer light source always limits effective
application of PDT and PTT to the lesions in deeper tissue since the light does not
penetrate far through due to the absorption and scattering by biological tissues.[11]
Effective photothermal agents should possess strong absorbance, effective
photothermal conversion efficiency, and good photostability in the NIR region, in
which the absorbance by biological tissues, blood and water is the lowest. Although
infrared light can reduce this shortcoming, unfortunately the development of
photosensitizers with highly efficient absorption of infrared light has proved a
challenge.
Since porphyrin-like nucleus based photosensitizer is first proposed,[3] a large
number of photosensitizers, including phthalocyanine,[11,13] BODIPY,[14]
fullerene,[15] and chlorin e6 derivatives [12] have been investigated. A survey of the
literatures on these PSs conveys the idea that most PSs suffer from several drawbacks,
including low absorption in the therapeutic window (650–900 nm), low photostability,
poor water-solubility and side effects toward normal tissues.[16] Thereby, the
development of high efficient photosensitizers for PDT, with the characteristics of

ACCEPTED MANUSCRIPT
intense and broad near-infrared (NIR) absorption, high photostability, good
biocompatibility and good water dispersibility, remains a big challenge.[17,18]
Our current research mainly focuses on the development of novel π-conjugated
materials, such as diketopyrrolopyrrole (DPP) derivatives for PDT
applications.[19,20] These DPP derivatives show excellent ROS generation
efficiency, good water-solubility, low toxicity and applicable fluorescence emission.
However, their absorption maximum locating at visible range of optical spectrum
greatly limits their clinical application.[21] To circumvent this limitation, the
development of novel DPP-based PDT agents with intense NIR absorption is
necessary.[22] Usually, NIR-absorbing organic semiconducting molecules can be
constructed by a rational donor-acceptor (D-A) design strategy. Because
intramolecular charge transfer (ICT) from electron-donating segments to
electron-accepting sites will enhance the absorption capability at longer wavelength
regime and achieve a narrow band gap.[23] For example, NIR-photosensitizers by
incorporating porphyrin[24] and triphenylamine[25] motifs with DPP have been
developed recently for PDT and photoacoustic imaging. On the other hand, the
intersystem crossing (ISC) process is highly dependent on the hybridized energy
levels and molecular structures, and the donor and acceptor components must be
carefully selected and paired in terms of PDT and PTT applications.[26, 27] Thus, the
fundamentals for rational design PDT/PTT dyes with DPP as core building blocks is
necessary. In this context, the donor unit is very crucial for the synthesis of
DPP-based D-A conjugated molecules for PDT and PTT applications.[28]

ACCEPTED MANUSCRIPT
On the basis of these considerations, we prepared three D-A-D NIR absorbing
compounds, DPP-TI, DPP-TIH and DPP-r-TI, based on thieno[2,3-b]indole (TI) as
donor unit and diketopyrrolopyrrole (DPP) as acceptor unit (see in Scheme 1).[29]
Their UV-vis-NIR absorption, photoluminescence, electronic distribution, energy
levels and thermally induced phase transitions were carefully determined and
compared. The photoactivated singlet oxygen generation efficiency of each compound
were measured to select the most efficient one. Water-soluble DPP-TI NPs,
displaying a pronounced photothermal conversion efficiency, were obtained by
encapsulating hydrophobic DPP-TI with amphiphilic polymer.[30] Also presented
was the applicability of DPP-TI NPs for fluorescence imaging as well as PDT/PTT
dual mode therapy in Hela cells after assessment of their dark cytotoxicity to
demonstrate their potential as a photosensitizer and an imaging agent under only one
excitation wavelength of light.
Scheme 1. Structures of DPP/TI based NIR compounds DPP-TI, DPP-TIH and DPP-r-TI.
2
. Experimental section

ACCEPTED MANUSCRIPT
2
.1. Materials and instruments
2,5-dibromonitrobenzene, 2-dodecyl-thiophene boron ester, tetrabutylammonium
bromide (TBAB), tetrakis(triphenylphosphine)palladium (Pd(PPh ) ), sodium sulfate
3
4
(
Na SO ), triphenylphosphine, 1-bromohexane, potassium hydroxide (KOH),
2 4
potassium
iodide
(KI),
dichloromethane
(DCM),
potassium
acetate,
bis(pinacolato)diboron, bis(triphenylphosphine)palladium(II) chloride (Pd(PPh ) Cl ),
3
2
2
N,N-dimethylformamide (DMF), Petroleum ether (PE), thiophene-2-boronic acid
pinacol ester, 1-bromo-2-nitrobenzene, 3-thiopheneboronic acid, N-bromosuccinmide,
n-butyllithium,
isopropoxyboronic
acid
pinacol
ester,
distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG2000)
were commercially delivered and used without any treatment. Anhydrous toluene and
tetrahedrofuran (THF) were freshly distilled in the presence of Na and benzophenone.
1
13
H NMR and C NMR tests were performed using a DRX 400 nuclear magnetic
resonance spectrometer from Bruker, Germany. The samples were dissolved in
1
13
deuterated chloroform and measured at 400 MHz ( H NMR) or 100 MHz ( C NMR).
Matrix assisted laser desorption ionization time-of-flight mass spectrometry
(MALDI-TOF MS) was recorded using a Bruker Autoflex II mass spectrometer using
anthracene-1,8,9-triol as the matrix. High resolution mass spectrum was determined
on a Finnigan MAT95XL mass spectrometer using the electron-ionization. Elemental
analysis was performed on a Vario EL III Elementar system (Elementar
Analyzen-systeme, Hanau, Germany). Elemental analyses are the average of three
runs. All samples were measured simultaneously for C, H, N and S. The fraction of O

ACCEPTED MANUSCRIPT
was deduced from the fractions of other atoms. The reported EA data were the
average of three entries. The electrochemical cyclic voltammetry (CV) was conducted
on PGSTAT-100N electrochemical analyzer (Wantong, Swiss). Gold electrode was
used as working electrode, Ag/AgCl electrode was used as reference electrode, and Pt
wire electrode was counter electrode, respectively. With a scan rate of 50 mV/s, the
CV curves were obtained directly in dried DCM with 0.1 M of Bu NPF . The
4
6
absorption spectra were measured on UV-3600 UV-vis spectrophotometer (Shimadzu,
Japan). Fluorescence spectra were measured on a spectrometer (HITACHI, Japan,
F-7000). Differential scanning calorimetry (DSC) analysis was performed on Mettler
DSC823e thermal analyzer. Simulation of molecular simulation theory was carried
out on DFT (B3LYP/6-31G) module. Transmission electron microscope (TEM) was
measured on JEOL JEM-1011 transmission electron microscope. The size of
nanoparticles was measured by a particle size analyzer (Brookhaven Instruments,
USA). Thermal images were observed by an infrared camera (FLIR, Arlington, VA,
E50).
2
.2. Synthesis
2-(4-bromo-2-nitrophenyl)-5-dodecylthiophene (3a). To
a
solution of
2
,5-dibromonitrobenzene (2) (3.10 g, 11.03 mmol) and 2-dodecyl-thiophene boron
o
ester (1a) (5.00 g, 13.23 mmol) in 50 mL of anhydrous toluene was stirred at 90 C
under nitrogen was added 23 mL of K CO (an aqueous solution (2 M) of K CO
3
2
3
2
(
44.12 mmol)), TBAB (0.01 g) and Pd(PPh ) (0.05 g, 0.04 mmol).The mixture was
3 4
refluxed overnight. After cooling to room temperature, the crude mixture was

ACCEPTED MANUSCRIPT
extracted with 100 mL of DCM and washed with 100 mL of water. Toluene was
evaporated under reduced pressure. The mixture dried over Na SO and purified by
2
4
column chromatography on silica gel using DCM/PE (1 : 10) as eluent. 3a (4.02 g,
1
yield: 80%). H NMR (400 MHz, CDCl ) δ 7.85 (d, J = 2.0 Hz, 1H), 7.68 (dd, J = 8.3,
3
2
.0 Hz, 1H), 7.43 (d, J = 8.3 Hz, 1H), 6.92 (d, J = 3.6 Hz, 1H), 6.76 (d, J = 3.6 Hz,
1
3
1
H), 2.83 (t, J = 7.5 Hz, 2H), 1.71 (s, 2H), 1.28 (s, 18H), 0.89 (d, J = 7.0 Hz, 3H). C
NMR (100 MHz, CDCl ) δ 134.79, 133.04, 127.25, 126.69, 125.07, 121.06, 31.94,
3
3
1.53, 30.14, 29.69, 29.66, 29.55, 29.37, 29.35, 29.15, 22.71, 14.14.
6-bromo-2-dodecyl-4H-thieno[3,2-b]indole
(4a).
A
mixture
of
2
-(4-bromo-2-nitrophenyl)-5-dodecylthiophene (3a) (3.00 g, 6.64 mmol) and
triphenylphosphine (5.23 g, 19.92 mmol) in 17 mL of anhydrous chlorobenzene was
refluxed under nitrogen for overnight. After cooling to room temperature, toluene was
evaporated under reduced pressure. A crude product was purified by column
chromatography on silica gel using DCM/PE (1 : 6) as eluent. 4a (2.18 g, yield: 78%).
1
H NMR (400 MHz, CDCl ) δ 8.07 (s, 1H), 7.54 (d, J = 1.6 Hz, 1H), 7.24 (d, J = 1.7
3
Hz, 1H), 6.76 (s, 1H), 2.90 (t, J = 7.5 Hz, 2H), 1.77–1.70 (m, 2H), 1.26 (s, 18H), 0.89
1
3
(
d, J = 6.6 Hz, 3H). C NMR (100 MHz, CDCl ) δ 149.53, 142.72, 140.90, 122.86,
3
1
2
19.29, 115.13, 114.57, 108.80, 77.21, 31.92, 31.70, 31.60, 29.70, 29.66, 29.64, 29.56,
9.38, 29.34, 29.09, 22.68, 14.10.
6-bromo-2-dodecyl-4-hexyl-4H-thieno[3,2-b]indole (5a). 6-bromo-2-dodecyl-
4
H-thieno[3,2-b]indole (4a) (1.00 g, 2.38 mmol), 1-bromohexane (0.53 g, 3.20 mmol),
KOH (0.40 g, 7.14 mmol) and KI (0.04 g, 0.24 mmol) in 6 mL of THF was stirred at

ACCEPTED MANUSCRIPT
o
7
0 C under nitrogen for 12 h. After being cooled to room temperature, the crude
mixture was brought in 100 mL of DCM and washed a few times with water. The
mixtures dried over Na SO and purified by column chromatography on silica gel
2
4
1
using pure PE as eluent. 5a (0.30 g, yield: 25%). H NMR (400 MHz, CDCl ) δ 7.50
3
(d, J = 8.4 Hz, 1H), 7.48 (d, J = 1.6 Hz, 1H), 7.22 (dd, J = 8.4, 1.7 Hz, 1H), 6.76 (s,
1
H), 4.15 (t, J = 7.2 Hz, 2H), 2.91 (t, J = 7.5 Hz, 2H), 1.86–1.79 (m, 2H), 1.77–1.70
1
3
(
m, 2H), 1.41–1.21 (m, 24H), 0.88 (q, J = 4.0 Hz, 6H). C NMR (100 MHz, CDCl ) δ
3
1
3
1
49.21, 121.89, 119.36, 114.80, 112.63, 107.79, 53.41, 45.30, 31.95, 31.76, 31.72,
1.49, 29.70, 29.67, 29.59, 29.42, 29.38, 29.15, 26.80, 22.71, 22.55, 14.13, 14.00,
.04.
2
-dodecyl-4-hexyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-thieno-
3,2-b]indole (6a). To solution of
-bromo-2-dodecyl-4-hexyl-4H-thieno[3,2-b]indole (5a) (1.48 g, 0.29 mmol),
[
a
6
potassium acetate (0.87 g, 0.88 mmol), bis(pinacolato)diboron (1.19 g, 0.47 mmol)
o
and Pd(PPh ) Cl (0.50 g, 0.12 mmol) in 50 mL of dry DMF was stirred at 90 C
3
2
2
under nitrogen for 10h. After being cooled to room temperature, the mixture was
brought in 100 mL of DCM and washed a few times with water. The mixture dried
over Na SO and purified by column chromatography on silica gel using DCM/PE (1 :
2
4
1
1
7
2
2
) as eluent. 6a (0.04 g, yield: 21.6%). H NMR (400 MHz, CDCl ) δ 7.83 (s, 1H),
3
.66 (d, J = 7.9 Hz, 1H), 7.58 (d, J = 7.9 Hz, 1H), 6.79 (s, 1H), 4.25 (t, J = 7.2 Hz, 2H),
.93 (t, J = 7.5 Hz, 2H), 1.85 (d, J = 7.1 Hz, 2H), 1.78 (s, 2H), 1.39 (s, 12H), 1.26 (s,
13
4H), 0.88 (dt, J = 7.0, 3.3 Hz, 6H). C NMR (100 MHz, CDCl ) δ 147.10, 125.05,
3

ACCEPTED MANUSCRIPT
1
3
2
24.47, 123.98, 119.13, 117.55, 116.21, 107.85, 83.54, 77.22, 45.03, 34.88, 34.53,
1.93, 31.78, 31.75, 31.54, 31.44, 30.33, 30.22, 29.95, 29.70, 29.66, 29.57, 29.41,
9.36, 29.16, 26.79, 24.93, 22.69, 22.57, 14.11, 14.02, 1.02.
Synthesis of DPP-TI. Compound DPP (0.10 g, 0.15 mmol),
2
-dodecyl-4-hexyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-thieno[3,2-b]i
ndole (6a) (0.2 g, 0.18 mmol) in 10 mL of anhydrous toluene under nitrogen was
added 1 mL of K CO (an aqueous solution (2 M) of K CO (0.88 mmol)), TBAB
2
3
2
3
o
(
0.01 g) and Pd(PPh ) (0.05 g, 0.04 mmol). The mixture was stirred at 90 C. After
3 4
cooling to room temperature, the compounds were brought in 100 mL of DCM and
washed with water. The mixture dried over Na SO and purified by column
2
4
chromatography on silica gel using DCM/PE (1 : 3) as eluent. DPP-TI (0.68 g, yield:
1
4
2%) H NMR (400 MHz, CDCl ) δ 9.01 (d, J = 4.1 Hz, 2H), 7.65 (d, J = 8.3 Hz, 2H),
3
7
.60 (s, 2H), 7.49 (d, J = 4.2 Hz, 2H), 7.46 (d, J = 9.5 Hz, 2H), 6.78 (s, 2H), 4.27–4.21
(m, 4H), 4.19–4.13 (m, 4H), 2.93 (t, J = 7.4 Hz, 4H), 1.89–1.74 (m, 12H), 1.28 (d, J =
1
3
1
1
7
2
4.9 Hz, 68H), 0.89–0.85 (m, 18H). C NMR (100 MHz, CDCl ) δ 151.77, 149.88,
3
46.25, 136.87, 126.63, 123.59, 122.66, 118.71, 117.72, 107.83, 107.63, 107.01,
7.22, 45.12, 42.31, 31.93, 31.84, 31.79, 31.69, 31.49, 30.08, 29.78, 29.69, 29.66,
9.60, 29.42, 29.37, 29.30, 29.19, 27.03, 26.83, 22.70, 22.66, 22.54, 14.11, 14.01.
＋
C H N O S : EI-HRMS: (M ): calc.: 1370.8451; found: 1370.8433. Anal Calc (%)
86
122
4
2 4
for C H N O S : C, 75.28; H, 8.96; N, 4.08; S, 9.35. Found: C, C, 75.32; H, 8.92;
8
6
122
4
2 4
N, 4.06; S, 9.34.

ACCEPTED MANUSCRIPT
2-(4-bromo-2-nitrophenyl)thiophene
(3b).
To
a
solution
of
2
,5-dibromonitrobenzene (2) (5.00 g, 17.80 mmol) and thiophene-2-boronic acid,
o
pinacol ester (1b) (2.73 g, 21.36 mmol) in 40 mL of toluene was stirred at 90 C under
nitrogen was added 30 mL of K CO (an aqueous solution (2 M) of K CO (71.20
2
3
2
3
mmol)), TBAB (0.01 g) and Pd(PPh ) (0.05 g, 0.04 mmol).The mixture was refluxed
3
4
overnight. After cooling to room temperature, the mixture was brought in 100 mL of
DCM and washed a few times with water. The mixtures dried over Na SO and
2
4
toluene was evaporated under reduced pressure. The crude mixture was purified by
column chromatography on silica gel using pure PE as eluent. 3b (2.36 g, yield: 47%).
1
H NMR (400 MHz, CDCl ) δ 7.89–8.03 (d, J = 2.0 Hz, 3H), 7.70–7.72 (dd, J = 8.3,
3
1
3
2
.0 Hz, 2H), 7.40 (m, 1H), 7.13 (m, 1H). C NMR (100 MHz, CDCl ) δ 143.9,
3
1
35.97, 134.98, 133.42, 127.98, 127.64, 127.51, 127.34, 126.84, 121.76.
6
-bromo-4H-thieno[3,2-b]indole (4b). A mixture of 2-(4-bromo-2-nitrophenyl)
thiophene (3b) (4.28 g, 15.06 mmol) and triphenylphosphine (12.64 g, 48.19 mmol) in
0 mL of dry chlorobenzene was refluxed at 140 ℃ under nitrogen for overnight.
2
After cooling to room temperature, toluene was evaporated under reduced pressure. A
crude product was purified by column chromatography on silica gel using DCM/PE
1
(
10 : 1) as eluent. 4b (2.26 g, yield: 60%). H NMR (400 MHz, CDCl ) δ 8.21 (s, 1H),
3
7
1
1
.61–7.59 (m, 1H), 7.59 (s, 1H), 7.39 (d, J = 5.2 Hz, 1H), 7.29 (dd, J = 8.4, 1.7 Hz,
1
3
H), 7.07 (d, J = 5.2 Hz, 1H). C NMR (100 MHz, CDCl ) δ 143.37, 141.83, 127.73,
3
23.02, 121.07, 119.98, 117.88, 116.02, 114.81, 111.51.

ACCEPTED MANUSCRIPT
6-bromo-4-hexyl-4H-thieno[3,2-b]indole (5b). 6-bromo-4H-thieno[3,2-b]indole
(4b) (3.5 g, 13.88 mmol), 1-bromohexane (2.29 g, 13.88 mmol), KOH (2.34 g, 41.64
o
mmol) and KI (0.23 g, 1.39 mmol) in 35 mL of THF was stirred at 70 C under
nitrogen for 12 h. After being cooled to room temperature, the mixture was brought in
1
00 mL of DCM and washed with water for few times. Compouds dried over Na SO
2 4
and purified by column chromatography on silica gel using DCM/PE (1 : 6) as eluent.
1
5
7
=
b (3.26 g, yield: 70%). H NMR (400 MHz, DMSO-d ) δ 7.60 (d, J = 8.4 Hz, 1H),
6
.53 (s, 1H), 7.40 (d, J = 5.2 Hz, 1H), 7.27 (s, 1H), 7.05 (d, J = 5.2 Hz, 1H), 4.20 (t, J
1
3
7.2 Hz, 2H), 1.89–1.80 (m, 2H), 1.36–1.26 (m, 6H), 0.87 (t, J = 6.9 Hz, 3H). C
NMR (100 MHz, CDCl ) δ 145.78, 142.03, 127.39, 122.05, 120.61, 120.02, 115.87,
3
1
15.71, 112.86, 110.41, 45.40, 31.48, 29.67, 26.80, 22.55, 14.04.
4
-hexyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-thieno[3,2-b]indole
6b). To a solution of 6-bromo-4-hexyl-4H-thieno[3,2-b]indole (5b) (3.00 g, 8.92
mmol), potassium acetate (2.63 g, 26.76 mmol), bis(pinacolato)diboron (3.62 mg,
4.27 mmol) and Pd(PPh ) Cl (0.05 g, 0.12 mmol) in 50 mL of dry DMF was stirred
(
1
3
2
2
o
at 90 C under nitrogen for 10 h. After being cooled to room temperature, the mixture
was brought in 100 mL of DCM and washed a few times with water. A crude product
dried over NaSO and purified by column chromatography on silica gel using
4
1
DCM/PE (1 : 1) as eluent. 6b (2.68 g, yield: 78%). H NMR (400 MHz, CDCl ) δ
3
7
.87 (s, 1H), 7.75 (d, J = 7.9 Hz, 1H), 7.62 (dd, J = 7.9, 0.8 Hz, 1H), 7.41 (d, J = 5.2
Hz, 1H), 7.07 (d, J = 5.2 Hz, 1H), 4.31 (t, J = 7.2 Hz, 2H), 1.88 (p, J = 7.2 Hz, 2H),
1
3
1
.40 (s, 18H), 0.91–0.83 (m, 3H). C NMR (100 MHz, CDCl ) δ 146.37, 140.94,
3

ACCEPTED MANUSCRIPT
1
4
27.75, 125.09, 124.05, 118.20, 116.47, 115.90, 110.46, 83.66, 77.41, 77.09, 76.77,
5.15, 31.55, 29.95, 26.82, 24.96, 22.59, 14.10, 14.07.
Synthesis of DPP-TIH. Compoud DPP (0.10 g, 0.15 mmol),
-hexyl-6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-thieno[3,2-b]indole (6b)
4
(0.13 g, 0.34 mmol) in 10 mL of anhydrous toluene under nigtrogen was added 1 mL
of K CO (an aqueous solution (2 M) of K CO (0.88 mmol)) and Pd(PPh ) (0.05 g,
2
3
2
3
3 4
o
0
.04 mmol). The mixture was stirred at 90 C. After cooling to room temperature, the
compound was brought in 100 mL of DCM and washed with water. The mixture dried
over Na SO and purified by column chromatography on silica gel using DCM/PE (1 :
2
4
1
3
) as eluent. DPP-TIH (0.065 g, yield: 43%). H NMR (400 MHz, CDCl ) δ 9.01 (d,
3
J = 4.2 Hz, 1H), 7.75 (d, J = 8.2 Hz, 1H), 7.63 (s, 1H), 7.56–7.46 (m, 2H), 7.42 (d, J =
5
2
.2 Hz, 1H), 7.07 (d, J = 5.2 Hz, 1H), 7.49 (d, J = 6.8 Hz, 4H), 7.42 (d, J = 5.1 Hz,
H), 7.07 (d, J = 5.3 Hz, 2H), 4.28 (d, J = 6.6 Hz, 4H), 4.17 (s, 4H), 1.87 (d, J = 28.6
1
3
Hz, 8H), 1.32–1.15 (m, 32H), 0.87 (s, 12H). C NMR (100 MHz, CDCl ) δ 161.30,
3
1
1
3
51.58, 146.79, 141.55, 139.19, 136.85, 128.01, 127.92, 127.39, 123.87, 122.26,
19.39, 117.78, 116.15, 110.44, 107.66, 107.19, 50.78, 45.22, 42.31, 31.82, 31.47,
0.05, 29.75, 29.28, 27.00, 26.82, 22.65, 22.52, 14.09, 14.00. C H N O S :
62
74
4
2 4
EI-HRMS: (M ＋ ): calc.: 1034.4695; found: 1034.4689. Anal Calc (%) for
C H N O S : C, 71.91; H, 7.20; N, 5.41; S, 12.38. Found: C, 71.96; H, 7.17; N, 5.40;
62
74
4
2 4
S, 12.41.
2-(2-nitrophenyl)thiophene (9). To a solution of 1-bromo-2-nitrobenzene (7)
(5.00 g, 24.75 mmol) and 3-thiopheneboronic acid (8) (3.80 g, 29.70 mmol) in 40 mL

ACCEPTED MANUSCRIPT
o
of dry toluene was stirred at 90 C under nitrogen was added 35 mL of K CO (an
2
3
aqueous solution (2 M) of K CO (100 mmol)), TBAB (0.01 g) and Pd(PPh ) (0.05 g,
2
3
3 4
0
.04 mmol). The mixture was refluxed overnight. After cooling to room temperature,
the crude mixture was brought in 100 mL of DCM and washed with 100 mL of water.
The solvent was evaporated under reduced pressure. The mixture dried over Na SO
2
4
and purified by column chromatography on silica gel using DCM/PE (1 : 10) as eluent.
1
9
(2.64 g, yield: 52%). H NMR (400 MHz, CDCl ) δ 7.79–7.72 (m, 1H), 7.62–7.55
3
1
3
(
m, 2H), 7.50–7.46 (m, 1H), 7.44–7.40 (m, 1H), 7.12–7.08 (m, 2H). C NMR (100
MHz, CDCl ) δ 149.46, 137.16, 132.29, 131.95, 128.65, 128.35, 128.00, 127.80,
3
1
27.18, 123.86.
4H-thieno[3,2-b]indole (10). A mixture of 2-(2-nitrophenyl)thiophene (9) (5.5 g,
2
6.79 mmol) and triphenylphosphine (21.09 g, 80.37 mmol) in 30 mL of
chlorobenzene was refluxed under nitrogen for 12 h. After cooling to room
temperature, chlorobenzene was evaporated under reduced pressure. A crude product
was purified by column chromatography on silica gel using DCM/PE (1 : 6) as eluent.
1
1
1
1
1
0 (3.15 g, yield: 68%). H NMR (400 MHz, CDCl ) δ 8.19 (s, 1H), 7.75 (dd, J = 7.8,
3
.4, 0.7 Hz, 1H), 7.46–7.42 (m, 1H), 7.37 (d, J = 5.2 Hz, 1H), 7.29 (dd, J = 7.2, 1.2 Hz,
1
3
H), 7.09–7.06 (m, 1H). C NMR (100 MHz, CDCl ) δ 143.10, 141.19, 127.01,
3
22.89, 122.12, 119.82, 118.88, 117.94, 112.00, 111.55.
4-hexyl-4H-thieno[3,2-b]indole (11). 4H-thieno[3,2-b]indole (10) (6.50 g, 37.52
mmol), 1-bromohexane (5.50 g, 33.77 mmol), KOH (6.32 g, 112.56 mmol) and KI
o
(
0.60 g, 3.75 mmol) in 40 mL of THF were stirred at 70 C under nitrogen for 12 h.

ACCEPTED MANUSCRIPT
After being cooled to room temperature, the crude mixture was brought in 100 mL of
DCM and washed with water. The mixture dried over Na SO and purified by column
2
4
1
chromatography on silica gel using pure PE as eluent. 11 (5.6 g, yield: 58%). H NMR
(
400 MHz, CDCl ) δ 7.77 (dd, J = 7.9, 1.1 Hz, 1H), 7.44–7.40 (m, 1H), 7.38 (d, J =
3
5
.2 Hz, 1H), 7.31 (dd, J = 8.4, 7.2, 1.2 Hz, 1H), 7.18 (dd, J = 8.0, 7.1, 1.0 Hz, 1H),
.08 (d, J = 5.2 Hz, 1H), 4.27 (t, J = 7.1 Hz, 2H), 1.88 (p, J = 7.2 Hz, 2H), 1.38–1.26
7
1
3
(
m, 6H), 0.91–0.85 (m, 3H). C NMR (100 MHz, CDCl ) δ 145.42, 141.34, 126.68,
3
1
2
22.33, 121.78, 118.99, 118.91, 115.92, 110.42, 109.93, 45.28, 31.58, 29.81, 26.90,
2.61, 14.10.
2-bromo-4-hexyl-4H-thieno[3,2-b]indole
(12).
To
a
solution
of
4
-hexyl-4H-thieno[3,2-b]indole (11) (4.47 g, 17.37 mmol) in 50 mL of THF was
stirred in an ice-water bath under nitrogen, and subsequently N-bromosuccinmide
3.09 g, 17.37 mmol) was added in the dark. The resulting mixture was stirred for 3 h.
(
The mixture was warmed slowly to room temperature. A crude product was brought in
PE and washed with water. Then the mixture dried over Na SO and purified by
2
4
column chromatography on silica gel using pure PE as eluent. 12 (5.23 g, yield: 83%).
1
H NMR (400 MHz, CDCl ) δ 7.67 (dd, J = 7.8, 1.1 Hz, 1H), 7.39 (d, J = 8.3 Hz, 1H),
3
7
.30 (dd, J = 8.3, 7.0, 1.2 Hz, 1H), 7.16 (dd, J = 8.0, 7.0, 1.0 Hz, 1H), 7.12 (s, 1H),
13
1
.84 (p, J = 7.2 Hz, 2H), 1.40–1.21 (m, 8H), 0.88–0.84 (m, 3H). C NMR (100 MHz,
CDCl ) δ 142.94, 140.04, 122.54, 121.52, 119.35, 118.76, 115.79, 113.93, 113.25,
3
110.03, 45.31, 31.53, 29.76, 26.84, 22.58, 14.09.

ACCEPTED MANUSCRIPT
4-hexyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-thieno[3,2-b]indole
(13). To a solution of 2-bromo-4-hexyl-4H-thieno[3,2-b]indole (12) (3.0 g, 8.92 mmol)
o
in 20 mL of dry THF were stirred at –78 C under nitrogen, and subsequently 6.2 mL
of n-butyllithium (1.6 M in hexane, 9.81 mmol) was added slowly. Isopropoxyboronic
acid pinacol ester (2.15 g, 11.60 mmol) was added after the mixture was stirred for 1
h, and then a crude product was warmed slowly to room temperature stirred for
overnight. The mixture was brought in 100 mL of DCM and washed with water. The
compound was purified by column chromatography on silica gel using DCM/PE (1 : 5)
1
as eluent. 13 (1.20g, yield: 35%). H NMR (400 MHz, CDCl ) δ 7.80 (d, J = 7.9 Hz,
3
1
7
0
1
2
H), 7.58 (s, 1H), 7.39 (d, J = 8.3 Hz, 1H), 7.32 (dd, J = 8.3, 7.0, 1.2 Hz, 1H),
.19–7.13 (m, 1H), 4.24 (t, J = 7.3 Hz, 2H), 1.86 (t, J = 7.3 Hz, 2H), 1.39 (s, 18H),
1
3
.85 (d, J = 7.0 Hz, 3H). C NMR (100 MHz, CDCl ) δ 146.69, 142.55, 123.37,
3
23.22, 121.39, 119.79, 118.98, 118.83, 109.98, 84.20, 45.28, 31.56, 29.75, 26.87,
4.84, 22.57, 14.05.
Synthesis of DPP-r-TI. Compound DPP (0.10 g, 0.15 mmol),
-hexyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-4H-thieno[3,2-b]indole (13)
4
(
(
(
0.13 g, 0.34 mmol) in 10 mL of toluene under nitrogen was added 1 mL of K CO3
2
an aqueous solution (2 M) of K CO (0.88 mmol)), TBAB (0.01 g) and Pd(PPh )
3 4
2
3
o
0.05 g, 0.04 mmol). The mixture was stirred at 90 C. After cooling to room
temperature, the mixture was brought in 100 mL of DCM and washed with water. The
mixture dried over Na SO , and purified by column chromatography on silica gel
2
4
using DCM/PE (1 : 3) as eluent. DPP-r-TI (0.058 g, yield: 38%). As shown in Figure

ACCEPTED MANUSCRIPT
S26, although the resonance signals of all protons could be recorded, it is difficult to
1
3
obtain precise integration. Meanwhile, no C NMR spectrum could be collected for
＋
DPP-r-TI. C H N O S : EI-HRMS: (M ): calc.: 1034.4695; found: 1035.4716.
6
2
74
4
2 4
Anal Calc (%) for C H N O S : C, 71.91; H, 7.20; N, 5.41; S, 12.38. Found: C,
6
2
74
4
2 4
7
1.97; H, 7.16; N, 5.39; S, 12.43.
2
.3. Singlet Oxygen Detection
1,3-diphenylisobenzofuran (DPBF) was introduced to detect the generation of
−5
singlet oxygen.[21] DPP-TI, DPP-TIH, and DPP-r-TI (~10 mol/L) was
−5
respectively mixed with DPBF (6 x 10 mol/L) in dichloromethane in darkness and
the absorption spectra were immediately recorded after laser irradiation (660 nm, 0.5
2
W/cm ). Methylene blue was the reference substance to calculate the yield of singlet
oxygen production yield.
2
.4. Preparation of DPP-TI NPs
100 µL (2 mg/mL) of DPP-TI tetrahydrofuran solution was slowly added into 5
mL water dissolved with 20 µg DSPE-mPEG2000 under vigorous stirring. After
further stirring for 5 min, tetrahydrofuran was removed by nitrogen blowing. DPP-TI
NPs were obtained by centrifugation.[30]
2
.5. Photostability
DPP-TI NPs (40 ꢀg/mL) of PBS solution was illuminated by a laser (660 nm, 1
2
W/cm ) for 0, 2, 4, 6, 8 and 10 min, respectively. Then, the absorbance of DPP-TI
NPs was measured by a UV–vis spectrophotometer.

ACCEPTED MANUSCRIPT
2
.6. In Vitro Photothermal Effect
DPP-TI NPs (40 ꢀg/mL, 1 mL) in PBS were put into a cuvette and irradiated by
2
6
60 nm laser (1.0 W/cm ) for 10 min and remove the laser for another 10 min. The
changes of temperature was recorded by an E50 infrared camera every 20 s.
2
.7. Cell Lines
HeLa cell line was provided by the Institute of Biochemistry and Cell Biology,
SIBS, CAS (China) and cultured in Dulbecco’s modified Eagle’s medium (DMEM,
o
Gibco) contained 10% fetal bovine serum (FBS) at 37 C under 5% CO .
2
2
.8. Cellular Uptake Study
HeLa cells incubated with DPP-TI NPs PBS (10 ꢀg/mL, 0.2 mL) in a confocal
o
dish and a 5% CO incubator at 37 C for 24 h. The medium was removed then and
2
rinsed with PBS for three times. The fluorescence images were viewed by and
Olympus IX 70 inverted microscope and the samples were excited at 630 nm laser
and collected from 640 to 700 nm. The HeLa cells were stained with nuclei-specific
dye, DAPI.
2
.9. Cytotoxicity Assay
HeLa cells were divided into 2 groups in 96-well plates. DPP-TI NPs PBS
solutions in various concentrations (200 µL) were added in the plates. DPP-TI NPs
First group of cells was maintained in normal, second group was irradiated by a laser
2
(
660 nm, 1 W/cm , 5 min) after 24 h. The cells were incubated for another 48 h and

ACCEPTED MANUSCRIPT
incubated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
solution (500 µg/mL) for 4 h at 37 °C in 5% CO , then treated with 150 ꢀL of DMSO.
2
The absorption at 570 nm was measured by Bio-Tek microplate reader.
2
.10. Fluorescence Images of Cellular ROS
HeLa cells were incubated with DPP-TI NPs (10 µg/mL, 0.2 mL) in a confocal
dish for 24 h in darkness, then the cells are further incubated with
2
,7-dichlorodihydrofluorescein diacetate (DCFH-DA, 10 ꢀM, 0.2 mL) for 1 h and
2
irradiated by a laser (660 nm laser, 1 W/cm , 5 min). The fluorescence images were
observed by an Olympus IX 70 inverted microscope, excited at 488 nm and collected
from 500 to 550 nm. The HeLa cells were stained with nuclei-specific dye, DAPI.

ACCEPTED MANUSCRIPT
Scheme 2. Synthetic routes toward DPP-TI, DPP-TIH and DPP-r-TI.
3
. Results and Discussion
Chemically, all three DPP-based compounds are structural analogues, whereas
DPP-TI has two C12 alkyl chains in compared to DPP-TIH but DPP-r-TI is an
isomer of DPP-TIH by coupling with DPP at its thieno-ring site. As we reported
previously [29] that the copolymers based on TI units and benzothiadiazole (BT) units
displayed red-shifted absorption spectrum and more efficient intermolecular charge
transfer (ICT) effect, indicating this tricyclic TI unit was more electron-rich than most
electron-donating units, such as carbazole, triphenylamine or other thiophene
derivatives. Moreover, the asymmetric chemical feature of TI led to regioselective

ACCEPTED MANUSCRIPT
chemistry, which facilitated the synthetic chemistry. Thus, TI was selected to
incorporate with DPP unit to afford a series of D-A geometric organic semiconducting
molecules. To tune the molecular energy levels further the light-absorption and
fluorescence emission properties, we designed these compounds by utilizing the
asymmetric feature of TI unit.
The synthetic routes toward DPP-TI, DPP-TIH and DPP-r-TI were depicted in
Scheme 2. Briefly, the synthetic work was divided into 3 parts, 1) DPP core
containing two bromine atoms suitable for Suzuki coupling reaction, 2) adverse
TI-boronic esters and 3) the coupling reaction toward three targeting compounds. The
key intermediate of DPP was obtained as we reported previously.[31] In detail,
2
,5-dibromo-1-nitro-phenyl underwent the regioselective Suzuki coupling reaction
with 2-thieno-picanacoboronic ester (1) to afford nitro-substituted compounds 3,
which was subjected to typical Cardogon annulation step with triphenylphosphine in
chlorobenzene as described previously[32] to give 6-bromo-4H-thieno[3,2-b]indole 4.
4
6
4
was alkylated using 1-bromohexane under basic condition to obtain
-bromo-4-hexyl-4H-thieno[3,2-b]indole in high yields. Afterwards,
-hexyl-6-(4,4,5,5-tetra- methyl-1,3,2-dioxaborolan-2-yl)-4H-thieno-[3,2-b]indole 6,
5
with/without alkyl chain at its 2-position, were synthesized by Suzuki-Miyaura
o
coupling of bis(pinacolato)diboron with 5 at 85 C for 5 hr under N atmosphere. The
2
target compound DPP-TI and DPP-TIH were obtained by Suzuki cross-coupling
reaction of 3,6-dibromo-DPP and 6 at an isolated yield of 65~78%. Similarly, using
2
-bromo-nitrobenzene as starting materials, compound 10 was prepared in two steps.

ACCEPTED MANUSCRIPT
1
0 was futher alkylated and selectively brominated at its thiophene ring with NBS
before it was converted into its boronic ester 13. By coupling 13 with
,6-dibromo-DPP, DPP-r-TI was obtained at an isolated yield of ca. 58%. All three
3
final products possess good solubility in common organic solvents. All new
compounds were determined by NMR ambiguously, except for DPP-r-TI, which
displayed strong intermolecular interaction due to π-π stacking further imparting
13
limitation on its C NMR measurement. After confirming their MS spectra with
MALDI-TOF mass spectrometer, DPP-TI, DPP-TIH and DPP-r-TI were further
confirmed by high resolution mass spectrum (Figure S1-3).
3
.1. Thermal properties
The thermally induced phase transition behaviour of three compounds was
investigated by differential scanning calorimetry (DSC). As shown in Figure 1, the
o
glass transition temperature (Tg) of DPP-TI was 91 C, corresponding to the melting
o
of long alkyl chains, whilst the melting point (m.p.) of 156 C and crystal temperature
o
(
T ) of 112 C for DPP-TI were observed during the heating and cooling process,
Cr
o
respectively.[9] As to DPP-TIH, two phase transition temperature of 187 and 192 C
o
during the heating process and T of 154 C were determined. Since no alkyl chains
Cr
pendent to DPP-TIH, the higher phase transition temperature observed during both
o
the heating and cooling cycles sounded reasonable. The m.p. for DPP-r-TI is 203 C
even higher in compared with DPP-TIH, because the dihedron angle between the TI
unit and DPP unit are smaller than those in DPP-TI, where TI unit was linked with
o
DPP thiophene motif at its thiophene site. The T of DPP-r-TI is 155 C, which is
Cr

ACCEPTED MANUSCRIPT
very close to that of DPP-TIH. This thermally induced crystalline phases determined
by DSC measurement indicate that their intrinsic inclination to form ordered
crystalline phase,[33] which is resulted from their molecular rigidity and planarity
(discussed in the theoretical simulation section).
Figure 1. Differential scanning calorimetry (DSC) analysis of (a) DPP-TI, (b) DPP-TIH, and (c)
o
DPP-r-TI. Measured under N with heating and cooling rates of 10 C/min.
2
3
.2. Optical and electrochemical properties
Figure 2. (a) Normalized UV-vis-NIR absorption spectra. (b) normalized photoluminescence
spectra of DPP-TI, DPP-TIH, and DPP-r-TI in toluene.
The optical properties of DPP-TI, DPP-TIH and DPP-r-TI were investigated by
ultraviolet-visible-NIR (UV-vis-NIR) absorption spectroscopy and fluorescence
−
5
spectroscopy. In the dilute toluene solutions (1×10 M), all compounds exhibited

ACCEPTED MANUSCRIPT
similar features (Figure 2). The weak absorption band between 280 and 470 nm can
be ascribed to π-π* electronic transitions of all aryl groups including TI and DPP units.
While the strong and broad absorption band ranging from 500 to 720 nm came from
the effective ICT between electron-donating TI unit and electron-deficient DPP unit.
Since all compounds contained the same acceptor unit of alkylated DPP, the maxima
absorption wavelength mainly were influenced by the donor units and the linking
fashion. For example, the electron-donating C12 alkyl group in DPP-TI led to a 7 nm
ab
ab
bathochromic shift of (λmax = 633 nm) in comparison with DPP-TIH (λmax = 626 nm).
ab
A further 28 nm bathochromic shift for DPP-r-TI (λmax = 661 nm) in comparison with
DPP-TI was observe by substitution of TI at its thiophene site. It was speculated that
the bathochromic shift of DPP-r-TI was attributed to the less steric hindrance
between TI unit and DPP core when two thiophene rings linked to each other in
DPP-r-TI in comparison with the linking of benzene and thiophene ring in DPP-TI.
The optical energy bandgap (E ) is 1.79, 1.82 and 1.70 eV for DPP-TI, DPP-TIH and
g
DPP-r-TI, respectively. This declared that enhanced ICT may reduce the energy gaps.
The photoluminescence spectra of DPP-TI, DPP-TIH and DPP-r-TI in different
solvents were obtained under the excitation at their maximum absorption wavelengths.
As shown in Figure 2b, the emission maxima for DPP-TI, DPP-TIH and DPP-r-TI
were 663 nm, 654 nm and 695 nm, respectively. Moreover, the fluorescence emission
efficiency of DPP-TIH was the highest one among all three compounds, while
DPP-r-TI exhibited very weak emission (see in Figure S5). It was assumed that the
long alkyl chains induced the relaxation of the excited state of DPP-TI to result in

ACCEPTED MANUSCRIPT
non-radiation relaxation further the lower fluorescence quantum efficiency in
comparison with DPP-TIH. As to DPP-r-TI, its strong absorption overlapped too
much with its fluorescence plot may account for its low fluorescence quantum
efficiency. There was only slight shift for the absorption spectra and fluorescence
spectra of DPP-TI, DPP-TIH and DPP-r-TI upon changing the solvents from THF,
DCM, and chloroform to toluene, indicating that the polarity of good solvents had
little effect on their optical properties (Figure S4 and S5).
Figure 3. Cyclic voltammetry of DPP-TI, DPP-TIH and DPP-r-TI.
Cyclic voltammetry (CV) measurements were carried out to elucidate the energy
levels and bandgaps of DPP-TI, DPP-TIH and DPP-r-TI. Figure 3 gave the
electrochemical curves of DPP-TI, DPP-TIH and DPP-r-TI in CH Cl solution at
2
2
2
98 K. All compounds showed two reversible oxidation waves, corresponding to the
two electron loss process of the TI units linked to DPP core, and one quasi-reversible
reduction wave, corresponding to the electron accept process of the DPP unit.
Because all compounds consisted of DPP and TI units, the observed oxidation
potentials (E ) and reduction potentials (E ) were very close to each other. For
ox
red

ACCEPTED MANUSCRIPT
ox
example, the observed oxidiazation onset potentials (Eonset) for DPP-TI, DPP-TIH and
red
DPP-r-TI were 0.52 eV, 0.56 eV and 0.53 eV, respectively, while the Eonset values for
each of these compounds was almost the same of −0.83 eV. The HOMO and LUMO
ox
red
energy levels were deduced from Eonset and Eonset, respectively, which were summarized
in Table 1. Accordingly, the calculated bandgaps were 1.35 eV (for DPP-TI), 1.39 eV
opt
g
(for DPP-TIH) and 1.36 eV (for DPP-r-TI). Although the measured E
value of
opt
g
DPP-r-TI was smaller than E
values of DPP-TI and DPP-TIH, the E obtained by
g
opt
g
CV measurement was similar. These difference was reasonable because the E
was
determined in dilute solutions whereas the E obtained by CV measurement was
g
performed in thicker solutions.
3
.4. Theoretical calculations.
Theoretical calculations were performed by using the density functional theory
(DFT) with the B3LYP/6-311G (d, p) basis set. Three model compounds with all alkyl
side chains replaced by methyl groups were subjected to the calculation in order to
simplify the job. The calculated HOMO levels for DPP-TI, DPP-TIH and DPP-r-TI
were −4.50 eV, −4.57 eV and −4.59 eV, LUMO levels for three compounds were
−
2.36 eV, −2.42 eV and −2.65 eV, respectively. According to the calculated HOMO
and LUMO energy levels, the calculated bandgap for each compounds was 2.13 eV
for DPP-TI), 2.15 eV (DPP-TIH) and 1.94 eV (DPP-r-TI). Obviously, the trends of
(
HOMO/LUMO levels and bandgaps were both in agreement with the experiment
results from CV investigation (see in Table 1). As illustrated in figures shown in
Figure 4, the LUMO energy levels were mainly located at around DPP unit, while the