Synthesis and determination of fluorescence properties of new soluble diketopyrrolopyrrole type photosensitizers

Article abstract of DOI:10.1016/j.molstruc.2019.06.022

Four organic small molecules bearing phenyl diketopyrrolopyrrole (DPP) unit as the main acceptor group and indole as the main thermal group with soluble units, coded as DPP3(a-b) and DPP4(a-b), were synthesized and their optical/electrochemical properties were investigated. Intense visible absorption bands around 480 nm were assigned to the DPP main core, as well as bands around 600 nm were attributed to the formation of charge-transfer complex between the electron-rich indole units and electron-withdrawing DPP core in chloroform solution. All of the compounds were found to be fluorescent in solution and on thin films with emission wavelengths between 500 and 700 nm. The fluorescence decay kinetic measurements of these dyes were also studied. The synthesized compounds have electrochemical energy band gaps from 2.15 to 2.28 eV. Then, the potential usage of the final products in bulk heterojunction solar cells (BHJ-OSCs) were evaluated.

Full text of DOI:10.1016/j.molstruc.2019.06.022

Accepted Manuscript
Synthesis and determination of fluorescence properties of new soluble
diketopyrrolopyrrole type photosensitizers
Sevil türkçen, Haluk dinçalp, Gözde murat saltan
PII:
S0022-2860(19)30735-5
10.1016/j.molstruc.2019.06.022
MOLSTR 26664
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Accepted Date:
24 February 2019
05 June 2019
Please cite this article as: Sevil türkçen, Haluk dinçalp, Gözde murat saltan, Synthesis and
determination of fluorescence properties of new soluble diketopyrrolopyrrole type photosensitizers,
Journal of Molecular Structure (2019), doi: 10.1016/j.molstruc.2019.06.022
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ACCEPTED MANUSCRIPT
Synthesis and determination of fluorescence properties of
new soluble diketopyrrolopyrrole type photosensitizers
1
1*
1
Sevil TÜRKÇEN , Haluk DİNÇALP , Gözde MURAT SALTAN
1Department of Chemistry, Faculty of Arts and Science, Manisa Celal Bayar
University, Yunus Emre, 45140 Manisa, Turkey
*
Corresponding author e-mail: haluk.dincalp@cbu.edu.tr (H. Dinçalp); Tel:
90 236 2013158; Fax: +90 236 2412158
+
Abstract: Four organic small molecules bearing phenyl diketopyrrolopyrrole
DPP) unit as the main acceptor group and indole as the main thermal group with
(
soluble units, coded as DPP3(a-b) and DPP4(a-b), were synthesized and their
optical/electrochemical properties were investigated. Intense visible absorption
bands around 480 nm were assigned to the DPP main core, as well as bands
around 600 nm were attributed to the formation of charge-transfer complex
between the electron-rich indole units and electron-withdrawing DPP core in
chloroform solution. All of the compounds were found to be fluorescent in
solution and on thin films with emission wavelengths between 500 and 700 nm.
The fluorescence decay kinetic measurements of these dyes were also studied.
The synthesized compounds have electrochemical energy band gaps from 2.15 to
1

ACCEPTED MANUSCRIPT
2
.28 eV. Then, the potential usage of the final products in bulk heterojunction
solar cells (BHJ-OSCs) were evaluated.
Key words: Diketopyrrolopyrrole, indole, charge transfer, decay time, organic
solar cell
1
. Introduction
Since the first synthesis of DPP chromophore described by Farnum et al.
in 1974 [1] as an original dye for painting and ink industries, [2] these
chromophores have found great applications in many areas such as organic field
effect transistors (OFETs), [3-6] organic solar cells, [7-12] organic light emitting
diodes (OLEDs), [13, 14] fluorescent sensors, [15] photodetectors, [16] biological
molecular probes, [17] and photodynamic therapy [18] etc. Because of their many
advantages such as their bright colors, excellent stabilities, high mobility values,
high fluorescence quantum yields, broad absorption ranges in visible region, two-
photon absorption activities and simple synthesis/modification procedures, [2,
1
9-23] DPP dyes attracted great attention especially in organic electronics.
DPP has a planar structure and shows molecular packing due to strong
intermolecular H-bonding between the amide hydrogen atoms and neighboring
heteroatoms. [2, 15] This type re-organization of the molecules is responsible for
the remarkable red-shifts of the absorption bands to the wavelength beyond 540
nm. Furthermore, the solubility problem of DPP-based dyes can be overcome by
attaching long alkyl chains to the nitrogen atoms of amide side of the molecule.
2

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[
24, 25] The charge transfer possibility and photo-electron injection ability of
DPP dyes can be improved by extending π-conjugation and optimizing the
organization of the molecules on substrate surface. [26-30] DPP-based molecules
posses good field-effect transistor performance values recorded at 0.7
2
−1
−1
2
−1
−1
cm V cm [31] for hole mobility and 0.96 cm V cm [32] for electron mobility.
In the field of BHJ-OSCs, remarkable power conversion efficiencies (PCEs)
have been obtained by the challenging DPP structures in both polymer and also
small molecule designs. Since the first reports on the photovoltaic performances
in solar photovoltaics for polymer and small molecule DPPs by Nguyen [33] and
Janssen, [34] respectively, DPP-based polymer structures get the highest PCE
value around 9.4% as the donor material. [35] Up to date, the PCE for the small
molecule DPP donor structure catched the notable value at 8%. [36] DPP
derivatives have also been preferred as acceptor component in the active layer of
BHJ-OSCs with the high PCE of 5.1% in the literature. [37] Recently, DPP-based
small molecules with different molecular arrangements gave promising
efficiencies in solar cells. Thin film quality and suitable morphology of the
molecules depend on the molecular packing and crystallinity of DPP molecules,
which will be crucial effect on photovoltaic performance. Molecular shape and
chain length of solubilizing alkyl groups have remarkable effect on molecular
packing of DPP structures. [12] In addition, energy levels and optical properties
of DPP molecules can be easily varied by the formation of intramolecular charge
transfer (ICT) complex between the acceptor and donor sites of the structure.
Incorporation of donor subunits such as indole with suitable solubilizing
groups on the main DPP core may be good combination for promising dye
3

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molecule for BHJ-OSC device. In the present work, four different small molecules
coded as DPP3(a-b) and DPP4(a-b) were designed and synthesized (Scheme
1
). The effects of extending π-conjugated indole groups on the absorption,
emission and redox changes of the DPP cores were investigated. The main
purpose of this study is to provide a detailed spectroscopic data for these new DPP
dyes which will be focused on the photovoltaic responsibilities.
Scheme 1 [38-41]
2
. Experimental
.1. General
2
The main reagents used for the synthesis of DPP dyes, 4-
bromobenzonitrile, sodium, Iron(III) chloride, diethyl succinate, 5-
indolylboronic acid, N-Boc-indole-2-boronic acid, 2-ethylhexyl bromide, di-tert-
butyl dicarbonate, 4-(dimethylamino)pyridine were purchased from Sigma
Aldrich. Tetrakis(triphenylphosphine)palladium(0) (Pd(PPh ) ) catalyst was
3
4
purchased from TCI company. [6,6]-Phenyl C -butyric acid methyl ester
6
1
(
PCBM), poly(3-hexylthiophene-2,5-diyl) (P3HT), were purchased from Adrich.
All other chemicals and solvents were purchased from Merck, and used without
further purification. The purification and isolation of the products were
performed by column chromatography on silica gel 60 (0.060-0.200 mm).
1
13
H NMR and C NMR spectra were recorded using a Bruker 400 MHz
spectrometer with tetramethylsilane (TMS) as the internal reference, and their
4

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chemical shifts were recorded in ppm values. FT-IR spectra were recorded on a
Perkin Elmer-Spectrum BX spectrophotometer preparing KBr pellets. UV–vis
absorption spectra were recorded on a Perkin Elmer Lambda 950
spectrophotometer. The fluorescence emission of DPP dyes have been measured
by using FLS 920 Edinburg instrument. Single photon counting measurements
have been taken at the excitation wavelength of 472.4 nm on an apparatus
described elsewhere. [42] Fluorescence decays were analyzed globally using
exponential tail fit method. [43] Fluorescence decay data were collected at
λdetection = 520 nm for the dyes. The quality of the fits has been judged by the fitting
2
parameters such as χ ≤ 1.2. [44] PL quenching experiments were performed on
a Perkin Elmer LS 55 Luminescence Spectrometer. Cyclic voltammetry (CV)
measurements of compounds DPP dyes in MeCN solution were measured using
1
00 mM [TBA][PF ] as the electrolyte in a CH instruments 660B-Electrochemical
6
Workstation at a scan rate of 100 mV/s. Ferrocene was used as the internal
standard and its oxidation potential was detected at +0.53 V. A standard three-
electrode configuration cell composed of a platinum wire auxiliary electrode, a
+
glassy carbon working electrode, and an Ag/Ag reference electrode (SCE) was
used to measure the oxidation and reduction potentials of the target compounds.
The HOMO and LUMO energy levels were calculated from the CV measurements
using the given equations below: [45]
표푛푠푒푡
표푘
표푛푠푒푡
푖푛푑
퐸퐻푂푀푂 = ―푒
(
퐸
)
+ 4.8 ;
퐸 퐿푈푀푂 = ―푒
(
퐸
+ 4.8
)
1
240
표푝푡
푔
= 퐸퐻푂푀푂 ― 퐸 표푔 푝푡
퐸
=
;
퐸
퐿푈푀푂
표푛푠푒푡
휆
푎푏푠
5

ACCEPTED MANUSCRIPT
2
.1. Synthesis
.1.1. Synthesis of 3,6-Bis(4-bromophenyl)-2,5-dihydropyrrolo[3,4-
2
c]pyrrole-1,4-dione (DPP1)
Sodium metal (75 mg, 3.26 mmol) was dissolved in tert-amyl alcohol (10
mL), and then trace amounts of FeCl were added. The mixture was refluxed
3
0
under an argon atmosphere at 100 C until the solution became clear. 4-
bromobenzonitrile (0.5 g, 2.75 mmol) and diethyl succinate (0.24 g, 1.38 mmol)
were added to this solution. The mixture was refluxed at 120 °C for 2 h, and then
stirred at room temperature for 24 h. The resulting mixture poured into 20 mL
of distilled water. The resulting red-colored solids were filtered. The solids were
washed with cold MeOH and warm MeOH, respectively, finally dried in the oven.
‒
1
Yield 75%, FT-IR (KBr pellet, cm ): 3141 (aromatic νC‒H stretching), 1639
(
νC=O), 1603 (aromatic νC=C), 1493, 1438, 1323, 1193, 1140, 1072, 1009, 817, 752,
‒
1
1
6
95 cm . H NMR (400 MHz, DMSO-d δ 2.48 ppm): δ = 7.71-7.85 (8H,
6
multiplet) ppm.
2.1.2.
Synthesis
of
3,6-Bis(4-bromophenyl)-2,5-bis[(2S)-2-
ethylhexyl]-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP2a)
To a solution of DPP1 (50 mg, 0.11 mmol) in NMP (1.5 mL) were added
potassium carbonate (62 mg, 0.45 mmol) and 2-ethylhexyl bromide (64 mg, 0.33
mmol). After addition, the mixture was refluxed for 24 h at 100 °C under an argon
atmosphere. After completion, the mixture was poured into 20 mL of water, and
then extracted with dichloromethane (3×20 mL). The collected organic phases
6

ACCEPTED MANUSCRIPT
were dried over MgSO , and then evaporated. The product mixture was purified
4
by column chromatography on silica gel eluting with n-hexane:ethylacetate (4: 1).
‒
1
Yield 60 %, FT-IR (KBr pellet, cm ): 2957, 2923 ve 2851 (aliphatic ν
C‒H
‒
1
stretching), 1723 (νC=O), 1590 (aromatic νC=C), 1463, 1384 1271, 1115, 1012, 824 cm .
1
H NMR (400 MHz, CDCl δ 7.26 ppm): δ = 7.89 (4H, d, J = 8.5 Hz), 7.57 (4H, d,
3
J = 8.5 Hz), 4.24 (2H, d, J = 1.7 Hz), 4.23 (2H, d, J = 1.7 Hz), 2.00-2.07 (2H, m),
1
3
1
.25-1.30 (16H, m), 0.88-0.94 (12H, m) ppm. C NMR (100 MHz, CDCl δ 77.1
3
ppm): δ = 166.3, 132.4, 131.9, 131.3, 130.3, 128.1, 115.4, 67.8, 39.2, 30.8, 29.2,
4.1, 23.3, 14.3, 11.3 ppm.
2
2.1.3.
Synthesis
di-tert-butyl
3,6-bis(4-bromophenyl)-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (DPP2b)
A 25 mL of Schlenk tube was charged with DPP1 (50 mg, 0.11 mmol), 4-
(
(
dimethylamino)pyridine (DMAP) (20 mg, 0.16 mmol), di-tert-butyldicarbonate
22 mg, 0.10 mmol), and THF (8 mL). After addition, the mixture was stirred for
2
4 h at room temperature under an argon atmosphere.The crude product was
purified by flash chromatography using toluene:ethylacetate (4:1) as eluent, and
the solvent was removed in vacuo to obtain the pure product.
‒
1
Yield 70%, FT-IR (KBr pellet, cm ): 2968 ve 2920 (aliphatic νC‒H stretching),
1
1
754 (ester νC=O), 1716 (amide νC=O), 1600 (aromatic νC=C), 1484, 1395, 1371, 1279,
‒
1 1
260, 1213, 1153, 1115, 1058, 889, 860 cm . H NMR (400 MHz, CDCl δ 7.28
3
1
3
ppm): δ = 7.61-7.65 (8H, multiplet), 1.45 (18H, s) ppm. C NMR (100 MHz,
CDCl δ 76.9 ppm): δ = 159.0, 147.9, 145.2, 130.4, 129.8, 126.9, 126.2, 112.5, 85.7,
3
2
7.6 ppm.
7

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2.1.4. General method for Suzuki-Miyaura coupling reactions
In a Schlenk flask, the Ar-X (1.00 eq.), potassium carbonate (2.00 eq.) and
the boronic acid (3.50 eq.) were set under inert atmosphere by three
vaccum/argon cycles. Then, the corresponding solvent, toluene (typically 10 mL),
and trace amounts of Pd(PPh ) were added. The mixture was degassed by
3
4
0
bubbling an argon through and heated to 65 C overnight. The residue was
purified by column chromatography eluting with toluene:ethyl acetate (4:1) to
give the desired product.
2.1.5. Synthesis of 2,5-Bis[(2S)-2-ethylhexyl]-3,6-bis[4-(1H-indol-5-
yl)phenyl]-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP3a) and
Di-tert-butyl-3,6-bis[4-(1H-indol-5-yl)phenyl]-1,4-dioxopyrrolo[3,4-
c]pyrrole-2,5 (1H,4H)-dicarboxylate (DPP3b)
Both DPP3a and DPP3b were prepared according to general procedure,
starting from the materials DPP2a and DPP2b, respectively. The boronic acid
derivative used in the syntheses was 5-indolylboronic acid.
‒
1
For DPP3a: Yield 50%, FT-IR (KBr pellet, cm ): 3412 (νN‒H stretching),
957, 2924 ve 2851 (aliphatic νC‒H stretching), 1712 (νC=O), 1604 (aromatic νC=C),
2
‒
1 1
1
455, 1413, 1334, 1277, 1245, 1091, 1009, 742 cm . H NMR (400 MHz, CDCl δ
3
7
.25 ppm): δ = 8.26 (2H, s), 8.10 (2H, d, J = 8.6 Hz), 7.91 (1H, s), 7.86 (1H, s),
.72 (2H, d, J = 8.6 Hz), 7.65 (2H, d, J = 9.6 Hz), 7.41-7.48 (8H, multiplet), 6.63
7
(
(
2H, d, J = 9.6 Hz), 4.27 (2H, d, J = 3.4 Hz), 4.25 (2H, d, J = 3.4 Hz), 1.72-1.77
1
3
2H, m), 1.25-1.35 (16H, m), 0.98-0.85 (12H, m) ppm. C NMR (100 MHz, CDCl
3
8

ACCEPTED MANUSCRIPT
δ 76.8 ppm): δ = 163.6, 156.7, 150.2, 133.3, 129.9, 128.6, 127.4, 127.0, 126.1, 124.6,
1
22.0, 116.1, 111.2, 107.4, 103.1, 67.1, 38.9, 30.6, 29.8, 23.8, 22.8, 14.0, 11.0 ppm.
‒
1
For DPP3b: Yield 60%, FT-IR (KBr pellet, cm ): 3333 (νN‒H stretching),
2
957, 2918 ve 2851 (aliphatic νC‒H stretching), 1753 (ester νC=O), 1672 (amide νC=O),
‒
1 1
1
602 (aromatic νC=C), 1471, 1367, 1281, 1253, 1146, 1107, 1060, 802 cm . H NMR
(
(
(
400 MHz, CDCl δ 7.26 ppm): δ = 8.32 (2H, s), 7.88 (2H, d, J = 7.7 Hz), 7.74
3
4H, d, J = 6.4 Hz), 7.71 (4H, d, J = 6.4 Hz), 7.62 (2H, s), 7.42-7.50 (2H, m), 7.28
1
3
2H, d, J = 9.6 Hz), 6.64 (2H, d, J = 9.6 Hz), 1.45 (18H, s) ppm. C NMR (100
MHz, CDCl δ 76.8 ppm): δ = 169.0, 159.4, 149.7, 146.9, 135.9, 132.4, 131.3, 129.8,
3
1
27.8, 125.2, 121.4, 119.6, 119.3, 111.5, 109.7, 103.2, 84.1, 27.5 ppm.
2.1.6. Synthesis of Di-tert-butyl 2,2'-[{2,5-bis[(2S)-2-ethylhexyl]-3,6-
dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl}bis(4,1-
phenylene)]bis(1H-indole-1-carboxylate) (DPP4a) and Di-tert-butyl
3
,6-bis{4-[1-(tert-butoxycarbonyl)-1H-indol-2-yl]phenyl}-1,4-
dioxopyrrolo[3,4-c]pyrrole-2,5(1H,4H)-dicarboxylate (DPP4b)
Compound DPP4a and DPP4b were synthesized following the general
prosedure, starting from the materials DPP2a and DPP2b, respectively. The
boronic acid derivative used in the syntheses was N-Boc-indole-2-boronic acid.
‒
1
For DPP4a: Yield 40%, FT-IR (KBr pellet, cm ): 2957, 2929, 2862
(
aliphatic νC‒H stretching), 1734 (νC=O), 1605 (νC=O), 1451, 1337, 1251, 1160, 1119, 1023,
‒
1 1
8
50, 746 cm . H NMR (400 MHz, CDCl δ 7.29 ppm): δ = 8.04 (2H, s), 7.87 (2H,
3
s), 7.61 (2H, s), 6.94-7.04 (10H, m), 6.36 (2H, s), 3.95 (2H, broad), 3.75 (2H,
broad), 2.22-2.35 (2H, m), 1.39 (18H, s), 0.96-1.14 (16H, m), 0.62 (12H, broad)
9

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1
3
ppm. C NMR (100 MHz, CDCl δ 77.1 ppm): δ = 165.9, 157.6, 149.7, 131.7, 131.0,
3
1
28.7, 125.7, 124.7, 124.0, 122.7, 122.5, 120.9, 115.5, 115.1, 111.2, 107.2, 83.2, 67.7,
8.8, 30.5, 29.7, 28.1, 27.7, 22.9, 13.9, 11.0 ppm.
For DPP 4b: Yield 45%, FT-IR (KBr pellet, cm ): 3054, 2979, 2933
aliphatic νC‒H stretching), 1733 (νC=O), 1608 (amide νC=O), 1595 (aromatic νC=C), 1452,
3
‒
1
(
‒
1 1
1
369, 1335, 1252, 1159, 1134, 1025, 851, 747 cm . H NMR (400 MHz, CDCl δ
3
7.26 ppm): δ =8.17 (2H, dd, J = 12.1, J = 6.5 Hz), 7.67 (4H, d, J = 8.6 H), 7.49-
1 2
7
.55 (6H, m), 7.35 (2H, dd, J = 12.1, J = 6.5 Hz), 7.23 (2H, d, J = 8.6 Hz), 6.64
1
2
1
3
(
2H, s), 1.37 (18H, s), 1.33 (18H, s) ppm. C NMR (100 MHz, CDCl δ 76.9 ppm):
3
δ = 169.0, 159.1, 156.0, 139.4, 138.3, 137.6, 132.0, 131.5, 129.2, 128.9, 125.1, 123.3,
20.8, 118.8, 115.4, 111.7, 111.0, 84.6, 84.1, 27.7, 27.6 ppm.
1
3
3
. Results and Discussion
.1. Optical properties and time resolved measurements
Diethylsuccinate in tert-AmOH is condensed with 4-bromobenzonitrile
using metalic sodium to afford the desired product DPP1 via pseudo-Stobbe
condensation pathway. [46] In order to increase the solubility of this dye, DPP2a
and DPP2b derivatives substituted with ethylhexyl and di-tert-butyl dicarbonate
groups at the 2, 5-positions of the DPP moiety were synthesized, respectively.
Then, DPP3a, DPP3b, DPP4a and DPP4b were prepared by Pd(PPh3)4
assisted Suzuki coupling reaction of DPP2a and DPP2b with 5-indolylboronic
acid, N-Boc-indole-2-boronic acid, respectively. The chemical structures and
1
13
purity of all compounds were identified by FT-IR, H-NMR, C-NMR. In the FT-
1
0

ACCEPTED MANUSCRIPT
IR spectrum of DPP2b, DPP3b, DPP4a and DPP4b, the typical ester C=O
stretch band between 1733 and 1754 cm−1 was taken as the evidence of the
1
attachment of Boc group the main core. The H NMR spectra of indole-
substituted DPP3(a-b) and DPP4(a-b) dyes are compatible with the proposed
1
structures. The H NMR spectrum of heteroaromatic side of the structures
showed slightly remarkable up-field shifts around 6.64 ppm in which indicated
the indole aromatic C−H bond.
Figure 1a
Figure 1b
Fig. 1a gives the comparison of the normalized UV−vis absorption spectra
of DPP3(a-b) and DPP4(a-b) dyes in chloroform solution, and the
corresponding optical properties are summarized in Table 1. In the studied
solvents, DPP3(a-b) and DPP4(a-b) dyes give broad absorption bands within
the range of 457-486 nm wavelength in which were assigned to the localized π–
π* transitions. These absorptions were attributed to the loss of the H-bonding
capability of DPP core because of the distorted molecular packing system for
pyrrole rings initiated by N-substitution with Boc or ethylhexyl groups. Similar
short-wavelength absorption values were observed for Boc-protected derivatives
of DPP molecules in the previous studies. When the protected groups are released
from the nitrogen atom, λmax values for all DPP structures are shifted to the
wavelength above 540 nm. [38, 47] The absorption bands in much higher energy
states could be generated to from the specific aromatic sides of the structures.
1
1

ACCEPTED MANUSCRIPT
Comparison of the normalized UV–vis absorption spectra of DPP3a dye
in different solvents and, also on thin film is given in Fig. 1b. The most striking
observation is the appearance of low-lying broad band around 60o nm for
DPP3(a-b) and DPP4(a-b) dyes in chloroform solution. Noting that this
observation is corresponded to the ICT transition between the DPP core and
indole units, known from the literature. [48, 49] Interestingly, this red-shift in
λmax value was not observed in more polar MeCN solution. Also, the absorption
maximum of all dyes are slightly shifted to blue region in MeCN solution. Both
observations are more consistent with much lower polarizability of the excited
dye with respect to its ground state in MeCN solution, which then heightens the
LUMO energy level of the studied dyes. This hampers the charge transfer from
indole group to the central DPP side. As can be seen from Table 1 that absorption
maximum of DPP3a and DPP4a dyes are more shifted to red region as
compared to that of DPP3b and DPP4b in the studied solvents. Because
ethylhexyl groups contribute to ring resonance by giving their electrons to the
nitrogen atom of DPP core through sigma bonds. Also, compared to the
absorption spectra in solution, these ones in the solid state have slightly red-
*
shifted (around 4-19 nm) indicating that π–π interaction due to molecular
packaging existed in the solid state.
Figure 2a
Figure 2b
Table 1
1
2

ACCEPTED MANUSCRIPT
The fluorescence emission spectra of DPP3(a-b) and DPP4(a-b) dyes in
chloroform are plotted as shown in Fig. 2a. DPP core shows mainly two emission
regions when excited at 485 nm. Emission bands are observed between 514 and
598 nm and their maximas are changed according to the polarity of the used
solvents and the attached groups. The emission maxima of DPP3a dye slightly
shifts more red region when compared the other dyes in the studied solvents.
Comparison of fluorescence emission spectra of DPP3a and DPP4a dyes coated
on thin films are also shown in Fig. 2b. The thin films show similar emission
profiles, but emission maxima on thin films displays slightly larger red-shifts as
compared to that of solution phases.
Figure 3a
Figure 3b
Fig. 3a compares the fluorescence emission spectra of DPP core with its
indole subunit for DPP3a dye in chloroform solution by changing the setting of
excitation wavelength from 260 to 540 nm. When we excite the sample at the
wavelengths between 260 and 340 nm in which mainly indole can absorb, the
emission peak of indole fragment was located around 400 nm (0–0). At this
situation, emission of DPP part of the structure seems to arise from the energy
transfer between the excited indole and DPP core. The absorption spectrum of
acceptor DPP group could overlap partially with the fluorescence emission
spectrum of indole donor, as a result resonance energy transfer occurs in the
structure of DPP3a dye to generate DPP emission signal. As the excitation
wavelengths approach to the DPP absorption region, the fluorescence spectra
show only one broad emission signal belonging to the DPP core. We could not
1
3

ACCEPTED MANUSCRIPT
detect any emission signals beyond the excitation wavelength of 540 nm due to
limitations of the optical absorptions of the studied dyes in this region. Fig. 3b
displays the excitation spectrum of all dyes in chloroform solution at the collected
emission wavelength of 520 nm. Excitation spectrum is very well-matched with
the absorption profile of the dyes as illustrated in Fig. 1a excluding ICT
absorption. Noting that the collected emission signal were generated from the
DPP absorption profile as described above.
Figure 4
Fig. 4 shows the fluorescence decay of DPP3a in chloroform solution at
detection wavelength of 520 nm. Analysis of the decays revealed mono-
exponential decays for all dyes in chloroform and acetonitrile as given in Table 1.
Fluorescence lifetimes of all dyes were calculated with the range of 2.79–6.63 ns
depending on the structure of the dyes and used solvents.
3
.2. CV measurements and PL quenching studies
For getting better efficiencies from BHJ-OSCs in which organic dyes are
used in their photoactive layer, the energy levels of the dyes must be compatible
with each other and also metal electrodes to achieve efficient electron transfer. In
order to clarify the efficient electron transfer, the HOMO/LUMO energy levels
including electrochemical band gaps of all dyes were determined from the
electrochemical measurements with cyclic voltammetry. The reduction and
oxidation voltammograms of all dyes on glassy carbon working electrode in 0.1M
[
TBA][PF ]/Me-CN are illustrated in Fig. 5(a-b) and their electrochemical data
6
are summarized in Table 2. While compounds DPP4(a-b) exhibit two reduction
1
4

ACCEPTED MANUSCRIPT
waves and two oxidation waves, while compounds DPP3(a-b) exhibit one
reduction-oxidation wave. The HOMO energy levels of all dyes range from –5.45
eV and –5.79 eV, and the LUMO energy levels of DPP3(a-b) and DPP4(a-b)
are calculated to be about –3.45, –3.57 eV, and –3.51, –3.22 eV, respectively.
Figure 5a
Figure 5b
Table 2
Fast photoinduced charge transport from donor to acceptor is very
essential issue for an effective BHJ-OSC devices. In order to analyze the charge
transfer possibilities between the synthesized dyes and organic photovoltaic
materials such as P3HT and PCBM in device structure, we report PL quenching
of P3HT polymer donor by DPP3b dye and, also all dyes by PCBM acceptor.
–4
The solution of 4.2 × 10 M DPP3b dye was prepared in THF and at each
addition 20 µL of this solution was poured into the 2.7 mL THF solution of 1.1 ×
–6
1
0 M P3HT which was placed in a quartz cuvette. After each addition, change in
fluorescence intensity of P3HT was followed. Fig. 6 revealed that the PL peak
intensity of pristine P3HT (λ =440 nm) increased dramatically by the addition
exc
–6
–6
of DPP3b dye over the concentration starting from 3.1 × 10 M to 76.4 × 10 M.
This increase can be due to 440 nm excitation also exciting DPP3b dye, and it
can also be attributed to the additional emission integral of the emissive DPP3b
dye. Then, PL quenching studies were repeated using dye:PCBM system to
analyze the charge transfer possibilities. PL quenching experiments were
–4
performed by the addition of 4.2 × 10 M THF solution of PCBM into the 2.7 mL
1
5

ACCEPTED MANUSCRIPT
THF solutions of ~3 × 10–6 M DPP3(a-b) and DPP4(a-b) dyes. After each
addition of 20 µL of PCBM solution, dyes were excited at 485 nm to get much
better PL signal. Fig. 7(a-d) revealed that the PL peak intensity of each pristine
dyes decreased dramatically over the increasing PCBM concentrations. The
decrease could be mainly assigned to an efficient charge transfer from the donor
dyes to PCBM acceptor. This observation is supported by the appropriate HOMO-
LUMO energy levels of PCBM acceptor and synthesized dyes to get better charge
injection. It was noted that DPP3(a-b) and DPP4(a-b) dyes may be used as
donor component instead of P3HT donor towards PCBM acceptor in BHJ-OSCs.
Figure 6
Figure 7a
Figure 7b
Figure 7c
Figure 7d
Corresponding Stern-Volmer plots for PL quenching process for
DPP3b:PCBM and DPP4b:PCBM are illustrated in Fig. 8. The Stern-Volmer
quenching constants (K ) for DPP3b:PCBM and DPP4b:PCBM titrations were
sv
–1
–1
–1
–1
found to be about 750.9 M ns and 1193.5 M ns , respectively. These high
quenching rates can be taken as evidences of occurrence electron transfer from
diketopyrrolopyrrole dyes to strong acceptor PCBM.
Figure 8
1
6

ACCEPTED MANUSCRIPT
4. Conclusions
In this work, four new small molecules based on linear D-A-D type DPP
consisting of different aryl electroactive and different soluble groups were
designed and successfully synthesized. All dyes represented an optical band gap
of 2.15-2.28 eV with suitable energy levels. According to these values, the
calculated LUMO energy levels of the new dyes are above the LUMO energy level
of standart PCBM acceptors (~3.9 eV). This indicates that there may be an
efficient electron transfer between donor DPP molecule and PCBM acceptor in
the BHJ-OSC device charge transfer mechanism. It is advisable that these new
dyes can be applicable as a donor component in the photo-active layer of BHJ-
OSCs. In conclusion, these results can be an efficient new approach to obtain high
performance organic solar cells with improved processability.
Acknowledgments
Financial support for this work was provided by the Research Council of
Manisa Celal Bayar University with the project number of 2016-018.
References
[
1] D.G. Farnum, G. Mehta, G.G.I. Moore, F.P. Siegal, Attempted reformatskii
reaction of benzonitrile, 1,4-diketo-3,6-diphenylpyrrolo[3,4-C]pyrrole. A lactam
analogue of pentalene, Tetrahedron Lett. 15(29) (1974) 2549–2552.
1
7

ACCEPTED MANUSCRIPT
[
2] B. Tieke, A.R. Rabindranath, K. Zhang, Y. Zhu, Conjugated polymers
containing diketopyrrolopyrrole units in the main chain, Beilstein J. Org. Chem.
(2010) 830–845.
3] C.B. Nielsen, M. Turbiez, I. McCulloch, Recent advances in the development
6
[
of semiconducting DPP-containing polymers for transistor applications, Adv.
Mater. 25(13) (2013) 1859–1880.
[
4] A.K. Palai, H. Cho, S. Cho, T.J. Shin, S. Jang, S.-U. Park, S. Pyo, Non-
functionalized soluble diketopyrrolopyrrole: Simplest p-channel core for organic
field-effect transistors, Org. Electron. 14(5) (2013) 1396–1406.
[
5] P. Sonar, S.P. Singh, Y. Li, M.S. Soh, A. Dodabalapur, A low-bandgap
diketopyrrolopyrrole-benzothiadiazole-based copolymer for high-mobility
ambipolar organic thin-film transistors, Adv. Mater. 22(47) (2010) 5409–5413.
[
(
6] Y. Li, P. Sonar, L. Murphy, W. Hong, High mobility diketopyrrolopyrrole
DPP)-based organic semiconductor materials for organic thin film transistors
and photovoltaics, Energ. Environ. Sci. 6(6) (2013) 1684–1710.
7] D. Chandran, K.-S. Lee, Diketopyrrolopyrrole: A versatile building block for
organic photovoltaic materials, Macromol. Res. 21(3) (2013) 272–283.
8] J.C. Bijleveld, V.S. Gevaerts, D. Di Nuzzo, M. Turbiez, S.G. Mathijssen, D.M.
[
[
de Leeuw, M.M. Wienk, R.A. Janssen, Efficient solar cells based on an easily
accessible diketopyrrolopyrrole polymer, Adv. Mater. 22(35) (2010) E242–246.
[
9] A.B. Tamayo, X.-D. Dang, B. Walker, J. Seo, T. Kent, T.-Q. Nguyen, A low
band gap, solution processable oligothiophene with dialkylated
a
diketopyrrolopyrrole chromophore for use in bulk heterojunction solar cells,
Appl. Phys. Lett. 94(10) (2009) 103301(1–3).
1
8

ACCEPTED MANUSCRIPT
[
10] E. Zhou, S. Yamakawa, K. Tajima, C. Yang, K. Hashimoto, Synthesis and
Photovoltaic Properties of Diketopyrrolopyrrole-Based Donor−Acceptor
Copolymers, Chem. Mater. 21(17) (2009) 4055–4061.
[
11] S. Loser, C.J. Bruns, H. Miyauchi, R.P. Ortiz, A. Facchetti, S.I. Stupp, T.J.
Marks, A naphthodithiophene-diketopyrrolopyrrole donor molecule for efficient
solution-processed solar cells, J. Am. Chem. Soc. 133(21) (2011) 8142–8145.
[
12] A. Tang, C. Zhan, J. Yao, E. Zhou, Design of diketopyrrolopyrrole (DPP)-
based small molecules for organic-solar-cell applications, Adv. Mater. 29(2)
(
[
2017) 1600013.
13] T. Beyerlein, B. Tieke, S. Forero-Lenger, W. Brütting, Red
electroluminescence from a 1,4-diketopyrrolo[3,4-c]pyrrole (DPP)-based
conjugated polymer, Synthetic Met. 130(2) (2002) 115–119.
[
14] D. Cao, Q. Liu, W. Zeng, S. Han, J. Peng, S. Liu, Diketopyrrolopyrrole-
containing polyfluorenes:ꢀ facile method to tune emission color and improve
electron affinity, Macromolecules 39(24) (2006) 8347–8355.
[
15] M. Kaur, D.H. Choi, Diketopyrrolopyrrole: brilliant red pigment dye-based
fluorescent probes and their applications, Chem. Soc. Rev. 44(1) (2015) 58–77.
16] J. Qi, J. Han, X. Zhou, D. Yang, J. Zhang, W. Qiao, D. Ma, Z.Y. Wang,
[
Optimization of broad-response and high-detectivity polymer photodetectors by
bandgap engineering of weak donor–strong acceptor polymers, Macromolecules
4
8(12) (2015) 3941–3948.
[
17] S. Tang, E.H. Ghazvini Zadeh, B. Kim, N.T. Toomey, M.V. Bondar, K.D.
Belfield, Protein-induced fluorescence enhancement of two-photon excitable
water-soluble diketopyrrolopyrroles, Org. Biomol. Chem. 15(31) (2017) 6511–
6
519.
1
9

ACCEPTED MANUSCRIPT
[
18] Y. Cai, Q. Tang, X. Wu, W. Si, Q. Zhang, W. Huang, X. Dong, Bromo-
substituted diketopyrrolopyrrole derivative with specific targeting and high
efficiency for photodynamic therapy, ACS Appl. Mater. Inter. 8(17) (2016) 10737–
1
0742.
[
19] F. Ponsot, N. Desbois, L. Bucher, M. Berthelot, P. Mondal, C.P. Gros, A.
Romieu, Near-infrared emissive bacteriochlorin-diketopyrrolopyrrole triads:
Synthesis and photophysical properties, Dyes Pigments 160 (2019) 747–756.
[
20] X. Liu, L. Kong, H. Du, Y. Zhang, J. Zhao, Y. Xie, Synthesis and
electrochromic properties of electrochromic polymers based on
propylenedioxythiophene, diketopyrrolopyrrole and benzodithiophene units,
Org. Electron. 64 (2019) 223–235.
[
21] W. Li, L. Wang, H. Tang, D. Cao, Diketopyrrolopyrrole-based fluorescent
probes for detection and bioimaging: current progresses and perspectives, Dyes
Pigments 162 (2019) 934–950.
[
22] K. Nie, S. Xu, X. Duan, H. Shi, B. Dong, M. Long, H. Xu, X.-F. Jiang, Z. Liu,
Diketopyrrolopyrrole-doped hybrid FONs as two-photon absorbing and dual-
2
+
emission fluorescent nanosensors for Hg , Sensors Actuat. B-Chem. 265 (2018)
–9.
23] Y. Lin, Y. Li, X. Zhan, Small molecule semiconductors for high-efficiency
organic photovoltaics, Chem. Soc. Rev. 41(11) (2012) 4245–4272.
24] H. Lee, H. Han, J. Jeong, H. Kimꢀ, D.-I. Song, Y. Kim, Broadband-solubility
1
[
[
diketopyrrolopyrrole derivative with both polar cyano and nonpolar alkyl groups
for stable organic photosensors and diffusion-processed organic solar cells,
ChemistrySelect 1(8) (2016) 1716–1722.
2
0

ACCEPTED MANUSCRIPT
[
25] H.-Y. Lee, J.-S. Yoo, H.-S. Kwon, J.-K. Oh, J.-H. Choi, Preparation and
characterizations of solvent soluble dyes based on dimerized diketo-pyrrolo-
pyrrole pigment, Mol. Cryst. Liq. Cryst. 617(1) (2015) 73–81.
[
26] H. Shi, Z. Gu, X. Gu, H. Pan, J. Pan, X. Hu, C. Fan, M. Shi, H. Chen, Effect
of end-groups on the photovoltaic property of diphenyl substituted
diketopyrrolopyrrole derivatives, Synthetic Met. 188 (2014) 66–71.
[
27] Y. Chen, Z. Du, W. Chen, L. Han, Q. Liu, M. Sun, R. Yang, Near-infrared
response thienoisoindigo-based small molecule for solution-processed bulk-
heterojunction solar cells, Synthetic Met. 187 (2014) 24–29.
[
28] H.-F. Feng, W.-F. Fu, L. Li, Q.-C. Yu, H. Lu, J.-H. Wan, M.-M. Shi, H.-Z.
Chen, Z.a. Tan, Y. Li, Triphenylamine modified bis-diketopyrrolopyrrole
molecular donor materials with extended conjugation for bulk heterojunction
solar cells, Org. Electron. 15(10) (2014) 2575–2586.
[
29] S. Li, J. Yuan, P. Deng, W. Ma, Q. Zhang, A comparative study of
diketopyrrolopyrrole and isoindigo based polymers for organic photovoltaic
applications, Dyes Pigments 106 (2014) 121–127.
[
30] J. Chen, M. Xiao, W. Su, X. Duan, L. Duan, W. Peng, H. Tan, R. Yang, W.
Zhu, Synthesis, characterization and photovoltaic properties of two-dimensional
conjugated polybenzodithiophene derivatives appending diketopyrrolopyrrole
units as side chain, Polym. 55(19) (2014) 4857–4864.
[
31] S.L. Suraru, U. Zschieschang, H. Klauk, F. Wurthner, Diketopyrrolopyrrole
as a p-channel organic semiconductor for high performance OTFTs, Chem.
Commun. 47(6) (2011) 1767–1769.
2
1

ACCEPTED MANUSCRIPT
[
32] W.S. Yoon, S.K. Park, I. Cho, J.-A. Oh, J.H. Kim, S.Y. Park, High-mobility n-
type organic transistors based on a crystallized diketopyrrolopyrrole derivative,
Adv. Funct. Mater. 23(28) (2013) 3519–3524.
[
33] A.B. Tamayo, B. Walker, T.-Q. Nguyen*, A Low Band Gap, Solution
processable oligothiophene with a diketopyrrolopyrrole core for use in organic
solar cells, J. Phys. Chem. C 112(30) (2008) 11545–11551.
[
34] M.M. Wienk, M. Turbiez, J. Gilot, R.A.J. Janssen, Narrow-bandgap diketo-
pyrrolo-pyrrole polymer solar cells: the effect of processing on the performance,
Adv. Mater. 20(13) (2008) 2556–2560.
[
35] H. Choi, S.J. Ko, T. Kim, P.O. Morin, B. Walker, B.H. Lee, M. Leclerc, J.Y.
Kim, A.J. Heeger, Small-bandgap polymer solar cells with unprecedented short-
circuit current density and high fill factor, Adv. Mater. 27(21) (2015) 3318–3324.
[
36] R.S. Ashraf, I. Meager, M. Nikolka, M. Kirkus, M. Planells, B.C. Schroeder,
S. Holliday, M. Hurhangee, C.B. Nielsen, H. Sirringhaus, I. McCulloch,
Chalcogenophene comonomer comparison in small band gap
diketopyrrolopyrrole-based conjugated polymers for high-performing field-effect
transistors and organic solar cells, J. Am. Chem. Soc. 137(3) (2015) 1314–1321.
[
37] J.W. Jung, W.H. Jo, Low-Bandgap Small Molecules as non-fullerene
electron acceptors composed of benzothiadiazole and diketopyrrolopyrrole for all
organic solar cells, Chem. Mater. 27(17) (2015) 6038–6043.
[
38] R. Beninatto, G. Borsato, O. De Lucchi, F. Fabris, V. Lucchini, E. Zendri, New
,6-bis(biphenyl)diketopyrrolopyrrole dyes and pigments via Suzuki–Miyaura
coupling, Dyes Pigments 96(3) (2013) 679–685.
39] X. Zeng, Z. Li, J. Ren, T. Ge, Z. Zang, Q. Sun, H. Wang, Y. Hao, Low bandgap
diketopyrrolopyrrole-based polymers with an asymmetric unit of fluoridated
3
[
2
2

ACCEPTED MANUSCRIPT
phenylene-thiophene for efficient polymer solar cells, Synthetic Met. 240 (2018)
3
0–36.
[
40] G. Zhang, L. Wang, X. Cai, L. Zhang, J. Yu, A. Wang, A new
diketopyrrolopyrrole (DPP) derivative bearing boronate group as fluorescent
probe for fluoride ion, Dyes Pigments 98(2) (2013) 232–237.
[
41] S.-i. Kato, T. Matsumoto, M. Shigeiwa, H. Gorohmaru, S. Maeda, T. Ishi-i, S.
Mataka, Novel 2,1,3-Benzothiadiazole-based red-fluorescent dyes with enhanced
two-photon absorption cross-sections, Chem–Eur. J. 12(8) (2006) 2303–2317.
[
42] G.M. Saltan, H. Dinçalp, M. Kıran, C. Zafer, S.Ç. Erbaş, Novel organic dyes
based on phenyl-substituted benzimidazole for dye sensitized solar cells, Mater.
Chem. Phys. 163 (2015) 387–393.
[
43] J.R. Knutson, J.M. Beechem, L. Brand, Simultaneous analysis of multiple
fluorescence decay curves - a global approach, Chem. Phys. Lett. 102(6) (1983)
01–507.
44] M. Zuker, A.G. Szabo, L. Bramall, D.T. Krajcarski, B. Selinger, Delta-function
5
[
convolution method (DFCM) for fluorescence decay experiments, Rev. Sci.
Instrum. s 56(1) (1985) 14–22.
[
45] J. Pommerehne, H. Vestweber, W. Guss, R.F. Mahrt, H. Bassler, M. Porsch,
J. Daub, Efficient 2-layer LEDs on a polymer blend basis, Adv. Mater. 7(6) (1995)
51–554.
46] A. Iqbal, M. Jost, R. Kirchmayr, J. Pfenninger, A. Rochat, O. Wallquist, The
synthesis and properties of 1,4-diketo-pyrrolo[3,4-C]pyrroles, B. Soc. Chim. Belg.
7(8‐9) (1988) 615–644.
47] E.D. Glowacki, H. Coskun, M.A. Blood-Forsythe, U. Monkowius, L. Leonat,
M. Grzybowski, D. Gryko, M.S. White, A. Aspuru-Guzik, N.S. Sariciftci,
5
[
9
[
2
3

ACCEPTED MANUSCRIPT
Hydrogen-bonded diketopyrrolopyrrole (DPP) pigments as organic
semiconductors, Org. Electron. 15(12) (2014) 3521–3528.
[
48] M. Chandrasekharam, M.A. Reddy, K. Ganesh, G.D. Sharma, S.P. Singh, J.L.
Rao, Synthesis and photovoltaic properties of D–A–D type small molecules
containing diketopyrrolopyrrole (DPP) acceptor central unit with different donor
terminal units, Org. Electron. 15(9) (2014) 2116–2125.
[
49] G.D. Sharma, J.A. Mikroyannidis, S.S. Sharma, M.S. Roy, K.R. Justin
Thomas, Efficient bulk heterojunction photovoltaic devices based on
diketopyrrolopyrrole containing small molecule as donor and modified PCBM
derivatives as electron acceptors, Org. Electron. 13(4) (2012) 652–666.
Figure Captions
Scheme 1: Synthesis of targeted DPP compounds. Reagents and conditions:
(
i) metalic Na, anhydrous FeCl , diethylsuccinate/tert-AmOH [38], (ii) for
3
DPP2a; 2-ethylhexyl bromide, NMP/K CO ; [39] for DPP2b; DMAP/THF, [40]
2
3
(
iii) 1H-indole-5-yl]boronic acid, 2M K CO , Pd(PPh ) , toluene, 65 °C; [39] (iv)
2 3 3 4
1
-Boc-indole-2-boronic acid, 2M K CO , Pd(PPh ) , toluene, 65 °C. [41]
2 3 3 4
Figure 1. (a) Comparison of the normalized UV–vis absorption spectra of
DPP3(a-b) and DPP4(a-b) dyes in chloroform solution. (b) Comparison of the
normalized UV–vis absorption spectra of DPP3a dye in different solvents and,
also on thin film.
2
4

ACCEPTED MANUSCRIPT
Figure 2. (a) Comparison of the normalized fluorescence emission spectra of all
DPP dyes in chloroform solution (b) Comparison of the normalized fluorescence
emission spectra of DPP3a and DPP4a dyes on thin films (λ =485 nm).
exc
Figure 3. (a) Comparison of the fluorescence emission spectra of DPP3a dye
in chloroform solution with different excitation wavelenghts increasing from 360
−4
to 540 nm (CDPP3a: 3.1×10 M). (b) Normalized excitation spectrum of DPP3(a-
b) and DPP4(a-b) dyes in chloroform solution at the emission wavelength of
5
20 nm.
Figure 4. Fluorescence decay analysis of DPP3a dye in chloroform solution
λdetection = 520 nm)
(
Figure 5. Cyclic voltammograms of (a) DPP3(a-b), and (b) DPP4(a-b) dyes
on glassy carbon working electrode in 0.1 M [TBA][PF ]/Me-CN (Scan rate: 100
6
−
1
mV s ).
Figure 6. PL spectra of P3HT at incresing concentrations of DPP3b dye in THF
–6
–6
at the excitation wavelength of 440 nm (0 M, 3.1 × 10 M, 11.5 × 10 M, 19.8 ×
–6
–6
–6
–6
–6
–6
1
0 M, 28.0 × 10 M, 36.2 × 10 M, 44.4 × 10 M, 52.5 × 10 M, 60.5 × 10 M,
–6
–6
6
8.5 × 10 M, 76.4 × 10 M).
Figure 7. PL spectra of (a) DPP3a, (b) DPP4a, (c) DPP3b and, (d) DPP4b
at incresing concentrations of PCBM in THF at the excitation wavelength of 485
–6
–6
–6
–6
–6
nm (0 M, 1.6 × 10 M, 6.0 × 10 M, 10.4 × 10 M, 14.7 × 10 M, 19.0 × 10 M,
–6
–6
–6
–6
2
3.2 × 10 M, 27.5 × 10 M, 31.7 × 10 M, 35.9 × 10 M).
Figure 8. Stern-Volmer plots of DPP3b and DPP4b dyes PL quenched by
2
PCBM in THF (y = 2681x + 0.0034 R :0.976 for DPP3b, and y = 3330x + 0.0019
2
R :0.995 for DPP4b).
2
5

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Table Captions
Table 1
UV–visible absorption (λ (nm)), emission (λem (nm)) wavelengths and
fluorescence decay times (f(n) (ns)) of all dyes in different solvents and, also on
thin films (λexc = 485 nm, λdetection = 520 nm).
Table 2
Electrochemical values and HOMO-LUMO energies of DPP3(a-b) and
DPP4(a-b) dyes with respect to the vacuum level.
2
6

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Research Highlights
1
. ICT was observed between the indole donor and the DPP core acceptor.
2
. High quenching rates can be taken as evidence of electron transfer.
. Synthesized dyes can be used as donor component in BHJ-OSCs.
3