Selectively Fluorinated Furan-Phenylene Co-Oligomers Pave the Way to Bright Ambipolar Light-Emitting Electronic Devices

Article abstract of DOI:10.1002/adfm.202104638

Linearly conjugated oligomers attract ever-growing attention as promising systems for organic optoelectronics because of their inherent lucky combination of high charge mobility and bright luminescence. Among them, furan-phenylene co-oligomers (FPCOs) are distinguished by outstanding solubility, very bright luminescence, and good hole-transport properties; however, furan-containing organic semiconductors generally lack electron transport, which makes it impossible to utilize them in efficient light-emitting electronic devices, specifically, ambipolar light-emitting transistors. In this work, 1,4-bis(5-phenylfuran-2-yl)benzene (FP5) derivatives are synthesized with the fully/partially fluorinated central and edge phenyl rings. It is shown that the selective fluorination of FPCOs lowers the energies of frontier molecular orbitals, maintaining the bandgap, solubility, and bright luminescence, dramatically improves the photostability, tunes the π-π stacked packing, and allows the first realization of electron transport in FPCOs. It is found that selectively fluorinated 2,2′-(2,3,5,6-tetrafluoro-1,4-phenylene)bis[5-(3,5-difluorophenyl)furan] demonstrates well-balanced ambipolar charge transport and efficient electroluminescence in an organic light-emitting transistor (OLET) with external quantum and luminous efficiencies as high as 0.63% and 5?cdA^?1, respectively, which are among the best reported for OLETs. The findings show that “smart” fluorination is a powerful tool to fine-tune the stability and performance of linearly conjugated small molecules for organic optoelectronics.

Full text of DOI:10.1002/adfm.202104638

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Selectively Fluorinated Furan-Phenylene Co-Oligomers
Pave the Way to Bright Ambipolar Light-Emitting Electronic
Devices
Igor P. Koskin, Christina S. Becker, Alina A. Sonina, Vasiliy A. Trukhanov,
Nikita A. Shumilov, Anatoly D. Kuimov, Yuliya S. Zhuravleva, Yuliya O. Kiseleva,
Inna K. Shundrina, Peter S. Sherin, Dmitry Yu. Paraschuk,* and Maxim S. Kazantsev*
1. Introduction
Linearly conjugated oligomers attract ever-growing attention as promising
Linear π-conjugation in arylene-based
small molecules is a highly promising
approach to create molecular systems for
organic optoelectronics because of the
simultaneous enhancement of two hardly
compatible but key properties: bright
luminescence and efficient charge trans-
port. Single crystals of these compounds
are believed to be promising materials for
optoelectronic devices, such as, light-emit-
ting diodes and transistors, optically- and
electrically-pumped lasers.[1] Several classes
of linearly conjugated small molecules,
for example, oligothiophenes,[1e,g] oligo-
furans,[2] distirylbenzenes,[1b] thiophene-
phenylene co-oligomers (TPCOs),[1d,g,3]
and many others[1f,g,4] were synthesized,
studied, and applied in light-emitting
devices. Among them, furan-phenylene
co-oligomers (FPCOs), showed superior
solubility[5] (compared to their thiophene
counterparts), high molecular rigidity,[6]
decent hole mobility up to 0.4 cm2 V−1 s−1,[7]
and excellent photoluminescence quantum
yields (PL QYs, up to ≈80% in crystals).[8]
Furan-based semiconductors are also
systems for organic optoelectronics because of their inherent lucky combina-
tion of high charge mobility and bright luminescence. Among them, furan-
phenylene co-oligomers (FPCOs) are distinguished by outstanding solubility,
very bright luminescence, and good hole-transport properties; however,
furan-containing organic semiconductors generally lack electron transport,
which makes it impossible to utilize them in efficient light-emitting elec-
tronic devices, specifically, ambipolar light-emitting transistors. In this work,
1,4-bis(5-phenylfuran-2-yl)benzene (FP5) derivatives are synthesized with
the fully/partially fluorinated central and edge phenyl rings. It is shown that
the selective fluorination of FPCOs lowers the energies of frontier molecular
orbitals, maintaining the bandgap, solubility, and bright luminescence,
dramatically improves the photostability, tunes the π-π stacked packing,
and allows the first realization of electron transport in FPCOs. It is found
that selectively fluorinated 2,2′-(2,3,5,6-tetrafluoro-1,4-phenylene)bis[5-(3,5-
difluorophenyl)furan] demonstrates well-balanced ambipolar charge trans-
port and efficient electroluminescence in an organic light-emitting transistor
(OLET) with external quantum and luminous efficiencies as high as 0.63%
and 5 cdA−1, respectively, which are among the best reported for OLETs. The
findings show that “smart” fluorination is a powerful tool to fine-tune the
stability and performance of linearly conjugated small molecules for organic
optoelectronics.
I. P. Koskin, Ch. S. Becker, A. A. Sonina, N. A. Shumilov, A. D. Kuimov,
Yu. O. Kiseleva, I. K. Shundrina, M. S. Kazantsev
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry of Siberian
Branch of Russian
V. A. Trukhanov, D. Yu. Paraschuk
Faculty of Physics
Lomonosov Moscow State University
Leninskie Gory 1/62, Moscow 119991, Russia
Yu. S. Zhuravleva, P. S. Sherin
International Tomography Center
Institutskaya 3A, Novosibirsk 630090, Russia
Yu. S. Zhuravleva, P. S. Sherin
Novosibirsk State University
Pirogova 2A, Novosibirsk 630090, Russia
Academy of Sciences
Lavrentiev Avenue 9, Novosibirsk 630090, Russia
E-mail: kazancev@nioch.nsc.ru
V. A. Trukhanov, D. Yu. Paraschuk
Enikolopov Institute of Synthetic Polymeric Materials of Russian
Academy of Sciences
Profsoyuznaya St. 70, Moscow 117393, Russia
E-mail: paras@physics.msu.ru
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.202104638.
DOI: 10.1002/adfm.202104638
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believed to be highly useful for mass production because of
their building blocks can be extracted from renewable sources
by a carbon-neutral technologies.[9] These features make FPCOs
very promising for organic optoelectronics; however, the lack of
electron transport in them (even in the case of using low work-
function Ca electrodes)[8] has been a big obstacle for their prac-
tical application in high-performance organic optoelectronics.
Moreover, electron transport has been a “bottleneck” of many
other furan-based systems,[2b,c,e,10] which has inspired us for the
current study.
The introduction of electron-withdrawing substituents, espe-
cially fluorine atoms, is one of the most efficient strategies
used earlier to realize or improve electron transport in conju-
gated organics.[1d,11] Being the most electronegative element,
fluorine as a substituent may turn the herringbone packing
(i.e., edge-to-face) into (face-to-face) π-π stacking[12] driven
by dipolar, quadrupolar, or/and dispersion interactions.[12a]
Moreover, fluorination of linearly conjugated oligomers lowers
the energy of both highest occupied (HOMO) and lowest
unoccupied (LUMO) molecular orbitals maintaining the optical
bandgap (e.g., required for blue-emitting devices), increase the
electrochemical stability, inhibit oxidation, and facilitate effi-
cient electron injection and transport.[1d,11] The introduction
of perfluorophenyl groups also enhanced the operational sta-
bility of organic field-effect transistors (OFETs) assigned to the
increased hydrophobicity and steric protection of π-conjugated
units.[13]
Previously synthesized and comprehensively investigated
1,4-bis(5-phenylfuran-2-yl)benzene (FP5, Scheme 1) seems a
perfect platform for subsequent modification and investiga-
tion of fluorinated FPCOs because of its high solubility and
molecular rigidity, bright luminescence, long exciton diffu-
sion length, and efficient hole transport.[5,8] As fluorination of
the furan moiety is a significant synthetic challenge, there is
a wide possibility to combine fluorinated phenyl(-ene) groups
in FP5. Moreover, usually, only partially-fluorinated deriva-
tives of various conjugated organics demonstrate the best
crystal packing and optoelectronic performance as was previ-
Scheme 1. Synthetic scheme and structures of target compounds with their respective abbreviations; ϕ1, ϕ2 and b1, b2 denote dihedral angles and
interring bonds.
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ously reported for TCNQ derivatives,[14] benzodifurandiones,[15]
phtalocyanines,[16] acenes,[11a] oligophenylenes,[11b] and TPCOs
with perfluorinated benzene rings.[11c–e] Specifically, partial
perfluorination of phenyl(-ene) rings of TPCOs was reported
to induce molecular planarization because of attractive elec-
trostatic interactions, to increase the solubility, to facilitate a
crossover from the herringbone packing motif to the π-stacking
one, and, remarkably, to provide ambipolar charge transport in
phenylene-perfluorinated 2,2′-(2,3,5,6-tetrafluoro-1,4-phenylene)
bis(5-phenylthio-phene).[11e]
In this work, we show that selective fluorination of FPCOs
is an extremely efficient strategy leading to electron trans-
port and improving or maintaining their other key proper-
ties indispensable for optoelectronic devices. We synthesized
and studied FPCOs with fluorinated (central) phenylene
rings or/and fluorinated (terminal) phenyl rings (Scheme 1).
According to our findings, the introduction of fluorine atoms
in proximity to the oxygen (full fluorination of phenyls)
results in decreased molecular rigidity and deplanarization
of FPCOs so that, to weaken this effect, one needs selec-
tive fluorination. Our single-crystal X-ray study revealed the
π-stacking motif in crystals of fluorinated FP5s, which could
be finely tuned by the position of fluorination. Fluorination
is highlighted to increase the photostability of FPCOs. We
report electron transport and electroluminescence (EL) for a
few fluorinated FPCOs in thin-film devices. And finally, we
found an optimally fluorinated FPCO that showed well-bal-
anced ambipolar charge transport and bright EL in organic
light-emitting transistors (OLETs) with the external quantum
and luminous efficiencies reaching 0.63% and 5 cd A−1, cor-
respondingly, which are among the highest values reported
so far.[1a,17]
2,2′-(2,3,5,6-tetrafluoro-1,4-phenylene)bis[5-(pentafluorophenyl)-
furan] (F5-FPF5). The synthesized compounds were charac-
terized by 1H, 19F, 13C NMR, IR, HRMS spectroscopies and
elemental analysis (Figures S1–S25, Supporting Information).
As a next step in our characterizations we measured
FPCOs’ solubility being an attractive feature of furan-based
semiconductors[2c,e] and providing a potential for easy purifi-
cation, handling and processing, which is also important for
coming to solution-processed devices, for example, OLETs
as was recently reported for FP5.[8] Figure 1a summarizes the
solubility of the synthesized compounds, which followed two
distinct trends: An increase with fluorination of the (central)
phenylene ring and a decrease with fluorination of the (ter-
minal) phenyl rings. As a result, F5-FP5 demonstrated the
lowest solubility because of its fully fluorinated phenyl rings
and unsubstituted phenylene one. According to the differential
scanning calorimetry (DSC) analysis (Figure S26, Supporting
Information), the melting points among the FP5 family exhibit
a mirror trends (Figure 1b): A decrease/increase upon fluori-
nation of the phenylene/phenyl moiety reaching a maximum
of 261 °C for F5-FP5. Therefore, fluorination of the phenylene
moiety weakens intermolecular interactions, whereas the sub-
stitution in the phenyl groups strengthens intermolecular inter-
actions. To balance these effects and maintain an inherent for
FPCOs solubility one needs a selective fluorination. According
to the thermal gravimetric analysis, all FP5s demonstrated high
thermal stability with complete sublimation in an inert atmos-
phere (Figure S26, Supporting Information).
Figure 1c presents the energies of HOMO, LUMO, and
electrochemical gaps estimated from cyclic voltammetry (CV)
(Figure S27, Supporting Information), as well as, the optical
gaps estimated from the absorption spectra (vide infra). Both
HOMO and LUMO energies generally decrease upon fluorina-
tion of FPCOs due to strong inductive effect of fluorine atoms.
However, the position of fluorination plays a crucial role: i) The
introduction of four fluorine atoms in central phenylene ring
(FPF5) is as efficient as the introduction of 10 fluorine atoms
in F5-FP5; ii) the perfluorination of the terminal phenyl groups
broadens both electrochemical and optical gaps due to intramo-
lecular electrostatic repulsion and deplanarization (vide infra).
This site-specific stabilization of the frontier molecular orbitals
in F2-FPF5 might also be explained by the small HOMO and
LUMO LCAO (linear combination of atomic orbitals) coef-
ficients at the meta-carbon atom of the terminal phenyl ring,
according to the Hückel theory, resulting in a negligible desta-
bilization by a mesomeric effect and strong stabilization by
inductive effect of the fluorine substituent as was early reported
for fluorinated pentacene.[19] Accordingly, the fluorination of
the phenylene ring and the introduction of two fluorine atoms
in 3,5-positions in the phenyls (F2-FPF5) is the most beneficial
to balance lowering the HOMO/LUMO energy and preserving
the bandgap, molecular planarity, and rigidity (vide infra).
2. Results and Discussion
2.1. Synthesis and Characterizations
All fluorinated derivatives were synthesized by cross-coupling
reactions using various palladium-based catalytic systems with
yields from moderate to good depending on the activity of
phenylboronic acid used (see Scheme 1). For moderately acti-
vated phenylboronic and 4-fluorophenylboronic acids Pd(PPh3)4
in aqueous 1 m Na2CO3 solution and mixture of toluene/
methanol as well as a drop of Aliquat 336 were used to obtain
2,2″-(2,3,5,6-tetrafluoro-1,4-phenylene)bis(5-phenylfuran)
(FPF5) and 2,2″-(2,3,5,6-tetrafluoro-1,4-phenylene)bis[5-(4-fluo-
rophenyl)furan] (F1-FPF5), respectively. For the synthesis of
2,2″-(2,3,5,6-tetrafluoro-1,4-phenylene)bis[5-(3,5-difluorophenyl)
furan] (F2-FPF5) palladium(II) acetate in the presence of dried
potassium carbonate was used. In this case more active catalyst
allowed us to overcome lower reactivity of 3,5-difluorophenylbo-
ronic acid as compared to that of 4-fluorophenylboronic acid
and to achieve a better yield (63% against 53%, Scheme 1). In
the reactions with relatively deactivated pentafluorophenylbo-
ronic acid silver oxide was used as an additive to Pd(PPh3)4 and
K3PO4, according to ref. [18] in order to activate the intermediate
and turn the equilibrium to the formation of desired products:
2,2″-(1,4-phenylene)bis[5-(pentafluorophenyl)furan] (F5-FP5) or
2.2. Calculations for Isolated Molecules
After DFT optimization (see Tables S13–S17, Supporting Infor-
mation, for atomic coordinates), all the fluorinated FPCOs retain
the planar equilibrium conformation in the gas phase except for
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under fluorination previously reported for the phenylenevi-
nylene family was assigned to the F···O repulsive interac-
tions.[20] In the case of fluorinated FPCOs, according to atomic
charge distribution calculated by the CHarges from Electro-
static Potentials using a Grid-based method (CHELPG) scheme,
the oxygen and fluorine atoms indeed possess almost similar
negative charges of ≈−0.2 a.u. (see Tables S13—S17, Supporting
Information, for CHELPG atomic charges). The corresponding
energy of coulomb repulsion between these two atoms varies
between 14 and 20 kJ mol−1, which is roughly comparable with
the typical value of the torsional barrier of the furan-phenyl(-
ene) moiety (see Table S2, Supporting Information, for exact
energies of electrostatic interactions). Therefore, when two fluo-
rine atoms are in the close vicinity to furan’s oxygen (in the case
of F5-FPF5), these interactions add up resulting in a force desta-
bilizing the typical planar geometry of FP5. In other words, a
FPCO molecule can apparently accommodate one F···O repul-
sion (with a particular furan moiety involved) maintaining the
planarity (by slight bond elongation and larger bond angles; see
Table S1, Supporting Information) compared to the non-fluor-
inated situation; however, it cannot accommodate two F···O
interactions maintaining the planarity. Our subsequent analysis
of non-covalent dispersion interactions (see Note S1, Supporting
Information) revealed that even though O···F dispersion inter-
actions are attractive, they are too weak to have any significant
influence on the molecular conformation (Figures S28–S32,
Supporting Information). Moreover, the fluorination does not
lead to any noticeable loss of π-conjugation as follows from the
Wiberg indices of bonds between the aromatic cycles (Table S4,
Supporting Information). Since both non-covalent dispersion
interactions and conjugation loss demonstrate either a negli-
gible or non-existent effect on the molecular conformation, we
conclude that electrostatic repulsion is the primary driving force
of F5-FPF5 deplanarization.
The calculated torsional barriers of the relaxed potential
energy surfaces (PES) demonstrated (Figure 2 and Figures S33
and S34, Supporting Information) that the FPCOs featuring
a fluorine atom in the ortho-position of the phenylene (with
Figure 1. a) Solubility in toluene, b) melting temperatures, c) HOMO
(red) and LUMO (blue) energies, electrochemical (olive) and optical
(magenta) gaps of FP5s. *The data for FP5 taken from ref. [5].
Figure 2. Torsional barriers of PES around ϕ1 and ϕ2 dihedral angles
of the FPCOs. Red and blue dashed lines show torsional energies
(ϕ1 and ϕ2 dihedral angles, respectively) of FP5. Level of theory:
B3LYP[GD3BJ]/6-311++G**.
F5-FPF5 exhibiting a distorted geometry with ϕ1 and ϕ2 dihedral
angles equal to ≈20° and ≈10°, respectively (see Table S1, Sup-
porting Information, for details). The strong molecular twisting
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Figure 3. Fluorescent optical images of fluorinated FP5s’ single crystals captured in 405-nm light. The arrows and Miller indices indicate the orientation
of crystallographic axes and the main crystal facet (facet with the maximal area), respectively.
respect to furan) exhibited the lower respective torsional bar-
riers as compared with FP5.[6] This finding agrees well with the
electrostatic repulsion of O···F atoms surpassing the disper-
sion attraction between them. This effect also correlates with
the experimentally observed loss of the vibronic structure in the
absorption spectra of the heavily fluorinated FPCOs (Figure 5a).
Therefore, fluorination generally decreases the torsional rigidity
of FP5s and selectively fluorinated FP5s are more promising
because they partially retain the torsional rigidity and planarity.
of crystallographic axes. For all the crystals, the fastest growth
direction corresponded to the a-axis.
The fluorinated FP5s crystallize in triclinic (P for F5-FP5)
1
and monoclinic (P21/c for FPF5, F2-FPF5, and F5-FPF5; P21 for
F1-FPF5) space groups (see Table S5, Supporting Information).
The molecular conformations are planar for all of them with
exception of F1-FPF5 (Figure S36, Supporting Information),
ϕ′
2
which exhibits a slightly distorted conformation (ϕ1′ and
are

about 10°) because of interlayer C H···F interactions.
All the fluorinated FP5s possess a face-to-face π-stacking
arrangement (Figure 4, Table S6, Supporting Information) con-
trary to the herringbone motif of unsubstituted FP5.[21] Since
the phenyl fluorination causes a deficit of the electron density at
the center of this ring, the phenyls in π-π stacks are aligned with
the furans with a lateral displacement (Figure 4, Figure S37).
To quantify these displacements from the ideal π-stack, pitch
(δP) and roll angles (δR) were evaluated (Figure 4).[22] FPF5 and
2.3. Crystal Structure Analysis
To reveal the effect of selective fluorination on the crystal struc-
ture of FP5s, their single crystals were grown, and the cor-
responding X-ray measurements were performed. Figure 3
demonstrates optical images of the crystals with the orientation
Figure 4. Nearest neighbor dimer arrangements in fluorinated FPs crystals. Lateral displacement from the ideal π-stack along the long (δP is the pitch
angle, top) and short (δR is the roll angle between the orange lines, bottom) axes of the molecules. Blue lines represent planes perpendicular to the long
molecular axis; dashed blue lines represent π-π stacking interactions; red solid lines correspond to main crystal facets; red dashed lines correspond to
the line connecting the terminals of nearest-neighboring molecules; the tilt angle δT corresponds to the angle between the main crystal facet and the
long molecular axes; the Miller indices are shown in parenthesis.
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F5-FPF5 exhibit similar δP of 47° (Figure 4a,e), while F1-FPF5
has δP of 41°, but with weaker overlapping of the neighboring
conjugated systems resulting from the lack of π-π interactions
between the non-planar parts of the molecules (Figure 4b).
F2-FPF5 demonstrated the lowest δP of 7° and slipped
π-stacking with δR of 25° (Figure 4c). The largest δP among all
the fluorinated FPCOs was found for F5-FP5 (≈70°, Figure 4d).
F5-FP5 has two types of π-π stacks with distances between the
aromatic rings centers (centroids, Cg) of 3.56 and 3.73 Å (Table
S6, Supporting Information) and corresponding δP and δR (See
Figure 4). The π-π stacking interactions are additionally sta-

bilized by C F···π interactions, whose contributions to the
Hirshfeld surfaces increase with the increase of the number
of fluorine atoms (Figure S38, Supporting Information). Note
that fluorination leads to the increase of the crystal density
(Table S5, Supporting Information) owing to the increase of
molecular weight and closer packing.
Almost all crystals had the main crystal facet (001) except
FPF5 (its main facet is the (010) plane) as shown in Figures 3
and 4. FPF5, F1-FPF5, F2-FPF5, and F5-FPF5 crystals exhibited
elongated prism or elongated plate habits (Figure 3), and the
direction of π-π-stacking corresponded to the direction of crystal
growth, that is, along the a-axis and for F5-FP5 with the prism-
shaped habit—along the b-axis as well (Figure 4d). Molecules
in F5-FP5 and F2-FPF5 crystals exhibit nearly perpendicular
orientations of the long molecular axes (connecting carbons
in p-positions of the terminal phenyls) in respect to the main
crystal facet (δT
F1-FPF5, and F5-FPF5 demonstrate a remarkable inclination
(δT 42°/44°/33°, correspondingly, Figure 4). According to
our intermolecular interactions analysis in all fluorinated FP5s
= 78°/87°, correspondingly), whereas FPF5,
=

their molecular π-stacks are connected by intralayer C H···F
interactions and F···F close contacts in phenyl-perfluorinated
FPCOs (see Note S2, Supporting Information).
In summary, all crystals of the fluorinated FP5s have face-
to-face π-stacking arrangement with pitch- and roll-angles pre-
cisely tuned by selective fluorination. Assuming the transition
dipole moments being oriented nearly along the long molecular
axes,[23] the only dimer arrangement of F5-FP5 may be a candi-
date to J-aggregation according to the point dipole model (due
to a large molecular displacement, Figure 4d), whereas the evi-
dence obtained by spectroscopic methods is presented below.
Taking into account the π-stacking and interstack (intralayer)
interactions (Figure S39, Supporting Information), F1-FPF5,
F2-FPF5, and F5-FPF5 are expected to have better overlapping of
the electronic wavefunctions and hence more efficient charge
transport (see Section 2.6).
2.4. Optical Properties
The optical properties of fluorinated FP5s were studied in THF
solution, Paraloid B72 solid solution, aggregates, and single
crystals. Figure 5a demonstrates the optical absorption spectra
of the studied compounds in THF solution and that of the
parent FP5.[5] Two representative trends are observed: i) The
increase of fluorine atom number blue-shifts the absorption
and emission maxima and ii) the full fluorination of terminal
Figure 5. a) Optical absorption and b) PL spectra of FP5s studied in THF
(solid lines), binary mixtures THF:H2O (aggregates, dash-dotted lines)
and single crystals (panel (b), dashed lines); c) ratio of 00 to 10 absorp-
tion peak intensities for THF solutions and aggregates with the character-
istic water fractions (Figure S43, Supporting Information).
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phenyl groups causes a smoothing of the fine structure of
optical absorption spectrum, which was the most pronounced
for the unsubstituted FP5.[5] The smoothing, previously shown
for the distyrylbenzene family,[24] was assigned to the molecular
deplanarization and decrease of rigidity due to intramolecular
O···F repulsion (vide supra).[20] The hypsochromic shift upon
fluorination might be explained by both geometrical effect,[12a]
characteristic, for example, for the distyrylbenzene family,[20]
and electronic contribution that is rather uncommon but can
occur upon specific fluorination as the inductive effect can
compete with the mesomeric effect as was previously reported
for oligothiophenes.[12a,25] The Stokes shift for the phenyl(-ene)-
perfluorinated FP5 (F5-FPF5) (Table S8, Supporting Informa-
tion) is also higher than that of unsubstituted FP5 supporting
the molecular deplanarization. The PL kinetics of each FP5
derivative in THF were the same over the emission spectrum,
and they are well reproduced with a monoexponential function.
PL lifetimes were about 1.1 ns for all the studied compounds
(Figure S44a, Table S8, Supporting Information). However, PL
QYs for fluorinated FP5s in THF demonstrated slightly lower
values (≈80%) as compared with FP5, which correspond to an
increase of the non-radiative decay rate (Table S8, Supporting
Information), and this increase is assigned to their lower tor-
sional rigidity. The radiative rates for all FP5s in THF were cal-
culated to be ≈0.75 ns−1.
In solid solutions (i.e., polymer films) all FP5 deriva-
tives demonstrated absorption spectra with slight blue shifts
and similar shapes as compared to those in liquid solutions
(Figure S42, Supporting Information). Smoothing of the
absorption fine structure of the heavily fluorinated oligomers
(F5-FPF5 and F5-FP5) in solid solution was also assigned to
their lower rigidity and a possibility for intramolecular motions
in a free volume of polymer matrix.[4,24,26] The PL kinetics for
all solid solutions were monoexponential with PL lifetimes in
the range 1.1–1.4 ns (Figure S44b, Table S8, Supporting Infor-
mation). It should be noted that PL decay of F5-FP5 demon-
strates complex dynamics, which could be assigned to partial
aggregation of these molecules in the polymer matrix caused
by their low solubility. Assuming the isolated molecules as the
major contributor to PL kinetics at 420 nm (blue side of spec-
trum), its PL lifetime obtained from the monoexponential fit
was 1.12 ns. The radiative rate constants for fluorinated FP5s in
solid solutions (Table S8, Supporting Information) were about
two times lower as compared with those in THF. As the PMMA
matrix might provide cavities up to 5Å in size, this could result
in weaker fixation of the fluorinated FP5s by the matrix as com-
pared with the more polar liquid solvent (THF).[4,24] On the
other hand, the difference in the radiative rate constant for FP5
for the liquid and solid solutions is less pronounced (Table S8,
Supporting Information), which is also in agreement with its
higher torsional rigidity as compared with the fluorinated FP5s.
To examine the effect of aggregation on the optical proper-
ties of FP5s, absorption and PL spectra in binary mixtures
THF:H2O were recorded (Figure S43, Supporting Information,
and Figure 5a,b). As FP5s are practically insoluble in water the
stepwise increase of water content in the mixtures resulted in
formation of suspensions. The pronounced concentration of
the oscillator strength in the blue part of the absorption spectra
for F2-FPF5 and parent FP5 hints at the H-aggregation behavior
(Figure 5a) as was previously reported for distyrylbenzene.[27]
For the other co-oligomers the aggregation type is not evident
from the absorption spectra as the polarizability (solid-state)
effects may take place and affect the resulting spectral features.
To distinguish between the J-/H-aggregation patterns, we cal-
culated the relative spectral intensities I00 and I10 of the first
two characteristic absorption peaks (Figure 5c) according to
ref. [28]. As the ratio I00/I10 decreased for all the co-oligomers
studied except F5-FP5, we conclude that they demonstrate
H-aggregation. In turn, the slight increase in I00/I10 for aggre-
gated F5-FP5 may be assigned to J-aggregates. These data are in
a good agreement with our preliminary assignment based on
the X-ray data (vide supra) and also with the calculated absorp-
tion spectra of FP5s molecules and dimers (adopted from X-ray
data) in gas phase (see Figure S35, Supporting Information).
PL of the studied aggregates demonstrated quenching upon the
increase of water content (Figure S43, Supporting Information),
which could be assigned mainly to exciton trapping at grain
boundaries of the aggregates and defects.[27] Time-resolved PL
measurements (Figure S45, Supporting Information) of the
aggregates demonstrated more complex transients as com-
pared to those in solution, specifically, the PL dynamics were
inhomogeneous along the spectra and did not follow mono- or
biexponential functions. We assign this complex behavior to
different effects stemming from aggregation: exciton diffu-
sion,[8] PL quenching at the defects/surface of aggregates,[27]
and energy transfer to molecular self-dopants.[8] To minimize
these effects, whose contributions are expected to increase with
time after photoexcitation, we analyzed only the initial parts
of the PL transients (decay of PL signal by one order of magni-
tude) by fitting them with a biexponential function convolved
with the instrument response function. While the initial PL
dynamics was similar for FP5, F1-FPF5, and F5-FPF5 over the
emission band (Figure S45, Supporting Information), the evo-
lution of PL signal for FPF5, F2-FPF5, and F5-FP5 was essen-
tially diverse at different wavelengths. For the FPF5 aggregate,
the PL dynamics was affected by the dissolved (unaggregated)
molecules (Figure S43c, Supporting Information) and, to mini-
mize their contribution, we analyzed the kinetics at the red
spectral part (550 nm) corresponding to the aggregates. The
corresponding amplitude-weighted averaged PL lifetimes for
aggregated FP5, FPF5, F1-FPF5, and F5-FPF5 are presented in
Table S8, Supporting Information. All these aggregates demon-
strate the longer decay times as compared with those for solu-
tions. The lowest radiative rate constants of 0.13 and 0.09 ns−1
were obtained for FPF5 and F5-FPF5, respectively, supporting the
suggested H-aggregation behavior. The radiative rate constants
for F1-FPF5 and FP5 were slightly higher (0.34 and 0.39 ns−1,
respectively) but still being lower than the corresponding radia-
tive rates in solution so that these observations are signatures
of H-aggregation. For the F2-FPF5 and F5-FP5 aggregates, the
mentioned inhomogeneity of the PL transients at different
wavelengths does not allow us to correctly calculate the radia-
tive rate constants. Nevertheless, the PL kinetics for the F5-FP5
aggregate contains a large contribution of a fast component,
which does not contradict J-aggregation assignment. As the
F2-FPF5 suspensions exhibit the strongest H-aggregation
behavior according to the measured (Figure 5a) and calculated
(Figure S35, Supporting Information) absorption spectra, the
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fast and spectrally inhomogeneous PL dynamics in the aggre-
gates could be assigned to efficient exciton diffusion in them
with subsequent energy transfer to molecular self-dopants.[8,29]
Indeed, as our materials were synthesized by the cross-coupling
reactions, self-dopants, arising as by-products, were found in
the fluorinated FP5 samples (see Note S3, Supporting Informa-
tion) as earlier reported for FP5.[8,29]
The PL spectra of single crystals (Figure 5b) measured
with an integrating sphere were red-shifted as compared with
those in solutions and aggregates (except F5-FPF5, Table S8,
Supporting Information). Similar to the case of the suspen-
sions, we assign this to an interplay between a solid-state shift,
H-aggregation, reabsorption, and energy transfer to the self-
dopants. The PL QYs for all studied crystals are about 47–60%
(Table S8, Supporting Information), which is in agreement with
the PL QY values for variously-doped FP5 crystals.[8] Although
we are not able to estimate the intrinsic (dopant-free) PL QY
of our crystals, we conclude that the fluorination and crossover
from the herringbone packing to the π-π stacking motif do not
result in PL quenching, and the fluorinated FP5s are brightly
luminescent as their unsubstituted counterparts.[7]
2.5. Photodegradation in Solution
The decrease of both HOMO and LUMO energies generally
should affect the molecule photostability, which is important
as it may i) allow solution processability and ii) improve the
operational stability by the chemical resistance to the residue
oxygen of organic thin films in optoelectronic devices.[7,30] We
studied the photodegradation dynamics of fluorinated FP5s
and the parent FP5 compound in toluene solutions saturated
by air oxygen. Figure S47, Supporting Information, demon-
strates the evolution of optical absorption spectra of FP5s
under the irradiation. The decrease of co-oligomers’ absorp-
tion and the increase of short-wavelength bands was clearly
observed. The latter was assigned to the less-conjugated deg-
radation products of FP5, most probably carbonyl-containing
derivatives, due to the destruction of furan ring.[31] Since the
concentration of oxygen in saturated toluene solution[32] is
about two orders higher than that of studied molecules, the
kinetics of photodegradation may be considered as a pseudo
1st-order reaction. Figure 6a demonstrates normalized FP5
optical absorption at 00 peak as a function of irradiation time.
All kinetics perfectly matched the monoexponential behavior,
and the corresponding degradation constants were extracted
(Figure 6a,b). The photodegradation constants were about
two (for F2-FPF5 and F5-FP5) and three (for F5-FPF5) orders
of magnitude lower than that of the parent FP5 compound.
Remarkably, upon increase of the number of fluorine atoms
the photodegradation constant decreases exponentially with
the HOMO energy (Figure 6b, inset). This is reasonable to
explain by an increase of the energy barrier for, for example,
cycloaddition reaction of FPCO with oxygen arising from
the lowering of the HOMO energy.[31] The lower the HOMO
energy, the less willingly the molecule donate electrons for
the photochemical oxidation. Therefore, we conclude that
fluorination of FPCOs is a powerful tool for increasing their
photostability.
Figure 6. Photodegradation data for the studied co-oligomers in air-satu-
rated toluene solution. a) Normalized optical density of 00 band (≈3.1 eV)
for all the co-oligomers studied during continuous 405-nm irradiation;
b) the photodegradation constants and their dependence on the HOMO
energy (inset); the line represents the linear approximation.
2.6. Charge Transport and Electroluminescence
Initially, we simulated charge-carrier mobility in FP5s’ crystals
using the X-ray data. At the first step, the reorganization ener-
gies for hole and electron transport (λh and λe, respectively)
were calculated (Figure 7a). To obtain the required single-point
energies, all cationic and anionic geometries were optimized
in the gas-phase; the required optimized neutral state geom-
etries were adopted from the calculations presented in Sec-
tion 2.2. Since the cationic and anionic geometries of all the
fluorinated FP5s were found to be planar, the oligomers with
the planar conformation in the neutral state (F5-FP5, FPF5,
F1-FPF5, F2-FPF5) exhibited relatively low reorganization ener-
gies for charge transfer (λh, λe ≈ 250 meV) typical for FP5.[6] On
the contrary, F5-FPF5 showed the higher charge reorganization
energies because of its non-planar conformation in the neutral
state. In general, the reorganization energies for the electron
transfer λe were found to be approximately 50–80 meV higher
as compared with λh, while overall λh and λe increased with the
increase of fluorination (Figure S48, Supporting Information).
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are just marginally lower as compared with those for F5-FPF5.
Therefore, F2-FPF5 and F5-FPF5 are expected to demonstrate
the best charge transport.
Single-crystal OFETs implemented in the top-contact top-gate
configuration (Figures S50 and S51, Supporting Information)
demonstrated hole transport only for FPF5 and F1-FPF5 with
the average mobilities of 0.06 and 0.03 cm2 V−1 s−1, respectively,
evaluated in the saturation regime (Figure 8a and Table S10,
Supporting Information). The threshold voltages were −35
and −55 V for FPF5 and F1-FPF5, correspondingly (Figure 8a),
which are significantly higher than those for unsubstituted FP5
measured with the similar device configuration and parameters
of the gate dielectric.[21] This poorer p-type OFET performance
for the fluorinated FP5s is assigned to impeding of hole injec-
tion from the graphite electrodes (the work function is about
−4.7 eV) to their relatively low-lying HOMOs (Figure 1c) and the
effect of the interface dipole at the device contacts that is formed
by strong intramolecular dipoles (induced by the fluorine
atoms) as suggested in Ref.[33] Possibly, this interface dipole
can be more effective in switching the OFET polarity from the
p- to n-type commonly observed upon fluorination[11f,h,i,30c,33]
than just the lowering of the LUMO energy. The deteriora-
tion of the hole injection reflects the slightly S-shaped output
characteristics near zero voltage, and this S-shape effect is
more pronounced for the OFET based on the more fluorinated
F1-FPF5 (Figure S51b,d, Supporting Information) explaining its
lower hole mobility and higher threshold voltage than those of
FPF5 and FP5. The other heavier terminally fluorinated FPCOs
did not show any hole transport at all, which agrees with fur-
ther lowering of their HOMO and LUMO energies (Figure 1c)
and enhancement of the interface dipoles upon fluorination.
However, this trend, in turn, should enhance the electron injec-
tion and facilitate the electron transport, which was unavailable
earlier for FPCOs.[2b,c,e,8]
To explore electron/ambipolar charge transport and light
emission in devices, we fabricated thin-film OFETs (see
Figure S52, Supporting Information, for device configura-
tion) with low (Ca) and high (MoO3/Au) work-function elec-
trodes and characterized them in an argon-filled glovebox (see
Section 4.5 for the details of fabrication and characterization).
Devices based on F1-FPF5, F2-FPF5, and F5-FPF5 demon-
strated electron charge transport and electroluminescence (EL)
as seen from images of working OLETs (Figure 8c). Figure 8e
and Figure S53, Supporting Information, show transfer char-
acteristics of the OLETs, the output characteristics and device
statistics data are presented in Figure S54 and Table S11, Sup-
porting Information. Figure 8b summarizes the average values
of charge mobilities and threshold voltages. The F1-FPF5-based
OLETs exhibited ambipolar charge transport characterizing the
maximal electron/hole mobility of 0.00074/0.00134 cm2 V−1 s−1
with relatively high threshold voltage for electrons (the average
Figure 7. a) Calculated averaged hole and electron mobilities and
b) mobility anisotropy defined as a ratio of maximal to the minimal
charge mobilities in the angular diagrams along the main crystal facets.
The calculations were performed at the B3LYP[GD3BJ]/6-311++G** level
of theory.
Taking into account the highly layered structure of the crys-
talline materials, charge-carrier mobilities were calculated for
the transport along the main crystal facets (Figure 3). As fol-
lows from Figure 7a and Figure S49, Supporting Information,
the electron mobilities are slightly lower than the hole ones
(both highest and average values), which results from the
higher reorganization energy for electron transport. The direc-
tion of the highest charge mobilities (Figure S49) coincided
with the direction of π-π stacking in the crystal structures, that
is, along the a-axis for all fluorinated FP5s except F5-FP5 (in
which the π-π stacking along the b-axis dominates). The highest
charge-carrier mobilities were calculated for F5-FPF5 since the
molecules exhibited the highest transfer integrals owing to
beneficial molecular orientation in the π-π stacks. Unlike the
other fluorinated FPCOs, F2-FPF5 exhibits a projection of
the π-π stacking direction also on the b-axis, which results in
the lowest mobility anisotropy (the ratio of the highest to the
lowest charge mobility; Figure 7b), while their average values
is 58
38 V) and very low threshold voltage for holes (the
average is −1 11 V). The F2-FPF5-based OFETs also showed
ambipolar charge transport with considerably higher electron
mobility reaching 0.0017 cm2 V−1 s−1 and the slightly lower hole
mobility (maximal value is 0.00043 cm2 V−1 s−1). The F5-FPF5-
based OFETs showed only electron transport with the mobility
and threshold voltage similar to those of the F1-FPF5 OFETs
(Figure 8b). The good charge transport observed in the F2-FPF5
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Figure 8. OFET and OLET data. a) Maximal (horizontal bars) and average mobilities and threshold voltages of single crystal and b) thin-film OFETs;
c) black-and-white images of F1-FPF5 (left), F2-FPF5 (center) and F5-FPF5 (right) thin-film OFETs under backlight with superimposed colored (the color
was chosen according to the EL spectra) EL images, inset illustrates EL stripes within the channel, corresponding to charge-carrier recombination in
the active layer at different values of gate voltage VG, which was changed stepwisely with a step of 2.5 V during the measurement inset shows relative
EL intensity vs the number of photons; d) EL spectra for F1-FPF5 and F2-FPF5 based thin-film OLETs; the PL spectra of the aggregates from Figure 5b
(dashed lines) are presented for comparison; e) typical transfer characteristics of F2-FPF5 thin-film OFET.
thin films for both electrons and holes well corresponds to the
lowest mobility anisotropy calculated for this material among
the fluorinated FP5s (Figure 7a). The measured charge mobili-
ties of our thin-film devices are lower than the calculated
values and also than those of the single-crystal devices, which
is assigned to the polycrystalline nature of the thin films. Note
that the FPF5 and F5-FP5 thin films did not exhibit any charge
transport, and this could be assigned to their extremely high
roughness (Figure S58, Supporting Information) comparable to
the layer thickness and also to the crystal packing unfavorable
for charge transport (low mobility and high anisotropy, vide
supra).
that of the F1-FPF5 OLET and about three orders of magnitude
higher than that of F5-FPF5 OLET. The highest EL intensity for
F2-FPF5 corresponded to the lowest threshold voltages for elec-
trons and holes (17 10 V and −7 22 V, respectively). These
relatively low threshold voltages provided a decent current value
at the minimum of the transfer characteristics in the ambipolar
regime (Figure 8e) resulting in high external quantum effi-
ciency (EQE) for F2-FPF5 OLET. The EQE was estimated from
the measured absolute EL power, and its maximal value reached
0.63 0.15% (the dependence of EQE on the gate voltage is
given in Figure S55, Supporting Information). The EQE value
of F2-FPF5 OLET is among the highest for the state-of-the-art
OLETs.[17b,34] The corresponding luminous efficiency reached
Figure 8d demonstrates EL spectra and relative intensities
for the studied OLETs. The F2-FPF5 OLET demonstrated the
highest EL intensity, which was about 2.5 times higher than
5
2 cd A−1 being inferior only to the record-performing OLET,
which was equipped with an optimized light outcoupling
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palladium(0)[38] and 2,2′-(1,4-phenylene)bis(5-phenylfuran) (FP5)[5] were
synthesized according to referred procedures. Reaction mixtures were
monitored by thin-layer chromatography (ALUGRAM Xtra SIL G/UV254
sheets by MACHEREY-NAGEL). The detailed description of the used
synthetic procedures is presented in Section S1, Supporting Information.
NMR spectra (1H, 13C, and 19F) were recorded with Bruker Avance-
300, Bruker Avance-400 and Bruker Avance-500 spectrometers.
Some 13C NMR spectra were not recorded because of low solubility
of the investigated compounds. IR spectra were recorded with a
Bruker Tensor 27 FT–IR spectrometer in potassium bromide pellets
(concentration ≈ 0.25%, pellet thickness ≈ 1 mm). High-resolution
mass-spectra of the investigated compounds were recorded with
Thermo Scientific DFS. Combustion analysis was performed with a
CHN-analyzer (EURO EA). Thermogravimetry and differential scanning
calorimetry analyses were performed in helium atmosphere using a
NETZSCH STA 409 instrument with a heating rate of 10 K min−1.
CV measurements were performed using a computer-controlled
P-8nano potentiostat (Elins) in combination with a three-electrode
cell (Gamry). Two solvents with different electrochemical windows
were used: CH2Cl2 and THF. The oxidation potentials of the studied
compounds were measured in CH2Cl2 solution. The reduction potentials
were measured in THF for films drop-cast (from CH2Cl2 solution)
on the surface of the working electrode. 0.1 m tetrabutylammonium
hexafluorophosphate was used as a supporting electrolyte. Pt, Pt wire,
and Ag/AgCl were used as working, counter, and reference electrodes,
respectively. The reference electrode was calibrated by measuring
the redox potential of ferrocene. Energies of HOMO and LUMO were
estimated from CV measurements according to the Koopmans theorem
using the following equations:
scheme.[35] Note, that for the F1-FPF5 OLET EL was emitted
near the electron-injecting Ca electrode (the right electrode in
Figure 8c) because the electron OLET performance (specifically,
the high threshold voltage) is less efficient than the hole one.
For the F2-FPF5 OLET EL was observed in the channel near the
hole-injecting electrode (as clearly seen in the inset, Figure 8c),
as the electron mobility is higher than the hole one. For
F5-FPF5 OFET very weak EL was observed at the hole injecting
electrode. The EL spectra for F1-FPF5 and F2-FPF5 OLETs well
correspond to the PL spectra of the aggregates (Figure 8d). As
F2-FPF5 showed the highest performance as an electron trans-
port material (the highest mobility and the lowest threshold
voltage), we fabricated and characterized OFET samples with
only electron-injecting electrodes (Ca) to study the electron
transport in more details (Figures S56 and S57, Supporting
Information). A noticeable kink near zero drain voltage in the
output characteristics of the unipolar device (Figure S56b, Sup-
porting Information) indicates the presence of contact issues
for electron injection. Moreover, the observed clear correlation
of the OFET mobility with the threshold voltage (Figure S57,
Supporting Information) in the device statistics data signifies
that the electron mobility extracted from the OFET data may be
affected by the contact issues.[36,35]
3. Conclusion
EHOMO = − Eonset + 4.8 eV
(1)
(
)
(
)
ox
In summary, we investigated the effect of selective fluorination
of FPCOs on their molecular, optical, physico-chemical and
electronic properties. The introduction of fluorine substitu-
ents in 1,4-bis(5-phenylfuran-2-yl)benzene led to π-π stacking
arrangements, the intermolecular slipping being tuned by the
position and the number of fluorine atoms. The fluorination
of FPCOs decreased their solubility, molecular rigidity, ener-
gies of frontier molecular orbitals maintaining the bandgap but
increased the lattice energy and enhanced the photostability by
three orders of magnitude. All the FPCOs were highly-emissive
with PL QY of 47–60% in crystals and H-aggregation behavior
except for F5-FP5 showing the signatures of J-aggregation.
Thin-film OLETs demonstrated electron (F5-FPF5) and ambi-
polar (F1- FPF5, F2-FPF5) transport and electroluminescence.
Remarkably, well-balanced ambipolar charge transport for
F2-FPF5 was achieved owing to its balanced HOMO/LUMO
levels, good crystal packing and low mobility anisotropy. The
OLET device based on F2-FPF5 demonstrated external quantum
and luminous efficiencies 0.63% and 5 cd A−1, respectively,
which are among those of the best OLETs. Finally, we conclude
that “smart” selective fluorination is an efficient tool to design
high-performance organic light-emitting furan-based semicon-
ductors paving the way to bright light-emitting devices.
ELUMO = − Eonset + 4.8 (eV)
(2)
(
)
red
UV–vis absorption and fluorescence spectra in 10−6 m THF, 10−5
m
binary mixtures (H2O:THF) and solid solutions were recorded using
Varian Cary 5000 UV–vis–NIR, Varian Cary Eclipse and Ocean Optics
QE-Pro spectrometers in 1-cm-thick quartz cuvettes. Optical gaps were
estimated from the optical absorption edges. The solubility in toluene
was estimated from the optical absorption measurements as follows.
An aliquot of a saturated solution was diluted with a prescribed ratio
and its optical density was determined using the molar extinction
coefficient. Subsequent calculation of the concentration in the saturated
solution was done using Beer-Lambert’s law. For the photodegradation
measurements air-bubbled toluene solutions with a FPCO concentration
of about 10−5 m were studied. The solutions in 1-cm-thick quartz
cuvettes were irradiated by radiation of a 405-nm diode with subsequent
measurements of the optical absorbance in dependence on the
irradiation time. The photodegradation was monitored by the intensity
of the 00 peak. For preparation of aggregates, THF solution of FPCO
was mixed with a distilled water with a prescribed ratio, the resulting
concentration was about 10−5 m and the typical optical density of
suspensions in THF/H2O was in the range 0.08–0.12. Solid solutions
in Paraloid B72 (Kremer Pigmente GmbH & Co. KG) were prepared
by dissolving FPCO and Paraloid B72 in toluene and subsequent
drop-casting on glass substrates. The resulting FPCO concentration
in the matrix was 0.06% (by weight). The PL QY of single crystals,
solid solutions, and suspensions in a 1-cm-thick quartz cuvette was
measured using a 3.3-inch-diameter integrating sphere (Newport 819C-
SL-3.3) coupled with an UV–vis spectrometer (QE Pro, Ocean Optics).
PL excitation was performed with a diode laser emitting at 405 nm
(Laserglow). The detailed experimental procedure is described in ref. [5].
4. Experimental Section
Materials and Characterization: Solvents and materials utilized in the
synthesis and physicochemical studies were purchased from commercial
sources (Acros Organic, Sigma-Aldrich) without additional purification
with the following exceptions: DMF was sustained over the alkali and
then doubly distilled over CaO; N-bromosuccinimide was recrystallized
from hot water; 1,4-bi(furan-2-yl)benzene,[37] tetrakis(triphenylphosphine)
PL dynamics were recorded using
a time-correlated single-
photon counting unit of a spectrofluorometer (FLSP920, Edinburgh
Instruments). A pulsed diode laser emitting at 375 nm (EPL-375, pulse
duration ≈ 100 ps) was used for irradiation of both liquid and solid
solutions. The emission was collected at the magic angle relative to
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the polarization of the diode laser. The time profiles were recorded at
three wavelengths of fluorescence bands (maximum and two at half-
maximum) for all samples. The obtained emission time profiles were
fitted using the numerical convolution of the instrument response
function with a monoexponential function for the solutions (THF and
Paraloid B72 films) and bi-exponential functions for the aggregates.
Computational Details: Ground state geometry of investigated
compounds was optimized utilizing DFT approach at B3LYP[39]/6-
311++G**[40,39] level of theory. Subsequent scanning of PES was carried
out at the same level of theory but with the addition of GD3BJ[41]
empirical dispersion. First ten vertically excited singlet and triplet states
were calculated for monomers (in the gas phase) and π-π stacked
dimers using X-ray data utilizing TD(A)-DFT approach coupled with
PBE0[42]/6-311++G** level of theory which was previously shown to give
the best correspondence with experimental data for FP5.[6] Energetics of
non-covalent interactions in single crystals were evaluated at the ωB97X-
[D][43]/6-311++G**level of theory. Transfer integrals required for various
charge transport computations utilizing Marcus theory (see Section
S6, Supporting Information, for additional computational details) were
evaluated at B3LYP/6-31+G*[44] level of theory.
All DFT and TD(A)-DFT calculations were made using ORCA
4.0.0[45,44] computational package except the estimations of energetics of
non-covalent interactions between molecular dimers inside single crystal
lattice, which were performed with CrystalExplorer[46] software coupled
with Tonto quantum chemical package. Calculation of CHELPG[47] atomic
charges, reduced density gradient,[48] second largest eigenvalue of the
electron density hessian (λ2), Wiberg bond order analysis,[49,48] overlap
integrals between orbitals in the molecular dimer were performed in
MultiWFN 3.7[50] computational package.
Crystal Growth and Optical Microscopy: The crystals were grown by
physical vapor transport method in flow (50–100 cm3 min−1) of high-
purity helium. The powders were sublimed in a glass tube (13 mm
i.d.) placed into a copper tube with a heater to create the temperature
gradient.[51] The sublimation temperature was set near the temperature
of 10% weight loss (Figure S26, Supporting Information). The crystal-
growth time typically was about 14 h. The crystals were examined using
an optical microscope (POLAM R-312, Lomo) under blue irradiation
(405 nm). All FPCO powders were usually purified by the PVT method at
least two times prior the crystal growth and sample preparation for the
optical and physical measurements.
X-Ray Study: The X-ray diffraction experiments were performed using
a diffractometer (Bruker KAPPA APEX II) with graphite monochromated
MoKα radiation at 293 K. Integration and scaling of the intensity data
were accomplished with SAINT.[52] Absorption corrections were applied
using SADABS.[53] The structures were solved by direct methods with
SHELXS.[54] Refinement was carried out by the full-matrix least-squares
technique with SHELXL[55] using Olex2 software.[56] All non-hydrogen
atoms in the structures were refined anisotropically. Hydrogen atoms
were calculated at idealized positions according to the riding model
then cleaned in an ultrasonic bath for 20 min in isopropanol at 70○C,
washed in distilled water, and dried in a stream of argon. After that
the substrates were exposed to ultraviolet radiation for 15 min (PL16-
110, SenLights). All the following steps of device fabrication and
characterization were conducted in argon-filled gloveboxes (≈1 ppm of
H2O and O2). The PMMA layer was deposited onto Si/SiO2 substrate
by spin coating at 3000 rpm for 2 min from 40 µL of 10 g L−1 solution in
toluene and then it was subsequently annealed on a hot plate at 70 °C
for 20 h and at 110 °C for 3 h. The materials studied were evaporated
onto Si/SiO2 substrates covered by PMMA by thermal deposition using
a vacuum system (Univex 300 G, Leybold) at a residual gas pressure of
2.3–4.4 × 10−6 mbar with deposition rates in the range of 1–4.5 Å s−1, until
the thickness reached 50 nm according to a thickness monitor (TM400,
Maxtek).
Atomic force microscopy (AFM) studies were conducted with an
atomic force microscope (NTEGRA Spectra, NT-MDT) by using silicon
probes (HQ:XSC11, MikroMasch). The active layer thickness was
calculated from the AFM profile of a scratch. The source and drain
electrodes were thermally evaporated in vacuum through shadow masks
(Ossila) on the substrates with vacuum-deposited thin films yielding 20
devices per substrate with channel length L of about 30 µm and nominal
channel width W of 1 mm. The two types of source/drain electrodes were
used: calcium (Ca) for electron injection and bilayer of molybdenum
oxide and silver (MoO3/Ag) for hole injection. MoO3/Ag layers were
evaporated with some lateral shift relatively to the Ca layer by using
the shadow effect, to allow both hole and electron-injecting electrodes
have contacts with the active layer. Electrical and electroluminescence
measurements were performed in argon atmosphere (≈1 ppm of H2O
and O2) with a source meter (Keithley 2636A) using a probe station
(ProbeStation 100, Printeltech LLC). The charge-carrier mobility and the
threshold voltage were evaluated according to Shockley’s equations in
the linear and saturation regimes:



V
2
W
L
ID
=
µlinC VG −VT − D VD, |VG |> VD
(3)
(4)
S 
ID
=
µ
satCS V −V 2 , |VG |< VD
G T
W
2L
(
)
where μlin and μsat are the charge-carrier (electron or hole) mobilities
in the linear and saturation regimes, respectively; CS is the gate
insulator capacitance per unit area of SiO2/PMMA (1.38 × 10−4 F m−2
)
layer calculated using the SiO2 layer thickness provided by the supplier
(200 nm), the AFM-measured thickness of PMMA layer (50 nm) and
the almost equal dielectric constants of SiO2 and PMMA (3.9); ID is
the source-drain current, VD is the source-drain voltage, VG is the gate
voltage, and VT is the threshold voltage. A typical sweep rate during
current–voltage characteristics measurements was 60 V s−1, the voltage
was changed stepwise with a step of 2.5 V. Light emission was captured
using a microscope equipped with a CCD-camera (Infinity 3, Luminera)
at an exposition time of 60 s during the transfer characteristics
measurement. The relative electroluminescence intensity was
calculated in arbitrary units as a sum of intensities of pixels belonging
to the channel area in the captured light-emission image. The EL
spectra were measured using a custom-made spectrograph (vertical
Ebert scheme, relative aperture 1:5, spectral resolution ≈1 nm)
equipped with a CCD camera (Trius PRO-694, Starlight Xpress). The
absolute EL power was measured by a photodetector based on a wide-
area silicon photodiode with the tabulated responsivity spectrum
(Hamamatsu S1227-66BR) for estimation of the EL EQE and luminance
efficiency. Power conversion efficiency and luminous efficacy values
are given in Supporting Information. The photosensitive area of the
photodiode (5.8 mm square) was located 5 mm above the studied
OLET sample. The EL power was calculated from the photodetector
signal (photocurrent) and its spectral photosensitivity in the EL
spectral range. The EL EQE was calculated assuming that the EL is
emitted into hemisphere at the top of active layer and its radiation
pattern obeys Lambert’s law.
with Uiso(H)
= 1.5Ueq(C) for alkyl H atoms and 1.2 Ueq(C) otherwise.
Additional experimental details and parameters characterizing data
collection and refinement, as well as, crystal data, are presented in
Supporting Information. The intermolecular interactions in crystals were
analyzed using PLATON[57] and Mercury.[58] The crystallographic data for
the structures have been deposited at the Cambridge Crystallographic
Data Centre as supplementary publication CCDC no. 2 079 639
(FPF5), 2 079 640 (F1-FPF5), 2 079 641 (F2-FPF5), 2 079 642 (F5-FP5),
2 079 643 (F5-FPF5). Copy of the data can be obtained, free of charge,
on application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
+44 122 3 336 033 or e-mail: deposit@ccdc.cam.ac.uk; internet: www.
ccdc.cam.ac.uk). The structure data for FP5 was taken from the CCDC
(number 1 520 459).
Thin-Film Organic Field-Effect Transistors/Organic Light-Emitting
Transistors Fabrication and Characterization: Thin-film OFETs were
fabricated in the top-contact bottom-gate architecture on precleaned
Si/SiO2 substrates. 20 × 15 mm silicon substrates coated with a
thermally grown 200-nm-thick layer of SiO2 were used after the following
cleaning steps. First, the substrates were wiped by tissue with toluene,
Adv. Funct. Mater. 2021, 2104638
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6256; e) O. Gidron, A. Dadvand, W.-H. Sun, I. Chung, L. Shimon,
M. Bendikov, D. Perepichka, J. Mater. Chem. C 2013, 1, 4358.
[3] a) S. Hotta, T. Yamao, J. Mater. Chem. 2011, 21, 1295; b) T. Komori,
H. Nakanotani, T. Yasuda, C. Adachi, J. Mater. Chem. C 2014, 2,
4918; c) V. A. Postnikov, Y. I. Odarchenko, A. V. Iovlev, V. V. Bruevich,
A. Y. Pereverzev, L. G. Kudryashova, V. V. Sobornov, L. Vidal,
D. Chernyshov, Y. N. Luponosov, O. V. Borshchev, N. M. Surin,
S. A. Ponomarenko, D. A. Ivanov, D. Yu. Paraschuk, Cryst. Growth
Des. 2014, 14, 1726; d) L. G. Kudryashova, M. S. Kazantsev,
V. A. Postnikov, V. V. Bruevich, Y. N. Luponosov, N. M. Surin,
O. V. Borshchev, S. A. Ponomarenko, M. S. Pshenichnikov,
D. Yu. Paraschuk, ACS Appl. Mater. Interfaces 2016, 8, 10088.
[4] J. Gierschner, J. Shi, B. Milián-Medina, D. Roca-Sanjuán,
S. Varghese, S. Park, Adv. Opt. Mater. 2021, 9, 2002251.
[5] M. S. Kazantsev, E. S. Frantseva, L. G. Kudriashova,
V. G. Konstantinov, A. A. Mannanov, T. V. Rybalova,
E. V. Karpova, I. K. Shundrina, G. N. Kamaev, M. S. Pshenichnikov,
E. A. Mostovich, D. Yu. Paraschuk, RSC Adv. 2016, 6, 92325.
[6] I. P. Koskin, E. A. Mostovich, E. Benassi, M. S. Kazantsev, J. Phys.
Chem. C 2017, 121, 23359.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
The work on materials synthesis, characterizations, X-ray study, quantum
chemical calculations, optical spectroscopy measurements in solutions
and crystals, and single-crystal OFET study was supported by RSF project
#20-73-10090 and was performed in the N. N. Vorozhtsov Novosibirsk
Institute of Organic Chemistry. The work on thin film OFETs and OLETs
was supported by RSF project #18-12-00499 and was performed in
the Institute of Synthetic Polymeric Matserials. The characterization
of thin films was conducted using the equipment purchased under
the Lomonosov Moscow State University Program of Development.
The study of optical properties of solid solutions and aggregates was
supported by the State Assignment of Ministry of Science and Higher
Education of Russian Federation, project #0238-2019-0004 and was
performed in N. N. Vorozhtsov Novosibirsk Institute of Organic
Chemistry. The authors acknowledge Multi-Access Chemical Service
Center SB RAS for spectral and analytical measurements, Ministry of
Science and Higher Education of Russian Federation for the access to
the time-resolved fluorescent equipment, Siberian Supercomputing
Center (http://www2.sscc.ru/) for computational resources.
[7] M. S. Kazantsev, A. A. Beloborodova, A. D. Kuimov, I. P. Koskin,
E. S. Frantsev, T. V. Rybalova, I. K. Shundrina, C. S. Becker,
E. A. Mostovich, Org. Electron. 2018, 56, 208.
[8] A. A. Mannanov, M. S. Kazantsev, A. D. Kuimov,
V. G. Konstantinov, D. I. Dominskiy, V. A. Trukhanov, D. S. Anisimov,
N. V. Gultikov, V. V. Bruevich, I. P. Koskin, A. A. Sonina,
T. V. Rybalova, I. K. Shundrina, E. A. Mostovich, D. Yu. Paraschuk,
M. S. Pshenichnikov, J. Mater. Chem. C 2019, 7, 60.
Conflict of Interest
The authors declare no conflict of interest.
[9] F. A. Kucherov, L. V. Romashov, G. M. Averochkin, V. P. Ananikov,
ACS Sustainable Chem. Eng. 2021, 9, 3011.
[10] A. D. Hendsbee, J.-P. Sun, T. M. McCormick, I. G. Hill, G. C. Welch,
Org. Electron. 2015, 18, 118.
[11] a) A. N. Lakshminarayana, A. Ong, C. Chi, J. Mater. Chem. C
2018, 6, 3551; b) B. Maiti, K. Wang, S. Bhandari, S. D. Bunge,
R. J. Twieg, B. D. Dunietz, J. Mater. Chem. C 2019, 7, 3881;
c) S. E. Koh, B. Delley, J. E. Medvedeva, A. Facchetti, A. J. Freeman,
T. J. Marks, M. A. Ratner, J. Phys. Chem. A 2006, 110, 24361;
d) X. Cui, C. Xiao, W. Jiang, Z. Wang, Chem. - Asian J. 2019, 14, 1443;
e) A. Y. Sosorev, M. K. Nuraliev, E. V. Feldman, D. R. Maslennikov,
O. V. Borshchev, M. S. Skorotetcky, N. M. Surin, M. S. Kazantsev,
S. A. Ponomarenko, D. Yu. Paraschuk, Phys. Chem. Chem. Phys.
2019, 21, 11578; f) Z. Bao, A. J. Lovinger, J. Brown, J. Am. Chem.
Soc. 1998, 120, 207; g) S. B. Heidenhain, Y. Sakamoto, T. Suzuki,
A. Miura, H. Fujikawa, T. Mori, S. Tokito, Y. Taga, J. Am. Chem. Soc.
2000, 122, 10240; h) A. Facchetti, M.-H. Yoon, C. L. Stern, H. E. Katz,
T. J. Marks, Angew. Chem., Int. Ed. 2003, 42, 3900; i) J. A. Letizia,
A. Facchetti, C. L. Stern, M. A. Ratner, T. J. Marks, J. Am. Chem. Soc.
2005, 127, 13476.
Data Availability Statement
The data that support the findings of this study are available from the
corresponding author upon reasonable request.
Keywords
ambipolar charge transport, electroluminescence, fluorination, light-
emitting transistor, organic optoelectronics
Received: May 17, 2021
Revised: July 12, 2021
Published online:
[12] a) B. Milián-Medina, J. Gierschner, J. Phys. Chem. Lett. 2017, 8,
91; b) M. L. Renak, G. P. Bartholomew, S. Wang, P. J. Ricatto,
R. J. Lachicotte, G. C. Bazan, J. Am. Chem. Soc. 1999, 121,
7787; c) G. W. Coates, A. R. Dunn, L. M. Henling, J. W. Ziller,
E. B. Lobkovsky, R. H. Grubbs, J. Am. Chem. Soc. 1998, 120, 3641;
d) J. Gierschner, M. Ehni, H. J. Egelhaaf, B. M. Medina, D. Beljonne,
H. Benmansour, G. C. Bazan, J. Chem. Phys. 2005, 123, 144914;
e) M.-H. Yoon, A. Facchetti, C. E. Stern, T. J. Marks, J. Am. Chem.
Soc. 2006, 128, 5792; f) B. Kobin, L. Grubert, S. Mebs, B. Braun,
S. Hecht, Isr. J. Chem. 2014, 54, 789.
[13] S. Kumagai, C. P. Yu, S. Nakano, T. Annaka, M. Mitani, M. Yano,
H. Ishii, J. Takeya, T. Okamoto, J. Phys. Chem. Lett. 2021, 12, 2095.
[14] Y. Krupskaya, M. Gibertini, N. Marzari, A. F. Morpurgo, Adv. Mater.
2015, 27, 2453.
[15] J.-H. Dou, Y.-Q. Zheng, Z.-F. Yao, Z.-A. Yu, T. Lei, X. Shen, X.-Y. Luo,
J. Sun, S.-D. Zhang, Y.-F. Ding, G. Han, Y. Yi, J.-Y. Wang, J. Pei, J.
Am. Chem. Soc. 2015, 137, 15947.
[1] a) M. A. Varghese, A. Anjali, D. Harshini, S. Nagarajan, ACS Appl.
Electron. Mater. 2021, 3, 550; b) J. Gierschner, S. Y. Park, J. Mater.
Chem. C 2013, 1, 5818; c) H.-H. Fang, J. Yang, J. Feng, T. Yamao,
S. Hotta, H.-B. Sun, Laser Photonics Rev. 2014, 8, 687; d) S. Hotta,
T. Yamao, S. Z. Bisri, T. Takenobu, Y. Iwasa, J. Mater. Chem. C 2014,
2, 965; e) J. Gierschner, S. Varghese, S. Y. Park, Adv. Opt. Mater.
2016, 2, 348; f) A. J. C. Kuehne, M. C. Gather, Chem. Rev. 2016,
116, 12823; g) Y. Jiang, Y.-Y. Liu, X. Liu, H. Lin, K. Gao, W.-Y. Lai,
W. Huang, Chem. Soc. Rev. 2020, 49, 5885.
[2] a) K. Niimi, H. Mori, E. Miyazaki, I. Osaka, H. Kakizoe, K. Takimiya,
C. Adachi, Chem. Commun. 2012, 48, 5892; b) K. Oniwa,
T. Kanagasekaran, T. Jin, M. Akhtaruzzaman, Y. Yamamoto,
H. Tamura, I. Hamada, H. Shimotani, N. Asao, S. Ikeda, K. Tanigaki,
J. Mater. Chem. C 2013, 1, 4163; c) O. Gidron, M. Bendikov,
Angew. Chem., Int. Ed. 2014, 53, 2546; d) O. Gidron, N. Varsano,
L. J. W. Shimon, G. Leitus, M. Bendikov, Chem. Commun. 2013, 49,
Adv. Funct. Mater. 2021, 2104638
2104638 (13 of 14)
© 2021 Wiley-VCH GmbH

www.advancedsciencenews.com
www.afm-journal.de
[16] H. Jiang, P. Hu, J. Ye, Y. Li, H. Li, X. Zhang, R. Li, H. Dong, W. Hu,
C. Kloc, Adv. Mater. 2017, 29, 1605053.
[17] a) Y. Liu, C. Li, Z. Ren, S. Yan, M. R. Bryce, Nat. Rev. Mater. 2018,
3, 18020; b) D. Yuan, V. Sharapov, X. Liu, L. Yu, ACS Omega 2020,
5, 68.
[18] T. Korenaga, T. Kosaki, R. Fukumura, T. Ema, T. Sakai, Org. Lett.
2005, 7, 4915.
[19] B. Milián-Medina, J. E. Anthony, J. Gierschner, ChemPhysChem
2008, 9, 1519.
[35] M. C. Gwinner, D. Kabra, M. Roberts, T. J. K. Brenner,
B. H. Wallikewitz, C. R. McNeill, R. H. Friend, H. Sirringhaus, Adv.
Mater. 2012, 24, 2728.
[36] a) A. F. Paterson, S. Singh, K. J. Fallon, T. Hodsden, Y. Han,
B. C. Schroeder, H. Bronstein, M. Heeney, I. McCulloch,
T. D. Anthopoulos, Adv. Mater. 2018, 30, 1801079; b) C. Liu, G. Li,
R. Di Pietro, J. Huang, Y.-Y. Noh, X. Liu, T. Minari, Phys. Rev. Appl.
2017, 8, 034020.
[37] P. A. Peart, J. D. Tovar, Macromolecules 2009, 42, 4449.
[38] D. R. Coulson, L. C. Satek, S. O. Grim, in Inorganic Syntheses: Rea-
gents for Transition Metal Complex and Organometallic Syntheses (Ed:
R. J. Angelici), Wiley InterScience 1990, p. 107.
[20] R. Milad, J. Shi, A. Aguirre, A. Cardone, B. Milián-Medina,
G. M. Farinola, M. Abderrabba, J. Gierschner, J. Mater. Chem. C
2016, 4, 6900.
[21] M. S. Kazantsev, A. A. Beloborodova, E. S. Frantseva,
T. V. Rybalova, V. G. Konstantinov, I. K. Shundrina, D. Yu. Paraschuk,
E. A. Mostovich, CrystEngComm 2017, 19, 1809.
[22] M. D. Curtis, J. Cao, J. W. Kampf, J. Am. Chem. Soc. 2004, 126, 4318.
[23] A. A. Sonina, I. P. Koskin, P. S. Sherin, T. V. Rybalova, I. K. Shundrina,
E. A. Mostovich, M. S. Kazantsev, Acta Crystallogr., Sect. B: Struct.
Sci., Cryst. Eng. Mater. 2018, B74, 450.
[24] J. Shi, L. E. A. Suarez, S.-J. Yoon, S. Varghese, C. Serpa, S. Y. Park,
L. Lüer, D. Roca-Sanjuán, B. Milián-Medina, J. Gierschner, J. Phys.
Chem. C 2017, 121, 23166.
[25] B. Milián-Medina, D. Beljonne, H.-J. Egelhaaf, J. Gierschner, Int. J.
Chem. Phys. 2007, 126, 111101.
[39] A. D. Becke, J. Chem. Phys. 1993, 98, 5648.
[40] a) A. D. McLean, G. S. Chandler, J. Chem. Phys. 1980, 72, 5639;
b) R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. Phys.
1980, 72, 650.
[41] S. Grimme, S. Ehrlich, L. Goerigk, J. Comput. Chem. 2011, 32, 1456.
[42] J. P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 1996, 77, 3865.
[43] J.-D. Chai, M. Head-Gordon, Phys. Chem. Chem. Phys. 2008, 10,
6615.
[44] a) R. Ditchfield, W. J. Henre, J. A. Pople, J. Chem. Phys. 1971, 54,
724; b) W. J. Hehre, R. Ditchfield, J. A. Pople, J. Chem. Phys. 1972,
56, 2257.
[45] a) F. Neese, WIREs: Comput. Mol. Sci. 2012, 2, 73; b) F. Neese,
WIREs: Comput. Mol. Sci. 2018, 8, e1327.
[26] a) S. Sharafy, K. A. Muszkat, J. Am. Chem. Soc. 1971, 93, 4119; b)
M. A. Haidekker, E. A. Theodorakis, J. Biol. Eng. 2010, 4, 11.
[27] J. Gierschner, L. Luer, B. Milian-Medina, D. Oelkrug, H.-J. Egelhaaf,
J. Phys. Chem. Lett. 2013, 4, 2686.
[46] a) M. A. Spackman, D. Jayatilaka, CrystEngComm 2009, 11, 19;
b) M. A. Spackman, J. J. McKinnon, D. Jayatilaka, CrystEngComm
2008, 10, 377.
[28] N. J. Hestand, F. C. Spano, Chem. Rev. 2018, 118, 7069.
[29] O. D. Parashchuk, A. A. Mannanov, V. G. Konstantinov,
D. I. Dominskiy, N. M. Surin, O. V. Borshchev, S. A. Ponomarenko,
M. S. Pshenichnikov, D. Yu. Paraschuk, Adv. Funct. Mater. 2018, 28,
1800116.
[30] a) R. Riehn, J. Morgado, R. Iqbal, S. C. Moratti, A. B. Holmes,
S. Volta, F. Cacialli, Macromolecules 2000, 33, 3337; b) A. Raya,
M. A. Mora, Polymer 2004, 45, 6391; c) C. R. Newman, C. D. Frisbie,
D. A. d. S. Filho, J.-L. Brédas, P. C. Ewbank, K. R. Mann, Chem.
Mater. 2004, 16, 4436; d) L. Zhu, F. Tong, C. Salinas, M. K. Al-
Muhanna, F. S. Tham, D. Kisailus, R. O. Al-Kaysi, C. J. Bardeen,
Chem. Mater. 2014, 26, 6007; e) F. Anger, T. Breuer, A. Ruff,
M. Klues, A. Gerlach, R. Scholz, S. Ludwigs, G. Witte, F. Schreiber,
J. Phys. Chem. C 2016, 120, 5515.
[47] C. M. Breneman, K. B. Wiberg, J. Comput. Chem. 1990, 11, 361.
[48] E. R. Johnson, S. Keinan, P. Mori-Sánchez, J. Contreras-García,
A. J. Cohen, W. Yang, J. Am. Chem. Soc. 2010, 132, 6498.
[49] a) K. B. Wiberg, Tetrahedron 1968, 24, 1083; b) O. V. Sizova,
L. V. Skripnikov, A. Y. Sokolov, J. Mol. Struct.: THEOCHEM 2008,
870, 1.
[50] T. Lu, F. Chen, J. Comput. Chem. 2012, 33, 580.
[51] R. W. I. De Boer, M. E. Gershenson, A. F. Morpurgo, V. Podzorov,
Phys. Status Solidi A 2004, 201, 1302.
[52] SAINT, Bruker, SAINT, Data Reduction and Frame Integration
Program for the CCD Area-detector System, Bruker AXS Inc.,
Madison, Wisconsin, USA, 1997–2006.
[53] G. M. Sheldrick, SADABS, Program for Area Detector Adsorption
Correction, Institute for Inorganic Chemistry, University of
Goettingen, Goettingen, Germany 1996.
[31] H. Saadeh, T. Goodson, L. Yu, Macromolecules 1997, 30, 4608.
[32] R. Battino, T. R. Rettich, T. Tominaga, J. Phys. Chem. Ref. Data 1983,
12, 163.
[54] G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr. 2008,
64, 112.
[33] G. Heimel, I. Salzmann, S. Duhm, N. Koch, Chem. Mater. 2011, 23,
359.
[55] G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3.
[56] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard,
H. Puschmann, J. Appl. Crystallogr. 2009, 42, 339.
[57] A. L. Spek, Acta Crystallogr., Sect. D: Struct. Biol. 2009, 65, 148.
[58] C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock, G. P. Shields,
R. Taylor, M. Towler, J. van de Streek, J. Appl. Crystallogr. 2006, 39,
453.
[34] a) C.-F. Liu, X. Liu, W.-Y. Lai, W. Huang, Adv. Mater. 2018, 30,
1802466; b) T. Oyamada, C.-H. Chang, T.-C. Chao, F.-C. Fang,
C.-C. Wu, K.-T. Wong, H. Sasabe, C. Adachi, J. Phys. Chem. C
2007, 111, 108; c) T. Sakanoue, M. Yahiro, C. Adachi, H. Uchiuzou,
T. Takahashi, A. Toshimitsu, Appl. Phys. Lett. 2007, 90, 171118.
Adv. Funct. Mater. 2021, 2104638
2104638 (14 of 14)
© 2021 Wiley-VCH GmbH