Acenequinocumulenes: Lateral and Vertical π-Extended Analogues of Tetracyanoquinodimethane (TCNQ)

Article abstract of DOI:10.1002/chem.201704314

We have designed a series of molecules and developed synthetic methodology that allows for the inclusion of structural diversity along both the lateral and vertical axes of the basic TCNQ skeleton. In the lateral direction, benzoannulation extends the π-s

Full text of DOI:10.1002/chem.201704314

A Journal of
Accepted Article
Title: Acenequinocumulenes: Lateral and vertical π-extended analogs
of tetracyanoquinodimethane (TCNQ)
Authors: Marco Gruber, Kevin Padberg, Jie Min, Andreas Waterloo,
Frank Hampel, Harald Maid, Tayebeh Ameri, Christoph
Brabec, and Rik R Tykwinski
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201704314
Link to VoR: http://dx.doi.org/10.1002/chem.201704314
Supported by

10.1002/chem.201704314
Chemistry - A European Journal
Acenequinocumulenes: Lateral and vertical
π-extended analogs of tetracyanoquinodimethane
(TCNQ)
Marco Gruber,[a] Kevin Padberg,[a] Jie Min,[b] Andreas R. Waterloo,[a] Frank Hampel,[a]
Harald Maid,[a] Tayebeh Ameri,[b] Christoph J. Brabec,*[b] and Rik R. Tykwinski*[a,c]
[a] M. Gruber, K. Padberg, Dr. A. R. Waterloo, Dr. F. Hampel, Dr. H. Maid, Prof. Dr. R. R. Tykwinski
Department für Chemie und Pharmazie & Interdisciplinary Center for Molecular Materials (ICMM)
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Henkestraße 42, 91054 Erlangen
(Germany).
[b] J. Min, Dr. T. Ameri, Prof. Dr. C. J. Brabec
Materials for Electronics and Energy Technology (i-MEET), Friedrich Alexander Universität Erlangen-
Nürnberg (FAU), Martensstraße 7, 91058 Erlangen (Germany).
[c] Current address: Department of Chemistry, University of Alberta, Edmonton AB T6G 2G2
(Canada).
E-mail: rik.tykwinski@ualberta.ca
1
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
Text for Table of Contents
New synthetic methodology extends the basic skeleton of tetracyanoquinodimethane
(TCNQ) along both the lateral and vertical axes, via benzoannulation and incorporation of a
[3]cumulene, respectively. Terminal functionalization of the cumulenic core allows
attachment of electron donor and acceptor functional groups.
Keywords pentacenes, donor-acceptor; organic materials; cumulenes; synthetic
methodology
2
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
Abstract:
We have designed a series of molecules and developed synthetic methodology that
allows for the inclusion of structural diversity along both the lateral and vertical axes of the
basic TCNQ skeleton. In the lateral direction, benzoannulation extends the π-system through
(hetero)acene formation, while incorporation of a [3]cumulene increases delocalization
vertically. The potential of these new molecules as semiconductors is explored through
UV-vis spectroscopy, cyclic voltammetry, X-ray crystallography, thin film formation, and
mobility measurements (via space charge limited current measurements).
Introduction
The past few decades have seen spectacular achievements in the development of
organic semiconductors in terms of stability, processability, and charge carrier mobility.[1,2]
This progress highlights the beauty of synthetic organic chemistry, which offers the tools to
design, explore, and tune the properties of molecules for use in devices such as organic
sensors,[3,4] field effect transistors (OFETs),[4–6] organic light-emitting diodes (OLEDs),[7–9] and
organic photovoltaics (OPVs).[10–13] Organic semiconductors are often classified into two
categories, p-type (donor, hole conducting) and n-type (acceptor, electron conducting). In the
case of p-type organic semiconductors, many requisite properties have been fulfilled,[1,2,6,14,15]
while the realization of n-type organic materials remains troubled by issues such as complex
synthesis, instability in air, poor solubility, large electron injection barriers, and low charge
carrier mobilities.[16–19]
One of the most common non-fullerene compound classes used as n-type
semiconductors are cyano-based acceptors such as tetracyanoethylene (TCNE, Figure 1)[20–
23]
and the more stable, π-extended analogue tetracyanoquinodimethane (TCNQ).[24] First
reported in 1960 by Acker et al.,[25,26] pristine TCNQ has become one of the most extensively
studied acceptor materials.[26–29] The electron accepting abilities of TCNQ have been further
fine-tuned through substitution,[24,30–32] incorporation of heteroatoms,[24,32–34] and, most
commonly, extension of the π-system by lateral benzoannulation to give π-extended TCNQ
3
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
derivatives (exTCNQs).[24,32,35–38] It was originally expected that exTCNQs could offer more
stable and improved conducting materials.[37,39] In reality, however, the π-expansion does not
necessarily result in enhanced acceptor properties, and derivatives such as TCAQ, TCTQ,
and TCPQ[24,32,36–38] show non-planar structures that give rise to the so-called “butterfly”
conformation and can hinder π-communication and effective charge transport.[40,41] Despite
lower electron accepting properties, exTCNQs have been remarkably adapted through
structural modification.[42] For example, TCTQ and BDCNBA undergo photoinduced electron
transfer (PET) almost as efficiently as fullerene C60,[43,44] while TCAQ derivatives have
demonstrated effectiveness in a range of PET processes.[45–49] These results are significant,
since they emphasize that device efficiency is not solely dictated by acceptor strength, and
that shape and/or solid-state packing of the material are also crucial parameters.[50]
NC
CN
NC
CN
NC
CN
NC
CN
NC
NC
CN
CN
TCNE
NC
CN
NC
CN
NC
CN
NC
CN
TCNQ
TCAQ
TCTQ
BDCNBA
Head X = O, C(CN)2
NC
CN
NC
CN
This work
S
Wings
π
=
,
X
5,14-TCPQ
NC
CN
R = 4-t-BuPh
R = 4-MeOPh
Tail
π
π
NC
CN
•
•
=
Ph
Ph
Ph
Ph
R
R
NC
CN
R
R
NC
CN 6,13-TCPQ
TBPQ
Figure 1. Molecular structure of TCNE, TCNQ, a series of benzoannulated π-extended derivatives of
the TCNQ family; inset, dicyanovinylacenequino[3]cumulenes (1a–c and 2) and the corresponding
keto derivatives (3a–c and 4) introduced in this work.
To date, there are few exTCNQ derivatives that exceed the length of TCTQ,[37,50–53]
and most derive from the pioneering work of Martin and Hanack, including 5,14-TCPQ and
6,13-TCPQ,[37,51] and Yamada et al. who reported TBPQ.[52] In these cases, however, the
4
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
poor solubility in common organic solvents restricts practical use, while large HOMO-LUMO
gaps limit visible absorptions.[51,52]
We became fascinated by the question of whether lateral and vertical substitution of
exTCNQ derivatives could be used to augment desirable properties. We hypothesized that a
[3]cumulene spacer at the “tail” position could be used to provide air-stable, soluble
exTCNQs with more planar conformations.[40,41,54] Furthermore, the cumulene moiety has
been shown to have an effect of lowering the energy of LUMO,[55] and it can be easily
functionalized for the incorporation of electronically neutral, donor, or acceptor groups
(Figure 1). On the other hand, the “head” position would allow tuning of the overall electron
deficiency through incorporation of either a ketone or dicyanovinyl moiety. Finally, we
expected that the “wings” of the butterfly could be varied through the formal exchange of the
acene unit with a heteroacene.
We report herein the development of an efficient synthetic pathway for the synthesis
of stable and soluble dicyanovinylacenequino[3]cumulene derivatives (1a–c and 2), as well
as their corresponding keto analogs (3a–c and 4).[56] Our synthetic protocol is versatile and
readily allows the modification of every part of the acenequino[3]cumulenic butterfly
framework, namely the head, the wings, and the tail (Figure 1). The structural modifications
are correlated by changes in physical and optoelectronic properties, as detailed via UV-vis
spectroscopy, cyclic voltammetry (CV), X-ray crystallography, as well as thin-film formation,
and charge mobility determination.
Synthesis
Ketoacenequino[3]cumulenes 3a–c and 4 were formed in good yield using a two-step
process of desymmetrization of pentacenequinone[57,58] followed by reductive elimination
(Scheme 1).[59] Specifically, the nucleophilic addition of acetylides 5a–c to pentacene-6,13-
quinone and subsequent recrystallization of the product from CH2Cl2 gave alcohols 6a–c.[60]
Reductive elimination using SnCl2 and HCl yielded ketoacenequino[3]cumulenes 3a–c as
intensely red to purple colored products, following purification by recrystallization from
CH2Cl2. With ketones 3a–c in hand, dicyanovinyl derivatives 1a–c were targeted. Direct
5
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
conversion from 3a–c to 1a–c was attempted using standard Knoevenagel conditions, such
as the Lehnert reagent (TiCl4, pyridine).[61,62] These reaction conditions, however, led to
complex mixtures, and the desired products were not identified. Likewise, the conversion of
alcohols 6a–c to 7a–c under standard Knoevenagel conditions was also unsuccessful and
thus, these routes were abandoned.[63] Ultimately, an adaption of the procedure reported by
Hayashi and coworkers in 2005[64] was successfully devised, which allowed for formation of
7a–c via reaction of 6a–c in neat malononitrile and Ti(Oi-Pr)4 (Scheme 1). The dicyanovinyl
products 7a–c could be isolated pure via crystallization (7a–b) or column chromatography
(7c). Reductive elimination of 7a–c using SnCl2 and HCl gave [3]cumulenes 1a–c in good
yields.
CN
CN
SnCl2
HCl
Li
THF
malononitrile
O
O
+
CN
R
R
CN
HO
HO
THF
–78 °C
Ti(i-PrO)4
O
•
OMe
5a–c
Δ
R
R
R
•
R
R
OMe
OMe
R
6a (87%), 6b (93%), 6c (83%)
7a (96%), 7b (49%), 7c (89%) 1a (74%), 1b (79%), 1c (59%)
for compounds 5–7
SnCl2
HCl
THF
MeO
t-Bu
X
R
R
=
malononitrile
base or
catalyst
for compounds 1 and 3
MeO
t-Bu
O
Ph
Ph
Ph
R
R
•
=
R
•
a
MeO
Ph
b
t-Bu
R
Ph
Ph
3a (75%), 3b (73%), 3c (80%)
MeO
t-Bu
a
b
c
Ph
c
Ph
Scheme 1. Synthetic pathway to ketoacenequino[3]cumulenes 3a–c and their corresponding
dicyanovinyl derivatives 1a–c.
The synthetic transformations developed for 1a–c were then used to vary the electronic
constitution of the “wings” of the acene backbone (Scheme 2). Reaction of acetylide 5a with
antradithiophene-5,11-quinone gave 8 (as a diastereomeric mixture of syn- and anti-isomers;
see SI for details). Reductive elimination easily transformed 8 to cumulene 4. Once again,
attempt conversions of ketone 4 to dicyanovinyl derivative 2 with e.g., the Lehnert reagent,
failed. Thus, as described above, Knoevenagel condensation was accomplished using 8 in
6
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
neat malononitrile and Ti(Oi-Pr)4, giving 9 in good yield, which then allowed formation of 2 via
reductive elimination.
NC
CN
NC
CN
O
O
SnCl2
HCl
SnCl2
HCl
S
S
S
S
malononitrile
THF
Ti(i-PrO)4
THF
S
S
S
S
Δ
HO
R
HO
R
S
S
S
S
•
•
•
•
S
S
S
S
R
R
OMe
OMe
R
R
R
R
syn/anti-4 (81%)
syn/anti-8
syn/anti-9 (81%)
syn/anti-2 (77%)
Scheme 2. Synthetic pathway to ketoacenequino[3]cumulene 4 and the corresponding dicyanovinyl
derivative 2; all anthradithiophene products are a mixture of syn- and anti-isomers.
It is worth noting that, in spite of the fact that the target molecules feature large π-systems
and dipole moments that might lead to insolubility, the products 3a–c, 4, 1a, 1c, and 2, show
good solubility (>10 mg/mL) in a variety of organic solvents such as CH2Cl2, CHCl3, and THF
(1b shows only modest solubility <5 mg/mL).
Stability.
Ketone derivatives 3a–c and 4 show good “kinetic” stability under normal laboratory
conditions, with no observed sensitivity to light, air, or water. Thermal stability is excellent,
with decomposition points spanning from 255 °C (3b) to 301 °C (3c), as measured under
nitrogen by differential scanning calorimetry (DSC, Figures S51–S54).[65] Dicyanovinyl
derivatives 1a–c and 2 have slightly reduced thermal stability, and all four derivatives show
decomposition points by DSC in the range of ca. 200–230 °C (Figures S55–S58).
7
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
Figure 2. X-ray crystallographic structure and solid-state packing of a) 3a, b) 3c, c) 1a, and d) 1c
(hydrogen atoms omitted for clarity).
X-ray analysis.
X-ray crystallographic analysis of four molecules has been achieved (3a, 3c, 1a, and
1c) giving insight into the molecular structure, geometry, and solid-state order (Figure 2).
Bond lengths of the four derivatives are unremarkable, showing neither substantial trends nor
indication of distinct proacetylenic characteristics as described by Diederich and coworkers
for donor-acceptor cumulenes.[66]
The π-conjugated frameworks of keto derivatives 3a and 3c adopt a planar
arrangement, including the acene and cumulene moieties. In the case of 3a, the pendent aryl
rings of the tail are rotated out of plane slightly by 19° and 32°, whereas the phenyl
substituents of 3c are twisted out of plane of the cumulene by 33–53°. There are no
significant π-π-stacking interactions between neighboring acene units of 3a, although the
[3]cumulene chain is located at a distance of ca. 3.4 Å relative to the acenequinone moiety of
the adjacent molecule (Figure S1a). Symmetry related molecules of 3c stack “pair-wise” with
nearly complete overlap of the acene groups at a distance of 3.5 Å (Figure S1b). Neighboring
pairs are arranged to form a 1-D slipped stack, also at π-π-stacking distance of ca. 3.5 Å.
Dicyanovinyl derivative 1a crystallizes with two crystallographically unique molecules that
form a dimeric arrangement, in which one molecule is located directly on top of the other.
Pairs of molecules then stack to form a column in which the overall packing is dictated by
8
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
weak π-π-stacking interactions of adjacent naphthalene moieties that vary from 3.4 to 4.0 Å
(Figure S1c). Compound 1c shows a solid-state structure in which two molecules arrange as
centrosymmetric pairs with minor direct overlap of the π-systems, e.g., the
cyclopentadienylidene (CPD) rings are separated by a distance of 4.6 Å (Figure S1d). Thus,
unlike 1a, the packing of 1c appears dominated by CH-π interactions resulting from the
pendent phenyl groups of the tetraphenyl-CPD group, rather than π-stacking.
Dicyanovinyl derivatives 1a and 1c feature a non-planar, so-called “butterfly” structure
as a result of steric interactions between the peri-hydrogens of the acene core and the cyano
groups (Figures S2, S3). The acene scaffold of both molecules is distorted from planarity by
a little more than 30°, with angles between the wings for 1a and 1c of α = 146–148°
(Table 1). Because the pendent substituents on the tail of 1a and 1c are distanced from the
acene core by the [3]cumulene moiety, the bending is less that of TCAQ (α = 144.6°),[35]
TCTQ (α = 135.9°),[50] and TCPQ (α = 132.4°)[50] as summarized in Table 1. A similar trend
can also be seen when comparing the deviation of the dicyanovinyl groups relative to the
central ring of the acene skeleton, i.e., the tilt angles (Table 1): 1a (γ1 = 31.5, 37.9°) and 1c
(γ1 = 34.5°) versus TCAQ (γ1 = 34.7°; γ2 = 34.1°),[35] TCTQ (γ1 = 38.8°),[50] and 6,13-TCPQ
(γ1 = 39.6°; γ2 = 39.1°).[50]
Table 1. Comparison of bend and tilt angles of 1a and 1c to those of TCAQ, TCTQ, and 6,13-TCPQ.
Structure front view (left) and side view
(right)
Bend angle
Tilt angle Tilt angle
γ1 [°][a] γ2 [°][a]
Cmpd
α [°][a]
147.2
146.2
31.5
23.2
1a[b, c]
37.9
34.5
12.7
19.3
1c[b]
147.6
144.6
TCAQ[35]
34.7
34.1
9
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
–
TCTQ[50]
135.9
132.4
38.8
39.6
6,13-
39.1
TCPQ[50]
[a]
For details on the determination of the bend and tilt angles, see Figures S2 and S3. [b] Aryl tail-
[c]
groups omitted for clarity.
Two crystallographically independent molecules with different α- and γ-
angles are present in the unit cell.
UV-vis analysis
TCPQ derivatives are typically colorless or yellow, and they feature absorptions in the
UV or high-energy visible regions.[51] Dicyanovinylacenequino[3]cumulenes 1a–c and 2, on
the other hand, are dark red to black solids in the solid state and show brownish-red to dark
purple colors in solution. Ketoacenequino[3]cumulenes 3a–c and 4 are similarly dark red to
black as solids, but are less absorbing in solution, giving bright red colors. On the basis of
UV-vis spectroscopy, both keto (3a–c and 4) and dicyanovinyl (1a–c and 2) derivatives show
attractive panchromatic absorption behavior with intense absorption bands in the UV region
and broad absorptions in the visible region out to ca. 700 nm (Figure 3, Table 2).
Figure 3. Absorption spectra of a) ketoacenequino[3]cumulenes 3a–3c, and 4 and b) dicyano-
vinylacenequino[3]cumulenes 1a–c, and 2, recorded in THF.
10
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
Table 2. UV-vis spectroscopic data for 3a–c, 4, 1a–c, and 2, recorded in THF.
λmax
ε
λcutoff
[nm/eV][a]
λmax
ε
λcutoff
[nm/eV][a]
Cmpd
Cmpd
[nm]
[L mol–1 cm–1]
[nm]
[L mol–1 cm–1]
3a
3b
3c
538
547
563
536
32 700
20 300
36 000
38 900
582/2.13
616/2.01
634/1.96
582/2.13
1a
1b
1c
2
555[b]
579[b]
551
14 400
650/1.91
686/1.81
629/1.97
642/1.93
[c]
–
36 100
26 800
4
562
[a]
As estimated from the intercept of a tangent line to the lowest energy absorption of the UV-vis
spectrum with the x-axis (at ε = 0). [b] Shoulder absorption. [c] Not determined due to limited solubility.
As a result of the broadening of low energy absorptions, it is easier to use the values for λcutoff
in comparisons versus structure (i.e., the lowest energy of measurable absorption for each
molecule, Table 2). Using 3a as an “unfunctionalized” molecule for comparison, it is clear
that a more electron-rich acene framework (4) has almost no influence on λcutoff values
(Figure 3a). Formal exchange of the tail-group for a weak donor (3b) or an acceptor (3c)
leads to a distinct red-shift of ca. 0.1 eV and 0.2 eV, respectively, versus 3a. Changes in
absorptions are also correlated by DFT calculations (Figure S6).
Dicyanovinyl derivatives 1a–c, and 2 exhibit a similar absorption pattern as the
ketones (Figure 3b). The λcutoff values of the dicyanovinyl derivatives are consistently red-
shifted versus the analogous ketones by 0.2 eV, confirming the influence of the more
electron deficient head group. Unlike the keto-derivatives, where the CPD tail group gives the
most significant change in λcutoff (as a result of a lowering of the LUMO energy, Figure S6),
dicyanovinyl derivative 1b shows the largest change in λcutoff as a result of the addition of a
donor tail group and the associated increase in HOMO energy (Figure S6). Thus, both the
head and tail groups play a pivotal role in the absorptivity.
CV analysis
Calculations have established that the bending of the exTCNQs is one of two major
factors giving rise to lower acceptor strength compared to parent TCNQ (the second factor is
the introduction of new antibonding interactions induced by the additional fused benzene
11
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
rings).[40,41] Thus, planarized compounds 1a and 1b (relative to other exTCNQs) were
expected to exhibit comparable reduction potentials versus e.g., TCPQ, even though the
former feature only a single dicyanovinyl acceptor group. It was also hypothesized that the
presence of the CPD group in 1c should show a lowered LUMO energy level versus 1a and
1b (Figure S6). Cyclic voltammetry was used to explore these predictions (Tables 3 and S1;
Figures S4 and S5).
CV analysis shows that, unlike other exTCNQ derivatives, compounds 1–4 show
clear oxidation events (Table 3), and only the oxidation potential of 1b and 3b is significantly
affected by substitution. Keto-derivatives 3a, 3b, and 4 show reduction potentials in a similar
range of –1.41 V to –1.55 V, while the reduction of dicyanovinyl derivatives 1a, 1b, and 2
show facilitated reduction events in the range of –1.19 V to –1.25 V. This observation clearly
demonstrates the influence of the dicyanovinyl head group on the LUMO levels of these
compounds, while in the acene backbone (“wings”) had little effect within each series
(Figure S6). Dicyanovinyl derivative 1c (Ered1 = –0.98 V) and ketone 3c (Ered1 = –1.06 V), on
the other hand, show lower reduction potentials, facilitated by the CPD moiety.[67] Thus, the
acceptor strength of 1c is similar to that of 6,13-TCPQ and 5,14-TCPQ (Ered1 = –0.95 V
and −0.88 V, respectively), but not to the level of other exTCNQs such as TCAQ and TCTQ
(Table 3).
Table 3. First electrochemical reduction (Ered1) and oxidation (Eox1) potentials (measured in CH2Cl2,
versus Fc+/Fc) for 1a–c, 2, 3a–c, 4, in comparison to TCAQ,[35] TCTQ,[37] and TCPQs.[37]
Cmpd
Cmpd
Ered1 (V)
–1.47[a]
–1.55[b]
–1.06[d]
–1.41[a]
–0.67[e]
–0.82[e]
Eox1 (V)
0.59[d]
0.40[c]
0.61[b]
0.59[d]
Ered1 (V)
–1.23[b]
–1.25[c]
–0.98[d]
–1.19[c]
–0.88[e]
–0.95[e]
Eox1 (V)
0.63[d]
0.53[c]
0.63[d]
0.63[d]
3a
3b
1a
1b
3c
1c
4
2
TCAQ[35]
TCTQ[37]
–
5,14-TCPQ[37]
6,13-TCPQ[37]
–
[f]
[f]
[f]
[f]
–
–
[a] Peak potential used due to closely spaced reduction potential. [b] Estimated half-wave potential taken
[c]
from a quasi-reversible redox event.
Peak potential taken from an irreversible redox event.
[d] Reversible redox event, half-wave potential.[e] Measured in acetonitrile with tetraalkylammonium
12
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
perchlorate as the supporting electrolyte. [f] To our knowledge, oxidation events for TCAQ, TCTQ, and
TCPQs by electrochemical analysis have not been reported.
Thin-film formation and electron mobility characterization
Compounds 1a, 2, 3a, and 4 showed nice film formation and films with thicknesses of
85–110 nm were achieved from chloroform. In the case of 1c and 3c, limited solubility in
chloroform and o-DCB did not allow for smooth films to be formed and, consequently,
mobilities could not be measured. Testing of 1a, 2, 3a, and 4 for their hole-only mobility
revealed weak mobilities ranging from 2.1 • 10–7 (3a) to 5.8 • 10–6 (4) cm2 V–1 s–1 (Table S2).
In spite of the low mobilities, this result is, perhaps, counter intuitive in view of the ketone and
dicyanovinyl functionality that are both acknowledged acceptor groups. Investigations of the
n-type mobility for 1a, 2, 3a, and 4 were unsuccessful in this standard architecture due to the
higher lying LUMO levels.
Conclusions
To conclude, we have designed, synthesized, and characterized a series of new
dicyanovinylacenequino[3]cumulenes 1a–c and 2 and their corresponding keto analogs 3a–c
and 4. The target molecules are assembled via a sequence of nucleophilic addition,
Knoevenagel condensation, and reductive elimination reactions. The nature of the acene
wings of the molecule have little effect on the electronic make up, while both the head and
tail can be used to modify the structure and HOMO-LUMO energy gaps. The overall effect of
functionalization is demonstrated by panchromatic absorption for all molecules (1–4), with
λcutoff values reaching nearly 700 nm for compound 1b. Notably, inclusion of the [3]cumulene
group provides the desired result of a more planarized acene structure relative to other
exTCNQs, through distancing the tail functionalization from the acene core. Only the CPD
group serves as a reasonable acceptor, and LUMO energies of compound 1c are similar to
the two largest known exTCNQs, 6,13-TCPQ and 5,14-TCPQ. The combination of the two
motifs, a [3]cumulene and CPD moiety is, however, insufficient to provide the acceptor
strength comparable to “smaller” exTCNQs such as TCAQ and TCTQ. The suitability of 1c,
13
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
2, 3a, and 4 as semiconductors in solar cells was evaluated via examination of thin film
formation and charge carrier mobilities (films of 1c and 3c were limited by solubility,
preventing analysis). Films showed hole mobilities, in spite of the presence of the acceptor
groups, albeit mobilities were universally disappointing. Thus, it seems clear fundamental
design changes are necessary in order to obtain a promising next generation of n-type
materials based on the extended exTCNQ framework.
Acknowledgements.
The authors are grateful for support of this work in Germany from the Deutsche
Forschungsgemeinschaft (DFG – SFB 953, ‘‘Synthetic Carbon Allotropes’’), the DFG Cluster
of Excellence ‘‘Engineering of Advanced Materials’’ at FAU, and ‘‘Solar Technologies go
Hybrid’’ (an initiative of the Bavarian State Ministry for Science, Research and Art), and in
Canada from the Natural Sciences and Engineering Research Council of Canada (NSERC).
MG thanks the German Fonds der Chemischen Industrie (FCI) for financial support. We
acknowledge use of the images from the http://www.pngimg.com/img/insects/butterfly and
http://www.smartcc365.com/group/grass-wallpapers/ for the graphical abstract (accessed
26.08.2017).
References
[1]
H. E. Klauk, Organic Electronics: Materials, Manufacturing, and Applications, Wiley-
VCH, Weinheim, 2006, ISBN: 978-3527312641.
[2] H. Klauk, (Ed.) Organic Electronics II: More Materials and Applications, Wiley-VCH,
Weinheim, 2012, ISBN: 978-3527326471.
[3] D. A. Bernards, R. M. Owens, G. G. Malliaras (Eds.), Organic Semiconductors in
Sensor Applications, Springer, Berlin Heidelberg, 2008, ISBN: 978-3540763147.
[4] L. Torsi, M. Magliulo, K. Manoli, G. Palazzo, Chem. Soc. Rev. 2013, 42, 8612–8628.
[5] A. Facchetti, Mater. Today 2007, 10, 28–37.
[6] A. R. Murphy, J. M. J. Fréchet, Chem. Rev. 2007, 107, 1066–1096.
[7] N. Thejo Kalyani, S. J. Dhoble, Renew. Sust. Energ. Rev. 2012, 16, 2696–2723.
14
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
[8] J.-H. Jou, S. Kumar, A. Agrawal, T.-H. Li, S. Sahoo, J. Mater. Chem. C 2015, 3, 2974–
3002.
[9] M. D. Weber, M. Adam, R. R. Tykwinski, R. D. Costa, Adv. Funct. Mater. 2015, 25,
5066–5074.
[10] Y.-F. Lim, Y. Shu, S. R. Parkin, J. E. Anthony, G. G. Malliaras, J. Mater. Chem. 2009,
19, 3049–3056.
[11] D. N. Congreve, J. Lee, N. J. Thompson, E. Hontz, S. R. Yost, P. D. Reusswig, M. E.
Bahlke, S. Reineke, T. Van Voorhis, M. A. Baldo, Science 2013, 340, 334–337.
[12] W. Cao, J. Xue, Energy Environ. Sci. 2014, 7, 2123–2144.
[13 ] L. Yang, M. Tabachnyk, S. L. Bayliss, M. L. Böhm, K. Broch, N. C. Greenham, R. H.
Friend, B. Ehrler, Nano Lett. 2015, 15, 354–358.
[14 ] J. E. Anthony, Chem. Rev. 2006, 106, 5028–5048.
[15] J. Zaumseil, H. Sirringhaus, Chem. Rev. 2007, 107, 1296–1323.
[16] Z. Bao, Adv. Mater. 2000, 12, 227–230.
[17] J. E. Anthony, A. Facchetti, M. Heeney, S. R. Marder, X. Zhan, Adv. Mater. 2010, 22,
3876–3892.
[18] Q. Meng, W. Hu, Phys. Chem. Chem. Phys. 2012, 14, 14152–14164.
[19] X. Gao, Y. Hu, J. Mater. Chem. C 2014, 2, 3099–3117.
[20] T. L. Cairns, R. A. Carboni, D. D. Caffman, V. A. Engelhardt, R. E. Heckert, E. L. Little,
E. G. McGeer, B. C. McKusick, W. J. Middleton, J. Am. Chem. Soc. 1957, 79, 2340–
2341.
[21] D. N. Dhar, Chem. Rev. 1967, 67, 611–622.
[22] A. J. Fatiadi, Synthesis 1986, 249–284.
[23] J. A. Januszewski, F. Hampel, C. Neiss, A. Görling, R. R. Tykwinski, Angew. Chem.
Int. Ed. 2014, 53, 3743–3747; Angew. Chem. 2014, 126, 3818–3822.
[24] For a short review on TCNQ-type electron acceptor molecules see: N. Martin, J. L.
Segura, C. Seoane, J. Mater. Chem. 1997, 7, 1661–1676.
[25] D. S. Acker, R. J. Harder, W. R. Hertler, W. Mahler, L. R. Melby, R. E. Benson, W. E.
Mochel, J. Am. Chem. Soc. 1960, 82, 6408–6409.
[26] D. S. Acker, W. R. Hertler, J. Am. Chem. Soc. 1962, 84, 3370–3374.
[27] A. J. Epstein, S. Etemad, A. F. Garito, A. J. Heeger, Phys. Rev. 1972, 5, 952–977.
15
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
[28] M. R. Bryce, L. C. Murphy, Nature 1984, 309, 119–126.
[29] M. R. Bryce, Chem. Soc. Rev. 1991, 20, 355–390.
[30] M. R. Bryce, S. R. Davies, A. M. Grainger, M. B. Hursthouse, M. Mazid, R. Bachmann,
F. Gerson, J. Hellberg, J. Org. Chem. 1992, 57, 1690–1696.
[31] R. C. Wheland, E. L. Martin, J. Org. Chem. 1975, 40, 3101–3109.
[32] N. Martin, C. Seoane, Handbook of Organic Conductive Molecules and Polymers,
Nalwa; H. S. (Ed.), Wiley-VCH, Chichester, 1997, Vol. 1, Chapter 1.
[33] F. Ogura, Y. Hama, Y. Aso, T. Otsubo, Synth. Met. 1988, 27, 295–300.
[34] H. Ishida, K. Yui, Y. Aso, T. Otsubo, F. Ogura, Bull. Chem. Soc. Jpn. 1990, 63, 2828–
2835.
[35] A. M. Kini, D. O. Cowan, F. Gerson, R. Moeckel, J. Am. Chem. Soc. 1985, 107, 556–
562.
[36] P. W. Kenny, T. H. Jozefiak, L. L. Miller, J. Org. Chem. 1988, 53, 5007–5010.
[37] N. Martin, R. Behnisch, M. Hanack, J. Org. Chem. 1989, 54, 2563–2568.
[38] P. De la Cruz, N. Martin, F. Miguel, C. Seoane, A. Albert, F. H. Cano, A. Gonzalez, J.
M. Pingarron, J. Org. Chem. 1992, 57, 6192–6198.
[39] A. F. Garito, A. J. Heeger, Acc. Chem. Res. 1974, 7, 232–240.
[40] E. Orti, R. Viruela, P. M. Viruela, J. Mater. Chem. 1995, 5, 1697–1705.
[41] R. Viruela, P. M. Viruela, E. Orti, N. Martín, Synth. Met. 1995, 70, 1031–1032.
[42] For a critical review on TCAQ see: R. Gomez, C. Seoane, J. L. Segura, Chem. Soc.
Rev. 2007, 36, 1305–1322.
[43] R. A. J. Jannsen, M. P. T. Christiaans, C. Hare, N. Martin, N. S. Sariciftci, A. J. Heeger,
J. Chem. Phys. 1995, 103, 8840–8845.
[44] A. J. Heeger, F. Wudl, N. Serdar Sariciftci, R. A. J. Janssen, N. Martin, J. Phys. I
France 1996, 6, 2151–2158.
[45] M. A. Herranz, B. M. Illescas, N. Martín, C. Luo, D. M. Guldi, J. Org. Chem. 2000, 65,
5728–5738.
[46] B. M. Illescas, N. Martín, J. Org. Chem. 2000, 65, 5986–5995.
[47] G. Zerza, A. Cravino, H. Neugebauer, N. S. Sariciftci, R. Gómez, J. L. Segura, N.
Martín, M. Svensson, M. R. Andersson, J. Phys. Chem. A 2001, 105, 4172–4176.
16
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
[48] F. Giacalone, J. L. Segura, N. Martín, M. Catellani, S.Luzzati, N. O. Lupsac, Org. Lett.
2003, 5, 1669–1672.
[49] M. Catellani, S. Luzzati, N. O. Lupsac, R. Mendichi, R. Consonni, F. Giacalone, J. L.
Segura, N. Martin, Thin Solid Films 2004, 451–452, 2–6.
[50] M. M. Bader, P.-T. T. Pham, B. R. Nassar, H. Lin, Y. Xia, C. D. Frisbie, Cryst. Growth
Des. 2009, 9, 4599–4601.
[51] M. Hanack, N. Martin, J. Chem. Soc., Chem. Commun. 1988, 1522–1524.
[52] K. Tanaka, N. Aratani, D. Kuzuhara, S. Sakamoto, T. Okujima, N. Ono, H. Uno, H.
Yamada, RSC Advances 2013, 3, 15310–15315.
[53] Q. Ye, C. Chi, Chem. Mater. 2014, 26, 4046–4056.
[54] Acenequino[3]cumulenes have been described as early as 1959, see: W. Ried, G.
Dankert, Chem. Ber. 1959, 92, 1223–1236.
[55] M. Franz, J. A. Januszewski, D. Wendinger, C. Neiss, L. D. Movsisyan, F. Hampel, H.
L. Anderson, A. Görling, R. R. Tykwinski, Angew. Chem. Int. Ed. 2015, 54, 6645–6649;
Angew. Chem. 2015, 127, 6746–6750.
[56] For the use of quinones as acceptors, see for example: Z. Liang, Q. Tang, J. Liu, J. Li,
F. Yan, Q. Miao, Chem. Mater. 2010, 22, 6438–6443. X. Gao, Y. Hu, J. Mater. Chem.
C 2014, 2, 3099–3117.
[57] D. Lehnherr, R. McDonald, R. R. Tykwinski, Org. Lett. 2008, 10, 4163–4166.
[58] D. Lehnherr, A. H. Murray, R. McDonald, R. R. Tykwinski, Angew. Chem. Int. Ed. 2010,
49, 6190–6194; Angew. Chem. 2010, 122, 6326–6330.
[59] J. L. Marshall, D. Lehnherr, B. D. Lindner, R. R. Tykwinski, ChemPlusChem 2017, 82,
967–1001.
[60] The addition protocol developed for desymmetrization of pentacene was found to
superior to that reported by Ried and Dankert in reference [54].
[61] B. S. Ong, B. Keoshkerian, J. Org. Chem. 1984, 49, 5002–5003.
[62] A. E. Murschell, W. H. Kan, V. Thangadurai, T. C. Sutherland, Phys. Chem. Chem.
Phys. 2012, 14, 4626–4634.
[63] Details of the optimization of this transformation will be published elsewhere.
[64] K. Yamashita, T. Tanaka, M. Hayashi, Tetrahedron 2005, 61, 7981–7985.
[65] DSC is used to assess thermal stability, rather than thermal gravimetric analysis (TGA),
because the solid-state decomposition of substituted acenes often occurs by
polymerization, which is not accompanied by weight loss observable by TGA (the
exotherm from polymerization, on the other hand, is clearly seen in DSC).
17
This article is protected by copyright. All rights reserved.

10.1002/chem.201704314
Chemistry - A European Journal
[66] P. Gawel, Y.-L. Wu, A. D. Finke, N. Trapp, M. Zalibera, C. Boudon, J.-P. Gisselbrecht,
W. B. Schweizer, G. Gescheidt, F. Diederich, Chem. Eur. J. 2015, 21, 6215–6225.
[67] The observed strong initial reduction peak in 1c (Figure S5) might be an indication of
potential inversion, which is known to dictate the reduction behavior in lateral
benzoannulated exTCNQs, see also ref. 40.
18
This article is protected by copyright. All rights reserved.