Carbazole-Terpyridine Donor-Acceptor Dyads with Rigid π-Conjugated Bridges

Article abstract of DOI:10.1002/cplu.201900213

A series of molecules in which 9H-carbazole (electron donor, D) and 2,2′:6′,2′′-terpyridine (electron acceptor, A) are connected through rigid π-conjugated bridges (D-π-A systems) have been synthesized and their photophysical properties examined in detail, with the support of DFT calculations. The bridges are made of different sequences of ethynylene, phenylene, and anthracene groups. The synthetic strategies involve condensation of 2-acetylpyridine with the aromatic aldehyde moiety on different functionalized π-conjugated bridges and couplings with carbazole derivatives. The system incorporating anthracene in the bridge shows the typical absorption and emission fingerprints of this polycyclic hydrocarbon. The other systems have HOMOs and LUMOs centred, respectively, over the carbazole and the bridge and exhibit solvatochromic charge-transfer (CT) luminescence with high photoluminescence yield up to 70 %, except when an ethynylene unit is directly attached to the carbazole ring, due to a trans-bent non-emissive π–σ* excited state.

Full text of DOI:10.1002/cplu.201900213

Accepted Article
Title: Carbazole-Terpyridine Donor-Acceptor Dyads with Rigid π-
Conjugated Bridges
Authors: Nicola Armaroli, Elia Matteucci, Andrea Baschieri, Letizia
Sambri, Filippo Monti, Eleonora Pavoni, and Elisa Bandini
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: ChemPlusChem 10.1002/cplu.201900213
Link to VoR: http://dx.doi.org/10.1002/cplu.201900213
A Journal of
www.chempluschem.org

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
Carbazole-Terpyridine Donor-Acceptor Dyads with Rigid
π-Conjugated Bridges
Elia Matteucci,[a] Andrea Baschieri,*[b] Letizia Sambri,*[a] Filippo Monti,*[c] Eleonora Pavoni,[c]
Elisa Bandini,[c] and Nicola Armaroli*[c]
Abstract: A series of molecules (1-7) in which 9H-carbazole (electron
donor, D) and 2,2’:6’,2”-terpyridine (electron acceptor, A) are
connected through rigid π-conjugated bridges (D-π-A systems) have
been synthesized and their photophysical properties examined in
detail, with the support of DFT calculations. The bridges are made of
acceptor (A) is particularly interesting, as it affords “push-pull”
systems, which are well suited for organic electronics,
semiconductors and photovoltaics.[17] The A/D subunits can be
covalently connected through different rigid and conjugated
systems, so as to prepare D-π-A architectures[18-23] which may
different sequences of ethynylene, phenylene and anthracene groups. show a characteristic photophysical behaviour, in particular
The synthetic strategies involve condensation of 2-acetylpyridine with
the aromatic aldehyde moiety on different functionalized p–
conjugated bridges and couplings with carbazole derivatives. The
system incorporating anthracene in the bridge (7) shows the typical
absorption and emission fingerprints of this π-extended system. 1-6
have HOMOs and LUMOs centered, respectively, over the carbazole
and the bridge and exhibit solvatochromic charge-transfer (CT)
luminescence with high photoluminescence yield up to 70%, except
when an ethynylene unit is directly attached to the carbazole ring (2,6),
due to a trans-bent non emissive π–s* excited state.
charge-transfer absorption (and possibly emission) bands,
typically red-shifted compared to spectral features arising from
local excited states centered on the individual subunits.[24]
Electron-rich moieties containing fused aromatic rings can exhibit
high carrier mobilities, enhanced fluorescence and reduced band
gaps. Among them, 9H-carbazole (Cbz, Scheme 1) is a popular
molecular platform made of a fused tricyclic structure with good
planarity and high stability, thanks to its fully aromatic
configuration.[25-27] The presence of a nitrogen atom in the 9
position enables easy coupling with other functional groups,
without altering the electronic and photophysical properties of the
molecule. Moreover, 1-C to 8-C positions can be easily
functionalized with suitable groups, opening the route to the
synthesis of many carbazole-based derivatives.[28,29]
Introduction
Organic conjugated systems exhibit wide interest as functional
materials in several applications.[1-7] They are generally easy to
prepare at low cost and their electronic and optical properties can
be predicted to a good extent, therefore displaying remarkable
advantages over inorganic materials. Accordingly, they are
extensively used as active layers in a variety of organic devices,
such as light-emitting diodes (OLEDs),[8] field-effect transistors
(OFETs),[9] photovoltaic cells (OPVC),[5,10,11] dye-sensitized solar
aryl
4’
5
4
6
3
2’
6’
7
2
N
N
9
N
2
2”
8
N
1
H
9H-Carbazole
(Cbz)
4’-aryl-substituted-2,2’:6’,2”-Terpyridine
(Tpy)
cells (DSSC)[12]
applications.[15,16]
,
sensors[13,14] as well as in bioimaging
Scheme 1. Chemical structure and numbering of the donor (Cbz) and acceptor
(Tpy) units used for the synthesis of the investigated dyads.
Among many options for the design of organic π-conjugated
molecules, the combination of an electron donor (D) and a related
9H-Carbazole and its derivatives have been extensively used as
electron donating (D) units in p–conjugated small molecules and
polymers.[30,31] On the other hand, 2,2’:6’,2”-terpyridine and its
derivatives are readily accessible molecules widely used in
organic and supramolecular chemistry, due to their electron
accepting (A) character and, most remarkably, to the ability of
serving as tridentate ligands,[32] also largely used in photoactive
polynuclear metal complexes.[33-36] Moreover, they can be used
as proton responsive units in multicomponent arrays.[37]
[a]
[b]
[c]
Dr. E. Matteucci, Prof. L. Sambri
Dipartimento di Chimica Industriale “Toso Montanari”
Università di Bologna
Viale Risorgimento 4, 40136 Bologna, Italy
E-mail: letizia.sambri@unibo.it
Dr. A. Baschieri
Dipartimento di Chimica “Giacomo Ciamician”
Università di Bologna
Via San Giacomo 11, 40126 Bologna, Italy
E-mail: andrea.baschieri2@unibo.it
Previous studies have shown that 4’-aryl-substituted 2,2’:6’,2’’-
terpyridine derivatives (Tpy, Scheme 1) exhibit excellent
luminescence properties.[38,39] These compounds can be
synthesized in one-pot under environmentally benign conditions,
via condensation of 2-acetylpyridine with different aromatic
aldehydes.[40,41] The 1,5-diones intermediates thus obtained are
then cyclized, without prior isolation, by adding concentrated
aqueous ammonia and affording the desired substituted
terpyridines.
Dr. F. Monti, Dr. E. Pavoni, Dr. E. Bandini, Dr. N. Armaroli
Istituto per la Sintesi Organica e la Fotoreattività
Consiglio Nazionale delle Ricerche
Via Piero Gobetti 101, 40129 Bologna, Italy
E-mail: filippo.monti@isof.cnr.it, nicola.armaroli@isof.cnr.it
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
A vast number of derivatives containing carbazole or terpyridine
units can be found in the literature, but relatively few reports on
compounds carrying both units separated by a π–conjugated
system.[42-47] Therefore, there is room for developing new
carbazole-terpyridine derivatives with enhanced optoelectronic
features, also to widen our knowledge on the relationship between
the structure and the electronic properties.[48] Our earlier work
carried out on this type of molecules showed that the absorption
and emission properties of carbazole-terpyridine dyads can be
finely tuned by changing the spacers between the two terminal
subunits.[49]
The synthetic approach is based on the preliminary preparation of
the properly functionalized p–conjugated bridge, on which the
carbazole unit is grafted and the terpyridine moiety is formed
through a one-pot condensation reaction.[40,41] The detailed
synthetic procedures affording the new compounds 3-7 are
described herein.
Dyad 3 is obtained in two steps (Scheme 3). First the
condensation of the commercially available p-bromo-
benzaldehyde with 2-acetylpyridine in the presence of NaOH and
ammonia leads to the terpyridine intermediate 9 in 73% yield. The
latter is then reacted with 9H-carbazole-9-(4-phenyl) boronic acid
pinacol ester 10 through a Suzuki coupling, giving the target
product 3 in 25% yields.
With the aim of expanding the availability and scope of this
versatile class of D-π-A compounds, herein we report a new
series of carbazole-terpyridine systems where the two terminal
units are connected through aromatic and triple bonds spacers. In
this way, the conjugation degree is tuned in an effort to obtain
stable architectures with high photoluminescence quantum yields
(PLQYs). In perspective, the presence of the free terpyridyl group
makes these systems suitable for chelation of transition metals,
opening the route to new photoactive coordination compounds.
Scheme 3. Synthesis of dyad 3.
Results and Discussion
Synthesis of the dyads
Compound 4 is prepared through a selective Ullman-type
condensation of p-iodo-bromobenzene 11 with 9H-carbazole
promoted by Cu(I),[50] which gives 12 in 71% yield (Scheme 4).
This intermediate is then reacted with p-ethynyl benzaldehyde 13
in a palladium-catalysed Sonogashira coupling, affording the
aldehyde 14 in 22% yield, which is finally condensed with 2-
acetylpyridine to form the terpyridine moiety and give compound
4 in 35% yield.
Expanding our previous approach to the preparation of Cbz-Tpy
dyads such as 1 and 2 (Scheme 2), we have designed and
synthesized five new carbazole-terpyridine derivatives (3-7), in
which the π-conjugated bridge between the donor and acceptor
units is progressively elongated with acetylene, phenylene and
even anthracene units.
Scheme 4. Synthesis of dyad 4.
Similarly to 4, the first step of the synthesis of 5 started from p-
iodo-bromobenzene 11 with p-ethynyl benzaldehyde through a
Sonogashira coupling to give the intermediate 15 equipped with
both aldehyde and bromine functionalities in 94% yield (Scheme
5). Eventually, the terpyridine moiety is assembled by reaction of
15 with 2-acetylpyridine in the presence of KOH and ammonia in
15% yield to obtain 16. The target product 5 is obtained by Suzuki
coupling of 16 with 9H-carbazole-9-(4-phenyl) boronic acid
pinacol ester 10 in 30% yields.
Scheme 2. Chemical structure of compounds 1-7.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
With the exception of the condensation step giving the terpyridine,
which occurs with moderate yields, the other synthetic steps are
generally efficient. However, the purification of the final products
turned out to be difficult. Separation of impurities (primarily
terpyridine derivatives with almost the same polarity) was difficult
and common purification procedures such as column
chromatography generally failed. Alternatively, we opted for
techniques that take advantage of the low solubility of the final
compounds in polar solvent (see Experimental Part). Due to these
problems, the overall yields of the final derivatives were
sometimes low, but the high purity achieved allowed extensive
structural and photophysical characterizations.
Scheme 5. Synthesis of dyad 5.
Ground-state theoretical calculations
In Scheme 6 is depicted the synthesis of 6. The TMS-protected p-
All the investigated molecules display an ideal C2 symmetry in
their optimized ground-state geometries. This is because these
carbazole-terpyridine dyads have been designed with rigid linear
bridges of different lengths, so that the donor (carbazole) and the
acceptor (terpyridine) moieties are separated by π-conjugated
spacers of well-defined lengths, but always in the direction of the
main molecular axis. In Table 1 are listed key calculated structural
geometric parameters of the investigated dyads, including the
calculated distances between the centroids of the carbazole-
donor and terpyridine-acceptor moieties (dDA).
ethynyl-bromobenzene 17 undergoes
a palladium-catalysed
Sonogashira coupling with p-ethynylbenzaldehyde 13, giving the
intermediate 18 in 44% yield, which reacts with N-
bromosuccinimide and AgF leading to the bromo-derivative 19 in
78% yield. The latter reacts with 9H-carbazole in an Ullmann-type
copper(II) catalysed coupling, giving the carbazole derivative 20
(47% yield), which affords the desired product
condensation with 2-acetylpyridine and ammonia in 15% yield.
6 upon
Table 1. Structural geometric parameters of the dyads, calculated at the
M06-2X/6-31+G(d) level of theory in toluene (using PCM).
S0 optimized geometry
S0 ® S1 excitation [a]
[c]
dDA
[Å]
aDA
Energy Oscillator
DCT
[Å]
DCT/dDA
Conf.[b]
[deg.]
[eV]
strength
10.71
10.71
18.8
89.0
4.20
4.20
0.744
0.700
5.11
5.22
0.48
0.49
Scheme 6. Synthesis of dyad 6.
1
2
2
1
13.28
29.0
3.97
1.67
4.67
0.35
Dyad 7 includes an anthracene moiety as spacer, in order to
increase the π-delocalization with respect to the analogue 5. The
synthesis (Scheme 7) starts from 9,10-dibromoanthracene 21,
which undergoes a palladium-catalysed Sonogashira coupling
with p-ethynylbenzaldehyde, giving the mono-substituted
intermediate 22 (35% yield). The latter is then reacted with 9H-
carbazole-9-(4-phenyl) boronic acid pinacol ester 10 through a
Suzuki coupling to afford the carbazole intermediate 23 in 38%
yield. The latter undergoes final condensation of the terminal
aldehyde with 2-acetylpyridine, giving 7 in 15% yield.
15.02
15.02
15.02
15.02
21.9
50.1
52.3
58.7
4.22
4.22
4.21
4.22
1.38
1.34
1.37
1.33
4.88
5.15
4.95
5.14
0.32
0.34
0.33
0.34
3
4
4
2
17.60
17.60
23.5
88.6
3.84
3.84
1.99
1.99
4.28
4.27
0.24
0.24
21.91
21.91
21.91
21.91
22.0
49.1
53.4
56.7
3.85
3.85
3.85
3.85
2.79
2.76
2.79
2.76
2.71
2.78
2.72
2.79
0.12
0.13
0.12
0.13
5
6
7
4
1
4
21.17
30.5
3.64
2.74
3.87
0.18
21.93
21.93
21.93
21.93
12.8
17.5
62.2
87.2
3.01
3.01
3.02
3.01
1.07
1.07
1.06
1.07
0.35
0.35
0.35
0.27
0.02
0.02
0.02
0.01
[a] Lowest-energy transition computed at the ground-state minimum-energy
geometry using TD-DFT methods and the PCM linear response formalism.
[b] Number of unique conformational minima. [c] Dihedral angle between the
plane of the carbazole and of the terpyridine moiety.
Scheme 7. Synthesis of dyad 7.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
Figure 1. Frontier molecular orbitals of 1–7, calculated in toluene at the M06-2X/6-31+G(d) level of theory.
The adopted spacers belong to the class of biphenyl and/or tolane
(i.e., diphenylacetylene) para-derivatives. Accordingly, the
corresponding dyads can adopt a large number of virtually
isoenergetic conformations, which are generated by the
reciprocal orientations of the optimal dihedral angles between the
different moieties of the dyads (Tables S1–S7). While the tolane
unit in known to be planar,[51,52] the biphenyl one is displays
torsional angles of about 40°, depending on the environment.[53,54]
As a consequence, the dihedral angle between the plane of the
carbazole and of the terpyridine moiety (i.e., aDA in Table 1) can
vary substantially within the different minima of a specific dyad,
ranging from nearly coplanar to almost perpendicular
conformations (as in the simplest case of 1, see Table 1, Table
S1 and Figure S1). However, it is worth noting that such
conformers are in fast equilibration since rotations are virtually
free at room temperature (Figure S2 and S3), especially when
they occur around the ethynyl linker.[55] The only notable
exception is when the carbazole moiety is linked directly to a
phenyl unit; in this case, a rather large barrier (i.e., 63.5 kJ/mol)
prevents the carbazole to easily swap above or below the plane
of the phenyl ring (as in the case of 1, see Figure S2, bottom).
In Figure 1 are reported the energy diagrams and the frontier
molecular orbitals of all the dyads. As we previously reported for
1 and 2,[49] the HOMO is predominantly centered on the carbazole
moiety in all cases, with the notable exception of 7 which is
equipped with an anthracene unit, providing a π orbital well above
that of carbazole. As a consequence, the HOMO energy is almost
constant in dyads 1–6 (i.e., approx. –6.8 eV), while it is
considerably higher for 7 (i.e., –6.54 eV, Figure 1). On the other
hand, the LUMO is mainly delocalized over the bridge and the
central pyridine ring of the terpyridine acceptor. Also in this case,
dyad 7 is an exception since its LUMO in centered only on the
ethynyl-anthracene moiety of the bridge and the terpyridine π*
orbitals start to play a role only in LUMO+1 and LUMO+2. Due to
the extended delocalization of the LUMO over the molecular
bridge, its energy changes much more markedly along the series;
generally, the longer the bridge, the higher the delocalization, the
lower the LUMO energy.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
Since the orbitals are rather localized on a specific part of the
dyads (i.e., the carbazole-donor, the terpyridine-acceptor or the
bridge), virtually no differences were observed in the energy and
topology of the frontier molecular orbitals within a set of analogous
conformers, regardless of the aDA dihedral angle between the
carbazole and terpyridine moieties, as representatively shown in
Figure S4 for dyad 1. Moreover, the ground-state properties are
virtually not affected by the polarity of the solvent; in fact, both the
optimized geometries and the energy and topology of molecular
orbitals of all the dyads are almost identical, if calculated in
toluene or in dimethylformamide (as representatively shown in
Figure S5 for dyad 2). Only a stabilization of around 0.1 eV is
observed for all the frontier molecular orbitals in the more polar
solvent.
All of the species exhibit absorption features above 340 nm, unlike
the individual moieties Cbz and 4’-p-tolyl-2,2’:6’,2’’–terpyridine
(Ttpy) (Figure S6). This may be tentatively attributed to low-
energy carbazole
®
terpyridine charge-transfer (CT)
transitions.[49] However, the absorption profiles of all dyads do not
display a remarkable solvatochromism when spectra in toluene
and dimethylformamide are compared (Figure 2).
Dyad 1 can be considered as the simplest donor-acceptor system
of the series, since the carbazole donor is directly linked to the 4’-
phenyl-terpyridine acceptor. In this archetypal array, the lowest-
energy CT band corresponding to the S0 ® S1 electronic transition
displays a maximum at approx. 325 nm (i.e., 3.82 eV) both in
toluene and dimethylformamide.
The addition of an ethynyl spacer, as in dyad 2, causes a red shift
of the lowest-energy absorption band of about 0.15 eV (i.e., from
325 to 345 nm, approximately).
Absorption properties
In Figure 2 are reported the absorption spectra of 1–7 in two
On the contrary, the absorption spectra of 1 and 3 are almost
superimposable, suggesting that the insertion of one phenyl ring
does not significantly affect the electronic properties of the
corresponding dyad.
solvents
of
different
polarity,
namely
toluene
and
dimethylformamide (DMF). The selection of these two solvents
allows to investigate the photophysical properties of all the donor-
acceptor dyads in media having different dielectric constant, in
which all the samples are completely soluble (i.e., no aggregation
phenomena) and where there is no risk of protonating the
terpyridine unit (i.e., protic solvents and/or solvents with potential
acid impurities were not considered).
However, if an ethynyl spacer is added between the two phenyl
moieties of 3 (i.e., dyad 4), a red shift of the S0 ® S1 electronic
transition is again observed and the absorption profile of 4 turns
out to be comparable to that of 2, despite a different vibronic
progression, a slightly red-shifted onset of the absorption band
and higher molar absorption coefficients.
Notably, the absorption spectra of 4 and 5 are very similar,
confirming that the addition of a phenyl ring on the carbazole side
has negligible influence on both the energy and the profile of the
lowest-energy absorption band of these dyads.
1
2
3
4
5
4
On the other hand, the replacement of the phenyl ring directly
attached to the carbazole side with an ethynyl unit (5 vs. 6) is able
to induce a red-shift of around 0.15 eV, as also observed when
passing from 3 to 2. Accordingly, dyad 6 displays the most red-
shifted CT band of the whole series.
3
2
1
0
Differently from all the other dyads, the absorption spectrum of 7
extends well beyond 400 nm, due to the π-π* transition centered
on the 9,10-disubstituted anthracene moiety of its bridge.[56] As a
consequence, this lowest-energy transition is vibronically
structured and display no solvatochromism. This scenario is well
predicted by TD-DFT calculations which estimate this excitation
to occur at (3.02 ± 0.01) eV, regardless the polarity of the solvent
(see below). On the other hand, for 7, the first CT transition is
calculated at (4.08 ± 0.01) eV above S0 (i.e., S0 ® S3 excitation in
Table S14).
300
320
340
360
380
400
420
440
460
480
Wavelength / nm
5
6
7
5
4
3
2
1
0
TD-DFT vertical excitations and analysis of the CT bands
In Table S8–S14 are reported the lowest singlet vertical
excitations calculated by the TD-DFT approach, both in toluene
and dimethylformamide. Due to the very high multiconfigurational
character of these transitions, in order to get a compact orbital
representation for the electronic transition density matrix, natural
transition orbitals (NTOs) are used.[57] The effect of the solvent
polarity on the computed transitions is negligible, as also
observed in the experimental absorption spectra (Figure 2). The
300
320
340
360
380
400
420
440
460
480
Wavelength / nm
Figure 2. Absorption spectra of 1–7 in toluene (full lines) and
dimethylformamide (dashed lines) at 298 K.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
results obtained by the adopted M06-2X level of theory were also
successfully compared to the ones calculated by the CAM-
B3LYP[58] and wB97XD[59] functionals, which are known to
properly evaluate charge-transfer excitation energies[60] and do
not underestimate the energy of the transitions toward planar
quinoid-like states in biphenyl.[54]
stabilization is confirmed by experimental findings (i.e., 0.20 vs.
0.15 eV, respectively).
Emission properties
The fluorescence spectra of 1–7 are reported in Figure 3 both in
in toluene (full lines) and in dimethylformamide solutions (dashed
lines). In contrast to what observed for absorption spectra, the
emission properties of the dyads are strongly affected by the
polarity of the solvent and very pronounced red-shifts are
generally observed when moving from toluene to the more polar
dimethylformamide solvent (Figure 3). This finding underpins the
CT nature of the emitting states, as already anticipated in the
previous section and in our earlier work.[49]
In general, for dyads 1–6, the first electronic transition always
displays a strong CT character with high oscillator strength, the
S0 ® S2 excitation is localized on the carbazole moiety, and the
next excited state involves a π–π* transition centred on the
terpyridine unit. In particular, this is perfectly fulfilled for dyads
equipped with a relatively short bridge (i.e., 1–4), while it becomes
more complicated for 5 and 6, due to the presence of low-lying π
and π* orbitals centered on the highly conjugated bridge. As a
consequence, intruder CT states centered on the bridging unit are
found in 5 and 6 (Tables S12 and S13).
1
2
3
4
The situation is totally different for dyad 7, in which the two lowest-
energy excitations are localized on the ethynyl-anthracene unit
(see above), while the local excitations on the carbazole moiety
and on the terpyridine are associated to the S0 ® S5 and S0 ® S6
transitions, respectively (Table S14).
Notably, the CT vertical excitation (i.e., S0 ® S1 in 1–6) is not a
through-space transition involving the π orbitals of the carbazole
donor and the π* orbitals of the terpyridine acceptor. As a
consequence, the mutual position of these two terminal moieties
has virtually no effect on the absorption properties of these dyads.
This is the reason why, also in this case, no substantial
differences were noticed when set of analogous conformers are
compared (i.e., differences in excitation energy well below 0.01
eV and associated oscillator strength within ±5%).
350
400
450
500
550
600
650
700
Wavelength / nm
5
6
7
By comparing the electron densities of the ground-state and of the
S1 CT state, according to the method described by Ciofini et
al.,[61,62] it is possible to quantitatively evaluate that the
barycenters of the spatial regions of positive and negative charge
are not centered on the carbazole and terpyridine units, but are
located along the two sides of the bridge (Figure S7). In Table 1
are reported the distance between such barycentres (DCT) for all
the dyads and it can be clearly observed that the DCT value is
always well below the actual distance of the carbazole-donor and
the terpyridine-acceptor groups (see DCT/dDA in Table 1).
Moreover, the degree of charge-separation of the S1 CT state
decreases with the bridge length, confirming that the higher the
π-conjugation of the bridging moiety, the higher the localization of
the CT state on that unit, as already observed for other push-pull
dyads.[61]
350
400
450
500
550
600
650
700
Wavelength / nm
Figure 3. Normalized fluorescence spectra of 1–7 in toluene (full lines) and
dimethylformamide (dashed lines) at 298 K.
In agreement with experimental data, the S0 ® S1 vertical
excitations of dyad 1 and 3 are the most blue-shifted of the series
and are estimated to be almost isoenergetic (Table 1 and Figure
2). The addition of one ethynyl spacer in the bridging unit induces
a red shift of about 0.36 eV in the CT transition, as observed when
passing from 1 (and 3) to 4 (and 5). This finding is also confirmed
by spectral data and is mainly due to LUMO stabilization (Figure
1). Finally, the S0 ® S1 transition computed for dyad 6 is the most
red-shifted of the series and a further stabilization of the
corresponding CT state is observed with respect to 4 and 5. This
In toluene, the emission properties of 3, 4 and 5 are very similar
to that of the simplest dyad 1, which has carbazole moiety directly
attached to the 4’-phenyl-terpyridine one. In fact, all of these
compounds exhibit a relatively unstructured emission band
centred at around 400 nm and display high photoluminescence
quantum yields (PLQYs, ranging between 50 and 70%) with
similar radiative and non-radiative decay constants (i.e., kr ≈ knr
4·108 s–1), as summarized in Table 2.
≈
On the contrary, in polar dimethylformamide media, the emission
spectra of these dyads are strongly red-shifted compared to
toluene and are no longer superimposable to one another (Table
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
2 and Figure 3). In fact, the bathochromic shift of the emission
maximum is more pronounced for the dyads having longer
bridges separating the carbazole and terpyridine units, as clearly
validated by the trend: 1 < 3 < 4 < 5, with emission maxima of 453,
475, 495 and 502 nm, respectively (Table 2).
not affected by the solvent polarity. As a matter of fact, the
anthracene moiety incorporated in the bridge serves as the final
sink of the excitation energy.
The emission properties of all the dyads were also investigated in
butyronitrile glass at 77 K (Figure 4 and Table 2). Under these
conditions, the geometrical relaxation of the excited states is
highly prevented and solvent reorganization effects are drastically
reduced. Therefore, all the emission profiles are similar to those
recorded in the most apolar liquid medium (i.e., toluene), as it can
be inferred by comparing Figure 4 and 3.
Moreover, it is worth noting that the radiative and non-radiative
rate constant are lower in DMF (i.e., kr ≈ knr ≈ 1·108 s–1) since the
singlet lifetimes are substantially longer compared to toluene,
while the PLQYs do not strongly change (Table 2).
Table 2. Luminescence properties and excited state lifetimes of the donor-
acceptor dyads.
1
2
3
4
5
6
7
Toluene, 298 K
DMF, 298 K
PLQY
Bu-CN, 77 K
lmax
[nm]
PLQY
[%]
t
[ns]
lmax
t
[ns]
lmax
t
[nm]
[%]
55.0
0.8
[nm]
[ns]
1
2
3
4
5
6
7
386
62.8
1.6
2.1
453
6.1
380
383
384
403
390
400
2.2
1.2
1.8
1.1
0.8
0.7
2.7
[a]
[a]
375, 415
365, 510
475
392, 400sh 66.0
390, 406sh 50.1
390, 407sh 68.5
1.2
1.0
70.9
44.3
45.6
5.2
3.9
4.0
495
350
400
450
500
550
600
650
700
Wavelength / nm
0.8
502
3.8
[b]
[b]
380
6.3
391, 490sh
475
Figure 4. Normalized fluorescence spectra of 1–7 in butyronitrile glass at 77 K.
462, 483sh 60.1
2.4
57.3
2.6 458, 485
It is also worth mentioning that, at 77 K, the population of
thermally-accessible locally-excited states is nearly suppressed,
leading to the emission only from the lower-lying CT minimum. As
a consequence, the 77 K fluorescence spectra of 2 and 6 display
only the unstructured CT band of the “bright” planar S1 conformer
(see next section) and are largely superimposed with all the other
spectral profiles of 1–6. Not surprisingly, only the spectrum of 7
clearly differs from all the others, but this is simply because its
fluorescence is due to the anthracene unit, as already discussed
above.
[a] Bi-exponential lifetime, see ref.[49] for further details. [b] Bi-exponential
lifetime with two components: 0.8 ns (predominant at shorter wavelengths)
and 0.5 ns (at longer wavelenghts).
A more complicated excited-state scenario is observed in the
case of 2 and 6 (i.e., the only dyads having an ethynyl spacer
directly linked to the carbazole donor moiety), since multiple
emission features are observed in both toluene and
dimethylformamide solutions (Figure 3). Such dual emissions are
attributed to the presence of two excited-state conformers, as we
already pointed out in our earlier work for dyad 2.[49] The rather
structured emission band around 380 nm is attributed to the
fluorescence of a local-excited (LE) state, centered on the
carbazole unit (see below); on the contrary, the emission at longer
wavelengths arises from a CT state, which is particularly
stabilized in polar media (Figure 3). Notably, the fluorescence
quantum yields of 2 and 6 are over 50 times smaller than those of
the other dyads, suggesting the presence of effective non-
radiative deactivation pathways to the ground state, due to the
presence of accessible dark states leading to S1/S0 conical
intersections (see below).
The emission properties were also explored in room-temperature
PMMA matrix, at different concentration of the dyads. In Figure
S8, the solid-state emission spectra of dyad 3 are reported, as a
representative example of the whole series. No substantial
differences in the luminescence profiles are observed, if
compared to toluene solution, and only a minor red shift is found
when increasing the concentration of the dyad (Figure S8).
TD-DFT optimization of the excited states
The nature of the emitting states was further elucidated by the TD-
DFT optimization of the lowest excited state of all the investigated
molecules. Upon S1 relaxation, all the dyads displaying a CT
emission (i.e., 1–6) undergo a substantial planarization, which is
due to the population of a quinoid-like π* orbital mainly localized
on the bridging unit (Tables S15–S21). For the short-bridged
dyads (i.e., 1 and 2), this planarization mainly entails the dihedral
angle between the terpyridine unit and the nearby phenyl moiety
The case of dyad 7 is completely different, as no CT bands are
detected in any solvent and only the fluorescence of the
anthracene unit is recorded in both solvents (lmax ≈ 460 nm, Table
2 and Figure 3). Accordingly, such emission band resembles that
of other phenylethynyl-anthracene derivatives[56] and it is virtually
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
of the bridge (i.e., angle q1 in Tables S1 and S2). On the contrary,
the flattening starts to mainly involve the bridge for dyads with
longer spacers (Tables S3–S6 and S17–20).
D2d orthogonal conformation) lead to molecular planarization and
to the same highly-emissive π–π* S1 minima already described
for the “standard” conformers of 4 (Table S4 and S18).
Such flattening relaxations are able to strongly stabilize the S1 CT
state, resulting in large Stoke shifts, as also found experimentally
(compare Figure 2 and 3). The CT emission of dyad 1, computed
using state-specific solvation,[63,64] is estimated to occur at 384 nm
(in excellent agreement with experimental data, see Table 2), and
it is the most blue-shifted of the series. When the bridge length is
increased, a gradual red-shift of the CT emission is observed (up
to 0.45 eV). Finally, the anthracene-centred S1 minimum of dyad
7 is computed to be 2.45 eV above S0 (i.e., 506 nm).
These theoretical findings are able to rationalize why only dyads
having the ethynyl spacer directly linked to the carbazole moiety
(i.e., 2 and 6) display a significant emission quenching, while the
presence of the ethynyl group in other parts of the dyad bridge
does not cause any appreciable reduction in the PLQYs (Table 2).
TD-DFT S1 optimizations were also carried out in dimethyl-
formamide, but no substantial differences were detected with
respect to toluene, as far as the nature of the emitting state is
concerned. On the contrary, a red-shift of about (0.43 ± 0.11) eV
is estimated for the emission of dyads 1–6, basically due to mere
solvation effects. This is in line with the experimentally observed
red-shift of (0.64 ± 0.07) eV (Table 2).
To get a deeper insight of the far lower PLQYs of 2 and 6 with
respect to the other dyads of the series (Table 2), we considered
that the rotation of the carbazole moiety around the CºC bridging
spacer is practically barrierless (Figure S3), so that the
perpendicular conformers of 2 and 6 are also populated at 298 K
(e.g., the relative population of the perpendicular and co-planar
conformers of 2 is 0.4 vs. 0.6, respectively). When the ethynyl-
carbazole moiety is orthogonal to the rest of the bridge, a slight
increase in the energy of the S0 ® S1 transition is observed, with
a substantial decrease in the associated oscillator strength
(compare Table S9 and S22 for dyad 2 in toluene).[49] Such
transition preserves the same CT nature as in the co-planar
conformers and is basically a π–π* excitation, but the π and the
π* molecular orbitals associated with such excitation are now
perpendicular to each other (Table S22). As a consequence, the
relaxation of such CT state leads to a TS with C2 symmetry and
an imaginary frequency of 278 cm–1 (Figure 5, top), which evolves
toward a low-lying trans-bent π–s* state with broken symmetry
(Figure 5, bottom).
This excited-state scenario, in which both a linear “bright” π–π*
state and a trans-bent “dark” π–s* state are located on the S1
potential energy surface, resembles those already investigated
for diphenylacetylene[52,65] and for other organic molecules with
CºX (X = C or N) groups.[66] However, in the present case, we did
not succeed in finding a minimum for the trans-bent π–s* state of
2 since TD-DFT optimizations failed. In fact, upon geometry
relaxation, this π–s* state rapidly approaches S0 (i.e., the
optimization failed with S1 being only 0.54 eV above S0),
suggesting the presence of a peaked S1/S0 conical intersection,
which could be responsible for the strong luminescence
quenching in this type of dyads.
Figure 5. (Top) Transition state (TS) on the S1 potential-energy surface of the
perpendicular conformer of dyad 2; the displacement vectors associated to its
imaginary frequency are also reported. (Bottom) Last point of the failed
optimization of the π–s* state, obtained by following the imaginary frequency of
the above-mentioned TS (at this geometry, S1 is only 0.54 eV above S0); the
orbitals contributing to such S0 ® S1 excitation are also reported. Calculations
are carried out in toluene at the TD-M06-2X/6-31+G(d) level of theory.
Conclusions
New luminescent organic systems to be used for optoelectronic
applications require careful synthetic design and a thorough
rationalization of structure-property relationships by means of
advanced theoretical tools. In this work, we have designed,
synthesized and examined in detail D-π-A systems where
carbazole (D) and terpyridine (A) moieties are connected through
Indeed, also highly emitting dyads 4 and 5 are equipped with a
bridge having a tolane-like moiety, so that the presence of dark
π–s* states could be potentially feasible upon S0 ® S1 excitation
and responsible for an emission quenching. However, TD-DFT
optimizations of the twisted S1 CT state of 4 (starting from
conformers having the diphenyl-acetylene moiety in the pseudo-
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
modification of a reported method.[40] 2-Acetylpyridine (1.3 mL, 12 mmol)
was added to a stirred suspension of crushed NaOH (480.0 mg, 12 mmol)
in PEG 200 (10 mL) at 0° C. After 30 minutes 4-bromobenzaldehyde (8)
(925.1 mg, 5 mmol) was added and stirring was continued at 0°C for 2 h.
Then a concentrated aqueous NH3 solution (15.0 mL) was added and the
suspension stirred at 100°C for 24 h. The precipitate was isolated by
vacuum filtration and washed with water (50 mL) and ethanol (10 mL) to
give product (9) as a white solid in 73% yield (1.42 g). Spectral data were
consistent with the literature.[40]
9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-9H-carbazole
(10) (184.6 mg, 0.5 mmol), ethanol (63 µL) and K2CO3 (2M in water, 250
µL, 0.5 mmol) were added to a solution of 4'-(4-bromophenyl)-2,2':6',2''-
terpyridine (9) (194.5 mg, 0.5 mmol) in anhydrous THF (1.5 mL) under
nitrogen atmosphere. The solution was degassed with nitrogen and after
10 minutes Pd(PPh3)4 (17.3 mg, 0.015 mmol) was added and the solution
stirred at 70°C overnight. When the reaction was terminated, the solvent
was evaporated, distilled water was added and the resultant solution was
extracted with dichloromethane (3 x 15 mL). The collected organic layer
was dried over anhydrous MgSO4 and then evaporated. The residue was
organic π-conjugated bridges of different length, connectivity and
structure, the latter including ethynyl, phenylene, and anthracenyl
groups (1-7). Effect of solvent polarity have been also examined.
All of the individual subunits in 1-7 are virtually free to rotate along
the molecular backbone at room temperature, except when the
carbazole moiety is linked directly to a phenyl unit. The absorption
spectra of 1-7 exhibit fairly negligible solvatochromic effects and
very minor changes on the addition of phenylene groups directly
attached to the carbazole donor (see e.g., 2 vs. 4). On the
contrary, when the carbazole donor is connected to an ethynyl
group, some red spectral shift is observed (see e.g., 1 vs. 2).
7 is a substantially different case with the characteristic absorption
and emission features of the anthracene moiety, which turns out
to be the lowest energy subunit within the molecular architecture.
1-6 are characterized by charge-transfer solvatochromic
emissions with high PLQY (» 45-70%), except when an ethynyl
group is attached directly to the carbazole unit. In this case, the
emission bands are broadened and much weaker (PLQY » 1-6%),
due to the presence of thermally-accessible trans-bent non
emissive π–s* excited states. DFT calculations have enabled a
full rationalization of the photophysical properties, in relation to
structural and electronic peculiarities of each investigated dyad.
The results presented here provide a deeper insight of structure-
activity relationships of these D-π-A systems, widening the
possibility to rationally design and prepare carbazole-terpyridine
chromophores and luminophores with tailored photophysical
properties, to be potentially used for optoelectronic applications.
purified by alumina column chromatography using
a mixture of
CH2Cl2/MeOH (98:2) to give product (3) as a white solid in 25% yield (69.3
mg). 1H NMR (CD3Cl, 400 MHz) δ 8.86 (s, 2H), 8.78 (d, J = 4.8 Hz, 2H),
8.72 (d, J = 8.0 Hz, 2H), 8.09 (d, J = 8.8 Hz, 2H), 7.96-7.89 (m, 4H), 7.86
(d, J = 8.8 Hz, 2H), 7.69 (d, J = 8.0 Hz, 2H), 7.51 (d, J = 8.0 Hz, 2H), 7.47-
7.37 (m, 4H), 7.32 (dt, Jt = 8.0 Hz, Jd = 1.1 Hz, 2H); 13C NMR (CD3Cl, 100
MHz) δ 156.0 (C), 149.7 (C), 149.0 (CH), 141.4 (C), 140.9 (C), 140.8 (C),
139.4 (C), 137.6 (C), 137.2 (CH), 137.2 (C), 128.5 (CH), 127.9 (CH), 127.6
(CH), 127.4 (CH), 126.0 (CH), 124.0 (CH), 123.5 (C), 121.5 (CH), 120.3
(CH), 120.0 (CH), 118.9 (CH), 109.8 (CH); HRMS (ESI-QTOF) m/z: calcd.
for C39H27N4+: 551.2230; found 551,2224 (M+H)+; ESI-MS: 551 [M+ + 1].
Synthesis
of
9-(4-((4-([2,2':6',2''-terpyridin]-4'-yl)phenyl)ethynyl)
phenyl)-9H-carbazole (4).
9-(4-bromophenyl)-9H-carbazole (12) was prepared according to
a
Experimental Section
modification of a reported method.[50] Carbazole (200 mg, 1.2 mmol),
Cs2CO3 (325.8 mg, 1.2 mmol), CuI (22.8 mg, 0.12 mmol) and LiCl (50.7
mg, 1.2 mmol) were added to a solution of 1-bromo-4-iodobenzene (11)
(372 mg, 1.32 mmol) in DMF (7 mL), and the resulting mixture was stirred
at 150°C for 48 hours. Eventually, water was added and the mixture was
extracted with ethyl acetate (5 x 10 mL). The organic phase was then
washed with brine, dried over Na2SO4 and the solvent evaporated. The
residue was purified by silica gel column chromatography using hexane as
eluent, to give product 12 as a pale-yellow solid in 71% yield (272.9 mg).
Spectral data were consistent with the literature.[50]
Materials. Analytical grade solvents and commercially available reagents
were used as received, unless otherwise stated. 4-Bromobenzaldehyde
(8), 9H-Carbazole-9-(4-phenyl) boronic acid pinacol ester (10), 1-Bromo-
4-iodobenzene
(11),
4-Ethynylbenzaldehyde
(13),
(4-Bromo-
phenylethynyl)trimethylsilane (17), 9,10-Dibromoanthracene (21), 2-acetyl
pyridine, carbazole were commercially available (Sigma Aldrich).
Chromatographic purifications were performed using 70-230 mesh silica
or aluminum oxide. Solvents were dried and distilled according to standard
procedure and stored under nitrogen. Compounds 4’-[p-(Carbazole-9-
yl)phenyl]-2,2’:6’,2’’-terpyridine[43]
ylethynyl)phenyl]-2,2’:6’,2’’-terpyridine[49] (2), used in the present
In a Schlenk flask, 13 (132.2 mg, 1.02 mmol), Pd(PPh3)2Cl2 (59.4 mg, 0.08
mmol) and CuI (16.2 mg, 0.08 mmol) were added to a solution of 12 (272.9
mg, 0.85 mmol) in TEA (7 mL) and toluene (1 mL); the solution was then
stirred under nitrogen atmosphere for 24 hours at 50°C. The progress of
the reaction was monitored using TLC analysis on silica gel petroleum
ether / dichloromethane (2:1). Upon completion, water was added and the
resulting mixture was extracted with dichloromethane (3 x 10 mL). The
combined organic phase was then washed with HCl 1M (1 x 10 mL), brine
and dried over Na2SO4. Solvent was evaporated and the residue was
(1)
and
4’-[4-(9H-Carbazol-9-
investigation, were prepared according to reported methods.
General information. 1H, 13C, NMR spectra were recorded on a Varian
Inova (300 and 600 MHz for 1H) or on a Varian Mercury (400 MHz for 1H)
spectrometer. Chemical shifts (δ) are reported in ppm relative to residual
solvent signals for 1H and 13C NMR (1H NMR: 7.26 ppm for CDCl3; 13C
NMR: 77.0 ppm for CDCl3). 13C NMR spectra were acquired with 1H broad
band decoupled mode. Coupling constants are given in Hz. The high-
resolution mass spectra (HRMS) were obtained with an ESI-QTOF (Agilent
Technologies, model G6520A) instrument and the m/z values are referred
to the monoisotopic mass. ESI-MS analyses were performed by direct
injection of methanol or water-acetonitrile solutions of the compounds
using a WATERS ZQ 4000 mass spectrometer.
purified by silica gel column chromatography using
a mixture of
dichloromethane / petroleum ether (2:8) to give 4-((4-(9H-carbazol-9-
yl)phenyl)ethynyl)benzaldehyde (14) as a pale white solid in 22% yield
(67.6 mg). Spectral data were consistent with the literature.[67]
2-Acetylpyridine (50 µL, 0.42 mmol) was added to a stirred suspension of
crushed NaOH (16.7 mg, 0.42 mmol) in PEG 200 (0.5 mL) at 0° C. After
30 minutes 4-((4-(9H-carbazol-9-yl)phenyl)ethynyl)benzaldehyde (14)
(67.6 mg, 0.21 mmol) was added and stirring was continued at 0°C for 2
h. Then concentrated aqueous NH3 solution (0.7 mL) was added and the
suspension stirred at 100°C for 24 h. Eventually, water was added and the
mixture was extracted with dichloromethane (3 x 10 mL). The organic
Synthesis of 9-(4’-([2,2’:6’,2”-terpyridin]-4’-yl)-[1,1’-biphenyl]-4-yl)-
9H-carbazole (3).
4'-(4-bromophenyl)-2,2':6',2''-terpyridine (9) was prepared according to a
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
phase was then washed with brine, dried over Na2SO4. Solvent was
evaporated and methanol was added. The precipitate solid was collected
by vacuum filtration and washed with water (50 mL) and ethanol (10 mL)
to give product (4) as a white solid in 35% yield (41.2 mg). 1H NMR (CD3Cl,
400 MHz) δ 8.82 (s, 2H), 8.77 (d, J = 4.4 Hz, 2H), 8.72 (d, J = 8.0 Hz, 2H),
8.16 (d, J = 8.0 Hz, 2H), 7.98 (d, J = 8.0 Hz, 2H), 7.93 (t, J = 8.0 Hz, 2H),
7.81 (d, J = 8.0 Hz, 4H), 7.74 (d, J = 8.0 Hz, 2H), 7.61 (d, J = 8.0 Hz, 2H),
7.50-7.38 (m, 6H) 7.31 (t, J = 7.6 Hz, 2H); 13C NMR (CD3Cl, 100 MHz) δ
156.0 (C), 155.9 (C), 149.4 (C), 149.0 (CH), 140.6 (C), 138.4 (C), 137.7
(C), 137.1 (CH), 133.2 (CH), 132.3 (CH), 127.4 (CH), 126.9 (CH), 126.1
(CH), 124.0 (CH), 123.8 (C), 123.6 (C), 122.1 (C), 121.5 (CH), 120.4 (CH),
120.2 (CH), 118.8 (CH), 109.8 (CH), 90.2 (Calk), 90.1 (Calk); HRMS (ESI-
QTOF) m/z: calcd. for C41H27N4+: 575.2231; found 575,2227 (M+H)+; ESI-
MS: 575 [M+ + 1], 597 [M+ + Na], 607 [M+ + MeOH].
dichloromethane and washed with methanol. Product (5) was collected by
filtration of the solution as a white solid in 30% yield (16.2 mg). 1H NMR
(CDCl3, 400 MHz) δ 8.78 (s, 2H), 8.76 (d, J = 4.0 Hz, 2H), 8.70 (d, J = 8.0
Hz, 2H), 8.17 (d, J = 8.0 Hz, 2H), 7.95 (d, J = 8.4 Hz, 2H), 7.90 (dt, J1= 1.6
Hz, J2= 7.6 Hz, 2H), 7.86 (d, J = 8.4 Hz, 2H), 7.74-7.70 (m, 4H), 7.67 (d, J
= 8.4 Hz, 2H), 7.51-7.41 (m, 4H), 7.38 (dd, J1= 4.8 Hz, J2= 7.0 Hz, 2H),
7.31 (t, J = 7.0 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ 156.1 (C), 156.0 (C),
149.4 (C), 149.1 (CH), 140.8 (C), 140.1 (C), 139.3 (C), 138.2 (C), 137.2
(C), 137.0 (CH), 132.3 (CH), 132.2 (CH), 128.4 (CH), 127.4 (CH), 127.3
(CH), 127.0 (CH), 126.0 (CH), 124.0 (C), 123.9 (CH), 123.5 (C), 122.4 (C),
121.4 (CH), 120.3 (CH), 120.0 (CH), 118.7 (CH), 109.8 (CH), 90.7 (Calk),
90.1 (Calk); HRMS (ESI-QTOF) m/z: calcd. for C47H31N4+: 651.2543; found
651,2540 (M+H)+; ESI-MS: 651 [M+ + 1].
Synthesis of 9-((4-((4-([2,2':6',2''-terpyridin]-4'-yl)phenyl)ethynyl)
phenyl)ethynyl)-9H-carbazole (6).
In a Schlenk flask, Pd(PPh3)2Cl2 (40.3 mg, 0.06 mmol) and CuI (11.0 mg,
Synthesis of 9-(4'-((4-([2,2':6',2''-terpyridin]-4'-yl)phenyl)ethynyl)-
[1,1'-biphenyl]-4-yl)-9H-carbazole (5).
4-((4-bromophenyl)ethynyl)benzaldehyde (15) was prepared according to
the modification of a reported method.[68] In a Schlenk flask, 13 (106.5 mg,
0.82 mmol), Pd(PPh3)2Cl2 (10.9 mg, 0.02 mmol) and CuI (15.7 mg, 0.03
mmol) were added to a solution of 1-bromo-4-iodobenzene (11) (276.1 mg,
0.98 mmol) in TEA (8 mL); the solution was then stirred under nitrogen
atmosphere for 24 hours at room temperature. The progress of the
reaction was monitored using TLC analysis on silica gel petroleum ether /
ethyl acetate (9:1). Upon completion, water was added and pH was
adjusted to 5 using HCl 1M. The resulting mixture was extracted with
dichloromethane (3 x 10 mL). The combined organic phase was then
washed with brine and dried over Na2SO4. Solvent was evaporated and
the residue was purified by silica gel column chromatography using a
mixture of ethyl acetate / petroleum ether (2:98) to give product 15 as a
pale-yellow solid in 94% yield (265.2 mg). Spectral data were consistent
with the literature.[68]
2-Acetylpyridine (222 µL, 1.98 mmol) was added to a stirred suspension
of crushed KOH (110.9 mg, 1.98 mmol) in ethanol (5 mL). After 30 minutes
4-((4-bromophenyl)ethynyl)benzaldehyde (15) (281.2 mg, 0.99 mmol) was
added and stirring was continued for 2 h. Then concentrated aqueous NH3
solution (1 mL) was added and the suspension stirred at 100°C for 24 h.
Eventually, water was added and the mixture was extracted with
dichloromethane (3 x 10 mL). The organic phase was then washed with
brine and dried over Na2SO4. Solvent was evaporated and methanol was
added. The precipitate solid was collected by vacuum filtration and washed
with water (10 mL) and methanol (10 mL) to give 4'-(4-((4-
bromophenyl)ethynyl)phenyl)-2,2':6',2''-terpyridine (16) as a brown solid in
15% yield (71.0 mg). 1H NMR (CD3Cl, 300 MHz) δ 8,76 (s, 2H), 8.74 (dq,
Jq = 4.8 Hz, Jd = 0.9 Hz, 2H), 8,68 (dt, Jt = 8.1 Hz, Jd = 1.1 Hz, 2H), 7,94-
7,86 (m, 4H), 7,67 (d, J = 8.4 Hz, 2H), 7,51 (d, J = 8.4 Hz, 2H), 7,43 (d, J
= 8.4 Hz, 2H), 7,40 (ddd, J = 7.5 Hz, J = 4.8 Hz, J = 1.2 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) δ 156.1 (C), 156.0 (C), 149.3 (C), 149.1 (CH), 138.4 (C),
136.9 (CH), 133.1 (CH), 132.1 (CH), 131.7 (CH), 127.3 (CH), 123.9 (CH),
123.6 (C), 122.7 (C), 122.1 (C), 121.4 (CH), 118.6 (CH), 90.2 (Calk), 89.7
(Calk).
0.06
mmol)
were
added
to
a
solution
of
((4-
bromophenyl)ethynyl)trimethylsilane (17) (291.1 mg, 1.15 mmol) in TEA (3
mL) and toluene (1 mL), 13 (164.4 mg, 1.26 mmol); the solution was then
stirred under nitrogen atmosphere for 3 hours at 50°C. The progress of the
reaction was monitored using TLC analysis on silica gel petroleum ether /
ethyl acetate (2:1). Upon completion, water was added and the resulting
mixture was extracted with dichloromethane (3 x 10 mL). The combined
organic phase was then washed with HCl 1M (1 x 10 mL), brine and dried
over Na2SO4. Solvent was evaporated and the residue was purified by
silica gel column chromatography using a mixture of ethyl acetate /
petroleum ether (2:98) to give 4-((4-((trimethylsilyl)ethynyl)phenyl)
ethynyl)benzaldehyde (18) as a pale-yellow solid in 44% yield (150.2 mg).
Spectral data were consistent with the literature.[69]
Compound 18 (117.5 mg, 0.39 mmol) and AgF (49.3 mg, 0.39 mmol) were
dissolved in acetonitrile (10 mL). The reaction flask was wrapped in
aluminium foil and NBS (69.2 mg, 0.39 mmol) was added. The mixture was
stirred overnight at room temperature. Then the solid was filtered off and
washed with acetonitrile (10 mL). The solution was evaporated and the
resulting residue was dissolved in ethylic ether and washed with water (3
x 25 mL). The organic part was dried on anhydrous Na2SO4 and then
evaporated to give product 4-((4-(bromoethynyl)phenyl)ethynyl)
benzaldehyde (19) as a white solid in 78% yield (93.2 mg). 1H NMR (CD3Cl,
300 MHz) δ 10.02 (s, 1H), 8.87 (d, J = 8.4 Hz, 2H), 7.67 (d, J = 8.4 Hz,
2H), 7.49 (d, J = 8.4 Hz, 2H), 7.44 (d, J = 8.4 Hz, 2H).
Carbazole (45.9 mg, 0.27 mmol), K3PO4 (116.5 mg, 0.55 mmol),
CuSO4*5H2O (13.7 mg, 0.06 mmol) and 1,10-phenanthroline (19.8 mg,
0.11 mmol) were added to a solution of 4-((4-(bromoethynyl)phenyl)
ethynyl)benzaldehyde (19) (93.2 mg, 0.30 mmol)in anhydrous THF (7 mL).
The reaction mixture was purged with nitrogen and heated at 70°C for 5
days. The progress of the reaction was monitored using TLC analysis.
Upon completion, the reaction mixture was dried in vacuo and the residue
was dissolved in water and extracted with dichloromethane (3 x 15 mL).
The combined organic phases were dried with anhydrous Na2SO4 and
then evaporated. The crude residue was purified on silica gel flash
chromatography using a mixture of hexane / ethyl acetate (95:5) to give 4-
9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-9H-carbazole
(10) (30.3 mg, 0.08 mmol), ethanol (0.1 ml) and K2CO3 (2M in water, 41
((4-((9H-carbazol-9-yl)ethynyl)phenyl)ethynyl)benzaldehyde (20) as
a
µL, 0.08 mmol) were added to
a
solution of 4'-(4-((4-
pale-yellow solid in 47% yield (55.8 mg). 1H NMR (CD3Cl, 400 MHz) δ
10.04 (s, 1H), 8.06 (d, J = 8.4 Hz, 2H), 7.89 (d, J = 8.4 Hz, 2H), 7.74 (d, J
= 8.4 Hz, 2H), 7.70 (d, J = 8.4 Hz, 2H),7.59-7.50 (m, 2H), 7.45-7.35 (m,
2H), 7.28-7.21 (m, 4H).
2-Acetylpyridine (50 µL, 0.42 mmol) was added to a stirred suspension of
crushed NaOH (17.2 mg, 0.42 mmol) in PEG 200 (1.5 mL) at 0° C. After
30 minutes, 20 (55.8 mg, 0.14 mmol) was added and stirring was
continued at 0°C for 2 h. Then a concentrated aqueous NH3 solution (1.5
mL) was added and the suspension stirred at 100°C for 24 h. After this
time water was added and the mixture was extracted with dichloromethane
(3 x 10 mL). The organic phase was then washed with brine and dried over
bromophenyl)ethynyl)phenyl)-2,2':6',2''-terpyridine (16) (40.0 mg, 0.08
mmol) in THF (0.5 mL) under nitrogen atmosphere,. The solution was
degassed with nitrogen and after 10 minutes Pd(PPh3)4 (2.8 mg, 0.002
mmol) was added and the solution stirred at 70°C overnight. When the
reaction was terminated the solvent was evaporated, distilled water was
added, and the resultant solution was extracted with dichloromethane (3 x
15 mL). The collected organic layer was dried over anhydrous Na2SO4 and
then evaporated. The residue was purified by silica gel column
chromatography using a mixture of dichloromethane / methanol (99:1),
and the resulting fractions were concentrated and the residue dissolved in
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
Na2SO4. Solvent was evaporated and methanol was added. The
precipitate solid was collected by vacuum filtration and washed with water
(50 mL) and ethanol (10 mL) to give product (6) as a pale-yellow solid in
15% yield (12.6 mg). 1H NMR (CD3Cl, 400 MHz) δ 8.77 (s, 2H), 8.75 (dq,
Jq = 4.8 Hz, Jd = 1.0 Hz, 2H), 8.69 (dt, Jt = 8.0 Hz, Jd = 1.0 Hz, 2H), 8.05
(d, J = 8.0 Hz, 2H), 7.94 (d, J = 8.4 Hz, 2H), 7.74 (d, J = 8.0 Hz, 2H), 7.70
(d, J = 8.0 Hz, 4H), 7.61 (d, J = 1.6 Hz, 4H), 7.55 (dt, Jt = 7.6 Hz, Jd = 1.1
Hz, 2H), 7.37 (t, J = 6.8 Hz, 4H); 13C NMR (CD3Cl, 100 MHz) δ 156.2 (C),
156.1 (C), 149.4 (C), 149.2 (CH), 140.3 (C), 138.4 (C), 136.9 (CH), 132.2
(CH), 131.7 (CH), 131.1 (CH), 127.3 (CH), 126.8 (CH), 123.9 (C), 123.8
(CH), 123.7 (C), 123.0 (C), 122.4 (C), 122.2 (CH), 121.4 (CH), 120.4 (CH),
118.7 (CH), 111.3 (CH), 90.8 (Calk), 90.6 (Calk), 80.9 (Calk), 74.7 (Calk);
HRMS (ESI-QTOF) m/z: calcd. for C43H27N4+: 599.2231; found 599,2229
(M+H)+.
400 MHz) δ 8.83 (d , J = 10.8 Hz, 4H), 8.79 (d, J = 4.8 Hz, 2H), 8.72 (d, J
= 8.0 Hz, 2H), 8.22 (d, J = 8.0 Hz, 2H), 8.05 (d, J = 8.0 Hz, 2H), 7.96 (d, J
= 8.0 Hz, 2H), 7.92 (d, J = 8.0 Hz, 4H), 7.84 (t, J = 8.0 Hz, 4H), 7.69 (t, J =
8.4 Hz, 6H), 7.55-7.49 (m, 4H) 7.42-7.34 (m, 4H); 13C NMR (CD3Cl, 100
MHz) δ 156.0 (C), 149.5 (C), 149.1 (CH), 140.8 (C), 138.4 (C), 137.6 (C),
137.5 (C), 137.4 (C), 137.3 (C), 137.1 (CH), 132.7 (CH), 132.4 (C), 132.2
(CH), 130.1 (C), 127.5 (CH), 127.2 (CH), 127.1 (CH), 126.9 (CH), 126.6
(CH), 126.1 (CH), 126.0 (CH), 124.4 (C), 124.0 (CH), 123.6 (C), 121.5
(CH), 120.5 (CH), 120.2 (CH), 118.8 (CH), 117.7 (C), 109.9 (CH), 88.1
(Calk), 77.2 (Calk); HRMS (ESI-QTOF) m/z: calcd. for C55H35N4+: 751.2856;
found 751,2860 (M+H)+.
Computational Details. Density functional theory (DFT) calculations[71]
were carried out using the B.01 revision of the Gaussian 16 program
package,[72] in combination with the M06-2X hybrid meta exchange–
correlation functional,[73] which has been specifically designed to work well
with charge transfer excitations having intermediate spatial overlap.[74] The
Pople 6-31+G(d) basis set was used for all atoms.[75,76] The polarizable
continuum model (PCM) was employed to take in to account solvation
effects (i.e., toluene and dimethylformamide).[77-79] TD-DFT calculations,[80-
Synthesis of 9-(4-(10-((4-([2,2':6',2''-terpyridin]-4'-yl)phenyl)ethynyl)
anthracen-9-yl)phenyl)-9H-carbazole (7).
In a Schlenk flask, 13 (249.6 mg, 1.92 mmol), TEA (0.5 mL), Pd(PPh3)2Cl2
(28.0 mg, 0.04 mmol) and CuI (19.1 mg, 0.10 mmol) were added to a
solution of 9,10-dibromoanthracene (21) (645.2 mg, 1.92 mmol) in DMF
(10 mL) and 1,4-dioxane (4 mL); the solution was then stirred under
nitrogen atmosphere for 24 hours at 80°C. The progress of the reaction
was monitored using TLC analysis on silica gel petroleum ether / ethyl
acetate (9:1). Upon completion, water was added and the resulting mixture
was extracted with dichloromethane (3 x 10 mL). The combined organic
phase was then washed with HCl 1M (1 x 10 mL), brine and dried over
Na2SO4. Solvent was evaporated and the residue was purified by silica gel
column chromatography using a mixture of petroleum ether / ethyl acetate
(95:5) to give product 4-((10-bromoanthracen-9-yl)ethynyl)benzaldehyde
(22) as a yellow solid in 35% yield (253.2 mg). Spectral data were
consistent with the literature.[70]
82]
at the same level of theory used for ground-state optimizations, were
used to compute Franck-Condon excitations and to fully optimize the
lowest-energy excited state (S1) of the dyads. Natural transition orbitals
(NTOs) were used to get a compact orbital representation for the
computed excitations, both at the Franck-Condon regions and for relaxed
excited states.[57] The Ciofini’s charge-transfer diagnostic was adopted to
get a deeper insight on the photophysics of these donor-acceptor
dyads.[61,62] All the molecules were investigated within the C2-symmetry
point group. Analytical frequency calculations were always carried out to
confirm the nature of the stationary points found on the potential energy
surfaces of both S0 and S1. All the pictures of molecular orbitals and
density surfaces were created using GaussView 6.[83]
Compound 10 (242.7 mg, 0.66 mmol), ethanol (65 µL) and K2CO3 (2M in
water, 330 µL, 0.66 mmol) were added to
a solution of 4-((10-
bromoanthracen-9-yl)ethynyl)benzaldehyde (22) (253.2 mg, 0.66 mmol) in
THF (1.5 mL) under nitrogen atmosphere. The solution was degassed with
nitrogen and after 10 minutes Pd(PPh3)4 (19.0 mg, 0.02 mmol) was added
and the solution stirred at 70°C overnight. After the reaction was
terminated the solvent was evaporated, distilled water was added, and the
resultant solution was extracted with dichloromethane (3 x 15 mL). The
collected organic layer was dried over anhydrous Na2SO4 and then
evaporated. The residue was purified by silica gel column chromatography
using a mixture of dichloromethane / petroleum ether (1:9) to give product
4-((10-(4-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)ethynyl)benzaldehyde
(23) as a yellow solid in 38% yield (106.9 mg). 1H NMR (CD3Cl, 300 MHz)
δ 10.10 (s, 1H), 8.77 (d, J = 9 Hz, 2H), 8.22 (d, J = 7.8 Hz, 2H), 7.98 (dd,
J = 8.7 Hz, J = 12.3 Hz, 4H), 7.88-7.81 (m, 4H), 7.72-7.65 (m, 6H), 7.57-
7.48 (m, 4H), 7.36 (dt, Jt = 7.5 Hz, Jd = 1.0 Hz, 2H); 13C NMR (CD3Cl, 100
MHz) δ 191.4 (CHO), 140.8 (C), 138.3 (C), 137.4 (C), 137.3 (C), 135.6 (C),
132.6 (CH), 132.5 (C), 132.1 (CH), 130.0 (C), 129.9 (C), 129.8 (CH), 127.3
(CH), 126.9 (CH), 126.9 (CH), 126.8 (CH), 126.1 (CH), 126.0 (CH), 123.6
(C), 120.5 (CH), 120.2 (CH), 116.9 (C), 109.9 (CH), 100.2 (Calk), 90.6 (Calk).
Spectroscopic Measurements. Spectrophotometric-grade toluene and
dimethylformamide were used as solvent without further purification.
Absorption spectra were recorded with a PerkinElmer Lambda 950
spectrophotometer. For the photoluminescence experiments, the sample
solutions were placed in fluorimetric Suprasil quartz cuvettes (10.00-mm
path length) at concentrations in the range 1–10 µM. The uncorrected
emission spectra were obtained with an Edinburgh Instruments FLS920
spectrometer equipped with
a
Peltier-cooled Hamamatsu R928
photomultiplier tube (PMT) (spectral window: 185−850 nm). An Osram
XBO Xenon arc lamp (450 W) was used as the excitation light source. The
corrected spectra were obtained via a calibration curve, determined using
an Ocean Optics deuterium-halogen calibrated lamp (DH-3plus-CAL-
EXT). The photoluminescence quantum yields (PLQY) in solution were
obtained from the corrected spectra on a wavelength scale (nm) and
measured according to the approach described by Demas and Crosby,[84]
using an air-equilibrated water solution of quinine sulfate in 1 N H2SO4 as
reference (PLQY = 0.546).[85] The emission lifetimes (τ) were measured
through the time-correlated single photon counting (TCSPC) technique
using an HORIBA Jobin Yvon IBH FluoroHub controlling a spectrometer
equipped with a pulsed NanoLED (λexc = 331 nm; 200 ps time resolution
2-Acetylpyridine (66 µL, 0.59 mmol) was added to a stirred suspension of
crushed NaOH (24.0 mg, 0.59 mmol) in PEG 200 (1.0 mL) at 0° C. After
30 minutes, compound 23 (106.9 mg, 0.20 mmol) was added and stirring
was continued at 0°C for 2 h. Then concentrated aqueous NH3 solution (3
mL) was added and the suspension stirred at 100°C for 24 h. After this
time water was added and the mixture was extracted with dichloromethane
(3 x 10 mL). The organic phase was then washed with brine, dried over
Na2SO4. Solvent was evaporated and methanol was added. The
precipitate solid was collected by vacuum filtration and washed with water
(50 mL) and ethanol (10 mL). Then it was purified by silica gel column
chromatography using a mixture of dichloromethane / methanol (95:5) to
give product (7) as a yellow solid in 15% yield (22.3 mg). 1H NMR (CD3Cl,
after reconvolution) as the excitation source and
a red-sensitive
Hamamatsu R-3237−01 PMT as the detector (spectral window: 185−850
nm). The analysis of the luminescence decay profiles was accomplished
with the DAS6 Decay Analysis Software provided by the manufacturer, and
the quality of the fit was assessed with the χ2 value close to 1 and with the
residuals regularly distributed along the time axis. To record the 77 K
luminescence spectra, samples were put in quartz tubes (2 mm inner
diameter) and inserted into a special quartz Dewar flask filled with liquid
nitrogen. Experimental uncertainties are estimated to be ≈ 8% for lifetime
determinations, ≈ 20% for PLQYs, ± 2 and ± 5nm for absorption and
emission peaks.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
[34] L. Flamigni, J.-P. Collin, J.-P. Sauvage, Acc. Chem. Res. 2008, 41, 857-
871.
Acknowledgements
[35] S. Encinas, L. Flamigni, F. Barigelletti, E. C. Constable, C. E. Housecroft,
E. R. Schofield, E. Figgemeier, D. Fenske, M. Neuburger, J. G. Vos, M.
Zehnder, Chem.-Eur. J. 2002, 8, 137-150.
The financial support by CNR (PHEEL) is gratefully
acknowledged.
[36] D. J. Cardenas, J. P. Collin, P. Gavina, J. P. Sauvage, A. De Cian, J.
Fischer, N. Armaroli, L. Flamigni, V. Vicinelli, V. Balzani, J. Am. Chem.
Soc. 1999, 121, 5481-5488.
Keywords: carbazole • donor-acceptor dyads • fluorescence • π-conjugated
systems • terpyridine
[37] J. Palion-Gazda, B. Machura, T. Klemens, A. Szlapa-Kula, S. Krompiec,
M. Siwy, H. Janeczek, E. Schab-Balcerzak, J. Grzelak, S. Maćkowski,
Dyes Pigm. 2019, 166, 283-300.
[1]
[2]
[3]
L. Beverina, G. A. Pagani, Acc. Chem. Res. 2014, 47, 319-329.
H. Bohra, M. Wang, J. Mater. Chem. A 2017, 5, 11550-11571.
J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, B. Z. Tang, Chem.
Rev. 2015, 115, 11718-11940.
[38] M. Toshiki, A. Koji, Curr. Org. Chem. 2007, 11, 195-211.
[39] W. Goodall, K. Wild, K. J. Arm, J. A. G. Williams, J. Chem. Soc., Perkin
Trans. 2 2002, 1669-1681.
[4]
Z. Yang, Z. Mao, Z. Xie, Y. Zhang, S. Liu, J. Zhao, J. Xu, Z. Chi, M. P.
Aldred, Chem. Soc. Rev. 2017, 46, 915-1016.
[40] A. Winter, A. M. J. van den Berg, R. Hoogenboom, G. Kickelbick, U. S.
Schubert, Synthesis 2006, 2873-2878.
[5]
[6]
Z. Liu, G. Zhang, D. Zhang, Chem.-Eur. J. 2016, 22, 462-471.
J. Borges-González, C. J. Kousseff, C. B. Nielsen, J. Mater. Chem. C
2019, 7, 1111-1130.
[41] J. Wang, G. S. Hanan, Synlett 2005, 1251-1254.
[42] G. Accorsi, N. Armaroli, F. Cardinali, D. Wang, Y. Zheng, J. Alloys
Compd. 2009, 485, 119-123.
[7]
[8]
[9]
D. Kong, Z. Xiao, Y. Gao, X. Zhang, R. Guo, X. Huang, X. Li, L. Zhi,
Mater. Sci. Eng. R Rep. 2019, 137, 1-37.
[43] X. Chen, Q. Zhou, Y. Cheng, Y. Geng, D. Ma, Z. Xie, L. Wang, J. Lumin.
2007, 126, 81-90.
K. Brunner, A. van Dijken, H. Börner, J. J. A. M. Bastiaansen, N. M. M.
Kiggen, B. M. W. Langeveld, J. Am. Chem. Soc. 2004, 126, 6035-6042.
B. Souharce, C. J. Kudla, M. Forster, J. Steiger, R. Anselmann, H. Thiem,
U. Scherf, Macromol. Rapid Commun. 2009, 30, 1258-1262.
[44] T. He, Y. Gao, R. Chen, L. Ma, D. Rajwar, Y. Wang, A. C. Grimsdale, H.
Sun, Macromolecules 2014, 47, 1316-1324.
[45] S.-H. Hwang, P. Wang, C. N. Moorefield, L. A. Godinez, J. Manriquez, E.
Bustos, G. R. Newkome, Chem. Commun. 2005, 4672-4674.
[46] C. Kong, M. Peng, H. Shen, Y. Wang, Q. Zhang, H. Wang, J. Zhang, H.
Zhou, J. Yang, J. Wu, Y. Tian, Dyes Pigm. 2015, 120, 328-334.
[47] Q. Liu, X. Yang, M. Wang, D. Liu, M. Chen, T. Wu, Z. Jiang, P. Wang,
Tetrahedron 2019, 75, 2400-2405.
[10] Z.-S. Wang, N. Koumura, Y. Cui, M. Takahashi, H. Sekiguchi, A. Mori, T.
Kubo, A. Furube, K. Hara, Chem. Mater. 2008, 20, 3993-4003.
[11] C. B. Nielsen, S. Holliday, H.-Y. Chen, S. J. Cryer, I. McCulloch, Acc.
Chem. Res. 2015, 48, 2803-2812.
[12] N. Manfredi, B. Cecconi, A. Abbotto, Eur. J. Org. Chem. 2014, 2014,
7069-7086.
[48] A. Maron, A. Szlapa, T. Klemens, S. Kula, B. Machura, S. Krompiec, J.
G. Malecki, A. Switlicka-Olszewska, K. Erfurt, A. Chrobok, Org. Biomol.
Chem. 2016, 14, 3793-3808.
[13] M. Magliulo, K. Manoli, E. Macchia, G. Palazzo, L. Torsi, Adv. Mater.
2015, 27, 7528-7551.
[49] A. Baschieri, L. Sambri, I. Gualandi, D. Tonelli, F. Monti, A. D. Esposti,
N. Armaroli, RSC Adv. 2013, 3, 6507-6517.
[14] C. Zhang, P. Chen, W. Hu, Chem. Soc. Rev. 2015, 44, 2087-2107.
[15] Z. Yang, A. Sharma, J. Qi, X. Peng, D. Y. Lee, R. Hu, D. Lin, J. Qu, J. S.
Kim, Chem. Soc. Rev. 2016, 45, 4651-4667.
[50] J. H. Cho, Y. S. Ryu, S. H. Oh, J. K. Kwon, E. K. Yum, Bull. Korean Chem.
Soc. 2011, 32, 2461-2464.
[16] Y. Ha, H.-K. Choi, Chem.-Biol. Interact. 2016, 248, 36-51.
[17] F. Bures, RSC Adv. 2014, 4, 58826-58851.
[51] Y. Hirata, Bull. Chem. Soc. Jpn. 1999, 72, 1647-1664.
[52] J. Saltiel, V. K. Kumar, J. Phys. Chem. A 2012, 116, 10548-10558.
[53] H. Suzuki, Bull. Chem. Soc. Jpn. 1959, 32, 1340-1350.
[54] R. Fukuda, M. Ehara, Phys. Chem. Chem. Phys. 2013, 15, 17426-17434.
[55] K. Okuyama, T. Hasegawa, M. Ito, N. Mikami, J. Phys. Chem. 1984, 88,
1711-1716.
[18] S. V. Fedoseev, M. Y. Belikov, M. Y. Ievlev, O. V. Ershov, V. A. Tafeenko,
Dyes Pigm. 2019, 165, 451-457.
[19] E. Horak, M. Robić, A. Šimanović, V. Mandić, R. Vianello, M. Hranjec, I.
M. Steinberg, Dyes Pigm. 2019, 162, 688-696.
[20] M. Kivala, F. Diederich, Acc. Chem. Res. 2009, 42, 235-248.
[21] R. Li, Z.-L. Gong, J.-H. Tang, M.-J. Sun, J.-Y. Shao, Y.-W. Zhong, J. Yao,
Sci. China Chem. 2018, 61, 545-556.
[56] M. Mitsui, Y. Kawano, R. Takahashi, H. Fukui, RSC Adv. 2012, 2, 9921-
9931.
[57] R. L. Martin, J. Chem. Phys. 2003, 118, 4775-4777.
[58] T. Yanai, D. P. Tew, N. C. Handy, Chem. Phys. Lett. 2004, 393, 51-57.
[59] J. D. Chai, M. Head-Gordon, Phys. Chem. Chem. Phys. 2008, 10, 6615-
6620.
[22] E. Ortega, J. C. Bernède, A. M. R. Ramírez, G. Louarn, F. R. Díaz, L.
Cattin, M. A. del Valle, J. Mol. Model. 2019, 25, 81.
[23] J. Tydlitát, S. Achelle, J. Rodríguez-López, O. Pytela, T. Mikýsek, N.
Cabon, F. Robin-le Guen, D. Miklík, Z. Růžičková, F. Bureš, Dyes Pigm.
2017, 146, 467-478.
[60] A. Dreuw, M. Head-Gordon, J. Am. Chem. Soc. 2004, 126, 4007-4016.
[61] T. Le Bahers, C. Adamo, I. Ciofini, J. Chem. Theory Comput. 2011, 7,
2498-2506.
[24] Z. R. Grabowski, K. Rotkiewicz, W. Rettig, Chem. Rev. 2003, 103, 3899-
4032.
[62] C. Adamo, T. Le Bahers, M. Savarese, L. Wilbraham, G. García, R.
Fukuda, M. Ehara, N. Rega, I. Ciofini, Coord. Chem. Rev. 2015, 304-305,
166-178.
[25] S. M. Bonesi, R. Erra-Balsells, J. Lumin. 2001, 93, 51-74.
[26] A. R. Katritzky, G. W. Rewcastle, L. M. Vazquez de Miguel, J. Org. Chem.
1988, 53, 794-799.
[63] R. Improta, V. Barone, G. Scalmani, M. J. Frisch, J. Chem. Phys. 2006,
125, 054103.
[27] S. E. Creutz, K. J. Lotito, G. C. Fu, J. C. Peters, Science 2012, 338, 647-
651.
[64] R. Improta, G. Scalmani, M. J. Frisch, V. Barone, J. Chem. Phys. 2007,
127, 074504.
[28] S. Ameen, S. B. Lee, S. C. Yoon, J. Lee, C. Lee, Dyes Pigm. 2016, 124,
35-44.
[65] M. Z. Zgierski, E. C. Lim, Chem. Phys. Lett. 2004, 387, 352-355.
[66] M. Z. Zgierski, T. Fujiwara, E. C. Lim, Acc. Chem. Res. 2010, 43, 506-
517.
[29] T. Zhou, B. Li, B. Wang, Chem. Commun. 2017, 53, 6343-6346.
[30] J. Li, A. C. Grimsdale, Chem. Soc. Rev. 2010, 39, 2399-2410.
[31] N. Blouin, M. Leclerc, Acc. Chem. Res. 2008, 41, 1110-1119.
[32] A. K. Pal, G. S. Hanan, Chem. Soc. Rev. 2014, 43, 6184-6197.
[33] A. Arrigo, A. Santoro, F. Puntoriero, P. P. Lainé, S. Campagna, Coord.
Chem. Rev. 2015, 304, 109-116.
[67] K. Y. Chai, D. H. Lee, H. M. Hwang, Korea, 2014.
[68] A. Z. Muresan, P. Thamyongkit, J. R. Diers, D. Holten, J. S. Lindsey, D.
F. Bocian, The Journal of Organic Chemistry 2008, 73, 6947-6959.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
[69] L. Rigamonti, B. Babgi, M. P. Cifuentes, R. L. Roberts, S. Petrie, R.
Stranger, S. Righetto, A. Teshome, I. Asselberghs, K. Clays, M. G.
Humphrey, Inorg. Chem. 2009, 48, 3562-3572.
[70] R. Flamini, I. Tomasi, A. Marrocchi, B. Carlotti, A. Spalletti, J. Photochem.
Photobiol. A 2011, 223, 140-148.
[71] R. G. Parr, W. Yang, Density Functional Theory of Atoms and Molecules,
Oxford University Press, Oxford, U.K., 1989.
[72] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, G. Scalmani, V. Barone, G. A. Petersson, H. Nakatsuji,
X. Li, M. Caricato, A. V. Marenich, J. Bloino, B. G. Janesko, R. Gomperts,
B. Mennucci, H. P. Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L.
Sonnenberg, Williams, F. Ding, F. Lipparini, F. Egidi, J. Goings, B. Peng,
A. Petrone, T. Henderson, D. Ranasinghe, V. G. Zakrzewski, J. Gao, N.
Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, K. Throssell, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M.
J. Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N. Staroverov, T.
A. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. P. Rendell, J.
C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, J. M. Millam, M. Klene, C.
Adamo, R. Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O.
Farkas, J. B. Foresman, D. J. Fox, Gaussian Inc., Wallingford, CT, USA,
2016.
[73] Y. Zhao, D. G. Truhlar, Theor. Chem. Acc. 2008, 120, 215-241.
[74] R. Li, J. Zheng, D. G. Truhlar, Phys. Chem. Chem. Phys. 2010, 12,
12697-12701.
[75] G. A. Petersson, A. Bennett, T. G. Tensfeldt, M. A. Al‐Laham, W. A.
Shirley, J. Mantzaris, J. Chem. Phys. 1988, 89, 2193-2218.
[76] G. A. Petersson, M. A. Al‐Laham, J. Chem. Phys. 1991, 94, 6081-6090.
[77] J. Tomasi, M. Persico, Chem. Rev. 1994, 94, 2027-2094.
[78] J. Tomasi, B. Mennucci, R. Cammi, Chem. Rev. 2005, 105, 2999-3093.
[79] C. J. Cramer, D. G. Truhlar, Continuum Solvation Models, in Solvent
Effects and Chemical Reactivity Vol. 17 (Eds.: O. Tapia, J. Bertrán),
Springer Netherlands, 2002, pp. 1-80.
[80] R. E. Stratmann, G. E. Scuseria, M. J. Frisch, J. Chem. Phys. 1998, 109,
8218-8224.
[81] M. E. Casida, C. Jamorski, K. C. Casida, D. R. Salahub, J. Chem. Phys.
1998, 108, 4439-4449.
[82] R. Bauernschmitt, R. Ahlrichs, Chem. Phys. Lett. 1996, 256, 454-464.
[83] R. Dennington, T. A. Keith, J. M. Millam, Semichem Inc., Shawnee
Mission, KS, USA, 2016.
[84] G. A. Crosby, J. N. Demas, J. Phys. Chem. 1971, 75, 991-1024.
[85] S. R. Meech, D. Phillips, J. Photochem. 1983, 23, 193-217.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201900213
ChemPlusChem
FULL PAPER
Table of Contents
Layout 1
FULL PAPER
D-π-A systems. Seven
Carbazole-Terpyridine π-
bridged donor-acceptor
systems have been
Elia Matteucci, Andrea
Baschieri,* Letizia Sambri,*
Filippo Monti,* Eleonora
Pavoni, Elisa Bandini, Nicola
Armaroli
synthesized and
characterized. With the help
of DFT calculations, the
correlation between the
specific structure of the bridge
and the photophysical
properties of the whole
system has been fully
elucidated.
Page No. – Page No.
Carbazole-terpyridine donor-
acceptor systems with rigid
π-conjugated bridges
This article is protected by copyright. All rights reserved.