Intermolecular interactions-photophysical properties relationships in phenanthrene-9,10-dicarbonitrile assemblies

Article abstract of DOI:10.1016/j.molstruc.2019.07.036

Phenanthrene-9,10-dicarbonitriles show various luminescence behaviour in solution and in the solid state. Aggregation patterns of phenanthrene-9,10-dicarbonitriles govern their luminescent properties in the solid state. Single crystal structures of phenan

Full text of DOI:10.1016/j.molstruc.2019.07.036

Journal of Molecular Structure 1199 (2020) 126789
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Intermolecular interactions-photophysical properties relationships in
phenanthrene-9,10-dicarbonitrile assemblies
,
, *
Anastasiia M. Afanasenko a b, Alexander S. Novikov a, Tatiana G. Chulkova a
,
Yakov M. Grigoriev a, Ilya E. Kolesnikov a, Stanislav I. Selivanov a, Galina L. Starova a,
Andrey A. Zolotarev a, Anatoly N. Vereshchagin c, Michail N. Elinson c
a Saint Petersburg State University, 7/9 Universitetskaya Nab., Saint Petersburg, 199034, Russia
b Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, the Netherlands
c N. D. Zelinsky Institute of Organic Chemistry, 47 Leninsky Prospect, Moscow, 119991, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Phenanthrene-9,10-dicarbonitriles show various luminescence behaviour in solution and in the solid
state. Aggregation patterns of phenanthrene-9,10-dicarbonitriles govern their luminescent properties in
the solid state. Single crystal structures of phenanthrene-9,10-dicarbonitriles showed head-to-tail
Received 26 May 2019
Received in revised form
1 July 2019
Accepted 7 July 2019
Available online 30 August 2019
intraplane (or quasi-intraplane) intermolecular interactions and
p-stacking patterns with eclipsing of
molecules when viewed orthogonal to the stacking plane. The -stacking interactions were detected in
p
the X-ray structures of phenanthrene-9,10-dicarbonitriles and studied by DFT calculations at the M06
e2X/6e311þþG(d,p) level of theory and topological analysis of the electron density distribution within
Keywords:
Phenanthrene-9,10-dicarbonitriles
DFT studies
the framework of QTAIM method. The estimated strength of the C/C contacts responsible for the
p-
stacking interactions is 0.6e1.1 kcal/mol. The orientation of molecules in crystals depends on the sub-
stituents in phenanthrene-9,10-dicarbonitriles. Distinct molecular orientation and packing arrangements
in crystalline phenanthrene-9,10-dicarbonitriles ensured perturbed electronic communication among
the nearest and non-nearest molecules through an interplay of excimer and dipole couplings. As a result,
the intermolecular interactions govern the solid state luminescence of molecules.
© 2019 Elsevier B.V. All rights reserved.
Fluorescence
p-Stacking
1. Introduction
the opposite luminescence behaviour [6e15]. Congruently, in-
vestigations into the structureepackingeoptical property rela-
Luminescent compounds attract great attention as objects for
their potential applications in various research fields, including
organic light-emitting diodes (OLEDs), luminescent sensors, sur-
face coatings, inks, etc. [1e3] The aggregation patterns of lumi-
nescent compounds can influence their absorption and emission
properties. It is known, that photophysical properties of fused ar-
omatic compounds such as anthracene, pyrene, and benzocou-
marins depend greatly on their aggregation state. For example,
anthracene, pyrene, and methyl 8-(dimethylamino)-2-oxo-2H-
benzo[g]chromene-3-carboxylate possess strong fluorescence in
solution, but have poor emission in the solid state [4e6]. However,
cyanine-based dyes, perylene diimides, methyl 9-(dimethylamino)-
3-oxo-3H-benzo[f]chromene-2-carboxylate and porphyrins show
tionship in molecular aggregates have received much attention
from theoretical and experimental views. Most applications of
Frenkel exciton theory in molecular aggregate photophysics
employ the point-dipole approximation for the Coulomb coupling
between two neighbouring molecules,
À
Á
m2 1 ꢀ 3 cos2
q
JC
¼
4p
εR3
where
m
is the dipole moment corresponding to the S0 / S1
transition of two neighbouring molecules, respectively, R is the
displacement vector connecting the molecular mass centres, and ε
is the dielectric constant of the medium. The case for parallel
transition dipole moments, which characterizes packing geome-
tries with one molecule per unit cell, is depicted in Fig. 1.
Kasha initially identified two aggregation species based on the
relative orientation of molecules, which is determined by the angle
* Corresponding author.
E-mail address: t.chulkova@spbu.ru (T.G. Chulkova).
https://doi.org/10.1016/j.molstruc.2019.07.036
0022-2860/© 2019 Elsevier B.V. All rights reserved.

2
A.M. Afanasenko et al. / Journal of Molecular Structure 1199 (2020) 126789
Fig. 1. Relative orientation of transition dipole moments defining a J-aggregate (q < qM) and H-aggregate (qM < q < p/2) under the point dipole approximation. The magic angle qM
is 54.7ꢁ. Energy level diagrams for J- and H-aggregate dimers. Transitions from the ground state are allowed only to the state with in-phase transition dipole moments, which lie at
the bottom and top of the band in J- and H-aggregates, respectively. The symmetric splitting observed in both cases is 2jJCj.
q
in Fig. 1. In what is known as J-aggregates, the dipoles maintain a
Also, cofacial molecular assemblies with efficient p-orbital
“head-to-tail” orientation where
q
is less than the so-called “magic
overlap can lead to excited dimers or multimers [16e18]. Excimers
are undesired due to dramatic fluorescence quenching. As a result,
the fluorescence emission can be tuned, depending on the extent of
angle” qM ¼ 54.7ꢁ, the angle for which JC is zero. In this case, the
Coulomb coupling is negative (JC < 0). Conversely, H-aggregates
maintain a “side-by-side” orientation (qM
<
q
ꢂ
p
/2) leading to a
p -orbital overlap between the molecules [18e20]. The exact
positive Coulomb coupling (JC > 0). As shown by Kasha and co-
workers, the sign of the Coulomb coupling has a direct bearing
on the photophysical response. This is depicted in Fig. 1 for the
simplest case of a molecular dimer, where the Coulomb coupling JC
leads to the formation of two delocalized excited states split by
2jJCj. The two states consist of in- and out-of-phase linear combi-
nations of the two local excited states, je1g2〉 and jg1e2〉. The in-
phase or symmetric state, shifted by JC, is characterized by an
enhanced transition dipole moment relative to the monomer (by
√2), whereas the out-of-phase state, shifted by ꢀJC, is optically
dark due to a cancellation of the transition dipole moments. Hence,
in J-aggregates, the negative coupling (JC < 0) results in the
(absorbing) symmetric state having lower energy than the anti-
symmetric state, whereas in H-aggregates with JC > 0, the ordering
is reversed. The Coulomb-induced energetic shifts lead to predict-
able changes in the absorption spectrum: in J-aggregates, the main
absorption peak is red-shifted compared to the monomer, whereas
in H-aggregates, the absorption peak is blue-shifted.
Employing the exciton theory of Davydov, McRae and Kasha
surmised that in certain aggregates, which are known as H-ag-
gregates, the Coulomb coupling is positive, resulting in a band of
singlet states (excitons) in which the highest energy state con-
sumes all of the oscillator strength. Since in many cases fluores-
cence proceeds from the lowest excited state (Kasha's rule),
fluorescence is suppressed [3].
In contrast, when the Coulomb coupling is negative, as in J-ag-
gregates or Scheibe aggregates, the oscillator strength is focused in
the lowest energy exciton, and no suppression of fluorescence is
expected.
impact of short- (orbital overlap mediated excimer) and long-range
(Coulomb/dipole) couplings on the optical properties of a molec-
ular ensemble demands special attention [21].
In this work, we studied photophysical properties of substituted
9,10-dicyanophenanthrenes in solution and in the solid state. This
study demonstrates the potential of molecular shape control for the
development of solid-state luminescent materials.
2. Experimental
2.1. Materials and methods
All solvents were dried and purified by conventional methods
and were freshly distilled under argon shortly before use. Other
reagents were used without further purification. FTIR spectra were
recorded on Shimadzu FTIR-8400S (4000ꢀ400 cmꢀ1
)
and
IRAffinity-1 (4000ꢀ350 cmꢀ1) spectrometers using KBr pellets. 1H
and 13C NMR measurements were performed on a Bruker-DPX 400
instrument at ambient temperature. Electrospray ionization mass
spectra were obtained on a Bruker micrOTOF spectrometer equip-
ped with electrospray ionization (ESI) source using MeOH as the
solvent. The instrument was operated in both positive and negative
ion modes using a m/z range of 50e3000. The capillary voltage of
the ion source was set at ꢀ4500 V (ESIþ ꢀMS) and the capillary exit
at (70e150) V. The nebulizer gas flow was 0.4 bar and drying gas
flow 4.0 L/min. The absorption spectra were recorded on a Perki-
neElmer precision spectrophotometer Lambda 1050. The emission
spectra, excitation spectra, measurements of the lifetimes of
excited states were measured on a modular spectrofluorimeter

A.M. Afanasenko et al. / Journal of Molecular Structure 1199 (2020) 126789
3
Fluorolog-3 (Horiba Jobin Yvon). Fluorescence lifetime measure-
ments are based on time-correlated single photon counting
(TCSPC). The device also includes an integrating sphere Quanta-4
with fiber optics which enables direct measurement of quantum
yields of luminescence.
2.2.3. 3,6-Difluorophenanthrene-9,10-dicarbonitrile (2)
Yield: 54 mg (36%), beige powder, mp ¼ 290e291 ꢁC (291 ꢁC
from Ref. [27]). 1H NMR (400 MHz, CDCl3)
d, ppm: 8.46 (dd,
4
3
3JHF ¼ 9.60 Hz, JHH ¼ 2.0 Hz, 2H, H4, H5), 8.27 (dd, JHH ¼ 8.2 Hz,
3
3
4JHF ¼ 2.4 Hz, 2H, H1, H8), 7.69 (ddd, JHF ¼ 9.60 Hz, JHH ¼ 8.2 Hz,
4JHH ¼ 2.0 Hz, 2H, H2, H7). 1H NMR (400 MHz, DMSO‑d6)
d, ppm:
3
4
8.94 (dd, JHF ¼ 11.2 Hz, JHH ¼ 2.4 Hz, 2H, H4, H5), 8.35 (dd,
3JHH ¼ 8.4 Hz, JHF ¼ 2.4 Hz, 2H, H1, H8), 7.93 (ddd, JHF ¼ 11.2 Hz,
4
3
2.2. Synthetic procedures
3JHH ¼ 8.4 Hz, JHH ¼ 2.4 Hz, 2H, H2, H7). 13C{1H} NMR (100 MHz,
4
1
CDCl3)
d,
ppm: 164.0 (d, JCF ¼ 254.0 Hz, C3, C6), 132.8 (d,
Phenanthrene-9,10-dicarbonitriles (1e7) were synthesized
starting from commercially available phenylacetonitriles by two
step reaction. The synthetic scheme is shown in Fig. 2. Starting from
a series of arylacetonitriles, following Linstead's procedure [22,23],
the nitriles of 2,3-diarylbutenedioic acids (where aryl is phenyl, 4-
fluorophenyl, 4-methylphenyl, and 4-methoxyphenyl) were pro-
duced (See the Supporting Information). 2,3-Di(4-chlorophenyl)
fumaronitrile, 2,3-di(3,4-dichlorophenyl)fumaronitrile, and 2,3-
di(4-bromophenyl)fumaronitrile were produced electrochemically
from the appropriate arylacetonitriles (See the Supporting Infor-
mation) [24]. 2,3-Diarylbutenedioic acid dinitriles were converted
to the corresponding 9,10-dicyanophenanthrenes 1e7 under UV-
irradiation of chloroform solution at the presence of small
amounts of iodine [25].
3JCF ¼ 13.0 Hz), 130.3 (d, 3JCF ¼ 10.0 Hz), 124.8, 119.4 (d,
2JCF ¼ 24.0 Hz), 115.7, 114.7, 109.2 (d, 2JCF ¼ 23.0 Hz). HRMS (ESIþ), m/
z: 265.0572 [MþH]þ, 287.0391 [MþNa]þ. C16H7N2F2 calcd. m/z:
265.0577. C16H6N2F2Na calcd. m/z: 287.0397. IR spectrum (KBr,
selected bands, cmꢀ1): 3096 m (Сsp2ꢀH), 2230 s
n(C^N), 1620,
1524 s n
(СCAr). 1H NMR (400 MHz, DMSO‑d6) and IR (KBr) spectra
are comparable with those reported by E. M. Maya et al. [27].
2.2.4. 3,6-Dichlorophenanthrene-9,10-dicarbonitrile (3)
Yield: 47 mg (32%), beige powder, mp ¼ 243e244 ꢁC. 1H NMR
(400 MHz, CDCl3)
d
, ppm: 8.85 (d, 4J ¼ 2.0 Hz, 2H, H4, H5), 8.29 (d,
3J ¼ 8.0 Hz, 2H, H1, H8), 8.02 (dd, 3J ¼ 8.0 Hz, 4J ¼ 2.0 Hz, 2H, H2, H7).
13C{1H} NMR (100 MHz, CDCl3)
d, ppm: 133.3, 132.7, 131.3, 128.8,
126.8, 126.4, 116.7, 114.4. HRMS (ESIþ), m/z: 318.9800 [MþNa]þ.
C
16H6N2Cl2Na calcd. m/z: 318.9806. IR spectrum (KBr, selected
2.2.1. General procedure for the synthesis of phenanthrene-9,10-
dicarbonitriles (1e7)
bands, cmꢀ1): 3090 w
(СCAr).
n
(Сsp2ꢀH), 2220 m
n(C^N), 1599, 1489 s
n
A chloroform (70 mL) solution of 2,3-diarylbutenedioic acid
dinitrile (150 mg) and iodine (several crystals) was irradiated in a
quartz flask with a 450 W high pressure mercury lamp for 8 h. After
the solvent was evaporated, the residual product was recrystallized
from ethanol.
2.2.5. 2,3,5,6-Tetrachlorophenanthrene-9,10-dicarbonitrile (4)
Along with 4, 2,3,6,7-tetrachlorophenanthrene-9,10-
dicarbonitrile (4′) was obtained as a by-product. Pure compound
4 was prepared by recrystallization from chloroform/acetone sol-
vent mixture. Yield: 57 mg (38%), white powder. 1H NMR (400 MHz,
CDCl3)
d
, ppm: 10.12 (s, 1H), 8.54 (s, 1H), 8.35 (d, 3J ¼ 8.8 Hz, 1 H),
2.2.2. Phenanthrene-9,10-dicarbonitrile (1)
Yield: 65 mg (44%), beige powder, mp ¼ 290e291 ꢁC
8.02 (d, 3J ¼ 8.8 Hz, 1H). 13C{1H} NMR (100 MHz, CDCl3)
d, ppm: IR
(mp ¼ 290e291 ꢁC [26]). 1H NMR (400 MHz, CDCl3)
d, ppm: 8.79
spectrum (KBr, selected bands, cmꢀ1): 3146 w
n
(Сsp2ꢀH), 2232 m
(dd, 3J ¼ 8.4 Hz, 4J ¼ 1.2 Hz, 2H, H4, H5), 8.42 (dd, 3J ¼ 8.4 Hz,
4J ¼ 1.2 Hz, 2H, H1, H8), 7.96 (ddd, 3J ¼ 8.4 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.2 Hz,
2H, H3, H6), 7.82 (ddd, 3J ¼ 8.4 Hz, 3J ¼ 7.2 Hz, 4J ¼ 1.2 Hz, 2H, H2, H7).
n
(C^N), 1582, 1472 s n(СCAr).
2.2.6. 2,3,6,7-Tetrachlorophenanthrene-9,10-dicarbonitrile (40)
1H NMR (400 MHz, CDCl3)
, ppm: 9.52 (s, 2H), 8.40 (s, 2H).
1H NMR (400 MHz, DMSO‑d6)
d
,
ppm: 9.11 (dd, 3J ¼ 8.4 Hz,
d
4J ¼ 1.2 Hz, 2H, H4, H5), 8.32 (dd, 3J ¼ 8.4 Hz, 4J ¼ 1.2 Hz, 2H, H1, H8),
8.08 (ddd, 3J ¼ 8.4 Hz, 3J ¼ 7.6 Hz, 4J ¼ 1.2 Hz, 2H, H3, H6), 8.01 (ddd,
3J ¼ 8.4 Hz, 3J ¼ 7.6 Hz, 4J ¼ 1.2 Hz, 2H, H2, H7). 13C{1H} NMR
2.2.7. 3,6-Dibromophenanthrene-9,10-dicarbonitrile (5)
(100 MHz, CDCl3)
d
, ppm: 131.3, 131.2 (C3, C6), 129.2 (C2, C7), 127.8,
Yield: 45 mg (30%), beige powder, mp ¼ 265e266 ꢁC. 1H NMR
127.4 (C1, C8), 123.4 (C4, C5), 116.8, 115.0 (CN). Using the COSY and
1He13C HSQC techniques, assignment of the 1H and 13C NMR sig-
nals is achieved (See the Supporting Information). HRMS (ESIþ), m/
z: 229.0760 [MþH]þ, 251.0580 [MþNa]þ. C16H9N2 calcd. m/z:
229.0766, C16H8N2Na calcd. m/z: 251.0585. IR spectrum (KBr,
(400 MHz, CDCl3)
d
, ppm: 8.67 (s, 2H, H4, H5), 8.37 (d, 3J ¼ 8.0 Hz,
2H), 7.88 (d, 3J ¼ 8.0 Hz, 2H). 13C{1H} NMR (100 MHz, CDCl3)
d, ppm:
138.4, 131.3, 130.6, 128.9, 126.5, 123.3, 116.5, 114.5. HRMS (ESIþ), m/
z: 384.8970 [MþH]þ. C16H7N2Br2 calcd. m/z: 384.8976. IR spectrum
(KBr, selected bands, cmꢀ1): 3097 w
n
(Сsp2ꢀH), 2230 m
n(C^N),
selected bands, cmꢀ1): 2226 s
n(C^N), 1608 m
n
(СCAr).
1603, 1502 s n(СCAr).
Fig. 2. Synthesis of phenanthrene-9,10-dicarbonitriles.

4
A.M. Afanasenko et al. / Journal of Molecular Structure 1199 (2020) 126789
Table 1
2.2.8. 3,6-Dimethylphenanthrene-9,10-dicarbonitrile (6)
Yield: 78 mg (52%), beige powder, mp ¼ 246e247 ꢁC. 1H NMR
Crystallographic data and refinement parameters.
(400 MHz, CDCl3)
d
, ppm: 8.48 (s, 2H, H4, H5), 8.18 (d, 3J ¼ 8.0 Hz,
2
6
7
2H, H1, H8), 7.64 (d, 3J ¼ 8.0 Hz, 2H, H2, H7), 2.71 (s, 6H, CH3). 1H NMR
Empirical formula
Molecular weight
Temp (K)
C16H6N2F2
264.23
100(2)
CuK
Monoclinic
Cc
3.73677(9)
20.2474(5)
15.6017(4)
90
94.366(2)
90
1177.00(5)
4
1.491
0.946
5206
1593
1.070
0.0278
0.0206
0.0304
0.0752
0.0298
0.0745
C18H12N2
256.30
100(2)
CuK
Monoclinic
P21/c
11.1090(2)
17.7567(3)
14.0781(3)
90
109.077(2)
90
2624.52(9)
8
1.297
0.601
14792
5113
1.034
0.0407
0.0378
0.0568
0.1323
0.0456
0.1258
C18H12N2O2
288.30
100(2)
MoKa
Monoclinic
P21/c
7.7888(4)
21.946(1)
7.8773(4)
90
98.517(4)
90
1331.66(11)
4
1.438
0.096
7794
2769
1.033
0.0268
0.0377
0.0628
0.1109
0.0451
0.1016
(400 MHz, DMSO‑d6)
d
, ppm: 8.86 (s, 2H, H4, H5), 8.14 (d, 3J ¼ 8.0 Hz,
2H, H1, H8), 7.81 (d, 3J ¼ 8.0 Hz, 2H, H2, H7), 2.67 (s, 6H, CH3). 13C{1H}
NMR (100 MHz, CDCl3) d
, ppm: 141.6 (C4a, C4b), 130.9 (C3, C6), 130.8
Radiation
a
a
Crystal system
Space group
a (Å)
b (Å)
c (Å)
(C2, C7), 127 (C1, C8), 125.9 (C8a, C10a), 122.9 (C4, C5), 115.3 (C9, C10),
115.2 (CN), 22.4 (CH3). Full assignment of the 1H and 13C NMR
spectra was successfully achieved by means of 1He13C HSQC and
1He13C HMBC measurements (See the Supporting Information,
Fig. S2). HRMS (ESIþ), m/z: 257.1073 [MþH]þ, 279.0893 [MþNa]þ.
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
C
18H13N2 calcd. m/z: 257.1079 [MþН]þ, C18H12N2Na calcd. m/z:
279.0898. IR spectrum (KBr, selected bands, cmꢀ1): 2920 w
V (Å3)
Z
n
(Сsp3ꢀH), 2226 s
n(C^N), 1618 s n(СCAr).
rcalc (mg/mm3)
m
(mmꢀ1
)
2.2.9. 3,6-Dimethoxyphenanthrene-9,10-dicarbonitrile (7)
Total reflections
Unique reflections
GOOF (F2)
Rint
Yield: 34 mg (23%), beige powder, mp ¼ 241e242 ꢁC. 1H NMR
(400 MHz, CDCl3)
d
, ppm: 8.30 (d, 3J ¼ 8.8 Hz, 2H, H1, H8), 7.97 (d,
4J ¼ 2.4 Hz 2H, H4, H5), 7.48 (dd, 3J ¼ 8.8 Hz, 4J ¼ 2.4 Hz, 2H, H2, H7),
4.10 (s, 6H, OCH3). 1H NMR (400 MHz, DMSO‑d6)
d, ppm: 8.38 (d,
Rs
R1 (all data)
wR2 (all data)
4J ¼ 2.0 Hz, 2H, H4, H5), 8.18 (d, 3J ¼ 8.8 Hz, 2H, H1, H8), 7.63 (dd,
3J ¼ 8.8 Hz, 4J ¼ 2.0 Hz, 2H, H2, H7), 4.10 (s, 6H, OCH3). 13C{1H} NMR
R1 (jFoj ꢃ 4sF
)
wR2 (jFoj ꢃ 4sF
)
(100 MHz, CDCl3) d, ppm: 161.3, 132.5, 129.1, 122.6, 119.0, 115.8,
113.6, 105.3, 55.6 (OCH3). HRMS (ESIþ), m/z: 289.0999 [MþH]þ,
311.0822 [MþNa]þ. C18H13N2O2 calcd. m/z: 289.0977, C18H12N2O2Na
calcd. m/z: 311.0796. IR spectrum (KBr, selected bands, cmꢀ1): 2980
R1 ¼ SjjFoj
e
jFcjj/SjFoj;
wR2 ¼ {S[w(F2o
e
F2c)2]/S[w(F2o)2]}1/2
;
w ¼ 1/
[
s
2(F2o) þ (aP)2 þ bP], where P ¼ (F2o þ 2Fc2)/3; s ¼ {S[w(Fo2 e Fc2)]/(n e p)}1/2 where n is
the number of reflections and p is the number of refinement parameters.
w
n
(Сsp3ꢀH), 2226 s
n(C^N), 1616, 1510 s n(СCAr).
The Hessian matrix was calculated analytically for the optimized
structure of 1 in order to prove the location of correct minima (no
imaginary frequencies). The topological analysis of the electron
density distribution with the help of the atoms in molecules
(QTAIM) method developed by Bader [33] has been performed by
using the Multiwfn program [34]. The Cartesian atomic coordinates
of model structures are presented in Table S1 (See the Supporting
Information).
2.3. Crystallography
The crystals of 2, 6, and 7 were obtained by a slow evaporation of
solvent at room temperature. Crystals of compounds 2, 6, and 7
were immersed in cryo-oil, mounted in a nylon loop, and analysed
at a temperature of 100 K. The X-ray diffraction data were collected
on an Agilent Technologies Excalibur Eos and Supernova Atlas
diffractometers. The temperature for all experiments was kept at
100 K. The structures have been solved by the direct methods and
refined by means of the SHELXLe97 [28] program incorporated in
the OLEX2 program package [29]. The carbon-bound H atoms were
placed in calculated positions and were included in the refinement
in the ‘riding’ model approximation, with Uiso(H) set to 1.5Ueq(C)
and CeH 0.96 Å for CH3 groups, Uiso(H) set to 1.2Ueq(C) and CeH
0.93 Å for the CH groups, and Uiso(H) set to 1.2Ueq(N) and NeH
0.86 Å for the NH groups. Empirical absorption correction was
applied in CrysAlisPro program complex [30] using spherical har-
monics, implemented in SCALE3 ABSPACK scaling algorithm.
The crystallographic details and refinement parameters are
summarized in Table 1. The crystallographic details are given in
Fig. S3 of the Supporting Information. Crystal data have been
deposited at the Cambridge Crystallographic Data Centre (CCDC)
with deposition numbers CCDC 1821025, ССDC 1821026, and ССDC
1820117 for 2, 6, and 7, respectively.
3. Results and discussion
The fluorescence excitation and emission spectra of 1¡7 were
measured in solution and solid states (Table 2, the Supporting In-
formation, Figs. S4ꢀS5). Strikingly, 7 showed weak fluorescence
(the fluorescence quantum yield (FF) is less than 1%) in the chlo-
roform solution, but relatively strong fluorescence (
F
F ¼ 46%) in
the solid state, whereas 1 and 2 showed opposite emission
behaviour (stronger fluorescence in solution than in solid state).
3e5 possessed weak fluorescence both in solution and in the solid
state, which is related to luminescence quenching by heavy
halogen atoms. As well as in the case of compound 7, 6 exhibits the
stronger fluorescence in the solid state (
chloroform solution (
these two values is not significant. The longest fluorescence lifetime
was observed for 7 (11.5 ns in chloroform solution and 25.3 ns in
the solid state), while the shortest one belongs to 4 (2.3 ns in
chloroform solution and 2.6 ns in the solid state).
F
F ¼ 22%) than in the
F
F ¼ 15%), however, the difference between
2.4. Computational details
The single point calculations based on the experimental X-ray
geometries of 1, 2, 6, and 7 and full geometry optimization of 1 in
the gas phase have been carried out at the DFT level of theory using
the M06e2X functional [31] (this functional was parameterized for
the main group elements and specifically developed to describe
weak dispersion forces and non-covalent interactions) with the
help of Gaussian-09 [32] program package. The standard
6e311þþG(d,p) basis sets were used for all atoms. No symmetry
restrictions have been applied during the geometry optimization.
The excitation and emission maxima for crystalline 1e7 are
redshifted compared with chloroform solutions.
To understand the differences in the luminescence properties of
phenanthrene-9,10-dicarbonitriles in solution and in the solid
state, we have analysed crystal packing patterns of 1, 2, 6, and 7.
Single crystals of 1, 2, 6, and 7 were grown from a dichloromethane
solution. The crystal structure of 1 was previously published (CCDC
1443835 [35]). The crystal packing patterns of 1, 2, 6, and 7 (Fig. 3)
show that they aggregate by
p-stacking with each other; the

A.M. Afanasenko et al. / Journal of Molecular Structure 1199 (2020) 126789
5
Table 2
Maximum excitation (lex) and emission (lem) wavelengths, Stokes shifts, and fluorescence quantum yields (
state.
F
F) for 1e7 in chloroform solution (c ¼ 5,10ꢀ5 M) and in the solid
Compd.
chloroform solution
solid
lex (nm)
lem (nm)
Stokes shift (nm)
FF (%)
lex (nm)
lem (nm)
Stokes shift (nm)
FF (%)
1
2
3
4
5
6
7
346
335
347
343
350
343
403
395, 416
374, 391, 413
388, 404
412, 426
384, 402, 427
396, 408
49
39
41
69
34
53
37
17
8
<1
1
1
15
<1
387
379
384
380
395
389
433
474
464
470
440
458
477
523
87
85
86
60
63
88
90
11
6
<1
2
3
22
46
440, 463
distances between the two stacked layers are 3.4e3.7 Å. The crystal
packing pattern of 1 molecules shows that in a stacked column they
aggregate by stacking with each other at an angle of 180ꢁ plausibly
owing to favourable dipoleꢀdipole interaction. The dipole mo-
ments of the two molecules exactly eclipse each other, but in the
opposite direction. However, it should be noticed, that the stronger
non-covalent bonds CN,,,H(C) assemble the molecules of 1 into
the net structure (See the Supporting Information, Fig. S3). In the
slip stacked column of 2, the molecules are oriented in an exactly
parallel way (Fig. 3). Also, the intermolecular CN,,,H(C) and
F,,,H(C) contacts are observed in the crystal structure of 2. The
molecules in the stacked columns of 6 and 7 are rotated relatively to
of
p
-stacking interactions in the crystal structures of 1, 2, 6, and 7.
-stacking interactions often impart
important luminescence properties, detailed computational
study of this phenomenon has been performed in this work. In
order to confirm or deny the hypothesis on the existence of
Taking into consideration that
p
a
p
-
stacking interactions in 1, 2, 6, and 7 and to calculate their energy
from theoretical viewpoint, we carried out DFT calculations at the
M06e2X/6e311þþG(d,p) level of theory and topological analysis
of the electron density distribution within the framework of Bader's
theory (QTAIM method) [33] for the model systems (Table 3 and
Table S1). This approach has already been successfully used by us
while studying of different non-covalent interactions in various
organic and organometallic or coordination compounds [36e47].
The contour line diagram of the Laplacian distribution V2r(r), bond
each other. The weak non-covalent CN,,,H(CAr) and CN,,,H(CMe
)
interactions occur between the neighbouring molecules in the
crystal of 6. In 7, the short contacts CN,,,H(CAr), O,,,H(CAr), and
CN,,,H(CMeO) are observed (See the Supporting Information,
Fig. S3).
paths, and selected zero-flux surfaces for the
teractions in 7 are shown in Fig. 4, corresponding atomic basins of
electron density gradient lines map are presented in Fig. S6 (See the
p-stacking in-
Inspection of the crystallographic data also reveals the presence
Supporting Information). To visualize studied
p-stacking
Fig. 3.
p-Stacking in 1, 2, 6, and 7.

6
A.M. Afanasenko et al. / Journal of Molecular Structure 1199 (2020) 126789
Table 3
Values of the density of all electrons e
r
(r), Laplacian of electron density e V2r(r),
energy density e Hb, potential energy density e V(r), and Lagrangian kinetic energy
-stacking in-
e G(r) (a.u.) at the bond critical points (3, ꢀ1), corresponding to
p
teractions in 1, 2, 6, and 7 as well as energies for appropriate C/C contacts Eint (kcal/
mol), are defined by two approaches.
2r(r)
Hb
V(r)
G(r)
Eint
Eint
a
b
Compd.
r(r)
V
1
2
6
7
0.006
0.006
0.005
0.006
0.016
0.017
0.015
0.016
0.001
0.001
0.001
0.001
ꢀ0.003
ꢀ0.003
ꢀ0.002
ꢀ0.003
0.003
0.004
0.003
0.003
0.9
0.9
0.6
0.9
0.8
1.1
0.8
0.8
a
Eint ¼ eV(r)/2 [49].
b
Eint ¼ 0.429G(r) [50].
Fig. 5. Isosurfaces of HOMO and LUMO for 1.
interactions, reduced density gradient (RDG) analysis [48] was
carried out, and RDG isosurface for 7 was plotted (Fig. 4). The
Poincare-Hopf relationship in all cases is satisfactory, thus all crit-
ical points have been found.
The QTAIM analysis demonstrates the presence of appropriate
bond critical points (BCPs) for the p-stacking interactions in 1, 2, 6,
and 7. The low magnitude of the electron density (0.005e0.006
a.u.), positive values of the Laplacian (0.015e0.017 a.u.), and close to
zero positive energy density (0.001 a.u.) in these BCPs are typical
for non-covalent interactions. We have defined energies for the
show larger electron distribution on the C9 and C10 atoms of
phenanthrene and on the cyano groups. When the HOMO and
LUMO of 6 and 7, in the plane-to-plane stacked mode as in the
crystal structure, are compared with respect to the orbital size and
symmetry, the orbital overlap is poor; in contrast, more effective
orbital overlap is present in the case of 1 (Fig. 3).
Because of the poor orbital interactions between stacked mol-
ecules of 6¡7, the excited state resonance interaction may become
insignificant, which precludes application of Kasha's resonant
dimer model to this case. 6e7 molecules in the solid state behave
independently and thus emit strong fluorescence. Also, poor
emission behaviour of 1 and 2 in the solid state is explained by
Kasha's exciton model of parallel transition dipoles. 6 and 7 show
strong fluorescence in the solid state, whereas 1 and 2 do not.
Analysis of the crystal structures and packing patterns reveals that
all compounds show parallel stacking patterns that conform to
Kasha's exciton model of parallel transition dipoles. 6e7, however,
seem to experience an unfavourable excited state resonance
interaction, providing an example of a nonresonant stacked model.
Frontier molecular orbital interactions between stacked molecules
suggest a different degree of orbital overlapping, offering a clue on
the different optical behaviour of compounds 1e2 and 6e7 in the
solid state.
C/C contacts responsible for the
p-stacking interactions using
procedures proposed by Espinosa et al. [49] and Vener et al. [50]
(Table 3), and one can state that strength of these non-covalent
interactions varies from 0.6 to 1.1 kcal/mol. The balance between
the Lagrangian kinetic energy G(r) and potential energy density
V(r) at the BCPs (3, ꢀ1) reveals the nature of these interactions, if
the ratio eG(r)/V(r) > 1 is satisfactory, then the nature of appro-
priate interaction is purely non-covalent, in case the eG(r)/V(r) < 1
some covalent component takes place [51]. Basing on this criterion
one can state that in all cases the covalent contribution in the
stacking interactions is absent.
p-
The molecules of 6 and 7 seem to behave as independent mol-
ecules in the solid state plausibly owing to the unfavourable excited
state resonance interaction and thus emit strong fluorescence
because each dipolar molecule now is in an inert environment
surrounded by other molecules.
For a qualitative estimation of orbital interactions between two
stacked molecules, we compared HOMO and LUMO orbitals of
phenanthrene-9,10-dicarbonitriles (Fig. 5). The HOMO and LUMO
interactions between two stacked molecules may be considered as
a model for estimating the excited state resonance interaction.
HOMOs of phenanthrene-9,10-dicarbonitriles show larger electron
distribution on the phenanthrene fragment, whereas their LUMOs
4. Conclusion
The influence of dipole-dipole and orbital interactions on the
luminescent properties of phenanthrene-9,10-dicarbonitriles in the
solid state has been studied. The insertion of different substituents
in the phenanthrene molecule leads to varied crystal packing,
orbital overlap, and, as a result, to emission from cooperative
Fig. 4. Contour line diagram of the Laplacian distribution V2r(r), bond paths and selected zero-flux surfaces (left) and RDG isosurface (right) referring to
p-stacking interactions in 7.
Bond critical points (3, ꢀ1) are shown in blue, nuclear critical points (3, ꢀ3) e in pale brown, ring critical points (3, þ1) e in orange. Length units e Å, RDG isosurface values are
given in a.u.

A.M. Afanasenko et al. / Journal of Molecular Structure 1199 (2020) 126789
7
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excimer and dipole coupling. The effectiveness of orbital overlap
was evaluated by DFT calculation. 6e7 demonstrate strong lumi-
nescence in the solid state in comparison to the luminescence in
solution, but 1e2 show the opposite behaviour. The luminescence
enhancement in solid 6e7 is explained by poor orbital interactions
in the excited state. To summarize, the dipole-dipole and orbital
intermolecular interactions control the excited state characteristics
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help to construct new luminescent materials.
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This work has been supported by Russian Foundation for Basic
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