Glass-forming derivatives of 2-cyano-2-(4H-pyran-4-ylidene) acetate for light-amplification systems

Article abstract of DOI:10.1016/j.dyepig.2018.11.041

A series of 2-cyano-2-(4H-pyran-4-ylidene) acetate derivatives with triphenyl and 9H-carbazole moieties were synthesized and investigated, mostly for potential applications in organic solid state lasers. Synthesized compounds show remarkable amorphous fil

Full text of DOI:10.1016/j.dyepig.2018.11.041

Dyes and Pigments 163 (2019) 62–70
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Glass-forming derivatives of 2-cyano-2-(4H-pyran-4-ylidene) acetate for
light-amplification systems
a,∗
a
b
b
a
Elmars Zarins , Karina Siltane , Julija Pervenecka , Aivars Vembris , Valdis Kokars
a
Institute of Applied Chemistry, Riga Technical University, 3/7 Paul Walden Str, Riga, LV-1048, Latvia
Institute of Solid State Physics, University of Latvia, 8 Kengaraga Str, Riga, LV-1063, Latvia
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Amplified spontaneous emission
A series of 2-cyano-2-(4H-pyran-4-ylidene) acetate derivatives with triphenyl and 9H-carbazole moieties were
synthesized and investigated, mostly for potential applications in organic solid state lasers. Synthesized com-
pounds show remarkable amorphous film formation ability, tunable thermal properties (thermal stability varies
from 190 °C to 387 °C and glass transition temperature from 94 °C up to 141 °C) with light absorption from
2
4
-cyanoacetates
H-pyran-4-ylidene
Laser dyes
Amorphous materials
400 nm to 600 nm and photoluminescence from 600 nm up to 800 nm. Dyes with incorporated mono-styryl-
electron donating fragment (KTB, KTBC and KTB3K) showed higher photoluminescence quantum yield (PLQY)
(
(
from 16% up to 23%), significantly lower amplified spontaneous emission (ASE) excitation threshold values
2
24–52 μJ/cm ) in pure thin films comparing to bis-styryl- electron donating fragment containing molecules (Bis-
2
K4C, Bis-K5C and Bis-K4CK) with PLQY of 5–7% and ASE excitation threshold between 165 and 223 μJ/cm .
Some of the investigated KTB-type laser dyes could be perspective materials for organic lasers as well as for laser
technology investigation and applications.
1. Introduction
Recently we have demonstrated [27–30] that incorporating bulky
triphenyl groups in the low molecular mass organic compounds enables
During the last two decades, D-π-A organic molecular compounds
their excellent solubility in non-polar organic solvents and enhances
their ability to form good optical quality transparent glassy films by
solution processing. Additionally, they improve photoluminescence
quantum yield (PLQY) of the compound in thin films due to the reduced
intermolecular interaction between the molecules. Till now such groups
were attached only to electron donor part of the molecule but not to the
acceptor part. 4H-Pyran-4-ylidene fragment containing molecules with
the 2-cyanoacetate electron acceptor group are a good candidate for
further incorporation of bulky moieties. Glass transition temperatures
for 2-(trityloxy)ethyl groups containing D-π-A type compounds have
limitations and could not be much higher than 115 °C [27,28,31]. It is
well known that 9H-carbazole fragment is a bulky functional group
with various chemical modification possibilities which provide the
ability for the whole organic molecules to form thin solid amorphous
and transparent films from solutions and exhibit high glass transition
temperatures [2,32–34], accordingly more stable thin films. Therefore,
in this report, we present a full synthesis of six glassy triphenyl and 9H-
carbazole groups containing 2-cyanoacetate derivatives. Their thermal
and optical characteristics are discussed with further perspectives in
potential applications in photonic devices, more specifically, for or-
ganic solid state lasers.
with charge transfer properties have been widely studied for potential
applications in various organic photonic and molecular electronic de-
vices due to their enhanced performance comparing to inorganic ma-
terials, low-cost production, simple processing possibility and physical
property tuning ability through chemical structure synthetic modifica-
tions [1–4]. One of the most notable and well-known such materials are
derivatives of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminos-
tyryl)-4H-pyran (DCM). In these compounds 4-dialkylaminostyryl
electron donor (D) part is bonded through 4H-pyran-4-ylidene π-con-
jugation bridge to the malonnonitrile electron acceptor (A) fragment
[
3,5–7]. Many DCM type derivatives have been synthesized and in-
vestigated for potential applications in solid state lasers [3,5–9], OLEDs
3,6,10–13], chemosensors [1,12,14], logic gates [1,12,15] and non-
linear optics (NLO) [1,16,17]. Similar organic molecules with the in-
corporated 2-cyanoacetate electron acceptor group so far have been
investigated for applications in OLED's [18], organic solar cells [19–21]
and as molecular switches [22–26], but to the best of our knowledge
never for organic lasers. Easily processable functional materials with
high light amplification properties and low excitation threshold en-
ergies are required for the development of such lasers [3,5,7–9].
[
∗
Corresponding author.
E-mail address: Elmars.Zarins@rtu.lv (E. Zarins).
https://doi.org/10.1016/j.dyepig.2018.11.041
Received 7 September 2018; Received in revised form 21 November 2018; Accepted 21 November 2018
Available online 22 November 2018
0143-7208/ © 2018 Elsevier Ltd. All rights reserved.

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
2
. Experimental section
(300 MHz; CDCl
3
) δ, ppm. 1.39 (9H, s), 1.47 (54H, s), 1.58–1.64 (4H,
m), 1.78–1.92 (4H, m), 3.08–3.19 (4H, m), 4.51–4.65 (4H, m),
6.39–6.54 (3H, m), 6.63–6.72 (1H, m), 7.25–7.35 (7H, m), 7.46–7.54
(6H, m), 7.57 (2H, dd, 3J = 8.7 Hz, J = 1.6 Hz), 7.72–7.91 (1H, m),
In all cases, the starting reactants have been purchased as com-
4
mercial products from chemical supply companies and used as received.
Detailed information about the synthesis, purification, structure char-
acterization, physical properties and/or related references
4
8.08–8.11 (2H, m), 8.13 (4H, d, J = 1.4 Hz). Elemental analysis: calcd.
109 5 3
for KTB3K (C90H N O ): C, 82.59; H, 8.39; N, 5.35, found C, 82.37; H,
[
29–31,35–40] of every chemical substance obtained in this article is
8.53; N, 5.48.
available within the associated supporting information.
Ethyl 2-(2,6-bis(4-(bis(5,5,5-triphenylpentyl)amino)styryl)-4H-
pyran-4-ylidene)-2-cyanoacetate (Bis-K4C) was synthesized by the
method described above and similar as reported in Ref. [31] from ethyl
General method of synthesis of (2,6-dialkyl-4H-pyran-4-yli-
dene)-2-cyanoacetate derivatives KTB, KTBC, KTB3K and Bis-K4C,
Bis-K5C, Bis-K4CK [29–31]. To a solution of the respective (2,6-dia-
lkyl-4H-pyran-4-ylidene)-2-cyanoacetate (4a, 4b, 4c, 5a, 5b or 5c)
2-cyano-2-(2,6-dimethyl-4H-pyran-4-ylidene)acetate
(4c)
(0.15 g,
0.68 mmol) and 4-(bis(5,5,5-triphenylpentyl)amino)benzaldehyde (8)
(
(
1.00 mmol) and the corresponding benzaldehyde (6,
1.00 mmol in case of KTB, KTBC, KTB3K or 2.00 mmol in case of Bis-
7
or 8)
[38] (1.18 g, 1.64 mmol). After the purification with a liquid column
chromatography (V(toluene)/V(ethyl acetate) = 10/1, silicagel),
a
K4C, Bis-K5C, Bis-K4CK) in dry pyridine (5.0 mL) 3 drops of piperidine
were added. The reaction mixture was stirred for 24 h at 90–100 °C,
then cooled to the room temperature. The obtained brownish slurry was
poured into 100 mL ethyl alcohol and the afforded precipitates were
filtered, washed with 10 mL cold methyl alcohol, dried, and then pur-
ified.
0.13 g (12%) of ethyl 2-(2,6-bis(4-(bis(5,5,5-triphenylpentyl)amino)
styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (Bis-K4C) as a dark red
−
1
powder was obtained. IR (KBr) υ, cm : 3058, 2198, 1686, 1636, 1595,
1
1532. H-NMR (300 MHz; CDCl ) δ, ppm. 1.02–1.19 (8H, m), 1.37 (3H,
3
3
t, J = 7.1 Hz), 1.47–1.64 (8H, m), 2.53–2.64 (8H, m), 3.03–3.18 (8H,
m), 4.28 (2H, q, J = 7.1 Hz), 6.45–6.61 (6H, m), 6.70 (1H, s),
3
Ethyl 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-tert-butyl-
7.13–7.33 (60H, m), 7.35–7.48 (6H, m), 8.02 (1H, s). Elemental ana-
4
H-pyran-4-ylidene)-2-cyanoacetate (KTB) was synthesized by the
lysis: calcd. for Bis-K4C (C118
111 3 3
H N O ): C, 87.53; H, 6.91; N, 2.60,
method described above and similar as reported in Refs. [29,30] from
found C, 87.56; H, 7.00; N, 2.61.
ethyl 2-(2-tert-butyl-6-methyl-4H-pyran-4-ylidene)-2-cyanoacetate (5c)
5,5,5-Triphenylpentyl 2-(2,6-bis(4-(bis(5,5,5-triphenylpentyl)
amino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (Bis-K5C) was
synthesized by the method described above and similar as reported in
Ref. [39] from 5,5,5-triphenylpentyl 2-(2-tert-butyl-6-methyl-4H-pyran-
4-ylidene)-2-cyanoacetate (4b) (0.35 g, 0.72 mmol) and 4-(bis(5,5,5-
triphenylpentyl)amino)benzaldehyde (8) [38] (1.28 g, 1.79 mmol).
After the purification with a liquid column chromatography (chloro-
form, silicagel), a 0.19 g (14%) of 5,5,5-triphenylpentyl 2-(2,6-bis(4-
(bis(5,5,5-triphenylpentyl)amino)styryl)-4H-pyran-4-ylidene)-2-cya-
noacetate (Bis-K5C) as a dark red powder was obtained. IR (KBr) υ,
(
(
0.73 g, 2.79 mmol) and 4-(bis(2-(trityloxy)ethyl)amino)benzaldehyde
7) [29,31] (1.55 g, 2.23 mmol). After the purification with a liquid
column chromatography (chloroform, silicagel), a 0.21 g (10%) of ethyl
-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-tert-butyl-4H-pyran-4-
ylidene)-2-cyanoacetate (KTB) as an orange amorphous powder was
2
−
1
1
obtained. IR (KBr) υ, cm : 2197, 1693, 1639, 1597, 1549. H-NMR
3
(
3
300 MHz; CDCl
3
) δ, ppm. 1.33–1.43 (12, m), 3.33 (4H, t, J = 5.4 Hz),
.63 (4H, t, J = 5.4 Hz), 4.21–4.34 (2H, m), 6.48–6.59 (3H, m),
3
4
6
.63–6.75 (1H, m), 7.22–7.44 (33H, m), 8.04 (1H, d, J = 1.8 Hz).
): C, 82.02; H, 6.45; N,
−
1
1
Elemental analysis: calcd. for KTB (C64
.99, found C, 83.79; H, 6.43; N, 2.62.
,5,5-Triphenylpentyl 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)
styryl)-6-tert-butyl-4H-pyran-4-ylidene)-2-cyanoacetate (KTBC)
H
60
2
N O
5
3
cm : 2196, 1689, 1636, 1593, 1532. H-NMR (300 MHz; CDCl ) δ,
2
ppm. 0.85–0.94 (2H, m), 1.11 (8H, m), 1.56 (8H, m), 1.78 (2H, m),
3
5
2.57–2.68 (10H, m), 3.11 (8H, m), 4.14 (2H, d, J = 6.8 Hz), 6.49–6.58
4
(6H, m), 6.70 (1H, d, J = 1.8 Hz), 6.95–7.30 (75H, m), 7.35–7.40 (6H,
was synthesized by the method described above and similar as reported
in Refs. [29,30] from 5,5,5-triphenylpentyl 2-(2-tert-butyl-6-methyl-4H-
pyran-4-ylidene)-2-cyanoacetate (5b) (0.61 g, 1.15 mmol) and 4-(bis(2-
m), 7.98 (1H, d, 4J = 1.8 Hz). Elemental analysis: calcd. for Bis-K5C
(C139
2.17.
H
129
3
N O
3
): C, 88.35; H, 6.88; N, 2.22, found C, 87.60; H, 7.08; N,
(
trityloxy)ethyl)amino)benzaldehyde (7) [29,31] (0.80 g, 1.15 mmol).
2-(3,6-Di-tert-butyl-9H-carbazol-9-yl)ethyl
2-(2,6-bis(4-(bis
After the purification with a liquid column chromatography (V(di-
chloromethane)/V(petroleum ether) = 5/1, silicagel), a 0.07 g (5%) of
(5,5,5-triphenylpentyl)amino)styryl)-4H-pyran-4-ylidene)-2-cya-
noacetate (Bis-K4CK) was synthesized by the method described above
and similar as reported in Ref. [39] from 2-(3,6-di-tert-butyl-9H-car-
5,5,5-triphenylpentyl 2-(2-(4-(bis(2-(trityloxy)ethyl)amino)styryl)-6-
tert-butyl-4H-pyran-4-ylidene)-2-cyanoacetate (KTBC) as an orange
bazol-9-yl)ethyl
2-(2-tert-butyl-6-methyl-4H-pyran-4-ylidene)-2-cya-
−1
amorphous powder was obtained. IR (UATR) υ, cm : 3056, 2923,
noacetate (4a) (0.35 g, 0.71 mmol) and 4-(bis(5,5,5-triphenylpentyl)
amino)benzaldehyde (8) [38] (1.28 g, 1.55 mmol). After the purifica-
1
2
(
222, 2205, 1694, 1639, 1597, 1550, 1501, 1448, 1407. H-NMR
300 MHz; CDCl ) δ, ppm. 1.13 (2H, m), 1.39 (9H, s), 1.59–1.75 (2H,
m), 2.48–2.63 (2H, m), 3.08–3.34 (4H, m), 3.38–3.65 (4H, m),
3
tion with
(acetone) = 25/1, silicagel), a 0.17 g (13%) of 2-(3,6-di-tert-butyl-9H-
carbazol-9-yl)ethyl 2-(2,6-bis(4-(bis(5,5,5-triphenylpentyl)amino)
styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (Bis-K4CK) as a dark red
a
liquid column chromatography (V(toluene)/V
3
7
.95–4.11 (2H, m), 6.41–6.48 (3H, m), 6.59 (1H, two singlets),
.10–7.40 (48H, m), 7.91 (1H, s). Elemental analysis: calcd. for KTBC
−
1
(
C
85
H
78
N
2
O
5
): C, 84.54; H, 6.51; N, 2.32, found C, 84.38; H, 6.61; N,
powder was obtained. IR (KBr) υ, cm : 3058, 2196, 1690, 1635, 1594,
1
2.41.
3
1530. H-NMR (300 MHz; CDCl ) δ, ppm. 1.02–1.20 (8H, m), 1.46 (18H,
2-(3,6-Di-tert-butyl-9H-carbazol-9-yl)ethyl 2-(2-(4-(bis(4-(3,6-
s), 1.51–1.64 (8H, m), 2.53–2.64 (8H, m), 3.03–3.20 (8H, m),
4.54–4.63 (4H, m), 6.43–6.60 (6H, m), 6.71 (1H, s), 7.12–7.32 (60H,
m), 7.36–7.46 (6H, m), 7.47–7.61 (4H, m), 7.80 (1H, s), 8.09 (2H, s).
di-tert-butyl-9H-carbazol-9-yl)butyl)amino)styryl)-6-tert-butyl-4H-
pyran-4-ylidene)-2-cyanoacetate (KTB3K) was synthesized by the
method described above and similar as reported in Refs. [29,30] from
134 4 3
Elemental analysis: calcd. for Bis-K4CK (C138H N O ): C, 87.39; H,
2-(3,6-di-tert-butyl-9H-carbazol-9-yl)ethyl 2-(2-tert-butyl-6-methyl-4H-
7.12; N, 2.95, found C, 87.22; H, 7.49; N, 3.03.
pyran-4-ylidene)-2-cyanoacetate (5a) (0.37 g, 0.84 mmol) and 4-(bis(4-
(
3,6-di-tert-butyl-9H-carbazol-9-yl)butyl)amino)benzaldehyde
(6)
3. Results and discussion
(
0.60 g, 0.84 mmol). After the purification with a liquid column chro-
matography (chloroform, silicagel), a 0.10 g (9%) of 2-(3,6-di-tert-
butyl-9H-carbazol-9-yl)ethyl 2-(2-(4-(bis(4-(3,6-di-tert-butyl-9H-car-
3.1. Synthesis of KTB-type dyes and their characterization
bazol-9-yl)butyl)amino)styryl)-6-tert-butyl-4H-pyran-4-ylidene)-2-cya-
2-Cyanoacetate derivatives 1a-c were obtained according to known
synthetic procedures [35,37,38]. In their further Knoevenagel con-
densation reactions (see Scheme 1) with 2,6-dimethyl-4H-pyran-4-one
noacetate (KTB3K) as an orange amorphous powder was obtained. IR
−
1
1
(
KBr) υ, cm
: 2962, 2199, 1694, 1639, 1598, 1549. H-NMR
63

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
Scheme 1. Synthesis of 4-(2-cyanoacetate-methyene)-2,6-dialkyl-4H-pyranes and 9H-carbazole fragments containing 2-cyanoacetate derivative KTB3K.
(
4
2) [31] and 2-tert-butyl-6-methyl-4H-pyran-4-one (3) [29] a series of
-substituted-4H-pyranes (4a-c and 5a-c) were obtained in 15–61%
for the purification process.
Dyes KTB, KTBC and KTB3K have non-symmetric chemical structure
and therefore are obtained as a mixture of diastereoisomers which is
yields. Aldehyde 6 with 9H-carbazole moieties was synthesized simi-
larly to literature [35]. It was subjected to further Knoevenagel con-
densation reaction with 2-tert-butyl-6-methyl-4H-pyran-4ylidene frag-
ment containing 2-cyanoacetate (5a) affording dye KTB3K (see Scheme
1
reflected in magnified fragmentations (see Fig. 1) of their respective H-
NMR spectra. For KTB and KTBC two small peaks at 6.62–6.72 ppm
with a common integral intensity ∼1 and 25–26 Hz “distance” between
them were observed. At first we considered those peaks as a coupling
constant between some protons, but the value was too large to corre-
spond to any known interaction between hydrogen atoms in organic
compounds. Their chemical shifts also couldn't be related with common
organic solvent trace impurities [41]. Thus these peaks (see supple-
mentary content for more detailed NMR analysis) not only could be
attributed to the each of the diastereoisomers of the KTB and KTBC dyes
but also indicates that their ratio of formation = 1:1. In case of dye
KTB3K (see Fig. 1, bottom part), two peaks with a common integral
intensity ∼1 of a single proton at 6.7 ppm and of another single proton
at 7.8 ppm could be seen indicating the ratio of diasteroisomer com-
position also to be 1:1. The formation of diastereoisomers in case of 2-
cyanoacetate derivates are utilized as the electron acceptor part of the
1
) with incorporated 9H-carbazole moieties also in the electron ac-
ceptor part of the molecule. Dyes KTB and KTBC were obtained (see
Scheme 2) from 2-cyanoacate derivatives 5b and 5c in similar Knoeve-
nagel condensation reactions with 4-(bis(2-(trityloxy)ethyl)amino)ben-
zaldehyde (7) [31]. 2,6-bis-Styrylsubstituted-4H-pyran-4-ylidene frag-
ment containing 2-cyanoacetates Bis-K4CK, Bis-K5C and Bis-K4CK were
successfully acquired (see Scheme 2) in the same type reactions from
4
H-pyranes 4a-c and 4-(bis(5,5,5-triphenylpentyl)amino)benzaldehyde
(
8) [38]. The purification process (separation from reactants and by-
products) via liquid column chromatography of the final products was
the main factor why these compounds were obtained in 5–14% yields.
Dispensation of the desirable products from the reaction mixture could
be still improved by further tuning the ratio of organic solvents required
64

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
Scheme 2. Synthesis of triphenyl groups containing 2-(2-tert-butyl-6-styryl-substituted)-4H-pyran-4-ylidene)-2-cyanoacetate and 2-(2,6-bis-styryl-substituted)-4H-
pyran-4-ylidene)-2-cyanoacetate derivatives.
molecule in the synthesis of different DCM-type dyes most likely could
be one of the reasons why such materials haven't been studied as much.
Despite of the incorporated bulky 9H-carbazole and triphenyl moieties,
these functional groups do not influence the formation of any specific of
the diastereoisomers in excess in the last two stages of the dye synth-
esis. Additionally, the same result could be expected in case of a less
bulky functional group containing derivatives of 4H-pyran-4-ylidene
fragment containing derivatives of 2-cyanoacetate are produced. All
synthesized KTB-type dyes were obtained with trans-configuration at
their vinyl groups (see supplementary content for more details).
3.2. Thermal properties
Among the 2-styryl-subsituted-6-tert-butyl-4H-pyran-4-ylidene
fragment containing cyanoacetates (KTB, KTBC and KTB3K) the highest
thermal stability and glass transition temperature was observed (see
Table 1) for KTB3K (T = 387 °C, T = 137 °C) with incorporated 9H-
d g
carbazole moieties in the electron donating and electron acceptor parts
of the molecule.
Dyes KTB and KTBC of the similar chemical structure with 2-(tri-
tyloxy)ethyl groups instead of 9H-carbazole moieties showed greatly
d
reduced thermal stability (T = 307 °C for KTB) and by about 40 °C
lower glass transition temperature in relation to KTB3K. 5,5,5-
Triphenylpentyl group incorporation in the electron acceptor part of
65

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
Fig. 2. Optical properties (solid lines – absorption; dashed lines – lumines-
cence) of the compounds in the solution of dichloromethane: (a) Compounds
with one donor group and (b) Compounds with two donor groups. 1- KTB, 2-
KTBC, 3- KTB3K, 4- Bis-K4C, 5- Bis-K5C, 6- Bis-K4CK.
Fig. 1. Magnified 1H-NMR spectra fragmentations of dyes KTB, KTBC and
KTB3K.
their influence on optical properties was significantly lower. As it was
expected - optical properties are mostly driven by the 4-(N,N-dialky-
lamino)-styryl- electron donor groups and 2-cyanoacetate electron
withdrawing fragment. The absorption maximum of the compounds
with only one electron donor group (KTB; KTBC; KTB3K) in solution
was around 460 nm. The red shift of absorption spectra approximately
by 21–32 nm of compounds with two identical electron donor groups
(Bis-K4C; Bis-K5C; Bis-K4CK) with respect to the molecules with one
donor group was observed (see Fig. 2 and Fig. 3). It is most probably
related to the number of donor groups and longer conjugation length in
the case of Bis-K4C, Bis-K5C and Bis-K4CK compounds.
Table 1
Yields and thermal properties of synthesized glassy 2-cyanoacetate derivatives.
o
o
o
Compound
Yield, %
T
g
, ( C) 1st heating
T
g
, ( C) 2nd heating
d
T , ( C)
KTB
KTBC
KTB3K
Bis-K4C
Bis-K5C
Bis-K4CK
10
5
9
12
14
13
–
–
141
104
–
94
99
137
101
99
307
221
387
383
362
190
107
107
Trityl groups do not have any influence on the shape of the ab-
sorption band but extinction coefficient is slightly depending on the
T
g
- glass transition temperature, T
d
- thermal decomposition temperature at the
level of 5% weight loss.
the molecule (in case of KTBC) reduced thermal stability of the material
by 80 °C more (T = 221 °C) in comparison to the dye KTB with ana-
d
logue chemical structure and sterically small ethyl substituent. In case
of 2,6-bis-styryl-subsituted-4H-pyran-4-ylidene fragment containing
cyanoacetates (Bis-K4K, Bis-K5C, Bis-K4CK), dye Bis-KCK4 with 5,5,5-
triphenylpentyl groups in the electron donating part and 9H-carbazole
moiety in the electron acceptor parts of the molecule showed highest
glass transition temperature (T
bility (T = 190 °C). Substituting 9H-carbazole moiety with bulky
,5,5-triphenylpentyl fragment (Bis-K5C) or sterically small ethyl
g
= 107 °C), but the lowest thermal sta-
d
5
groups (Bis-K4C) lead to a small decrease of glass transition tempera-
ture (by about 6–8 °C), but significantly increased thermal stability (by
170–193 °C) of the mentioned 2-cyanoacetate dyes in comparison to
Bis-K4CK. Notably increased (for KTB3K) or decreased (in case of KTBC,
Bis-K4CK) thermal stability of the dyes could be explained by the close
sterical interactions of the 9H-carbazole and triphenyl groups. Dyes
with 9H-carbazole groups (KTB3K, Bis-K4CK) showed higher glass
transition temperatures in comparison to the dyes with triphenyl moi-
eties (KTB, KTBC, Bis-K4C, Bis-K5C) as expected.
3
.3. Optical properties
Fig. 3. Optical properties (solid lines – absorption; dashed lines – lumines-
cence) of the compounds in the thin solid films: (a) Compounds with one donor
group and (b) Compounds with two donor groups.
Bulky groups considerably affected synthesized compound thermal
and glass forming (see in supplementary information) properties, but
66

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
incorporated bulky groups at the 2-cyanoacetate electron withdrawing
fragment (see Figs. 2 and 3). Presences of bulky 9H-carbazole moieties
in electron acceptor (Bis-K4CK) and also in the electron donating
sequence, we can arrange the volume of the bulky groups. It shows that
shift of the PL spectrum is related to the interaction between the dye
part of the molecule. Full width of half maximum (FWHM) of thin films
PL are broader than for solutions, but in opposite to observed in solu-
tions – broader are FWHM of one electron donating group containing
compounds. The results on PLQY of all compounds in thin films are
summarized in Table 3. Compounds with one donor group exhibit PLQY
higher than 15% with the highest value of 23% for KTB molecule. Less
PLQY was observed for molecules with two donor groups and they were
in the range between 5 and 7%. It is vice versa compared to solutions,
where small intermolecular interactions between the molecules take
place. Such relation points to stronger molecule interaction between the
molecules with the two donor groups.
(
3
KTBK3) parts of the molecule induce additional small (in the range of
–8 nm) red shift of absorption spectra compared with triphenyl and
ethyl group containing molecules (KTB, KTBC and Bis-K4C, Bis-K5C). It
means that despite the absence of conjugation between the chromo-
phore (backbone) part and bulky groups - 9H-carbazole moieties still
influence electron transitions in the molecule. And this influence is
more pronounced with a higher number of attached 9H-carbazole
groups (KTB3K) - more in solutions, less in the thin films.
Investigated compounds show emission in the red spectral region
(
see Fig. 2). The fluorescence spectra were unstructured and strongly
Stokes shifted in accordance with intramolecular charge-transfer nature
of the excited states [42]. Between compounds with similar acceptor
but a different number of donor groups also preserves approximately
3.4. Amplified spontaneous emission properties
40 nm big red shift of PL spectra maximum positions due to different
All prepared samples for amplified spontaneous emission (ASE)
conjugation length - caused by sizes and number of to the backbone of
the molecule attached bulky groups [43]. It means that with the in-
creases in conjugation length between attached donor and acceptor
groups – increases the spatial dimension of the molecule which in turn
causes increases of Stokes shift between absorption and PL spectra. It is
proved also with the at least 10 nm larger Stokes shift for the com-
pounds with two electron donating groups (see Table 2). 9H-Carbazole
groups have a similar impact on PL spectra as it was for absorption
spectra. PLQY is higher for the compounds with two electron donor
groups compared to one donor group molecules (see Table 2). More
donor groups also means more protecting fragments which could shield
molecules from solution. PL kinetics could be approximated with one
exponential function. Excited state lifetime is higher for the molecules
with two donor groups. The reason could be the same as for higher the
PLQY. The radiative decay rate is an important parameter determining
applicability of molecules for the light amplification since it is directly
related to the oscillator strength of the radiative transition and to the
stimulated emission cross section [29]. Thus, higher radiative decay
rates of the molecules with one donor group especially KTB and KTBC
molecules allow us to predict that these compounds are most suitable
for the light amplification and lasing applications. Molecules with two
donor groups are less suitable due to the smallest radiative decay rate.
This conclusion not directly applicable for the solid films since radiative
decay rates of molecules in solids may be different, but in close ap-
proximation could be used.
measurements were good optical quality without noticeable defects in it
see optical microscope images within the supplementary content).
(
Based on absorption spectra (see Fig. 3), excitation wavelength ap-
propriate to compound absorption maximum wavelength was used.
ASE of the neat thin films of studied compounds has been observed as
the appearance of the narrow high intense peak on top of the photo-
luminescence band (see Fig. 4). Despite of the fact that photo-
luminescence could be observed in all 6 compounds, ASE was possible
to excite only in 5 of them (Bis-K5C; Bis-K5C; KTB; KTBC; KTB3K). But,
due to Bis-K5C and Bis-K4C extremely high photosensitivity even at
comparably small excitation intensities, which less than 1.5 times ex-
ceed ASE threshold, appears rapid bleaching of lighted area of the film.
Therefore only 3 (KTB; KTBC; KTB3K) of investigated compounds could
be mentioned as good and perspective for future use. Bis-K4CK com-
2
pound was not able to excite ASE even at very high > 2 mJ/cm pulse
energy. It has one of the lowest PLQY values in thin film (see Table 3)
and also one of the largest overlaps between absorption and lumines-
cence spectra. Light emission peak FWHM is inversely proportional to
pump beam energy. With the increases of pump beam energy FWHM
decreases by around one order of magnitude. Compared with PL max-
imum position, ASE maximum position is red shifted. Shifts of each
compound differ from 12 nm (KTB3K) till 53 nm (Bis-K4C) (see
Table 3). These shifting between ASE and PL maximums positions could
be explained by the theory according to which cross section of stimu-
lated emission should be larger on the right sight of PL bands maximum
Comparably with solutions, absorption spectral bands of solid thin
films are slightly broader with small red-shift about 5 nm indicating a
weak excitonic interaction in the solid state (see Fig. 3). This is typical
for glass-forming amorphous materials. Less or even no (in the case of
molecules with one electron donating groups) influence of 9H-carba-
zole moieties on absorption spectra was observed. Bulky groups at-
tached to the electron withdrawing fragment have a larger impact on
thin film PL spectra than it was for solutions. Most blue-shifted PL
spectra were observed for compounds with 2-trityloxyethyl groups. In
the middle are compounds with 9H-carbazole moieties and the most
red-shifted are compounds without any bulky group. In the same
[
29]. Additional overlapping of PL and absorption spectrum bands
should be taken in to account. According to this dependence, ASE peaks
form only in those PL spectral regions, where optical gain is bigger than
absorption coefficient [29]. Moreover, the stimulated emission will
appear where the difference between the stimulated emission and ab-
sorption cross section will be positive. There is overlapping of PL and
absorption spectrum at the left side of the PL band. It means that the
largest positive difference between cross sections should be at the left
side of PL band. How could be seen from Table 3 and Fig. 4 the theo-
retical statement about red-shifting of ASE band relative to the PL band
is valid for all studied compounds. The ASE threshold values were
Table 2
Optical properties of KTB-type laser dyes in solutions of dichloromethane.
k*10 9, s−1
−
k
r
*10−9, s−1
k
nr*10−9, s−1
Compound
λ
abs, nm
λ
PL, nm
PLQY, %
KTB
KTBC
KTB3K
Bis-K4C
Bis-K5C
Bis-K4CK
462 ±
462 ±
470 ±
490 ±
491 ±
494 ±
2
2
2
2
2
2
580 ±
579 ±
586 ±
633 ±
635 ±
639 ±
2
2
2
2
2
2
25 ±
18 ±
25 ±
45 ±
44 ±
46 ±
2
2
2
2
2
2
2,70 ± 0.02
2,17 ± 0,03
1,19 ± 0,02
0,37 ± 0,01
0,37 ± 0,01
0,38 ± 0,01
0,68 ± 0.04
0,39 ± 0.02
0,30 ± 0.01
0,16 ± 0.01
0,16 ± 0.01
0,18 ± 0.01
2,03 ± 0.12
1,78 ± 0.11
0,89 ± 0.04
0,20 ± 0.01
0,21 ± 0.01
0,21 ± 0.01
λ
abs – absorption maximum wavelength, λPL – photoluminescence maximum wavelength, PLQY – photoluminescence quantum yield, k-decay rate, k
r
- radiative
decay rates, knr - nonradiative decay rates.
67

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
Table 3
Optical properties of KTB-type laser dyes in pure thin films.
2
Compound
λ
abs, nm
λ
PL, nm
FWHMPL, nm
PLQY, %
λ
ASE, nm
FWHMASE, nm
Eth, μJ/cm
KTB
KTBC
KTB3K
Bis-K4C
Bis-K5C
Bis-K4CK
471 ±
465 ±
470 ±
492 ±
494 ±
495 ±
2
2
2
2
2
2
618 ±
608 ±
614 ±
661 ±
649 ±
654 ±
2
2
2
2
2
2
170 ±
187 ±
180 ±
168 ±
151 ±
147 ±
2
2
2
2
2
2
23 ±
16 ±
16 ±
5 ±
7 ±
7 ±
2
2
2
2
2
2
633 ±
629 ±
626 ±
714 ±
659 ±
–
2
2
2
2
2
15 ±
15 ±
19 ±
20 ±
12 ±
–
2
2
2
2
2
24 ± 10
25 ± 10
52 ± 10
165 ± 10
223 ± 10
–
λ
abs – wavelength of absorption maximum, λPL – wavelength of photoluminescence maximum, PLQY – photoluminescence quantum yield, λASE – wavelength of
amplified spontaneous emission maximum, FWHM – full width of half maximum of PL or amplified spontaneous emission band, Eth – irradiation threshold energy
density at which amplified spontaneous emission appears.
optimized and solution processed (pure) KTB dye is 8 times lower in
relation to previously investigated mono-styryl-4H-pyran-4-ylidene
fragment containing compounds with triphenyl moieties (DWK-1TB)
[
45], 3–4 times lower than optimized vacuum deposited DCM dye
containing lasing medium [46], about the same as optimized vacuum
deposited DCM2:Aq3 with ADN “triplet manager” lasing system [9], but
still 8 times higher than optimized vacuum deposited DCM:Aq3 system
with distributed feedback component [47].
At the same time, the PLQY of pure KTB film is 3 times higher than
for pure DKW-1TB film [45], 7 times higher than for pure DWK-1 film
[
45] and about the same as for the optimized vacuum deposited DCM
dye containing mediums [8,9,47]. Threshold values of KTB-type dyes
are one order of magnitude larger in comparison to some other already
reported materials [44], however, it's quite difficult to make a direct
comparison between here mentioned and in different sources reported
compounds. The main reason of the appearance of those difficulties is
due to the fact that ASE threshold value depends not only on the
properties of the studied material but also on several parameters, such
as film thickness and purity. Nevertheless, the ASE threshold values
could still be decreased and the PLQY could still be increased by further
optimizing the investigated KTB-type compounds by one or several
approaches conducted for the 4H-pyran-4-ylidene fragment containing
light-emitting materials shown in Table 4.
4. Conclusions
Fig. 4. Amplified spontaneous emission properties (emitted light which went
through long pass filter with cut on wavelength till 532 nm) (a) Compounds
with one donor group and (b) Compounds with two donor groups. 1- KTB, 2-
KTBC, 3- KTB3K, 4- Bis-K4C, 5- Bis-K5C.
Physical properties and their relations with chemical structures of
six amorphous 2-cyano-2-(4H-pyran-4-ylidene) acetate derivatives with
different placement of 9H-carbazole and triphenyl functional groups
have been investigated. 6-tert-Butyl-2-styryl-substituted-4H-pyran-4-
ylidene 2-cyanoacetates (KTB, KTBC and KTB3K) are obtained as a
mixture of diastereoisomers. Ratio of diastereoisomers is 1:1 which is
not affected even by sterical dimensions of the bulky substituents at-
tached to the carboxyl group in the electron acceptor part of the mo-
lecule. Dyes with 9H-carbazole moieties (KTB3K, Bis-K4CK) showed
obtained from the ASE peak intensity dependence on irradiation pulse
energy at the point where the curve is changing the slope coefficient
and FWHM decrease by at least one order of magnitude as described
elsewhere [44] and showed in Table 3.
The threshold values of molecules with one electron donating group
KTB; KTBC; KTB3K) was one order of magnitude lower than in the
highest glass transition temperatures (T
triphenyl (KTBC, Bis-K5C) or ethyl (KTB, Bis-K4C) groups containing 2-
cyanoacetate derivatives (T varies from 99 °C to 107 °C). An increased
g
up to 137 °C) in comparison to
(
molecules with two electron donating groups (Bis-K4C; Bis-K5C). As
one of the reason is higher PLQY for the compounds with one donor
group. Dyes KTB and KTBC showed the lowest ASE excitation threshold
g
sterical interaction of the bulky moieties notably decreased thermal
stability of the corresponding molecules, in some cases even by more
than 100 °C. As it was expected, the bulky groups at electron donor and
acceptor parts of the molecule have a significant contribution in pro-
tecting the synthesized laser dyes from the intermolecular interaction
yielding high PLQY (from 16% up to 23%) and remarkably low ASE
2
2
values, sequentially – 24 μJ/cm and 25 μJ/cm , followed by KTB3K
2
with 52 μJ/cm . KTB also has the highest PLQY. Significantly higher
excitation threshold energies show all compounds with two donor
groups: Bis-K4C and Bis-K5C, sequentially – 165 μJ/cm and 223 μJ/
cm . One additional peak at 864 nm appears in the KTB sample. The
2
2
2
excitation threshold values (24–52 μJ/cm ) in case of organic glasses
intensity of the peak increases on the excitation energy but at the same
time it did not show ASE characteristics, like, excitation threshold en-
ergy or decreasing of full with at the half maximum.
The comparison of the three most effective KTB-type laser dyes
KTB, KTBC, KTB3K) with other most notable lasing medium systems
with only one incorporated electron donating fragment (KTB, KTBC and
KTB3K). Additionally, no bleaching of lighted area of their pure films
was observed. Therefore, these KTB-type dyes (KTB, KTBC and KTB3K)
could be potential low-cost solution processable materials for organic
lasers.
(
are shown in Table 4. ASE excitation threshold energy value of non-
68

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
Table 4
A comparison of KTB-type dyes with the most notable organic lasing mediums based on 4H-pyran-4-ylidene fragment containing compounds.
2
Laser dye
Lasing medium composition
Lasing medium deposition
PLQY, %
E
th, μJ/cm
Reference
DCM
DCM2
DCM
DWK-1
DWK-1
DWK-1TB
DWK-1TB
KTB
0.5–2% DCM doped in Alq3 + DFB
2% DCM2 + 28% Alq3 + 70% ADN
2% DCM + 98% PVK
100% dye only
20% DWK-1 + 80% PVK
100% dye only
20% DWK-1TB + 80% PVK
100% dye only
100% dye only
v. d.
v. d.
s. p.
s. p.
s. p.
s. p.
s. p.
s. p.
s. p.
s. p.
30
N/M
20
3
20
7.7 ±
25
23 ±
16 ±
16 ±
3
22
80
100
28
155 ±
21
24 ± 10
25 ± 10
52 ± 10
[8,47]
[9]
[46]
[45]
[46]
[29]
[46]
This work
This work
This work
1
7
2
2
2
KTBC
KTB3K
100% dye only
The PLQY and Eth results were measured for the lasing medium which was obtained by the described deposition. N/M − not measured; DFB – distributed feedback
component; PVK – polyvinylcarbazole; ADN – 9,10-di(naphtha-2-yl)anthracene; v. d. – vacuum deposition; s. p. – solution processing.
Acknowledgements
Isophorone- and pyran-containing NLO-chromophores: a comparative study.
Tetrahedron Lett 2010;51:3662–5.
[
[
17] Koeckelberghs G, De Groof L, Moreno JP, Asselberghs I, Clays K, Verbiest T, et al.
Synthesis and nonlinear optical properties of linear and Λ-shaped pyranone-based
chromophores. Tetrahedron 2008;64:3772–81.
18] Kwak G, Wang S, Choi MS, Kim H, Choi KH, Han YS, et al. 2D-π-A type pyran-based
dye derivatives: photophysical properties related to intramolecular charge transfer
and their electroluminescence application. Dyes Pigments 2008;78:25–33.
This work has been supported by the European Regional
Development Fund within the Activity 1.1.1.2 “Post-doctoral Research
Aid” of the Specific Aid Objective 1.1.1 “To increase the research and
innovative capacity of scientific institutions of Latvia and the ability to
attract external financing, investing in human resources and infra-
structure” of the Operational Programme “Growth and Employment”
[19] Li W, Li Q, Duan D, Liu S, Ying L, Huang F, et al. Design and synthesis of star-burst
triphenylamine-based π-conjugated molecules. Dyes Pigments 2015;113:1–7.
[
[
20] Awuah SG, Polreis J, Prakash J, Qiao Q, You Y. New pyran dyes for dye-sensitized
solar cells. J Photochem Photobiol, A 2011;224(1):116–22.
21] Bolag A, Nishida J, Hara K, Yamashita Y. Enhanced performance of dye-sensitized
solar cells with novel 2,6-diphenyl-4H-pyanylidene dyes. Org Electron
(
No. 1.1.1.2/VIAA/1/16/035). Financial support provided by European
Regional Development Fund within the Project No.1.1.1.1/16/A/046 is
greatly acknowledged. We express our gratitude to Kristine Lazdovica
for thermal decomposition temperature measurements and IR property
determination, Ilze Malina for conducting the elemental analysis and
Lauma Laipniece for HPLC and MS analysis.
2
012;13:425–31.
[
22] Kim SH, Hwang IJ, Gwon SY, Son YA. Photoregulated optical switching of poly(N-
isopropylacrylamide) hydrogel in aqueous solution with covalently attached spir-
onaphtoxazine and D-π-A type pyran based fluorescent dye. Dyes Pigments
2
010;87:158–63.
[
23] Lee EM, Gwon SY, Ji BC, Wang S, Kim SH. Multiple switching behaviors of poly(N-
isopropylacrylamide) hydrogel with spironaphtoxazine and D-π-A type dye. J
Lumin 2012;132:665–70.
Appendix A. Supplementary data
[
24] Wang S, Kim SH. Proton-induced fluorescent switching of new 2D-π-A type vi-
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.dyepig.2018.11.041.
nylcyanoacetate-pyran dye. Spectrochim Acta A 2009;72:677–81.
[
25] Li EM, Gwon SY, Ji BC, Kim SH. Temperature-induced phase transition and in-
tramolecular charge-transfer process based on poly(N-isopropylacrylamide) hy-
drogel with covalently attached D-π-A type dye. J Lumin 2011;131:1211–5.
26] Kwak G, Kim H, Kang IK, Kim SH. Charge transfer dye in various polymers with
different polarity: synthesis, photophysical properties, and usual aggregation-in-
duced fluorescence changes. Marcomolecules 2009;42:1733–8.
1- KTB, 2- KTBC, 3- KTB3K, 4- Bis-K4C, 5- Bis-K5C, 6- Bis-K4CK.
[
References
[
[
[
[
[
[
[
[
1] Hung LS, Chen CH. Recent progress on molecular organic electroluminescent ma-
terials and devices. Mater Sci Eng R 2002;39:143–222.
2] Strohriegel P, Grazulevicius JV. Charge-Transporting molecular glasses. Adv Mater
[27] Traskovskis K, Mihailovs I, Tokmakovs A, Jurgis A, Kokars V, Rutkis M. Triphenyl
moieties as building blocks for obtaining molecular glasses with nonlinear optical
activity. J Mater Chem 2012;22:11268–76.
[28] Traskovskis K, Zarins E, Laipniece L, Tokmakovs A, Kokars V, Rutkis M. Structure-
dependent tuning of electro-optic and thermoplastic properties in triphenyl groups
containing molecular glasses. Mater Chem Phys 2015;155:232–40.
[29] Zarins E, Vembris A, Misina E, Narels M, Grzibovskis R, Kokars V. Solution pro-
cessable 2-(trityloxy)ethyl and tert-butyl group containing amorphous molecular
glasses of pyranylidene derivatives with light-emitting and amplified spontaneous
emission properties. Opt Mater 2015;49:129–37.
[30] Zarins E, Tokmakovs A, Kokars V, Ozols A, Augustovs P, Rutkis M. Triphenyl group
containing molecular glasses of azobenzene for photonic applications. Opt Mater
2016;53:146–54.
(
Weinheim, Ger) 2002;14:1439–52.
3] Samuel DWI, Turnbull GA. Organic semiconductor lasers. Chem Rev
007;107:1272–95.
2
4] Ostroverkhova O, Moerner WE. Organic photorefractives: mechanisms, materials,
and applications. Chem Rev 2004;104:3267–314.
5] Kozlov VG, Forrest SR. Lasing action in organic semiconductor thin films. Curr Opin
Solid State Mater Sci 1999;4:203–8.
6] Tang CW, VanSlyke SA, Chen CH. Electroluminescence of doped organic thin-films.
J Appl Phys 1989;65:3610–6.
7] Kozlov VG, Bulovic V, Burrows PE, Forrest SR. Laser action in organic semi-
conductor waveguide and double-heterostructure devices. Nature 1997;389:362–4.
8] Kozlov VG, Bulovic V, Burrows PE, Baldo M, Khalfin VB, Parthasarathy G, et al.
Study of lasing action based on Forster energy transfer in optically pumped organic
semiconductor thin films. J Appl Phys 1998;84:4096–108.
[31] Vembris A, Zarins E, Jubels J, Kokars V, Muzikante I, Miasojedovas A, et al.
Thermal and optical properties of red luminescent glass forming symmetric and non
symmetric styryl-4H-pyran-4-ylidene fragment containing derivatives. Opt Mater
2
012;34:1501–6.
[9] Zhang Y, Forrest SR. Existence of continuous-wave threshold for organic semi-
[32] Grazulevicius JV, Strohriegl P, Pielichowski J, Pielichowski K. Carbazole-containing
polymers: synthesis, properties and applications. Prog Polym Sci
2003;28:1297–353.
[33] Boudreault TPL, Beaupre S, Leclerc M. Polycarbazoles for plastic electronics. Polym
Chem 2010;1:127–36.
[34] Grazulevicius JV. Charge-transporting polymers and molecular glasses for optoe-
lectronic applications. Polym Adv Technol 2006;17:694–6.
[35] Aziz H, Popovic ZD, Hu NX, Hor AM, Xu G. Degradation mechanism of small mo-
conductor lasers. Phys Rev B 2011;84. 241301-1-241301-4.
[
10] Yao YS, Xiao J, Wang XS, Deng ZB, Zhang BW. Starburst DCM-type red-light-
emitting materials for electroluminescence applications. Adv Funct Mater
2
006;16:709–18.
11] Chen CH, Tang CW, Shi J, Klubek KP. Recent developments in the synthesis of red
dopants for Alq hosted electroluminescence. Thin Solid Films 2000;363:327–31.
12] Guo Z, Zhu W, Tian H. Dicyanomehtylene-4H-pyran chromphores for OLED emit-
ters, logic gates and optical chemosensors. Chem Commun 2012;48:6073–84.
13] Hwang DH, Lee JD, Lee MJ, Lee C. Organic light-emitting diode using a new DCM
derivative as an efficient orange-red doping molecule. Curr Appl Phys
[
[
[
3
lecule-based organic light-emitting devices. Science 1999;283:1900–2.
[
36] Chen YH, Lin SL, Chang YC, Chen YC, Lin JT, Lee RH, et al. Efficient non-doped blue
light emitting diodes based on novel carbazole-substituted anthracene derivatives.
Org Electron 2012;13:43–52.
2
005;5:244–8.
[
14] Guo ZQ, Zhao P, Zhu WH, Huang XM, Xie YS, Tian H. Intramolecular charge-
transfer process based on dicyanomethylene-4H-pyran derivative: an integrated
operation of half-subtractor and comparator. J Phys Chem C 2008;112:7047–53.
15] Guo ZQ, Zhu WH, Shen LJ, Tian H. A fluorophore capable of crossword puzzles and
logic memory. Angew Chem Int Ed 2007;46:5549–53.
[37] Neises B, Steglich W. Simple method for the esterification of carboxylic acids.
Angew Chem Int Ed 1978;17:522–4.
[38] Traskovskis K, Lazdovica K, Tokmakovs A, Kokars V, Rutkis M. Modular approach
to obtaining organic glasses from low-molecular weight dyes using 1,1,1-triphe-
nylpentane auxiliary groups: nonlinear optical properties. Dyes Pigments
2013;99(3):1044–50.
[
[
16] Andreu R, Franco S, Galįn E, Garin J, N De Baroja M, Momblona C, et al.
69

E. Zarins et al.
Dyes and Pigments 163 (2019) 62–70
[39] Lueg C, Galla F, Frehland B, Schepmann D, Daniliuc CG, Deuther-Conrad W, et al.
4H-pyran-4-5 ylidene. Opt Mater 2013;36(2):529–34.
Hydroxyalkylation with cyclic sulfates: synthesis of carbazole derived CB
with increased polarity. Arch Pharm 2014;347:21–31.
2
ligands
[44] Li JY, Laquai F, Wegner G. Amplified spontaneous emission in optically pumped
neat films of a polyfluorene derivative. Chem Phys Lett 2009;478:37–41.
[45] Vembris A, Muzikante I, Gulbinas V, Karpicz R, Sliauzys G, Miasojedovas A, et al.
Fluorescence and amplified spontaneous emission properties of glass forming styryl-
4H-pyran-4-ylidene fragment containing derivatives. J Lumin 2012;132(9):2421–6.
[46] Vembris A, Zarins E, Kokars V. Stimulated emission and optical properties of pyr-
anyliden fragment containing compounds in PVK matrix. Optic Laser Technol
2017;95(1):74–80.
[
40] Wang C. An oxygen-sensing rhenium (I) complex with a carbazole “Shield” in its
diamine ligand: synthesis, characterization, photophysical property and sensing
performance. J Lumin 2014;145:531–8.
41] Gottlieb HE, Kotlyar V, Nudelman A. NMR chemical shifts of common laboratory
solvents as trace impurities. J Org Chem 1997;62:7512–5.
42] Grabowski ZR, Rotkiewicz K, Rettig W. Structural changes accompanying in-
tramolecular electron transfer: focus on twisted intramolecular charge-transfer
states and structures. Chem Rev 2003;103:3899–4031.
[
[
[47] Berggren M, Dodabalapur A, Slusher RE, Timko A, Nalamasu O. Organic solid-state
lasers with imprinted gratings on plastic substrates. Appl Phys Lett
1998;72(4):410–1.
[
43] Popova S, Pudzs K, Latvels J, Vembris A. Light emitting and electrical properties of
pure amorphous thin films of organic compounds containing 2-tert-butyl-6-methyl-
70