Synthesis and characterization of methoxy- or cyano-substituted thiophene/phenylene co-oligomers for lasing application

Article abstract of DOI:10.1039/d0ra04742b

As new candidates of thiophene/phenylene co-oligomer (TPCO) species, 5,5′′-bis(4′-methoxy-[1,1′-biphenyl]-4-yl)-2,2′:5′,2′′-terthiophene (BP3T-OMe) and 4′,4′′′-([2,2′:5′,2′′-terthiophene]-5,5′′-diyl)bis(([1,1′-biphenyl]-4-carbonitrile)) (BP3T-CN) were synthesized for lasing applications. Although most unsubstituted TPCO species crystallize in monoclinic form, BP3T-OMe and BP3T-CN crystallized in orthorhombic and triclinic forms, respectively. Since the unsubstituted species, 5,5′′-bis(4-biphenylyl)-2,2′:5′,2′′-terthiophene (BP3T), shows unique and superior lasing performance in single crystals, the newly synthesized BP3T-OMe and BP3T-CN have possibilities to show different or improved optoelectronic characteristics. Amplified spontaneous emission (ASE) and optically pumped lasing were observed from both of the single crystals based on their well-shaped crystalline cavity and high group refractive index values of 3.7-5.3 for excellent light confinement. The lasing threshold for the BP3T-OMe crystal was lower than that for the BP3T-CN crystal, which was attributed to their different molecular orientation, standing in the former and inclining in the latter. This journal is

Full text of DOI:10.1039/d0ra04742b

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis and characterization of methoxy- or
cyano-substituted thiophene/phenylene co-
oligomers for lasing application†
Cite this: RSC Adv., 2020, 10, 24057
abc
b
b
b
Takumi Matsuo,
*
c
Carina Rossiger, Jasmin Herr, Richard Gottlich,
¨ ¨
a
d
a
Derck Schlettwein, Hitoshi Mizuno, Fumio Sasaki and Hisao Yanagi
0
0
0
0
As new candidates of thiophene/phenylene co-oligomer (TPCO) species, 5,5 -bis(4 -methoxy-[1,1 -
0
0
00
0
000
0
0
00
00
biphenyl]-4-yl)-2,2 :5 ,2 -terthiophene (BP3T-OMe) and 4 ,4 -([2,2 :5 ,2 -terthiophene]-5,5 -diyl)
0
bis(([1,1 -biphenyl]-4-carbonitrile)) (BP3T-CN) were synthesized for lasing applications. Although most
unsubstituted TPCO species crystallize in monoclinic form, BP3T-OMe and BP3T-CN crystallized in
0
0
orthorhombic and triclinic forms, respectively. Since the unsubstituted species, 5,5 -bis(4-biphenylyl)-
0
0
00
2
,2 :5 ,2 -terthiophene (BP3T), shows unique and superior lasing performance in single crystals, the
newly synthesized BP3T-OMe and BP3T-CN have possibilities to show different or improved
optoelectronic characteristics. Amplified spontaneous emission (ASE) and optically pumped lasing were
observed from both of the single crystals based on their well-shaped crystalline cavity and high group
refractive index values of 3.7–5.3 for excellent light confinement. The lasing threshold for the BP3T-OMe
crystal was lower than that for the BP3T-CN crystal, which was attributed to their different molecular
orientation, standing in the former and inclining in the latter.
Received 3rd April 2020
Accepted 12th June 2020
DOI: 10.1039/d0ra04742b
rsc.li/rsc-advances
characteristics based on gain systems using excited state
Introduction
13
intramolecular proton transfer (ESIPT) or F ¨o rster resonance
14
Since the realization of an organic electroluminescence (EL) energy transfer (FRET) have been realized or proposed to
device composed of an anthracene single crystal reported by M. construct efficient gain systems. Of these, gain systems using
1
Pope et al. in 1963, organic light emissive p-conjugated FRET was also reported toward the realization of electrically
compounds have been paid great attention toward practical pumped lasing, by constructing a host-guest energy transfer
14
applications because of their tunability of light emission system from triplet excited state to singlet excited state.
wavelengths by changing the molecular structure and their Beyond optical pumping conditions, electrically pumped gain-
good processability. Aerwards, optically pumped gain- narrowed emissions have been recently reported from both
15
narrowed emissions and lasing have been reported for various organic light emitting diode (OLED) devices and organic light
2
16
organic materials such as p-conjugated polymers, dis- emitting eld-effect transistor (OLEFET) devices.
3
tyrylbenzene (DSB) derivatives, thiophene/phenylene co-
Among a large number of organic light emissive p-conju-
etc. Recently, carbon-bridged oligo-para- gated compounds, thiophene/phenylene co-oligomers (TPCO)
4–10
oligomers (TPCO)
phenylenevinylene (COPV) derivatives were synthesized to which are composed of linearly chained thiophene and phe-
realize low threshold lasing and especially high optoelectronic nylene units, are promising materials as active media for lasing
11,12
durabilities.
In addition, unique light amplication under both electrically and optically pumped conditions owing
to their high carrier mobilities, high thermal stabilities and
1
7–20
00
high refractive indices.
2
Of these, 5,5 -bis(4-biphenylyl)-
a
Graduate School of Science and Technology, Nara Institute of Science and Technology,
0
0
00
,2 :5 ,2 -terthiophene (BP3T) has been frequently used as an
8
916-5 Takayama, Ikoma, Nara 630-0192, Japan. E-mail: matsuo.takumi.mp2@ms.
active medium in OLEFET devices, and electrically pumped
gain narrowed emissions were observed due to their ambipolar
naist.jp
b
Institute of Organic Chemistry, Justus-Liebig-University Giessen, Heinrich-Buff-Ring
1
c
7, 35392 Giessen, Germany
carrier transport characteristics with high carrier mobilities and
Institute of Applied Physics, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 16, high internal quantum efficiency. Although single crystals of
21
3
5392 Giessen, Germany
BP3T have been prepared by physical vapor transport (PVT)
process, and gain narrowed emissions were successively
observed under both optical and electrical pumping, lasing
behaviours by self-cavity effect have hardly been investigated
due to their curved crystal edges. However, BP3T single crystals
d
Electronics and Photonics Research Institute, National Institute of Advanced
Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-
8
568, Japan
†
CCDC 1991924–1991925. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/d0ra04742b
This journal is © The Royal Society of Chemistry 2020
RSC Adv., 2020, 10, 24057–24062 | 24057

View Article Online
RSC Advances
Paper
show unusual light amplication behaviour, which cannot be
explained by the conventional stimulated emission (SE)
process. Stimulated resonant Raman scattering (SRRS) was
22
observed from a BP3T single crystal at 12 K, which indicates an
existence of coherent molecular vibrations. The SRRS has also
been observed for other TPCO single crystals even at room
temperature with emission lines more narrow than that of ASE
22,23
even without any cavity structure,
and their light emission
wavelength can be tuned by changing the excitation wavelength.
Moreover, the BP3T single crystal showed pulse-shaped light
emission with several tens picoseconds delay relative to the
24,25
excitation pulse at room temperature.
This time-delayed
emission in contrast to the SE strongly suggests a cooperative
light amplication process similar to superuorescence or
25
polariton lasing. As an origin of the delay time, phase relaxa-
tion to form a macroscopic ensemble of correlated emitters was Fig. 1 (a–c) Crystal structure of BP3T-OMe with a projection on ac-
expected among highly oriented molecules. According to liter- plane, ab-plane, and bc-plane, respectively. (d) Enlarged structure
2
6
showing interatomic distances between oxygen and neighboring
hydrogen atoms in the methoxy-groups.
ature, BP3T crystallizes in monoclinic form, and the molecular
long axis is perpendicular to the crystal basal plane. Since the
p–p* transition dipole moments are oriented parallel to the
molecular long axis, the emitted light propagates in a transverse
magnetic (TM) mode, and the light emission is conned
strongly inside a platelet single crystal. This condition of light
connement seems favourable for the formation of aforemen-
tioned macroscopic ensemble. Although it's still controversial
to interpret the relationships between structure – light ampli-
ꢀ
26
with a tilting angle of 2.6 . Therefore, the orientation of BP3T-
OMe seems more favourable to conne photons in a cavity
consisting of a single crystal, comparing to the case of BP3T.
The origin of the perpendicularly aligned molecular orientation
in the BP3T-OMe single crystal can be attributed to the H-
bonding interaction between methoxy-groups of adjacent

cation characteristics, several reports have shown the fact that
amplied spontaneous emission (ASE) or lasing characteristics
are critically changed by molecular arrangement depending on
the p-electronic interactions, which is controlled by the
modication of constituting molecules in organic crystals.
Here, we report on the synthesis of BP3T derivatives with
methoxy- or cyano-groups at the para-positions of the termi-
nating ends for further investigations of the aforementioned
unique light amplication characteristics. The introduction of
substituents leads to various intermolecular interactions, which
result in different crystal structures, molecular packings and
molecular orientations.
molecules as shown in Fig. 1(d). In a previous report about other
0
methoxy-substituted
TPCO
compounds,
2,5-bis(4 -
6
methoxybiphenyl-4-yl)thiophene (BP1T-OMe) showed the same
perpendicular orientation as a consequence of the hydrogen
bonding between the methoxy-groups.
On the other hand, BP3T-CN crystallized in a triclinic form (a
˚
˚
˚
ꢀ
ꢀ
¼
9.49 A, b ¼ 14.92 A, c ¼ 19.58 A, a ¼ 82.73 , b ¼ 87.51 , g ¼
Results and discussion
0
0
0
0
Here, we synthesized 5,5 -bis(4 -methoxy-[1,1 -biphenyl]-4-yl)-
0 0 00 0 000 0 0 00
2
,2 :5 ,2 -terthiophene (BP3T-OMe) and 4 ,4 -([2,2 :5 ,2 -ter-
00
0
thiophene]-5,5 -diyl)bis(([1,1 -biphenyl]-4-carbonitrile)) (BP3T-
2
6
CN), following a previously published report. XRD measure-
ments revealed crystal structures for both single crystals of
BP3T-OMe (CCDC-1991924) and BP3T-CN (CCDC-1991925).†
˚
BP3T-OMe crystallized in an orthorhombic form (a ¼ 65.19 A,
˚
˚
b ¼ 7.43 A, c ¼ 5.80 A, space group: Cmc2
1
, Z value: 4, cell
3
˚
volume: 2808 A ). Same as in the case of BP3T, the p-electronic
transition dipole moment is oriented parallel to the molecular
long axis. As shown in Fig. 1(a)–(c), BP3T-OMe takes perfectly
perpendicular molecular orientation to the crystal bottom plane
Fig. 2 (a) Crystal structure of BP3T-CN showing a tilted orientation of
the long molecular axes relative to the crystal basal plane. (b and c)
Crystal structure of BP3T-CN showing the molecular packing in
multiple unit cells. (d) Enlarged structure showing the interatomic
(
bc-plane), which is ideal to conne the cavity photon inside
a single crystal with in-plane direction. Although the orientation
of the molecular long axis of BP3T is also perpendicular to the
crystal bottom plane (ab-plane), however, it's a little inclined interaction between adjacent cyano-groups.
24058 | RSC Adv., 2020, 10, 24057–24062
This journal is © The Royal Society of Chemistry 2020

View Article Online
Paper
RSC Advances
ꢀ
˚
3
0.5
ꢀ
8
9.92 , space group: P1, Z value: 4, cell volume: 2746 A ). The Fig. 3(e) and (f) show plots of (photon yield) as a function of
ꢀ
molecular axis of BP3T-CN is tilted by about 45 against the incident photon energy in the measurements of photoelectron
bottom plane (ab-plane) as shown in Fig. 2(a) and (b). An origin spectroscopy in air (PESA). The highest occupied molecular
of the obliquely lying orientation is attributed to the electro- orbital (HOMO) levels estimated from the threshold photon
static interaction between cyano-substituents of neighbouring energy in Fig. 3(e) and (f) were ꢁ5.31 and ꢁ5.91 eV for BP3T-
0
molecules, as revealed in a previous report for 2,5-bis(4 - OMe and BP3T-CN, respectively. The lowest unoccupied
10
cyanobiphenyl-4-yl)thiophene (BP1T-CN). The cyano-groups molecular orbital (LUMO) levels calculated by the HOMO levels
are oppositely oriented at the intermolecular interface, there- and aforementioned frontier orbital gap energy values were
fore, the C(d+)–N(dꢁ) interaction is formed between the adja- ꢁ3.09 and ꢁ3.59 eV for BP3T-OMe and BP3T-CN, respectively.
cent molecular terminals as shown in Fig. 2(d). These lying The HOMO and LUMO levels of BP3T estimated by the same
molecular orientation is suitable for the realization of vertical procedures were ꢁ5.78 eV and ꢁ3.40 eV, respectively. These
cavity surface emitting lasers (VCSELs) using distributed Bragg results show that the methoxy- and cyano-group act as electron
reector (DBR) mirrors since the tilted transition dipole donating and electron withdrawing substituents, therefore, p-
moments allow sufficient emission components to the crystal type and n-type semiconducting characteristics can be ex-
2
8,29
surface direction.
Moreover, organic polariton lasers have pected in BP3T-OMe and BP3T-CN, respectively.
Lasing characteristics of their derivative crystals were
recently been investigated using VCSEL structures to realize low
threshold lasing devices. Actually, gain-narrowed emissions investigated under optical pumping using a Nd:YAG pulsed
from VCSEL structures were observed using cyano-substituted laser as an excitation source. As the excitation density is
28,29
TPCOs as active media in VCSELs.
elevated, the emission intensity was nonlinearly increased at
Next, we measured absorption and photoluminescence (PL) a certain threshold both for BP3T-OMe and BP3T-CN crystals,
spectra using vapour deposited thin lms as shown in Fig. 3(a) as shown in Fig. 4(a) and (b). The threshold excitation density
2
ꢁ2
ꢁ2
and (b). Fig. 3(c) and (d) show plots of (ahn) as a function of was estimated to be 17 mJ cm for BP3T-OMe and 152 mJ cm
photon energy where a and h and n represent the absorption for BP3T-CN, respectively. The threshold for the BP3T-OMe
coefficient, Plank's constant and the frequency, respectively. single crystal was lower than that of the BP3T-CN single
The values of a were obtained from the respective absorbance crystal, which can be attributed to their different molecular
divided by sample thickness. The frontier orbital gap value (Eg) orientation, as discussed in Results and discussion part. The
was obtained by extrapolating the linear slope of (ahn)2 to the perpendicular orientation to the crystal bottom plane in the
zero absorption coefficient (a ¼ 0). The obtained E values were BP3T-OMe single crystal is favourable for the efficient stimu-
g
2.22 eV and 2.32 eV for BP3T-OMe and BP3T-CN, respectively. lated emission along the planar cavity compared to the
inclining orientation in the BP3T-CN single crystal. As shown
in Fig. 4(c) and (d), longitudinal multi-mode lasing spectra
Fig. 4 (a) Excitation density dependence of integrated PL intensity for
Fig. 3 Absorption and PL spectra for BP3T-OMe (a) and BP3T-CN (b), 0–2 band taken from single crystals of BP3T-OMe (a) and BP3T-CN (b)
2
(
ahn) vs. energy plots for estimation of band-gap values of BP3T-OMe with their fluorescence image in the inset. PL spectra taken from single
0.5
ꢁ2
ꢁ2
(
c) and BP3T-CN (d), (photon yield) vs. energy plots for estimation of crystals of BP3T-OMe at 162 mJ cm (c) and BP3T-CN at 602 mJ cm
HOMO values for BP3T-OMe (e) and BP3T-CN (f).
(d) showing longitudinal multi-mode lasing.
This journal is © The Royal Society of Chemistry 2020
RSC Adv., 2020, 10, 24057–24062 | 24059

View Article Online
RSC Advances
Paper
were observed both for BP3T-OMe and BP3T-CN single crystal, for
2
hours. Tetrakis(triphenylphosphine)-palladium(0)
owing to the self-cavity effect in a well-shaped single crystal. (106.5 mg, 0.09220 mmol) was immediately added and
0
Group refractive index (n ) values were calculated using an subsequently 4-bromo-4 -methoxybiphenyl (1.743 g, 6.624
g
ꢁ
1
equation of n ¼ 1/2LDl , where L is the cavity length esti- mmol) dispersed in anhydrous tetrahydrofuran (5 mL) was
g
ꢀ
mated by the uorescence micrograph shown in Fig. 4(a) and added. The reaction mixture was warmed to 50 C and kept for
ꢁ
1
(
b), Dl is the mode intervals at each peaks of longitudinal 23 hours to yield a precipitate. The precipitate was washed
multi-mode lasing spectra. The calculated n value was 4.8 for with 50 mL THF, 50 mL H O, 10 mL 10% HCl, 50 mL H O,
g
2
2
BP3T-OMe while that of a BP3T-CN single crystal was 3.7–5.3. 50 mL acetone and 250 mL hot 1,2,4-trichlorobenzene,
As both single crystals of BP3T-OMe and BP3T-CN showed yielding 377 mg (0.615 mmol, 22%).
lasing performances based on those high group refractive
Synthesis of BP3T-CN. 4-Biphenylcarbonitrile (5.0037 g,
indices as similarly reported for other TPCO single crystals, 27.919 mmol) was mixed with acetic acid (13.7 mL) and water
these newly synthesized BP3T derivatives are strongly expected (2.8 mL) and 98% sulfuric acid (0.42 mL) in a one-neck ask.
as promising organic lasing media.
Iodine (3.646 g, 14.37 mmol) and periodic acid (1.405 g, 6.164
mmol) were added. Aer that, the mixture was warmed to 90 C
ꢀ
for 24 hours. During this time, the solution color changed from
colorless to red and a precipitate formed. The precipitate was
washed by water and methanol alternately 3 times, and dis-
solved in chloroform (100 mL). This solution was washed with
a saturated aqueous sodium chloride solution and dried over
anhydrous magnesium sulfate. Aer evaporating chloroform,
the remaining solid was dissolved in hot ethyl acetate (50 mL).
Experiments
Synthesis
To the best of our knowledge, only BP3T-OMe has been
3
0
synthesized via coupling reactions, so far. Here we synthesized
both BP3T-OMe and BP3T-CN via a Negishi coupling reaction as
shown in Scheme 1.
ꢀ
0
Methanol (25 mL) was added and cooled down to 5 C for
Synthesis of BP3T-OMe. 4-Bromo-4 -hydroxybiphenyl
crystallization. The precipitates were isolated by ltration and
(
5.004 g, 20.09 mmol), potassium carbonate (13.873 g, 100.38
mmol) and anhydrous acetone (50 mL) were put into a two-neck
ask. To this solution, iodomethane (1.6 mL) was added and
0
dried to give yellow crystals of 5.199 g (17.04 mmol, 61%) of 4 -
1
iodo-biphenyl-4-carbonitrile, which was identied by H NMR

(
solvent: deuteriochloroform) and showed the same chemical
then heated for 24 hours under reux. Then, all of the solution
was gathered in a beaker and water was added until all of the
solid was dissolved. Next, the solution was put into a separation
funnel, and extracted 3 times using 100–300 mL dichloro-
methane. Then, the dichloromethane phase was gathered in a 1
neck ask, and magnesium sulfate was added to remove
residual water. Aer ltrating this solution, all of the solvent
was removed, and the remaining solid was recrystallized 3 times
using acetone as highly soluble solvent and n-hexane as poor
27
shi and proton integral values as reported in the literature.
Using this obtained compound, BP3T-CN was synthesized
0
0
00
according to the reaction Scheme 1. 2,2 :5 ,2 -Terthiophene
671 mg, 2.701 mmol) was mixed with anhydrous THF (10 mL)
(
0
0
and N,N,N ,N -tetramethylethylenediamine (1.00 mL, 6.68
mmol). To this solution, 4 mL of 1.6 M n-butyllithium in
cyclohexane was added dropwise at 0 C and the reaction
ꢀ
mixture was heated under reux for 30 minutes and succes-
ꢀ
0
sively cooled down to ꢁ10 C. Anhydrous zinc chloride (1.335 g,
soluble solvent, yielding 4-bromo-4 -methoxybiphenyl (4.21 g,
9
.793 mmol) dispersed in anhydrous tetrahydrofuran (15 mL)
1
6.0 mmol, 80%).
ꢀ
0 0 00
was added and the reaction solution was kept at 25 C for 2
2
,2 :5 ,2 -Terthiophene (681 mg, 2.74 mmol) was mixed
0
0
hours. Tetrakis(triphenylphosphine)-palladium(0) (0.105 g,
with anhydrous THF (10 mL) and N,N,N ,N -tetramethylethy-
lenediamine (1.00 mL, 6.68 mmol). To this solution, 4 mL of
0
0
.0909 mmol) was immediately added and subsequently 4 -
iodo-biphenyl-4-carbonitrile (2.043 g, 6.696 mmol) dispersed in
anhydrous tetrahydrofuran (5 mL) were added. The reaction
1
0
.6 M n-butyllithium in cyclohexane was added dropwise at
C and the reaction mixture was reuxed for 30 minutes and
ꢀ
ꢀ
ꢀ
mixture was warmed to 50 C for 23 hours to yield a precipitate.
successively cooled down to ꢁ10 C. Anhydrous zinc chloride
This precipitate was ltered-off and washed with 50 mL THF,
(
(
1.233 g, 9.045 mmol) dispersed in anhydrous tetrahydrofuran
15 mL) was added and the reaction solution was kept at 25 C
ꢀ
50 mL H
O, 10 mL 10% HCl, 50 mL H O, 50 mL acetone, and
2 2
2
50 mL hot 1,2,4-trichlorobenzene, and further puried by
ꢀ
sublimation under a vacuum at 300 C. The solid remained in
the heating zone was collected as the puried target compound,
yielding 612 mg (1.02 mmol, 38%).
Due to the low solubility in any solvents for BP3T-OMe and
1
13
BP3T-CN, identication by H-NMR or C-NMR were unavail-
able. However, both of the target compounds were identied by
MALDI-TOF-MS, found [M] ¼ 612 and 602, for BP3T-OMe and
BP3T-CN respectively. Almost all of TPCO series were identied
by mass spectroscopy instead of using NMR spectroscopy in
27,30
previous reports.
Scheme 1 Synthesis protocol of BP3T-OMe and BP3T-CN where X ¼
methoxy, Y ¼ bromide for BP3T-OMe, and X ¼ cyano, Y ¼ iodide for
BP3T-CN.
24060 | RSC Adv., 2020, 10, 24057–24062
This journal is © The Royal Society of Chemistry 2020

View Article Online
Paper
RSC Advances
Preparation of single crystals and vapour deposited thin lms
connement in the single-crystal cavity in a TM mode
comparing to that of BP3T single crystals with slightly inclined
orientation. On the other hand, a molecular orientation of
BP3T-CN was oblique to the crystal basal plane, which is suit-
able for surface-emitting devices. The HOMO and LUMO levels
of BP3T-OMe and BP3T-CN estimated by absorption and
photoelectron spectroscopies revealed that the methoxy-group
and cyano-groups act as electron-donating and electron-
withdrawing groups, leading to expected p- and n-type semi-
conduction, respectively. Single crystals of BP3T-OMe and
BP3T-CN showed optically pumped lasing with especially high
group refractive index values, indicating the possibility to serve
as good active media for organic lasers, especially in OLED
structures due to their p- and n-type characteristics. Further-
more, the lasing threshold for the BP3T-OMe crystal was lower
than that for the BP3T-CN crystal, which was attributed to their
different molecular orientation, standing in the former and
inclining in the latter.
Single crystals for X-ray diffraction measurements were
prepared via a modied sublimation process. Puried powder
of BP3T-OMe or BP3T-CN was put in a quartz crucible, and the
molecules were sublimed and collected into another quartz
ꢁ4
crucible facing each other in a vacuum chamber (2 ꢂ 10 to 4
ꢁ
4
ꢂ 10 Pa). Single crystals of BP3T-CN for PL measurements
were prepared by the same process used in X-ray diffraction
measurements. Single crystals of BP3T-OMe for PL measure-
ments were prepared via a solution growth process. First,
ꢀ
a saturated BP3T-OMe solution was prepared at 150 C using
1
1
,2,4-trichlorobenzene as solvent. The solution was heated to
90 C, then, successively cooled down to 40 C for 18 hours.
ꢀ
ꢀ
Thin lms of BP3T-OMe and BP3T-CN for optical and photo-
electron spectroscopy measurements were prepared by vapour
deposition onto glass substrates. Puried powder of BP3T-OMe
or BP3T-CN was evaporated from a resistively heated a quartz
ꢁ
4
ꢁ4
crucible under a vacuum condition (2 ꢂ 10 to 4 ꢂ 10 Pa).
Their deposition rate and lm thickness were monitored by
a quartz crystal microbalance.
Conflicts of interest
Optical characterizations
There are no conicts to declare.
Absorption and PL spectra were measured for the vapour-
deposited thin lms of BP3T-OMe and BP3T-CN using an
ultraviolet-visible (UV-vis) spectrometer (JASCO V-530). The
Acknowledgements
work functions of BP3T-OMe and BP3T-CN were measured by This work was supported by the Japanese Society for the
photo-electron spectroscopy in air (PESA, Riken Keiki AC-3) at Promotion of Science (JSPS) KAKENHI No. 19H02172. This work
the vapour-deposited thin lms on ITO/glass substrates. Fluo- was also partly supported by a grant-in-aid from the Graduate
rescence images as well as PL spectra of single-crystal samples School of Science and Technology, Nara Institute of Science and
were measured using a uorescence microscope (Olympus BX- Technology.
51) equipped with a charge coupled device (CCD) spectrom-
eter (Hamamatsu PMA-50) through a 10ꢂ objective lens.
References
Observation of optically pumped lasing
1
M. Pope, H. P. Kallmann and P. Magnante, J. Chem. Phys.,
1963, 38, 2042–2043.
Single crystals of BP3T-OMe grown via the solution process were
transferred onto glass substrates by immersing the substrates
into the solution, and then dried at atmosphere. Single-crystals
of BP3T-CN were transferred onto glass substrates using a metal
needle. Their uorescence images were taken under ultraviolet
excitation. Optically pumped PL measurements were performed
using a Nd:YAG pulsed laser (lex ¼ 355 nm, pulse frequency: 1.2
kHz, pulse duration: 1.1 ns) at room temperature under
2 H. Xia, C. Hu, T. Chen, D. Hu, M. Zhang and K. Xie, polymers,
2019, 11, 443.
3 S. Varghese, S.-J. Yoon, S. Casado, R. Fischer,
R. Wannemacher, S.-Y. Park and J. Gierschner, Adv. Opt.
Mater., 2014, 2, 542–548.
4 M. Ichikawa, R. Hibino, M. Inoue, T. Haritani, S. Hotta,
K. Araki, T. Koyama and Y. Taniguchi, Adv. Mater., 2005,
17, 2073–2077.
5 M. Ichikawa, K. Nakamura, M. Inoue, H. Mishima,
T. Haritani, R. Hibino, T. Koyama and Y. Taniguchi, Appl.
Phys. Lett., 2005, 87, 221113.
ambient conditions. The excitation beam shaped into a stripe of
2
0
.24 ꢂ 0.04 cm through a cylindrical lens was focused on the
ꢀ
single crystal surface with an incident angle of ꢃ45 . Photo-
emission radiated from the single-crystal edge was detected
using a CCD spectrometer (Hamamatsu PMA-50) through an
optical ber.
6 J. Gierschner, S. Varghese and S. Y. Park, Adv. Opt. Mater.,
2016, 4, 348–364.
7
8
S. Hotta, Polym. Int., 2017, 66, 223–236.
H. Yanagi, Y. Marutani, F. Sasaki, Y. Makino, T. Yamao and
S. Hotta, Appl. Phys. Express, 2011, 4, 062601.
Conclusions
BP3T-OMe and BP3T-CN were successfully synthesized and
9 H. Mizuno, U. Haku, Y. Marutani, A. Ishizumi, H. Yanagi,
their crystal structures were identied. BP3T-OMe and BP3T-CN
F. Sasaki and S. Hotta, Adv. Mater., 2012, 24, 5744–5749.
crystallized in orthorhombic and triclinic forms, respectively. 10 H. Mizuno, T. Maeda, H. Yanagi, H. Katsuki, M. Aresti,
The molecular orientation of BP3T-OMe is perfectly perpen-
F. Quochi, M. Saba, A. Mura, G. Bongiovanni, F. Sasaki
dicular to the crystal basal plane, suggesting more efficient light
and S. Hotta, Adv. Opt. Mater., 2014, 2, 529–534.
This journal is © The Royal Society of Chemistry 2020
RSC Adv., 2020, 10, 24057–24062 | 24061

View Article Online
RSC Advances
Paper
1
1
1 X. Zhu, H. Tsuji, L. J. T. Navarrete, J. Casado and 20 T. Yamao, N. Sakamoto, S. Hotta, H. Mizuno and H. Yanagi,
E. Nakamura, J. Am. Chem. Soc., 2012, 134, 19254–19259. Jpn. J. Appl. Phys., 2012, 51, 5111PD03.
2 M. Morales-Vidal, P. G. Boj, J. M. Villalvilla, J. A. Quintana, 21 S. Kanazawa, M. Ichikawa, T. Koyama and Y. Taniguchi,
Q. Yan, N.-T. Lin, X. Zhu, N. Ruangsupapichat, J. Casado, ChemPhysChem, 2006, 7, 1881–1884.
H. Tsuji, E. Nakamura and M. A. Diaz-Garcia, Nat. 22 H. Yanagi, Y. Marutani, N. Matsuoka, T. Hiramatsu,
Commun., 2015, 6, 8458.
3 S. Park, O.-H. Kwon, S. Kim, S. Park, M.-G. Choi, M. Cha,
A. Ishizumi, F. Sasaki and S. Hotta, Appl. Phys. Lett., 2013,
103, 243301.
1
1
1
1
S. Y. Park and D.-J. Chang, J. Am. Chem. Soc., 2005, 127, 23 H. Yanagi, A. Yoshiki, S. Hotta and S. Kobayashi, J. Appl.
0070–10074. Phys., 2004, 96, 4240–4244.
4 Y. Jiang, P. Lv, J.-Q. Pan, Y. Li, H. Lin, X.-W. Zhang, J. Wang, 24 N. Matsuoka, T. Hiramatsu, H. Yanagi, F. Sasaki and
1
Y.-Y. Liu, Q. Wei, G.-C. Xing, W.-Y. Lai and W. Huang, Adv.
Funct. Mater., 2019, 29, 1806719.
5 S. Sandanayaka, T. Matsushima, F. Bencheikh, S. Terakawa,
S. Hotta, Jpn. J. Appl. Phys., 2010, 49, 01AD05.
25 T. Matsuo, H. Mizuno, F. Sasaki and H. Yanagi, Jpn. J. Appl.
Phys., 2020, 59, SDDB02.
W. J. Potscavage Jr, C. Qin, T. Fujihara, K. Goushi, J. Ribierre 26 S. Hotta, M. Goto, R. Azumi, M. Inoue, M. Ichikawa and
and C. Adachi, Appl. Phys. Express, 2019, 12, 061010. Y. Taniguchi, Chem. Mater., 2004, 16, 237–241.
6 T. Kanagasekaran, H. Shimotani, K. Kasai, S. Onuki, 27 T. Katagiri, S. Ota, T. Ohira, T. Yamao and S. Hotta, J.
R. D. Kavthe, R. Kumashiro and K. Tanigaki,
arXiv:1903.08869, 2019.
7 W. Takahashi, K. Maruyama, J. Li, M. Imakawa and
T. Takenobu, Jpn. J. Appl. Phys., 2014, 53, 02BB02.
8 Y. Sakurai, W. Hayashi, T. Yamao and S. Hotta, Jpn. J. Appl.
Phys., 2014, 53, 02BB01.
Heterocycl. Chem., 2007, 44, 853–862.
28 K. Yamashita, U. Huynh, J. Richter, L. Eyre, F. Deschler,
A. Rao, K. Goto, T. Nishimura, T. Yamao, S. Hotta,
H. Yanagi, M. Nakayama and R. H. Friend, ACS Photonics,
2018, 5, 2182–2188.
29 R. Hatano, K. Goto, K. Yamashita, F. Sasaki and H. Yanagi,
Jpn. J. Appl. Phys., 2017, 56, 04CL02.
1
1
1
9 T. Yamao, Y. Okuda, Y. Makino and S. Hotta, J. Appl. Phys.,
2011, 110, 053113.
30 Y. Inada, M. Koda, Y. Urabe, T. Katagiri, T. Yamao,
Y. Yoshida and S. Hotta, Sci. Rep., 2019, 9, 9739.
24062 | RSC Adv., 2020, 10, 24057–24062
This journal is © The Royal Society of Chemistry 2020