Design of Conjugated Molecules Presenting Short-Wavelength Luminescence by Utilizing Heavier Atoms of the Same Element Group

Article abstract of DOI:10.1002/asia.201800264

The introduction of heavy atoms into conjugated molecules often induces a redshift in the emission spectra. Conversely, we report here a blueshifting effect in the absorption and emission bands of a conjugated organic dye by employing a heavier atom from the same element group. Boron complexes having oxygen- and sulfur-bridged structures in the ligand moiety were synthesized, and their optical properties were compared. Significant optical bands in the absorption and luminescence spectra of the sulfur-bridged complex were observed in a shorter wavelength region than those of the oxygen-bridged complex. Theoretical calculations suggest that replacement of the bridging atom by a heavier one should reduce molecular planarity because of the larger atom size. As a result, the degree of electronic conjugation decreases, and this is followed by a blueshift in the optical bands. Finally, a blue-emissive crystal is demonstrated.

Full text of DOI:10.1002/asia.201800264

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Design for Presenting Short-Wavelength Luminescence by
Utilizing Heavier Atom of the Same Group Element Based on
Conjugated Molecule
Authors: Madoka Yamaguchi, Kazuo Tanaka, and Yoshiki Chujo
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.201800264
Link to VoR: http://dx.doi.org/10.1002/asia.201800264
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

10.1002/asia.201800264
Chemistry - An Asian Journal
Design for Presenting Short-Wavelength
Luminescence by Utilizing Heavier Atom of the
Same Group Element Based on Conjugated
Molecule
Madoka Yamaguchi, Kazuo Tanaka,* Yoshiki Chujo*
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
E-mail: kazuo123@chujo.synchem.kyoto-u.ac.jp (for K.T.);
chujo@chujo.synchem.kyoto-u.ac.jp (for Y.C.)
Key words: boron; chalcogen; conjugation; solid-state emission
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
ABSTRACT
Introduction of heavy atoms often induces red shift in the emission spectra with
conjugated molecules. Conversely, we report here the blue-shifting effect on the
absorption and emission band by employing a heavier atom in the same element group
based on the conjugated organic dye. The boron complexes having the oxygen- and
sulfur-bridged structures in the ligand moiety were synthesized, and their optical
properties were compared. It was observed that significant optical bands were observed
in the shorter wavelength region from the sulfur-bridged complex than those from the
oxygen one in the absorption and luminescence spectra. Theoretical calculation results
proposed that replacement of the bridging atom to the heavier one should reduce
molecular planarity because of the larger atom size. As a result, degree of electronic
conjugation could decrease, followed by blue-shifted optical bands. Finally, the blue-
emissive crystal was demonstrated.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
INTRODUCTION
Blue-color emissive dyes are versatile as a host material in a cascade of energy transfer
for producing any color.1 By combination with green and red-color emissive materials,
white-light luminescence which is applicable for illumination can be generated.2−5
Therefore, the development of blue-color emissive organic materials is an area of
particular interest with high relevance, especially for improving quality of organic
luminescent devices. So far, numerous numbers of materials having blue-color emission
were reported based on phosphorescence6−8 and thermally-activated delayed
fluorescence.9−11 However, there remains a challenge to have blue-color emission in the
condensed state because inevitable intermolecular interaction frequently induced red
shifts in the optical spectra and aggregation-caused quenching (ACQ). Thus,
establishment of a new design strategy not only for obtaining blue emission but also for
observing invariable optical properties even in the solid state is still of great significance.
To overcome ACQ and obtain solid-state luminescence, a class of compounds having
aggregation-induced emission (AIE), in which intense emission was observed only in the
solid state, while emission quenching occurred in the solution, has attracted attention.12−16
By employing AIE-active building blocks, various types of functional luminescent
materials have been developed.17−22 Recently, we have reported several AIE-active boron
complexes,23−27 and unique luminescent properties were found from boron
pyridinoiminates BPI and FBPI (Scheme 1).28 It was found that the pristine complex BPI
was the AIE-active molecule. From theoretical calculations, it was proposed that
structural relaxation should proceed after photo-excitation, and subsequently excitation
energy was consumed via the non-radiative processes. Based on this assumption, the ring
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
fusion structure was introduced into the ligand moiety to inhibit structural relaxation.
Accordingly, it was clearly indicated that the opposite behavior from FBPI, such as bright
emission only in the solution state and critical ACQ in the solid similarly to conventional
organic dyes, can be induced by the ring fusion at the ligand moiety. Thus, it can be said
that boron pyridinoiminate should be a property-tunable “element-block”, which is a
minimum functional unit composed of heteroatoms,29,30 for realizing solid-state
emission31 and both solution- and solid-state-specific luminescent materials based on the
single ligand complex.32 According to these data, we focused on the effect of the ring
fusion on the solid-state luminescent property. We presumed that optical properties can
be tuned by precisely modulating the bridged structure.33 To evaluate validity of this
assumption, the chalcogen-bridged boron pyridinoiminate complexes were designed.
Scheme 1
Herein, the synthesis and optical properties of the boron complexes with the oxygen-
(O-BPI) and sulfur-bridged (S-BPI) pyridinoiminate ligand are reported (Scheme 1).
From the UV−vis absorption and photoluminescence (PL) measurements, electronic
structures were investigated. Accordingly, it was observed that blue-shifting effects on
optical spectra were induced by the sulfur bridge. Theoretical calculation suggested that
molecular planarity could decrease by replacing the bridged atom to sulfur. As a result,
π-conjugation was weakened and subsequently blue-shifting effects were induced. In the
commodity organic dyes, replacement of the heavier element often induced red shifts in
the optical spectra, whereas the opposite property especially in the solid-state
luminescence was obtained in this study. The new strategy for tuning luminescent color
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
without critical loss of emission efficiency was presented by utilizing heteroatoms.
RESULTS AND DISCUSSION
Boron complexes were synthesized according to Scheme 2. The ligands were prepared
through the coupling reactions with 11-chlorodibenzocalcepine and lithiated
methylpyridine. By treating these ligands with BF3·OEt2, the boron complexes were
1
obtained. The products were characterized by H, 13C, and 11B NMR spectroscopies
(Charts S1‒S6) and mass measurements. From these data, it was confirmed that the
products had designed structures. Both products showed good solubility in common
organic solvents such as chloroform, dichloromethane, tetrahydrofuran and acetonitrile,
and decomposition was hardly observed in the air and during analyses. Therefore, it was
concluded that both boron complexes had high stability enough for evaluating the series
of optical properties.
Scheme 2
To examine electronic structures in the ground state, UV−vis absorption spectra with
O-BPI and S-BPI in the solution state were measured (Table 1). From the spectra in
CHCl3 (1.0 × 10−5 M), large absorption bands attributable to π−π* transition were
observed from both compounds (Figure 1a). S-BPI showed the smaller absorption band
in the shorter wavelength region than O-BPI. To evaluate energy levels of highest
occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
of both complexes, cyclic voltammetry (CV) was carried out with the solution samples
(Figure 2 and Table 2). From the onset values of redox waves, energy levels were
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
estimated. Accordingly, it was shown that S-BPI possessed lower HOMO and higher
LUMO levels than O-BPI. These data clearly indicate that O-BPI had a narrower band
gap than S-BPI.
Figures 1 and 2, Tables 1 and 2
To theoretically support these optical and electrochemical properties, quantum
chemical calculations with the density functional theory (DFT) method at the B3LYP/6-
31G(d) level were performed (Figure 3).34 Corresponding to the experimental data, S-
BPI presented a narrower band gap originating from higher HOMO and lower LUMO
levels. To estimate influence on the molecular structure by replacing oxygen to sulfur, the
bond angles at the chalcogen-bridged moiety and the dihedral angles between the phenyl
group and the boron-involving six-membered ring were focused (Figure 4). It was found
that the bond angle with sulfur was smaller than that of oxygen. In addition, the dihedral
angles in S-BPI was larger than that of O-BPI. These data mean that the complex
structure should be distorted by introducing the sulfur bridge. Because of the larger atom
size of sulfur, larger degree of molecular distortion should be induced. Hence, the larger
band gap, followed by blue-shifted emission was observed from S-BPI.
Figures 3 and 4
To examine electronic properties in the excited state, photoluminescence (PL) spectra
were measured with the solution samples (1.0 × 10−5 M in CHCl3) containing boron
complexes (Figure 1a and Table 1). Basically, both compounds showed small Stokes
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
shifts, indicating that structural relaxation should be suppressed by the chalcogen
bridging.28 This also means that molecular conformations should be preserved after
excitation. Similarly to the absorption spectra, the emission band of S-BPI was observed
in the shorter wavelength region than that of O-BPI. The distorted structure represented
as larger dihedral angles in S-BPI contributed to restriction of π-conjugation. As a
consequence, emission was obtained in the blue region. The luminescence quantum yields
of boron complexes were about 0.10. In the absence of the bridging atom, slight emission
() was observed from BPI, while the ring fusion contributed to drastic
enhancement of the efficiency () as observed in FBPI. It was assumed that
introduction of the chalcogen bridge could produce room to cause molecular tumbling.
Thereby, comparing to the emission efficiency of the complex having the fused ring
structure, those of the bridged complexes could decrease. To evaluate influence of
molecular motions on emission efficiency, PL spectra were measured in 2-
methyltetrahydrofuran (2-MeTHF) at 77 K (1.0 × 10−5 M, Figure 5 and Table 3). Under
frozen condition, both complexes showed much larger emission bands in the shorter
wavelength regions than those at room temperature. This fact means that molecular
motion should be responsible for excitation decay. It was found that boron complexes
presented phosphorescence at low temperature (Figure 6 and Table 4). According to the
previous report on boron pyridinoiminate, it is implied that the existence of the lone-pair
electrons on pyridine or imine groups might enhance intersystem crossing rates to the
triplet-excited state.28 It should be mentioned that the peak wavelengths of emission bands
both in chloroform and 2-MeTHF were similar, indicating that solvatochromicity in
luminescence was not observed from O-BPI and S-BPI. This fact means that emission
properties of these compounds hardly have charge transfer character.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figures 5 and 6, Tables 3 and 4
Emission properties were examined in the crystal state (Figure 1b and Table 1). From
the PL spectra in the crystalline state, it was observed that S-BPI showed the emission
band in the shorter wavelength region than O-BPI similarly in the solution state.
Apparently, blue-color emission was obtained from S-BPI (Figure 1c). Both compounds
showed slightly weaker emission (ΦPL ) in the crystalline state than that in the
solution state (ΦPL ≈ ), indicating that these molecules are not an AIE-active molecule,
similarly to FBPI.28 ACQ should occur due to intermolecular interaction in the closed
packing. To evaluate influence of intermolecular interaction in the solid state on emission
quenching, optical properties were monitored in the poly(methyl methacrylate) (PMMA)
matrix (Figure 7, Table 5). Significant emission bands with similar emission efficiencies
(O-BPI: ΦPL = 0.45; S-BPI: ΦPL = 0.44) were detected from both film samples. It was
likely that each boron complex would be spatially isolated in the polymer matrices, and
less intermolecular interaction should occur similarly to the previous AIE-active boron
complexes.35−37 In addition, molecular motions can be efficiently suppressed. Thus,
intense emission clearly indicates that intermolecular interaction induces ACQ in the
solid state of boron complexes. The kinetics were estimated from the degree of the rates
of radiative decay (kr) and non-radiative decay (knr) processes in each state according to
emission lifetimes (Table 6). In all states, larger knr values were obtained originating from
low ΦPL. In the solution state, it was found that knr of S-BPI was larger than that of O-
BPI. It is likely that the distorted structure should be unfavorable for accelerating the
emission process. Meanwhile, in the crystalline state, knr of O-BPI was larger, implying
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
that ACQ might occur in O-BPI because of the relative planar structure.
Figure 7, Tables 5 and 6
CONCLUSION
It was demonstrated that emission of boron pyridinoiminate complexes in the shorter-
wavelength region was induced by using heavier element as a bridge. From structural
estimation with theoretical calculations, the sulfur bridge played a critical role in
distortion of the molecular skeleton, and restricted π-conjugation should be responsible
for the shorter-wavelength region. Heavy atoms often induced bathochromic shifts in the
optical spectra, meanwhile blue-shifted optical bands were demonstrated from the sulfur-
containing molecule by applying the difference in atomic size for modulating molecular
planarity. From these results, it can be said that our findings described here could be valid
for molecular design of luminescent materials for advanced opto-electronic devices.
ACKNOWLEDGMENTS
This work was partially supported by the Mitsubishi Foundation (for K.T.) and a Grant-
in-Aid for Scientific Research (B) (JP17H03067) and on Innovative Areas “New
Polymeric Materials Based on Element-Blocks (No.2401)” (JP24102013).
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
REFERENCES
1.
2.
3.
Y. Kawamura, S. Yanagida, S. R. Forrest, J. Appl. Phys. 2002, 92, 87−93.
S.-J. Su, E. Gonmori, H. Sasabe, J. Kido, Adv. Mater. 2008, 20, 4189–4194.
H. Sasabe, J. Takamatsu, T. Motoyama, S. Watanabe, G. Wagenblast, N. Langer,
O. Molt, E. Fuchs, C. Lennarts, J. Kido, Adv. Mater. 2010, 22, 5003–5007.
G. Schwartz, S. Reineke, T. C. Rosenow, K. Walzer, K. Leo, Adv. Funct. Mater.
2009, 19, 1319–1333.
4.
5.
G. Schwartz, M. Pfeiffer, S. Reineke, K. Walzer, K. Leo, Adv. Mater. 2007, 19,
3672–3676.
6.
7.
K. S. Yook, J. Y. Lee, Adv. Mater. 2012, 24, 3169–3190.
C.-H. Yang, Y.-M. Cheng, Y. Chi, C.-J. Hsu, F.-C. Fang, K.-T. Wong, P.-T.
Chou, C.-H. Chang, M.-H. Tsai, C.-C. Wu, Angew. Chem. Int. Ed. 2007, 46,
2418–421.
8.
9.
T. Tsuboi, W. Huang, Isr. J. Chem. 2014, 54, 885−896.
Q. Zhang, B. Li, S. Huang, H. Nomura, H. Tanaka, C. Adachi, Nat. Photonics
2014, 8, 326−332.
10.
11.
C. Adachi, Jpn. J. Appl. Phys. 2014, 53, 060101.
Y. Im, M. Kim, Y. J. Cho, J.-A Seo, K. S. Yook, J. Y. Lee, Chem. Mater. 2017,
29, 1946−1963.
12.
13.
14.
J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam, B. Z. Tang, Chem.
Rev. 2015, 115, 11718–11940.
H. Eguchi, H. Nishiyama, S. Inagi, I. Tomita, Asian J. Org. Chem. 2016, 6,
165−168.
J. Mei, Y. Hong, J. W. Y. Lam, A. Qin, Y. Tang, B. Z. Tang, Adv. Mater. 2014,
26, 5429−5479.
15.
R. Hu, N. L. C. Leung, B. Z. Tang, Chem. Soc. Rev. 2014, 43, 4494−4562.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
16.
17.
S. Mukherjee, P. Thilagar, J. Mater. Chem. C 2016, 4, 2647−2662.
H. Imoto, K. Nohmi, K. Kizaki, S. Watase, K. Matsukawa, S. Yamamoto, M.
Mitsuishi, K. Naka, RSC Adv. 2015, 5, 94344−94350.
H. Imoto, K. Kizaki, S. Watase, K. Matsukawa, K. Naka, Chem. Eur. J. 2015, 21,
12105−12111.
18.
19.
20.
21.
22.
S. Shimizu, T. Iino, A. Saeki, S. Seki, N. Kobayashi, Chem. Eur. J. 2015, 21,
2893−2904.
W. A. Morris, M. Sabat, T. Butler, C. A. Derosa, C. L. Fraser, J. Phys. Chem. C
2016, 120, 14289−14300.
W. A. Morris, M. Kolpacznska, C. L. Fraser, J. Phys. Chem. C 2016, 120,
22539−22548.
T. Butler, W. A. Morris, J. Samonina-Kosicka, C. L. Fraser, ACS Appl. Mater.
Interfaces 2016, 8, 1242−1251.
23.
24.
25.
R. Yoshii, A. Nagai, K. Tanaka, Y. Chujo, Chem. Eur. J. 2013, 19, 4506–4512.
R. Yoshii, A. Hirose, K. Tanaka, Y. Chujo, Chem. Eur. J. 2014, 20, 8320−8324.
R. Yoshii, A. Hirose, K. Tanaka, Y. Chujo, J. Am. Chem. Soc. 2014, 136,
18131−18139.
26.
K. Tanaka, K. Nishino, S. Ito, H. Yamane, K. Suenaga, K. Hashimoto, Y. Chujo,
Faraday Discuss. 2017, 196, 31−42.
27.
28.
K. Tanaka, Y. Chujo, NPG Asia Mater. 2015, 7, e223.
M. Yamaguchi, S. Ito, A. Hirose, K. Tanaka, Y. Chujo, Mater. Chem. Front.
2017, 1, 1573−1579.
29.
30.
31.
Y. Chujo, K. Tanaka, Bull. Chem. Soc. Jpn. 2015, 88, 633−643.
M. Gon, K. Tanaka, Y. Chujo, Polym. J. 2018, 50, 109−126.
S. Ohtani, M. Gon, K. Tanaka, Y. Chujo, Chem. Eur. J. 2017, 23, 11827−11833.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
32.
33.
K. Suenaga, K. Tanaka, Y. Chujo, Eur. J. Org. Chem. 2017, 2017, 5191−5196.
T. Matsumoto, H. Takamine, K. Tanaka, Y. Chujo, Org. Lett. 2015, 17,
1593−1596.
34.
35.
M. J. Frish, et al. GAUSSIAN 09 (Revision D.01), Gaussian, Inc., Wallingford
CT, 2009.
K. Suenaga, R. Yoshii, K. Tanaka, Y. Chujo, Macromol. Chem. Phys. 2016, 217,
414−417.
36.
37.
R. Yoshii, K. Suenaga, K. Tanaka, Y. Chujo, Chem. Eur. J. 2015, 21, 7231−7237.
M. Yamaguchi, S. Ito, A. Hirose, K. Tanaka, Y. Chujo, J. Mater. Chem. C 2016,
3, 5314−5319.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
FIGURES AND TABLES
Scheme 1. Chemical structures of boron pyridinoiminate complexes
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Scheme 2. Syntheses of boron complexes
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 1. (a) UV−vis absorption and PL spectra of O-BPI and S-FBPI in CHCl3 (1.0 ×
10−5 M) and (b) PL spectra in the crystalline state. (c) Photographs of the crystals under
UV irradiation (365 nm).
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Table 1. Optical properties of the complexes
λabs,max εmax λPL
τ
λPL
τ
a,e
e,g
ΦPL
ΦPL
(nm)a (M−1cm−1)b (nm)a
(ns)a,f (nm)g
(ns)f,g
0.68 (70%)
1.67 (30%)
0.60 (19%)
1.70 (81%)
430
27,400
460c
0.10
0.11
0.82
0.67
483
476
0.05
0.05
O-BPI
S-BPI
409
25,200
454d
a Measured in chloroform (10−5 M).
b Determined at the peak wavelength.
c Excited at 416 nm.
d Excited at 409 nm.
e Determined as an absolute value with the integration sphere method.
f Excited at 375 nm.
g Measured with the crystalline sample.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 2. Cyclic voltammograms of O-BPI and S-BPI from (a) 0 V to −2.4 V and (b) 0
V to 1.5 V in CH2Cl2 (1.0 × 10–3 M) with 0.1 M Bu4NPF6 as a supporting electrolyte,
AgCl/Ag as a reference electrode, Pt as working and counter electrodes, and scan rate at
100 mV/s. (c) Energy diagram of O-BPI and S-BPI calculated by CV measurements.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Table 2. Electrochemical results from CV measurements with O-BPI and S-BPI
a
b
EOx
[V]
Ered
[V]
HOMOc
[eV]
LUMOd
[eV]
0.61
0.65
−2.22
−2.28
−5.41
−5.45
−2.58
−2.52
O-BPI
S-BPI
a EOx is the onset potential of first oxidation wave.
b Ered is the onset potential of first reduction wave.
c Calculated from the empirical formula6, HOMO = ‒EOx ‒ 4.80 (eV).
d Calculated from the empirical formula6, LUMO = ‒Ered ‒ 4.80 (eV).
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 3. Structures and molecular orbital diagrams of LUMO and HOMO of O-BPI and
S-BPI obtained with DFT calculations (B3LYP/6-31G (d)//B3LYP/6-31G (d)).
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 4. Molecular structure of O-BPI and S-BPI from quantum chemical calculations.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 5. PL spectra of (a) O-BPI and (b) S-BPI in 2-MeTHF (1.0 × 10–5 M) at r.t. (solid
line) and at 77 K (dashed line). Photographs of (c) O-BPI and (d) S-BPI in 2-MeTHF
(1.0 × 10–5 M) at r.t. and 77 K under UV irradiation (365 nm).
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Table 3. PL properties of O-BPI and S-BPI in 2-MeTHF (1.0 × 10–5 M)
PL
(r.t.)
[nm]
458
PL
(77K)
[nm]
444
PL
PL
(r.t.)
(77K)
0.07
0.09
0.75
0.79
O-BPI
S-BPI
452
436
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 6. PL spectra of (a) O-BPI and (b) S-BPI in 2-MeTHF (1.0 × 10–5 M) at 77 K
which were collected with a 1 ms delay. Photographs of (c) O-BPI and (d) S-BPI in 2-
MeTHF (1.0 × 10–5 M) at 77K under UV irradiation (365 nm) and immediately after
tuning off UV irradiation.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Table 4. Phosphorescence properties of O-BPI and S-BPI in 2-MeTHF (1.0 × 10–5 M)
at 77K
λPL [nm]
538
527
O-BPI
S-BPI
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Figure 7. (a) PL spectra of O-BPI and S-BPI in a polymer matrix (1 wt% in PMMA). (b)
Photographs under UV irradiation (365 nm).
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Table 5. PL properties of O-BPI and S-BPI in PMMA
PL
[nm]
d
[ns]
c
PL
2.35
(50%)
1.51
4.01
(50%)
3.59
456a
450b
0.45
0.44
O-BPI
S-BPI
(18%)
(82%)
a Excited at 416 nm
b Excited at 409 nm.
c Determined as an absolute value.
d Excited at 375 nm.
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
Table 6. Kinetics of optical processes
solution
crystal
PMMA
kr
knr
kr
knr
kr
knr
(×109 s−1)a (×109 s−1)a (×109 s−1)b (×109 s−1)b (×109 s−1)b (×109 s−1)b
0.12
0.16
1.1
1.3
0.042
0.031
0.80
0.59
0.13
0.13
0.16
0.16
O-BPI
S-BPI
a kr = ΦPL/τ; knr = (1−ΦPL)/τ. b kr = ΦPL/τav, knr = (1 – ΦPL)/τav, τav = Σαiτi2/Σαiτi.31
This article is protected by copyright. All rights reserved.

10.1002/asia.201800264
Chemistry - An Asian Journal
GRAPHICALABSTRACT
This article is protected by copyright. All rights reserved.