Why Do Simple Molecules with "isolated" Phenyl Rings Emit Visible Light?

Article abstract of DOI:10.1021/jacs.7b08592

π-Bonds connected with aromatic rings were generally believed as the standard structures for constructing highly efficient fluorophores. Materials without these typical structures, however, exhibited only low fluorescence quantum yields and emitted in the ultraviolet spectral region. In this work, three molecules, namely bis(2,4,5-trimethylphenyl)methane, 1,1,2,2-tetrakis(2,4,5-trimethylphenyl)ethane, and 1,1,2,2-tetraphenylethane, with nonconjugated structures and isolated phenyl rings were synthesized and their photophysical properties were systematically investigated. Interestingly, the emission spectra of these three molecules could be well extended to 600 nm with high solid-state quantum yields of up to 70%. Experimental and theoretical analyses proved that intramolecular through-space conjugation between the "isolated" phenyl rings played an important role for this abnormal phenomenon.

Full text of DOI:10.1021/jacs.7b08592

Subscriber access provided by GRIFFITH UNIVERSITY
Article
Why do simple molecules with “isolated” phenyl rings emit visible light?
Haoke Zhang, Xiaoyan Zheng, Ni Xie, Zikai He, Junkai Liu, Nelson L. C. Leung,
Yingli Niu, Xuhui Huang, Kam Sing Wong, Ryan T. K. Kwok, Herman H.Y.
Sung, Ian D. Williams, Anjun Qin, Jacky W. Y. Lam, and Ben Zhong Tang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b08592 • Publication Date (Web): 24 Oct 2017
Downloaded from http://pubs.acs.org on October 24, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 11
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
Why do simple molecules with “isolated” phenyl rings emit visible
light?
Haoke Zhang,†,‡,§ Xiaoyan Zheng,†,‡ Ni Xie,†,‡,§ Zikai He,†,‡,§ Junkai Liu,¶ Nelson L. C. Leung,†,‡,§
Yingli Niu,∇Xuhui Huang,†,‡ Kam Sing Wong,⊥Ryan T. K. Kwok,†,‡,§ Herman H. Y. Sung,† Ian D.
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
¶
Williams,† Anjun Qin,¶ Jacky W. Y. Lam,†,‡,§ and Ben Zhong Tang*,†,‡,§,
†Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong
Kong, China. E-mail: tangbenz@ust.hk
‡Hong Kong Branch of Chinese National Engineering Research Center for Tissue Restoration and Reconstruction,
Institute for Advanced Study, Institute of Molecular Functional Materials, State Key Laboratory of Molecular Neu-
roscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
§Guangdong Provincial Key Laboratory of Brain Science, Disease and Drug Development, HKUST Shenzhen Re-
search Institute, No. 9 Yuexing 1st RD, South Area, Hi-tech Park Nanshan, Shenzhen 518057, China.
¶Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Lumi-
nescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
⊥
Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong
Kong, China
∇
National Center for Nanoscience and Technology, Beijing 100190, China
Supporting Information
ABSTRACT: π-Bonds connected with aromatic rings were generally believed as the standard structures for constructing
highly efficient fluorophores. Materials without these typical structures, however exhibited only low fluorescence quan-
tum yields and emitted in the ultraviolet spectral region. In this work, three molecules, namely bis(2,4,5-
trimethylphenyl)methane, 1,1,2,2-tetrakis(2,4,5-trimethylphenyl)ethane and 1,1,2,2-tetraphenylethane, with non-
conjugated structures and isolated phenyl rings were synthesized and their photophysical properties were systematically
investigated. Interestingly, the emission spectra of these three molecules could be well extended to 600 nm with high
solid-state quantum yields of up to 70%. Experimental and theoretical analyses proved that intramolecular through-space
conjugation between the “isolated” phenyl rings played an important role for this abnormal phenomenon.
Chemistry in 2008 and 2014 for the discovery of green
fluorescent protein and super-resolved fluorescence mi-
croscopy, respectively.
1. INTRODUCTION
Fluorescence is a gift from nature and plays an important
role in our colourful world. Inspired by nature, human
starts to study this “interesting phenomenon” in the early
nineteenth century. Deeper cognition on the fluorescence
process can not only reveal some natural laws but also
better utilise and reform the natural world. Considering
from the view of academic research, why a fluorophore
emits light and how to design a highly efficient fluoro-
phore are two important issues for scientists. With the
rapid development of science and technology, fluores-
cence-based techniques have been well applied in the
fields of biology,1 medicine,2 optoelectronics,3 mechanical
engineering4 etc., as evidence by the Nobel prize in
Generally, fluorophores can be divided into organic and
inorganic systems. Due to the good biocompatibility, ad-
justability and portability of organic fluorophores, many
scientists have attracted to work on this area. So far, most
of the organic fluorophores are conjugated systems, with
different emitting units linking together by double bonds,
triple bonds, heteroatoms and aromatic rings.5 However,
there are some special species which do not contain any
above linkers in their structures but still show visible flu-
orescent emission. Representative examples are given by
biological systems,6 artificial polymers like poly(N-vinyl
1
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 11
carbazole)7 and polystyrene,8 and peptide,9 whose emis-
tation and vibration of each subunit will lead to the loss
1
2
3
4
5
6
7
8
sions have been observed for a long time but the associat-
ed mechanisms are still unclear and hard to be explained
by the traditional photophysical theories. Thus, the de-
velopment of new reliable models to explain these ab-
normal phenomena is needed and will be of academic
importance.
of excited state energy in a non-radiative decay manner to
quench the fluorescent emission in solution. When ag-
gregates form, such molecular motion will be restricted to
block the non-radiative decay pathways. On the other
hand, the radiative decay will dominate the photophysical
process to enable the AIEgens to show strong emission in
the aggregate state. Inspired by the fluorescence of ho-
mopolymer and copolymer of styrene, DPM was synthe-
sized, in which two substituted phenyl rings were bridged
by a methylene group (Figure 1A). Figure S5A showed its
UV spectrum in THF/water mixture. The absorption max-
imum (λabs) was located at 278 nm in both solution and
aggregate states, and was almost identical to that of 1,2,4-
trimethylbenzene (λabs ≈ 277 nm).18 Its photoluminescence
(PL) spectrum in pure THF (Figure 1A) was peaked at 297
nm associated with the emission of individual phenyl
ring.19 The emission became stronger upon gradual addi-
tion of water into the THF solution but decreased when
the water fraction (fw) exceeded 70%. Meanwhile, a new
broad peak arose from 350 nm to 500 nm, which intensi-
fied with increasing fw. At 90% water fraction, the PL in-
tensity at 380 nm was 140 times higher than that in pure
THF solution (Figure 1B).20 Since aggregates of DPM
should be readily formed in the presence of such a large
amount of water, this suggests that the longer-wavelength
emission demonstrates an AIE phenomenon. In the solid
state, DPM showed an emission peak at 400 nm and its
PL spectrum was well extended to 600 nm (Figure S6 and
Table 1).
So far, it is believed that the development of highly effi-
cient fluorophores relies largely on high electronic conju-
gation. However, the biocompatibility and processability
of these materials are of concern when they are utilized in
biological applications. On the other hand, non-
conjugated systems, such as some natural materials, pos-
sess high molecular flexibility, biocompatibility and pro-
cessability. Thus, if they can be designed to own visible
range emission and high fluorescence quantum yield, a
new research area will be opened. Actually, some pub-
lished papers have already shown us some inspiring re-
sults. For example, Hirayama found that diphenyl- and
triphenyl-alkanes showed longer-wavelength emission at
around 330 nm and attributed such phenomenon as in-
tramolecular excimer formation.10 At the same time, iso-
tactic polystyrene was discovered to exhibit a similar fluo-
rescent property by Lumry et al.8 However, in this system,
the emission was located in the invisible range with a low
fluorescence quantum yield. Thus, this work had attract-
ed little attention. Traditionally, excimer formation was
generally considered as the reason for fluorescence
quenching. Thus luminogens are often designed to avoid
the excimer formation.11 Recently, many systems proved
that excimers could enhance and bathochromically shift
the emission depending on the packing structure.12,13
Thus, one question arises: is it possible to construct effi-
cient non-conjugated luminogens with high quantum
yield and visible emission?
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
700
560
420
280
140
0
4
3
2
1
150
100
50
f
w (vol %)
A
297 nm
B
90
80
70
60
50
40
30
20
10
0
297 nm
380 nm
In this work, three non-conjugated compounds, namely
bis(2,4,5-trimethylphenyl)methane
(DPM),
1,1,2,2-
tetrakis(2,4,5-trimethylphenyl)ethane (s-TPE-TM) and
1,1,2,2-tetraphenylethane (s-TPE) with isolated phenyl
rings were synthesized according to scheme S1 in support-
ing information and characterized satisfactorily by stand-
ard spectroscopic methods (Figure S1-S4). Their photo-
physical properties were studied. Results showed that s-
TPE showed high fluorescence quantum yield of ~70%
and longer-wavelength emission at ~470 nm. The intra-
molecular through-space conjugation was found to play a
0
290
330
370
410
450
490
0
30
60
90
Wavelength (nm)
Water fraction (vol %)
Figure 1. A) PL spectra of DPM in THF/water mixture with
different water fractions (fw). B) Plots of relative PL intensity
(I/I0) versus fw at different emission wavelengths. Concentra-
tion = 10-4 M, λex = 280 nm, I0 = intensity at fw = 0%.
major role rather than the π-electronic conjugation in the
Although visible emission was observed in DPM, the as-
sociated fluorescence quantum yield (ΦF) was quite low,
and was measured to be merely 2%. We then studied the
light-emitting property of s-TPE-TM, which could be re-
garded as dimer of DPM (Figure 2A). Its higher molecular
rigidity is expected endow it with a higher ΦF. Its absorp-
tion maximum was located at 280 nm and was similar to
1,2,4-trimethylbenzene (Figure S5B). It showed an emis-
sion behaviour resembled that of DPM (Figure 2). In
THF/water mixture with low water fraction, it exhibited
only one peak at 300 nm. Again, a new broad peak ap-
peared at 390 nm when fw >70%. The intensity of the
visible emission. Meanwhile, the restriction of the intra-
molecular motions (RIM),14,15 which served as a mecha-
nism of the aggregation-induced emission (AIE) phenom-
enon,16,17 helped to convert the harmful effect of excimer
formation on the light emission process into a construc-
tive one.
2. RESULTS AND DISCUSSION
Aggregation-induced emission
Generally, most of the AIE luminogens (AIEgens) possess
propeller-like structures, and the free motion such as ro-
2
ACS Paragon Plus Environment

Page 3 of 11
Journal of the American Chemical Society
s-TPE was further investigated (Figure 3B). The absorp-
shorter-wavelength peak increased gradually when the fw
1
2
3
4
5
6
7
8
increased from 0% to 50%, but decreased afterwards. On
the other hand, the emission band at the longer wave-
length was intensified progressively with increasing the
water fraction. The maximum intensity enhancement was
170-fold. Like DPM, s-TPE-TM emitted at 397 nm in the
solid state (Figure S6) but showed a higher ΦF of 9% (Ta-
ble 1).
tion maximum of s-TPE was 10 nm hypsochromic shift
from that of s-TPE-TM and was located at 270 nm (Figure
S5C). This may due to the absence of hyperconjugation
between the benzene ring and the methyl groups.19,23,24
Figure 3A showed that the PL spectrum in THF/water
mixture with low water fraction exhibited only a peak at
290 nm assigned to benzene emission.19 Similar to the
above two compounds, the intensity of this shorter-
wavelength peak increased first with increasing water
fraction and then decreased afterwards. Once aggregates
formed at fw > 60%, a marvellous longer-wavelength emis-
sion at 460 nm was observed. This peak was intensified
when more water was added and the maximum emission
enhancement could reach 400-fold. In the solid state, a
bright and sky blue fluorescence was observed under 365
nm UV light irradiation (Figure 3B inset). The emission
peak was broad spanning from 400 nm to 600 nm with its
maximum at 467 nm (Figure S6). The quantum yield was
measured to be 70%, which subverted our traditional
views to this kind of non-conjugated molecules (Table 1).
800
9
180
2.4
A
fw (vol %)
B
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
90
80
70
60
50
40
20
0
300 nm
300 nm
390 nm
600
400
200
0
120
60
0
1.6
0.8
0.0
390 nm
290
330
370
410
450
490
0
30
60
90
Water fraction (vol %)
Wavelength (nm)
Figure 2. A) PL spectra of s-TPE-TM in THF/water mixture
with different water fractions (fw). B) Plots of relative PL in-
tensity (I/I0) versus fw at different emission wavelengths.
3
2
1
0
400
300
200
100
0
460 nm
fw (vol %)
1000
800
600
400
200
0
A
B
290 nm
460 nm
90
80
70
60
50
40
30
20
10
0
Concentration = 10-4 M, λex = 280 nm, I0 = intensity at fw
=
0%. Inset: fluorescent photos of s-TPE-TM solid taken under
365 nm UV light irradiation.
290 nm
Traditional theories teach us that the intermolecular π-
π interaction is one of the causes for the aggregation-
caused quenching effect.11 However, some recent studies
show that inter- or intramolecular π-π interaction can
result in fluorescence enhancement once aggregates
form.21,22 However, the underlying reasons and theories
are under strong debate as such phenomenon was only
observed in molecules with specific structures. To have a
thorough conception and understanding of the photo-
physical properties of tetraphenylethane system, the PL of
290
330
370
410
450
490
0
30
60
90
Water fraction (vol %)
Wavelength (nm)
Figure 3. A) PL spectra of s-TPE in THF/water mixture with
different water fractions (fw). B) Plots of relative PL intensity
(I/I0) versus fw at different emission wavelengths. Concentra-
tion = 10-4 M, λex = 280 nm, I0 = intensity at fw = 0%. Inset:
fluorescent photos of s-TPE solid taken under 365 nm UV
light irradiation.
Table 1. Photophysical properties of DPM, s-TPE-TM and s-TPE.a
Fluorescence
λem, aggr (nm)
297, ~400
305, 385
Compound
λabs (nm)
ΦF,solid (%)
λem, soln (nm)
297
λem, solid (nm)
DPM
s-TPE-TM
s-TPE
278
280
270
400
397
467
2
9
300
290
310, 460
69
a
Abbreviation: λabs = absorption maximum in THF solution, λem, soln = emission maximum in THF solution, λem, aggr = emission
maximum in THF/water (1:9, v/v), λem, solid = emission maximum in solid powder, ΦF, solid = fluorescence quantum yield of solid
powder measured by an integrating sphere.
The PL analysis of all the molecules suggested that they
possessed similar photophysical properties and the longer-
wavelength emission showed typical AIE effect. The intensity
of the shorter-wavelength emission at around 300 nm in-
creased when the fw in THF/water mixture rose from 0 to
60% and then decreased once aggregates formed. Such in-
tensity annihilation should be ascribed to the energy transfer
to longer-wavelength emissive species. However, the intensi-
ty of the shorter-wavelength emission peak increases from fw
= 0 to ~60% should have no relationship with the aggregate
formation. Previous studies had shown that the molecular
fluorescence was sensitive to the solvent polarity.25 Thus, the
PL spectra of s-TPE-TM in THF/hexane and THF/ n-butanol
mixtures were also measured and compared (Figure S7-8).
Figure 4 showed the relationship between the relative emis-
sion intensity (I/I0) and dielectric constant (εm) of the mixed-
solvent (Table S1). By lowering the THF fraction (fT) in
THF/water mixture from 100 to 50%, the εm increased from
7.520 to 43.030 accompanying with an increased I/Io value to
2.3. Under the same fT change, εm of THF/ n-butanol mixture
increased from 7.520 to 16.772 along with an increase in I/Io
ratio to 1.2. However, the εm of THF/hexane mixture de-
3
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 11
creased to 2.453 at fT = 10%, decreasing the I/Io value to 0.5.
Figure 5. PL spectra of s-TPE-TM in THF solution (10-3 M) at
1
2
3
4
5
6
7
8
Compared with water, s-TPE-TM could be solubilized in
hexane and n-butanol in a certain amount. Thus the
aggregation-induced longer-wavelength emission was hard
to observe in THF/hexane and THF/ n-butanol mixtures and
the plots of I/Io versus fT in Figure 4B were nearly linear. The-
se data supported that the change of fluorescence intensity
in solution was polarity-dependent, and the increase of
mixed-solvent polarity resulted in the enhancement of emis-
sion intensity and vice versus.
different excitation wavelengths. A) 250−300 nm and B)
300−350 nm.
According to the traditional photophysical theory, vari-
ation in excitation could change only the emission inten-
sity but not the wavelength of luminophores, especially
for those with conjugated planar structures, such as py-
rene and perylene.26 The effect of excitation-dependent
emission has already been observed and reported in other
systems27,28 and was ascribed to the mechanism of anti-
Kasha’s rule in some case.29 However, our AIEgens possess
propeller-like structures. The free rotation of each group
in solution will result in different conformations and each
conformer show different electronic energy levels. The
calculation of emission of all conformers formed a broad
emission spectrum without any fine structure. With the
increase in excitation wavelength or decrease in excita-
tion energy, the number of excited conformers will de-
crease as only species with low electronic energy gap will
be excited. Thus, apparent “bathochromic shift” in the
emission wavelength was observed and was due to a
mathematical rather than a photophysical effect. Struc-
ture analysis of the molecules present in this work suggest
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.5
2.0
1.5
1.0
0.5
0.0
80
60
40
20
0
1.3
1.0
0.7
0.4
20
15
10
5
B
A
ε
ε
ε
ε
ε
ε
ε
ε
THF/n-butanol
THF/hexane
THF/Water
60
0
100
80
40
20
100
80
60
40
20
THF fraction (vol %)
THF fraction (vol %)
Figure 4. Plots of relative PL intensity (I/I0) and dielectric
constant (εm) versus THF fraction (fT) of s-TPE-TM in A)
THF/water and B) THF/n-butanol and THF/hexane mixtures.
Concentration = 10-4 M, λex = 280 nm, I0 = intensity at fT
=
that
their
chromophoric
units
were
1,2,4-
trimethylbenzene and benzene, which could be excited by
UV light at 250−280 nm. However, chromophores with
longer-wavelength emission and excitation could not be
easily identified. They should be generated through some
inter- or intramolecular interactions. Meanwhile, all the
present molecules showed typical AIE characteristic in
THF/water mixture even at the longer-excitation wave-
length (Figure 6, Figure S11 and S12). For example, as de-
picted in Figure 6, s-TPE showed longer-range with λem of
460 nm and demonstrated AIE characteristic at λex = 280
and 340 nm. The difference between the two spectra was that
100%.
Excitation-dependent emission
The dependence of PL of the present compounds on the
excitation wavelength (λex) was examined. Figure S9
showed the PL spectra of DPM in dilute THF (1 mM) ob-
tained at different λex. At λex of 250−290 nm, only a single
peak at 297 nm was observed. However, a longer-
wavelength and weak emission appeared at 370 nm when
the λex increased to 310 nm. This peak red-shifted slightly
and its intensity decreased slowly by gradual varying the
λex from 310 to 360 nm. Figure 5 depicted that more than
one peak was observed in s-TPE-TM at higher λex. For
example, four peaks at 320 nm, 352 nm, 391 nm and 433
nm were observed at λex = 300 nm. The peak at 352 nm
“bathochromically shifted” to 380 nm when the λex in-
creased to 340 nm. The emission behaviours of s-TPE are
similar to DPM and s-TPE-TM. Two peaks at 370 and 464
nm were observed when s-TPE was photoexcited at λex of
longer than 300 nm (Figure S10).
there was no shorter-wavelength emission at 290 nm at λex
=
340 nm.
250
200
150
100
50
300
200
100
0
460nm
A
B
fw (vol %)
90
80
70
60
50
40
0
500
400
300
200
100
0
100
80
60
40
20
0
0
390
430
470
510
550
590
0
30
60
90
B
A
λex (nm)
λex (nm)
Wavelength (nm)
Water fraction (vol %)
300
310
320
330
340
350
302 nm
250
260
270
280
290
300
352 nm
320 nm
Figure 6. A) PL spectra of s-TPE in THF/water mixtures with
different water fractions (fw). Solution concentration = 100
µM, λex = 340 nm. B) Plot of relative PL intensity (I/I0) versus
fw at 460 nm. I0 = fluorescence intensity at fw = 0%.
391 nm
433 nm
380 nm
Crystal structures
280
320
360
400
440
480 305
350
395
440
485
The distance and dihedral angle between different atoms
and planes in their crystal structures were measured to
demonstrate the inter- or intramolecular interaction. In
DPM, the dihedral angle between two intramolecular
Wavelength (nm)
Wavelength (nm)
4
ACS Paragon Plus Environment

Page 5 of 11
Journal of the American Chemical Society
their adjacent benzene rings (Figure 7B). The centroid-
benzene rings was 82.40o (Figure 7A). Its dimer structure
1
2
3
4
5
6
7
8
showed that the two intermolecular benzene rings were
parallel to each other. While the interplanar distance was
3.614 Å and the centroid o to centroid o’ was 5.163 Å, the
distances between carbon a’ and b, a’ and centroid o were
3.656 Å and 3.669 Å, respectively. These data suggested
that DPM showed weak intermolecular interaction. Simi-
larly, crystal structure analysis of s-TPE-TM also suggest-
ed minor intermolecular interaction (Figure S13), possibly
due to the steric hindrance introduced by the methyl
groups.
centroid distance was 4.409 Å and the vertical distance
between two benzene planes was 3.348 Å. The shortest
C−C distance was 3.425 Å, which was short enough to
generate weak intermolecular interaction. Thus, one
question arises: does this weak intermolecular−stacking
in s-TPE lead to the broad emission with λem = 467 nm
and high quantum yield in the solid state?
Through-space interaction
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
To answer the above question, simulation on these three
molecules was carried out. According to the dimer simu-
lation based on their crystal structures (Table S2−S4),30−33
the exciton coupling energy for all the dimers of the crys-
tals were merely around 1 meV. This value was much low-
er than those (around 200 meV) of system with strong
packing34 suggesting that the longer-wavelength emission
in the aggregate of the single bond-bridged AIEgens was
predominantly ascribed to intramolecular rather than
intermolecular interaction. Single molecule simulation in
the gas phase was then conducted, treating the crystal
structures of the molecules as the ground-state configura-
tion. The TD-DFT calculation with B3LYP/6-31G(d) was
utilised to simulate the ground- and excited-state frontier
molecular orbitals (Table 2 and Figure S14), including the
electron cloud distribution and energy levels of highest
occupied molecular orbitals (HOMO) and lowest unoc-
cupied molecular orbitals (LUMO). According to the ex-
perimental UV and PL data (Table 1), the λabs and the PL
peak at 300 nm of DPM, s-TPE-TM and s-TPE corre-
sponded to the absorption and emission of a single phe-
nyl ring.18 The calculated λabs of DPM, s-TPE-TM and s-
TPE was similar to TMB, demonstrating their non-
conjugated ground-state structures (Table 2).
A
B
Figure 7. Crystal packing diagrams of A) DPM and B) s-TPE.
Due to the absence of methyl group, s-TPE showed
tighter packing than other molecules. Each molecule
formed two pairs of intermolecular cofacial packing with
Table 2. Energy levels, energy gaps, calculated absorption and emission maximum of TMB, DPM, s-TPE-TM and s-TPE calculat-
ed by the TD-DFT, B3LYP/6-31G(d), Gaussian 09 program.a
HOMO (eV)
LUMO (eV)
Energy gap (eV)
Compound
λabs (nm) λem (nm)
GS
ES
GS
ES
GS
ES
TMB
DPM
-5.907
-5.727
-5.454
-5.978
-5.890
-5.711
-5.322
-4.845
0.428
0.486
0.148
-0.060
0.019
0.052
-0.358
-1.406
6.335
6.213
5.602
5.918
5.909
5.763
4.964
3.439
231
234
247
236
251
253
281
462
s-TPE-TM
s-TPE
a Abbreviation: HOMO = highest occupied molecular orbitals, LUMO = lowest unoccupied molecular orbitals, GS = ground state,
ES = excited state, λabs = absorption maximum, λem = emission maximum.
Simulation in the excited state was further carried out
as it had a direct relationship with the PL property. Ac-
cording to the previous researches on diphenylmethane,
homoconjugation between these two methylene-linked
benzene rings existed, which induced effective electron
delocalization and overlapping between benzene
rings.35,36 As shown in Figure S14A, the LUMO electron
cloud of DPM spread on the whole molecule, revealing
that the two phenyl rings were electronically conjugated.
On the other hand, it was found that the homoconjuga-
tion of diphenylmethane had close relationship with the
twisting angle and the distance between the benzene
rings. Generally, the homoconjugation was favored when
the phenyl rings were close to each other and packed in a
parallel fashion, as suggested by the comparing results
between compound C-1 to C-4 in Table 3. With an in-
crease in the twisting angle from conformer C1 to C3, the
energy gap slightly decreased from 6.239 to 6.214 eV. Fur-
ther shortening the distance between phenyl rings C3 and
C4 from 2.569 Å to 2.190 Å decreased the energy gap ob-
5
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 11
viously to 5.704 eV. Additionally, the broad emission of there was overlapping between phenyl ring electrons
1
DPM in the aggregate state was caused by different con-
formers. As each conformer had its specific emission
wavelength, this explained why DPM exhibited excita-
tion-dependent emission. Theoretically, the emission will
be located at the longer-wavelength region with an in-
crease in homo-conjugation. However, the calculated λem
for DPM was 253 nm and was similar to TMB and its solu-
tion value. Why the simulation result deviated from the
experimental result was that the simulation was carried
out in the gas phase. Thus, the two benzene rings could
undergo free rotation in the absence of strong steric hin-
drance. Molecular optimization in the excited state
showed that the two benzene rings were almost perpen-
dicular to each other (Figure S14A). Since the orthogonal
structure of diphenylmethane corresponded to the worst
through-space conjugation and largest energy gap, the
calculated λem will be bathochromically shifted once the
rigidity of single molecule increased. This could be veri-
fied by the simulation results on s-TPE-TM and s-TPE.
through the methylene bridge (Figure 8 and Figure S14B).
However, Table 4 showed that the distance between atom
1 and 4 became longer in the excited state and the elec-
tron clouds of the associated phenyl rings (B1 and B4)
were no longer overlapped. This resulted in a large simi-
larity in emission maximum and UV spectrum between s-
TPE-TM and DPM in the aggregate state, and also proved
that the through-space conjugation between phenyl rings
B1 and B2, and B3 and B4 played the predominated role in
its optical property. The interaction between B2 and B3 or
B1 and B4 should make little contribution. Because s-TPE-
TM possessed a crowded structure to impart stronger
molecular rigidity, that might account why the calculated
λem of s-TPE-TM was 30 nm longer than DPM. The ab-
sence of orthogonal structure between phenyl rings B1
and B2, and B3 and B4 could induce better through-space
conjugation to narrow the band gap.
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
A
Table 3. Energy levels, energy gaps in the ground state, cal-
culated maximum absorption of diphenylmethanes C1-C4
with different twisting angles and C-C distances calculated
by the TD-DFT, B3LYP/6-31G(d), Gaussian 09 program.a
LUMO
H
-0.358
-1.406
H
s-TPE
H
Egap = 3.439
-4.845
Egap = 4.964
H
λabs
HOMO LUMO
Energy
Compound
(nm)
(eV)
(eV)
gap (eV)
s-TPE-TM
-5.322
230
231
C-1
C-2
C-3
C-4
-6.357
-6.311
-6.294
-5.911
-0.118
-0.076
-0.08
6.239
6.235
6.214
5.704
HOMO
233
249
-0.207
a
Abbreviation: HOMO = highest occupied molecular orbit-
B
als, LUMO = lowest unoccupied molecular orbitals, λabs
=
absorption maximum.
Figure 8. A) Electron cloud distributions, energy levels of s-
TPE-TM and s-TPE in the excited state calculated by TD-
DFT B3LYP/6-31G(d), Gaussian 09 program. B) Schematic
definition of carbon atoms and phenyl rings in s-TPE-TM
and s-TPE.
The simulated λem of s-TPE-TM in the ground state was
281 nm, which was 30 nm red shift from that of DPM (Ta-
ble 1). This suggested that the four phenyl rings were not
totally isolated and they interacted intramolecularly in a
through-space manner.35−39 As observed from its LUMO,
Table 4. Calculated C-C distances and twisting angle of s-TPE-TM and s-TPE in the ground (GS) and excited (ES) states calcu-
lated by the TD-DFT, B3LYP/6-31G(d), Gaussian 09 program.
Excited state
Atomic distance (Å)
Twist angle (o)
Ground state
Atomic distance (Å)
Com-
Twist angle (o)
pound
1-2
2-3
3-4
4-1
B1
B2
B3
B4
1-2
2-3
3-4
4-1
B1
B2
B3
B4
2.508
3.018
2.519
3.047
70.93
60.59
56.17
71.59
2.491
2.831
2.492
3.262
78.17
65.66
65.65
78.14
s-TPE-TM
s-TPE
2.507
3.015
2.507
3.015
77.34
60.54
58.23
79.51
2.559
3.219
2.159
3.094
61.29
63.99
88.64
86.38
Set (1-2-O’) as the reference plane when calculated the twisting angle of phenyl rings B1 and B2. Set (3-4-O) as the reference
plane when calculated the twisting angle of phenyl rings B3 and B4.
6
ACS Paragon Plus Environment

Page 7 of 11
Journal of the American Chemical Society
The simulation results of s-TPE were correlated with
could help to elucidate the bright fluorescent emission in
the solid state. However, the calculated S1-S0 emission
wavelength was only 255 nm, which was quite bluer than
the calculated λem = 462 nm in the gas phase. The devia-
tion of calculated λem could be ascribed to the fixed sur-
rounding environment, the narrow space and steric hin-
drance restricted the centrally molecular motion and pre-
vented the central molecule from forming the through-
space conjugation. Then, another type of oniom calcula-
tion was performed by making the low layer optimized at
the MM level in order to evaluate different constrain ef-
fect on the QM molecule caused by the MM part. Indeed,
the calculated λem was bathochromic-shift to 277 nm.
Meanwhile, reorganization energy increased to 3314 cm-1,
Figure S15 showed that the percentage of dihedral angle-
change contribution to the reorganization energy in-
creased from 21.3% (fixed low layer mode) to 37.8% (ac-
tive low layer mode), which was more favorable to form
the intramolecular through-space conjugation. As the
limit of theoretical calculation in non-conventional sys-
tems, more advanced calculation methods and accurate
modes still need to be developed and constructed to sup-
port the solid-state through-space conjugation.
1
2
3
4
5
6
7
8
the experimental data (Table 1). For example, the calcu-
lated λem was 462 nm, which was equal to the experi-
mental one (460 nm). Table 4 showed that the twisting
angle of phenyl rings B3 and B4 in s-TPE synchronously
increased to ∼ 90o in the excited state and the distance
between atoms 3 and 4 decreased to 2.159 Å, forming an
almost cofacial dimer structure. This structure was
demonstrated by the fact that the electron clouds of the
associated phenyl rings (B3 and B4) were delocalized in
the excited state (Figure 8A). These data suggested that
the through-space conjugation between phenyl rings B3
and B4 made the greatest contribution to the longer-
wavelength emission in s-TPE. The single bond in s-TPE
also played an important role to promote the through-
space conjugation as it provided flexibility for the ben-
zene rings to rotate. The absence of methyl groups on the
benzene rings decreased their steric interaction, making
them to get closer with little constraint.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Photoluminescence quantum efficiency (ηpl) was de-
termined by the radiative (kr) and non-radiative (knr) de-
cay rate of the singlet excite. According to the
ꢃ
ꢄ
tions ꢀꢁꢂ
=
and kr = fΔE2/1.5, where f is the dimen-
ꢃ ꢅꢃ
ꢄ
ꢆꢄ
1600
1200
800
400
0
1600
1200
800
400
0
sionless oscillator strength and ΔE is the vertical transi-
tion energy. knr consists of two contributions: (i)the in-
ternal conversion kIC from S1 to S0 and (ii) the intersys-
tem crossing kISC from S1 to T1. In fluorescent AIE system,
ηpl was approximately proportional to the oscillator
strength (f) and inversely proportional to the reorganiza-
tion energy (λ).40,41 Then, these two factors were calculat-
ed for s-TPE in both gas phase and crystal state. The oscil-
lator strength for the electronic transition from S1 to S0
state of s-TPE in the gas phase was only 0.0036. Figure 9A
showed the reorganization energy at different wave-
numbers in gas phase. The total λ was as high as 15483
cm-1 and 63.5% of them was contributed to the change of
dihedral angle caused by the rotation of phenyl rings. The
small oscillator strength and large reorganization energy
led to weak emission at the longer wavelength in the so-
lution state. The aggregation effect was modeled through
a combined quantum mechanics and molecular mechan-
ics (QM/MM) approach by using Gaussian 09 package. A
cluster containing 73 molecules cut from the single crystal
structure set up the two-layer oniom model. The central
molecule acted as the high layer (QM) at the
(TD)B3LYP/6-31G(d) level and the surrounding ones were
treated as the low layer (MM) using Universal Force Field
(UFF). Firstly, the low layer was fixed and only the central
molecule was optimized by the (TD)B3LYP/6-31G(d). The
calculated oscillator strength enormously increased to
0.1259 which was 35-times bigger than that in the gas
phase. Meanwhile, its total λ sharply decreased to 1712 cm-
B
A
17.0%
19.5%
21.3%
20.1%
58.6%
63.5%
0
500
1000
1500
2000
0
500
1000
1500
2000
Normal mode wavenumber (cm-1)
Normal mode wavenumber (cm-1)
Figure 9. Plots of calculated reorganization energy versus
the normal mode wavenumber of s-TPE in A) gas phase and
B) crystal. Calculated by the TD-DFT, B3LYP/6-31G(d),
Gaussian 09 program.
Another interesting phenomenon was that their UV
spectra only showed peaks associated with the absorption
of 1,2,4-trimethylbenzene or benzene. Even no through-
space conjugation peaks were observed in their absorp-
tion spectra, these molecules could still be excited by
light with wavelength longer than their UV cut off and
phenyl emission. For example, the UV cut-off wavelength
of s-TPE was 275 nm (Figure S5C) and the emission tail of
benzene was located at 330 nm (Figure 3A). However, s-
TPE could still be excited by light at 340 nm in THF/water
mixtures (Figure 6). According to the previous research
on through-space interaction, π-π* transition stemmed
from through-space interaction was normally not ob-
served because it is forbidden in the ground state.37 The
calculated wavelength and oscillator strength of diphe-
nylmethanes C1-C4 with different twisting angles and C-C
distances could support this mechanism (Table S5).
Among these four structures, C-4 possessed the longest
wavelength (S1-S0 electronic transition) which indicated
the strongest through-space interaction. However, its
1
and 58.6 % of them was contributed to the change of
bond length (Figure 9B). The large oscillator strength and
small reorganization energy in the QM/MM calculation
7
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 11
(1) Stelzer, E. H. K. Nat. Methods 2015, 12, 23.
(2) Loizzo, M. R.; Tundis, R.; Conforti, F.; Statti, G. A.;
Menichini, F. Pharm. Biol. 2009, 47, 516.
oscillator strength was merely 0.0006, that was the reason
why this peak could not be detected in its absorption
spectrum.
1
2
3
4
5
6
7
8
9
(3) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51,
913.
(4) Chen, L.; Nakamura, M.; Schindler, T. D.; Parker, D.;
Bryant, Z. Nat. Nanotechnol. 2012, 7, 252.
(5) Zhao, Z. J.; Lam, J. W. Y.; Tang, B. Z. Soft Matter 2013, 9,
4564.
(6) Aubin, J. E. J. Histochem. Cytochem. 1979, 27, 36.
(7) Zhang, W. F.; Guo, H.; Ma, G. H.; Huang, Y. B.; Du, Z. L.
Chem. J. Chinese U. 1998, 19, 591.
3. CONCLUSION
In this work, three non-conjugated compounds were syn-
thesized by linking isolated phenyl rings with alkyl group.
While their UV spectra exhibited peaks related to the
absorption of isolated phenyl rings, their PL spectra in the
aggregate state showed emission from phenyl or 1,2,4-
trimethylphenyl ring and chromophore formed by
through-space interaction between methylene-linked
phenyl rings. These molecules could be excited by longer-
wavelength UV light and showed excitation-dependent
emission. The longer-wavelength emission induced by
through-space interaction was only observed in the ag-
gregate state due to the RIR mechanism. High quantum
yield of up to 69% would be reached in the solid state.
The simulated results were consisted with the experi-
mental results and supported the existence of through-
space conjugation in these molecules. These alkyl-linked
arenes broadened the type of fluorophore and suggested
that traditional conjugated structures were not necessary
for generating efficient light emission. Non-conventional
systems, such as clusteroluminogens,42,43 could also emit
fluorescence in the visible range with high fluorescence
quantum yield.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(8) Yanari, S. S.; Bovey, F. A.; Lumry, R. Nature 1963, 200,
242.
(9) Ye, R. Q.; Liu, Y. Y.; Zhang, H. K.; Su, H. F.; Zhang, Y. L.;
Xu, L. G.; Hu, R. R.; Kwok, R. T. K.; Wong, K. S.; Lam, J. W. Y.;
Goddard, W. A.; Tang, B. Z. Polym. Chem. 2017, 8, 1722.
(10) Hirayama, F. J. Chem. Phys. 1965, 42, 3163.
(11) Birks, J. B. Photophysics of aromatic molecules; Wiley-
Interscience: London, UK, 1970.
(12) Zhao, Z. J.; Chen, S. M.; Lam, J. W. Y.; Wang, Z. M.; Lu,
P.; Mahtab, F.; Sung, H. H. Y.; Williams, I. D.; Ma, Y. G.;
Kwok, H. S.; Tang, B. Z. J. Mater. Chem. 2011, 21, 7210.
(13) Kim, Y.; Bouffard, J.; Kooi, S. E.; Swager, T. M. J. Am.
Chem. Soc. 2005, 127, 13726.
(14) Mei, J.; Leung, N. L.; Kwok, R. T.; Lam, J. W.; Tang, B.
Z. Chem. Rev. 2015, 115, 11718.
(15) Nie, H.; Hu, K.; Cai, Y. J.; Peng, Q.; Zhao, Z. J.; Hu, R.
R.; Chen, J. W.; Su, S. J.; Qin, A. J.; Tang, B. Z. Mater. Chem.
Front. 2017, 1, 1125.
(16) Luo, J. D.; Xie, Z. L.; Lam, J. W. Y.; Cheng, L.; Chen, H.
Y.; Qiu, C. F.; Kwok, H. S.; Zhan, X. W.; Liu, Y. Q.; Zhu, D. B.;
Tang, B. Z. Chem. Commun. 2001, 1740.
(17) Chen, L.; Lin, G. W.; Peng, H. R.; Ding, S. Y.; Luo, W.
W.; Hu, R. R.; Chen, S. M.; Huang, F.; Qin, A. J.; Zhao, Z. J.;
Tang, B. Z. Mater. Chem. Front. 2017, 1, 176.
(18)http://webbook.nist.gov/cgi/cbook.cgi?Spec=C95636&I
ndex=0&Type=UVVis&Large=on&SVG=on
(19)http://omlc.org/spectra/PhotochemCAD/html/042.ht
ml
(20) Hong, Y. N.; Lam, J. W. Y.; Tang, B. Z. Chem. Soc. Rev.
2011, 40, 5361.
(21) Li, J.; Yang, C.; Huang, C.; Wan, Y.; Lai, W. Y. Tetrahe-
dron Lett. 2016, 57, 1256.
(22) Krukowski, P.; Tsuzuki, T.; Minagawa, Y.; Yajima, N.;
Chaunchaiyakul, S.; Akai-Kasaya, M.; Saito, A.; Miyake, Y.;
Katayama, M.; Kuwahara, Y. J. Phys. Chem. C 2016, 120, 3964.
(23) Pross, A.; Radom, L.; Riggs, N. V. J. Am. Chem. Soc.
1979, 102, 2253.
(24) Alabugin, I. V.; Gilmore, K. M.; Peterson, P. W. Com-
put. Mol. Sci. 2011, 1, 109.
(25) Karpovich, D. S.; Blanchard, G. J. J. Phys. Chem. 1995,
99, 3951.
(26) Lakowicz, J. R. Principles of Fluorescence Spectrosco-
py; Springer Science+Business Media: New York, USA, 2006.
(27) Cushing, S. K.; Li, M.; Huang, F. Q.; Wu, N. Q. ACS
Nano 2014, 8, 1002.
(28) Lee, K. M.; Cheng, W. Y.; Chen, C. Y.; Shyue, J. J.; Nieh,
C. C.; Chou, C. F.; Lee, J. R.; Lee, Y. Y.; Cheng, C. Y.; Chang, S.
Y.; Yang, T. C.; Cheng, M. C.; Lin, B. Y. Nat. Commun. 2013, 4,
1544.
ASSOCIATED CONTENT
Supporting Information
Details of the chemicals, instrumentation, synthesis and
characterization. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*tangbenz@ust.hk
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This work was partially supported by the National Basic Re-
search Program of China (973 Program; 2013CB834701 and
2013CB834702), the University Grants Committee of Hong
Kong (AoE/P-03/08), the Research Grants Council of Hong
Kong (16301614, 16305015, C2014-15G, A-HKUST605116 and
N_HKUST604/14), and the Innovation and Technology
Commission (ITC-CNERC14SC01 and TCPD/17-9). B. Z. T. is
also grateful for the support from the Guangdong Innovative
Research Team Program of China (201101C0105067115), the
Science and Technology Plan of Shenzhen (JCYJ
20160229205601482) and the Shenzhen Peacock Plan.
(29) Qian，H.; Cousins, M. E.; Horak, E. H.; Wakefield, A.;
Liptak, M. D.; Aprahamian, I. Nat. Chem. 2017, 9, 83.
REFERENCES
8
ACS Paragon Plus Environment

Page 9 of 11
Journal of the American Chemical Society
(30) Li, W. Q.; Peng, Q.; Xie, Y. J.; Zhang, T.; Shuai, Z. G.
1
Acta. Chim. Sinica. 2016, 74, 902.
2
3
(31) Hsu, C. P.; You, Z. Q.; Chen, H. C. J. Phys. Chem. C
2008, 112, 1204.
(32) http://www.shuaigroup.net/index.php
(33) Valiev, M.; Bylaska, E. J.; Govind, N.; Kowalski, K.;
Straatsma, T. P.; Van Dam, H. J. J.; Wang, D.; Nieplocha, J.;
Apra, E.; Windus, T. L.; Jong, W. A. Comput. Phys. Commun.
2010, 181, 1477.
(34) Plötz, P. A. Master thesis, University of Rostock,
Mecklenburg-Vorpommern, Germany, 2013.
(35) Martinez, A. G.; Barcina, J. O.; Cerezo, A. F.; Rivas, R.
G. J. Am. Chem. Soc. 1998, 120, 673.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(36) Caraballo-Martinez, N.; Heras, M. D. C.; Blazquez, M.
M.; Barcina, J. O.; Martinez, A. G.; Salvador, M. D. T. Org.
Lett. 2007, 9, 2943.
(37) Hoffmann, R. Acc. Chem. Res. 1971, 4, 1.
(38) Chen, L.; Wang, Y. H.; He, B. R.; Nie, H.; Hu, R. R.;
Huang, F.; Qin, A. J.; Zhou, X. S.; Zhao, Z. J.; Tang, B. Z. An-
gew. Chem. Int. Edit. 2015, 54, 4231.
(39) Zhang, Y. Y.; He, B. R.; Luo, W. W.; Peng, H. R.; Chen,
S. M.; Hu, R. R.; Qin, A. J.; Zhao, Z. J.; Tang, B. Z. J. Mater.
Chem. C 2016, 4, 9316.
(40) Shuai, Z.; Peng, Q. Natl. Sci. Rev. 2017, 4, 224.
(41) Zhang, T.; Jiang, Y.; Niu, Y.; Wang, D.; Peng, Q. Shuai,
Z. J. Phys. Chem. A 2014, 118, 9094.
(42) Viglianti, L.; Leung, L. C.; Xie, N.; Gu, X.; Sung, H. Y.;
Miao, Q.; Williams, I. D.; Licandroe, E.; Tang, B. Z. Chem. Sci.
2017, 8, 2629.
(43) Zhou, X.; Luo, W.; Nie, H.; Xu, L.; Hu, R.; Zhao, Z.;
Qin, A.; Tang, B. Z. J. Mater. Chem. C, 2017, 5, 4775
9
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 10 of 11
1
2
Table of Contents
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The photophysical properties of three non-conjugated compounds with isolated phenyl rings were studied, while they
emit deep blue light of isolated phenyl rings at ~300 nm in solutions, bright longer-wavelength emission at wavelength
>400 nm was observed in the aggregate state due to intramolecular through-space conjugation.
10
ACS Paragon Plus Environment

Page 11 of 11
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The photophysical properties of three non-conjugated compounds with isolated phenyl rings were studied,
while they emit deep blue light of isolated phenyl rings at ~300 nm in solutions, bright longer-wavelength
emission at wavelength >400 nm was observed in the aggregate state due to intramolecular through-space
conjugation.
81x40mm (300 x 300 DPI)
ACS Paragon Plus Environment