Temperature Controlling Polymorphism and Polymorphic Interconversion in Sublimation Crystallization of 5-Methoxy-salicylaldhyde Azine

Article abstract of DOI:10.1021/acs.cgd.8b01429

Traditional growth of organic crystals is mostly based on solution processing techniques, but facile crystal preparation of compounds with poor solubility or polymorphic characters remains a challenge. Here, we demonstrate an in-air sublimation method for

Full text of DOI:10.1021/acs.cgd.8b01429

Subscriber access provided by Kaohsiung Medical University
Article
Temperature Controlling Polymorphism and Polymorphic Interconversion
in Sublimation Crystallization of 5-Methoxy-salicylaldhyde Azine
Shen Shen, Guomin Xia, Zhengjun Jiang, Qingqing Shao, Wenzhe Shan, and Hongming Wang
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01429 • Publication Date (Web): 19 Nov 2018
Downloaded from http://pubs.acs.org on November 23, 2018
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 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 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.
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 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
Temperature Controlling Polymorphism and
Polymorphic Interconversion in Sublimation
Crystallization of 5-Methoxy-salicylaldhyde Azine
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
†,‡
†,§
†
†,
‡
†
Shen Shen, Guomin Xia, Zhengjun Jiang, Qingqing Shao, Wenzhe Shan, Hongming Wang
†,§,*
†Institute for Advanced Study, Nanchang University, Jiangxi, 330031, P.R. China
‡School of Materials Science, Nanchang University, Jiangxi, 330031, P.R. China
§College of Chemistry, Nanchang University, Jiangxi, 330031, P.R. China
ABSTRACT: Traditional growth of organic crystals is mostly based on solution processing
techniques, but facile crystal preparation of compounds with poor solubility or polymorphic
characters remains a challenge. Here we demonstrate an in-air sublimation method for strategical
preparation of 5-methoxy-salicylaldhyde azine (compound 1) in two polymorphic crystal forms
o
by controlling sublimation temperature. The kinetic stable one was offered under 180 C with the
opposite orientation of methoxy group with respect to the longest chain in the molecule (termed
o
1
-anti), while the thermodynamic stable one was offered above 200 C with that in same
orientation (termed 1-syn). Moreover, the overall dynamic forming and interconversion between
1-anti and 1-syn crystals in sublimation process were well studied by powder X-ray diffraction,
ACS Paragon Plus Environment
1

Crystal Growth & Design
Page 2 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
IR, emission spectra and DFT calculations. All the results revealed this sublimation
crystallization technique should be helpful for detection and even selective preparation of pure
organic crystals with polymorphic characters.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
INTRODUCTION
The performance of organic crystalline materials are known to have great relationship with
their molecular arrangement in crystals.1-6 As such, effective preparation of organic crystals in
desired packing modes will definitely provide benefits to many frontier fields, including
advanced optical materials,7-10 electronic devices,11-14 biomedical appliances.15-17 Generally,
crystal growth methods are mostly focused on solution evaporation/cooling,18-22 liquid
diffusion,16,23-25 vapor diffusion and hydrothermal/solvothermal,24,26,27 and all those solvents-
involved methods are economical, simple, highly processable and largely favor the growth of
functional pseudopolymorph crystals which incorporating guest solvents.28-31 Although state-of-
the-art, these methods still face the challenge in the preparation of those materials with poor
solubility or polymorphic characters.32,33
Recently, more and more attentions have been paid to sublimation growth organic materials,
which turned out to be more applicable in preparing those guest-free single crystals or insoluble
organic crystal materials.32,33 Moreover, high-quality crystals and undiscovered polymorphs of
organic materials can also be achieved under certain sublimation conditions.12,33-36 For instance,
Koga and co-workers obtained the syn conformer crystals of 1,8-naphthyridine derivative by
3
7
subliming anti counterparts. Besides, a sublimation method to grow new polymorphs of 2,6-
3
8
dichloro-naphthalene diimide was also first reported by Würthner and colleagues. In fact, it is
conceivable and intriguing for controlling polymorphism in the crystallization of organic
ACS Paragon Plus Environment
2

Page 3 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
compounds by adjusting sublimation temperature,39-41 through which two polymorphic crystal
forms of 1,1-bis(4-hydroxyphenyl)cyclohexane can be confirmed.42 Impressively,
McArdle ’group had revealed the use of low-temperature gradient sublimation to attain two pure
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
43
samples of polymorphic stanozolol in vacuum. Still and all, it remains a challenge but of great
importance to discover and effectively isolate polymorphic organic crystals by sublimation.
In this paper, we first discovered and decoded the polymorphism of 5-methoxy-salicylaldhyde
azine (1) by controlling the sublimation temperature under ambient conditions, which has been
attained in one crystal form by Yousuf and co-workers.44 With the sublimation temperature
increased, the sublimed crystal structures gradually change from the kinetically stable crystals
(termed 1-anti crystal) to thermodynamically stable one (termed 1-syn crystal), accompanying
with the emission color changed from orange yellow to red. Single crystal X-ray diffraction
revealed the two polymorphs were distinguished from each other in the orientation of methoxy
group with respect to the longest chain in the molecule, thereby leaded to significantly different
molecular arrangements. To the best of our knowledge, this is the first report in controlling
crystallization of polymorphic salicylaldehyde azine derivatives through sublimation temperature
adjustment in air. By photoluminescence (PL), IR spectra, X-ray diffraction analysis and DFT
calculations, the overall dynamic forming and interconversion between 1-anti and 1-syn crystals
in sublimation process were illustrated in detail.
RESULTS AND DISCUSSION
Synthesis of 1. 2-hydroxy-5-methoxybenzaldehyde was refluxed with hydrazine hydrate at a
o
molar ratio of 2:1 at 80 C for 5 hours. The resulting product was filtrated and washed with
ethanol to give yellowish powder (1, Scheme 1). The powder was then dried in vacuum at low
temperature.
ACS Paragon Plus Environment
3

Crystal Growth & Design
Page 4 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
HO
MeO
2
CHO
EtOH
MeO
N
•
H O
H N
NH2
2
2
+
OMe
N
OH
reflux
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
OH
Scheme 1. Synthesis of 5-methoxy-salicylaldhyde azine (1).
Preparation and Crystallography of Polymorphs. Since the powders were stable and
unchanged after being exposed to air at room temperature for several days, it was assumed
whether the single crystals can be prepared by sublimation.33,34,43 The device employed in the
sublimation experiments was consists of an electricity hot jacket and a micro sublimator. As
schematized in Figure 1a, the obtained yellowish powders were put in the bottom of the micro
sublimator in air, then placed inside the electricity hot jacket. After that, setting the temperature
and adding the adjustable lid at the top of the electricity hot jacket to ensure constant
temperature. At the meanwhile, the sublimation temperature was also monitored by a
thermometer attached to the sublimator to ensure the same temperature as the settings. By
controlling the temperature, the powders of 1 will be sublimed, and then the sublimate was
collected on quartz tube wall with cooling water. In order to explore the feasibility of this
experiment and the appropriate temperature for sublimation, we first raised the temperature
o
every 10 C and stop for 1 hour to reach the melting point. Results revealed that only small
o
crystals appeared on quartz tube wall until heated to 160 C in apparatus and grew larger to
o
o
display rodlike shapes at 170 C. When the temperature in the micro sublimator reached 170 C
and kept for 2 hours, the collected sublimates were rodlike crystals (polymorph A) while it
o
turned to be lamellar crystals (polymorph B) with temperature at 220 C, illustrated in Figure 1b
and 1c. More importantly, the collected sublimate were crystals with lengths of several hundreds
ACS Paragon Plus Environment
4

Page 5 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
of micrometers, fitting for single crystal X-ray diffraction. Further increasing the temperature is
o
not recommended since the substrates in the bottom of sublimator had all melted at 220 C.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 1. Sublimation crystallization growth of polymorphous 1. (a) Schematic drawing of the
applied sublimation apparatus for crystal growth. (b) Fluorescence microscope images of
polymorph A in the solid state under UV light excitation. (c) Fluorescence microscope images of
polymorph B in the solid state under UV light excitation.
With the aid of single crystal X-ray diffraction analysis, the main difference of the two
polymorphs was the mutual orientation of the two methoxy groups correspond to the hydroxyl
groups, in which the methoxy and the hydroxyl groups were oriented in the opposite direction for
polymorph A (Figure 2a, termed 1-anti), and oriented in the same direction for polymorph B
(Figure 3a, termed 1-syn). In both forms, the molecules all located inversion centers which are at
the midpoint of the N-N bond. The crystal data of the two crystals were summarized in Figure S1
and Table S1-4 (Supporting Information).
As shown, 1-anti crystal belonged to monoclinic space group P2 /c with two
1
crystallographically independent half molecules per asymmetric unit and four molecules per unit
cell. The O-HN hydrogen bonding interaction between H atoms on the hydroxyl groups and
adjacent N atoms was 1.723 Å (Figure 2a). As for 1-syn crystal, it crystallized in the monoclinic
space group P2 /c with one half molecule per asymmetric unit and two molecules per unit cell
1
ACS Paragon Plus Environment
5

Crystal Growth & Design
Page 6 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
according to X-ray analysis. The O-HN hydrogen bonding interaction between H atoms on the
hydroxyl groups and adjacent N atoms was 1.788 Å (Figure 3a). While 1-anti crystal emitted
intense orange yellow color (Figure 1b, Φ = 11.70 %) at λem = 580 nm (Figure 4), the 1-syn
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
crystal emitted weak red fluorescence (Figure 1c, Φ = 1.70 %) at λ = 650 nm (Figure 4). For 1-
em
anti and 1-syn crystals, the adjacent parallel-packed molecules were observed with the
o
interplanar distance of 3.297 Å and 3.475 Å and slipping angles along the long axis of 46.1 and
o
3
2.1 , respectively, both resulted in typical face-to-face π-π stackings. (Figure 2f and 3f). From
the top view of the adjacent parallel-packed molecules, the overlaps ratio in 1-anti crystal was
larger than 1-syn ones (Figure 2c and 3c). However, the strong π-π interactions caused by higher
degree of overlap in 1-anti crystal did not result in general observed red-shifted emission in
common fluorescence materials, which brought an investigation in its fluorescence mechanism at
single molecular level.
Figure 2. The molecular structures and stackings in 1-anti crystal. (a,b) The molecular
conformation in front and side view, respectively. (c) The molecular overlap between adjacent
ACS Paragon Plus Environment
6

Page 7 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
molecules. (d) Molecular stacking structures. (e) Front view with the illustration of pitch angle
and interplanar distance. (f) Side view with the illustration of roll angle and interplanar distance.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. The molecular structures and stackings in 1-syn crystal. (a,b) The molecular
conformation in front and side view, respectively. (c) The molecular overlap between adjacent
molecules. (d) Molecular stacking structures. (e) Front view with the illustration of pitch angle
and interplanar distance. (f) Side view with the illustration of roll angle and interplanar distance.
1
1
-anti crystal
-syn crystal
450
500
550
600
650
700
Wavelength (nm)
Figure 4. Normalized PL spectra of compound 1 in solid state. (λ = 365 nm)
ex
ACS Paragon Plus Environment
7

Crystal Growth & Design
Page 8 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
In terms of the salicylaldehyde azine derivatives were extensively used in probing its excited-
state intramolecular proton transfer (ESIPT) process in the photoluminescence procedure.45-48
Further studies were conducted by solid UV absorption spectrum and time-correlated single-
photon counting (TCSPC) technique method shown in Figure S2 and S3 (Supporting Information)
and Table S5 (Supporting Information). Combining the large stokes shifts of 1-anti and 1-syn
crystals with the fluorescence decay properties, it was deduced that an ESIPT process had taken
place in the two polymorphs after photoexcitation.49-53 From TDDFT calculation to reveal this
ESIPT mechanism, the optimized geometric conformations of the enol (ES ), enol* (ES ), keto
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0
1
(
KS ) and keto* (KS ) forms and the results are shown in Figure S4 (Supporting Information). It
0 1
can be seen that both for 1-anti and 1-syn crystals, upon excitation of the S state, the OH bond
1
would be prolonged, and then transferred to one of N atom to form KS state. Eventually, the
1
excited KS structure decayed to the ground state KS by radiative processes followed by a
1
0
reverse proton transfer, returning to the original ES state. Therefore, the smaller energy gap of
0
1
-syn compared to 1-anti (Figure S4, Supporting Information) was consistent with the observed
red shift of the ESIPT fluorescence.
Temperature controlled sublimation crystallization. Since two polymorphic crystals of 1
were obtained in different sublimation temperatures, it was reasonable to deduce that the
temperature should play a crucial role in the growth of the crystal structures. We raised the
o
o
temperature at each subsequent 5 C interval with 2 hours stopovered from 170 to 220 C, and
then collected each interval samples for further characterization. It was worth mentioning that
whether the substrates for sublimation was 1-anti, 1-syn crystals or the mixture of the two
polymorphs, the characteristics of the sublimate in the sublimation process were the same.
ACS Paragon Plus Environment
8

Page 9 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
o
o
o
o
o
o
o
o
o
o
1
-syn.simu
o
o
o
o
o
2
2
2
1
20 C
o
o
o
10 C
o
×
o
o
o
00 C
o o×
o×
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
×
×
o
×
×
95 C
o
o
×
o
1
90 C
(
a)
×
×
×
×
×
×
o
1
85 C
×
×
o
180 C
×
×
×
×
o
1
75 C
× ×
× ×
×
o
1
1
70 C
×
×
-anti.simu
10
15
20
25
30
35
2
 (deg.)
o
1
1
70 C
o
75 C
o
1
1
1
1
2
2
80 C
o
85 C
o
90 C
o
95 C
o
00 C
o
10 C
o
(
b)
220 C
550
600
650
4
50
500
550
600
650
700
Wavelength (nm)
Figure 5. Characterization of crystallization conversion of sublimate. (a) Powder X-ray
diffraction (PXRD) patterns of sublimate at different sublimation temperature. (b) PL spectra of
sublimate in the solid state at different sublimation temperature (λ = 365 nm).
ex
ACS Paragon Plus Environment
9

Crystal Growth & Design
Page 10 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
The collected sublimate were measured for PXRD patterns directly without further treatment,
as shown in Figure 5a. The strong preferred orientation and the small number of observed peaks
in the PXRD patterns were ascribed to the needle shapes of the sublimed crystals.41,43 The
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
o
o
o
o
needle-shaped sublimates collected at 170 C showed four peaks at 10.3 , 13.2 , 14.9 and 19.3
of simulate 1-anti crystal (which are marked with ‘×’ in Figure 5a). After rising the temperature
o
to 220 C, the diffraction peaks of the collected sublimate showed characteristics of simulated 1-
o
o
o
o
o
o
syn crystal at 11.3 , 13.4 , 14.3 , 17.4 , 21.4 , 22.6 (which are marked with ‘o’ in Figure 5a).
o
During the heating process, the sublimate collected at 170-180 C had characteristic peaks of 1-
anti crystal according to the simulated XRD patterns. The diffraction peaks of the gathered
o
sublimate at 185-195 C began displayed peaks of both 1-anti and 1-syn crystals, indicating the
o
existence of mixed crystals. When the sublimate was collected at 200 C, its PXRD pattern
o
o
exhibited both sharp and intense peaks of 1-syn crystal at 14.3 and 22.6 , and weak
o
characteristic peak of 1-anti crystal at 13.2 , which indicated that 1-syn crystal occupied the
o
majority. As the temperature increased to 210 C, the diffraction peaks of the collected sublimate
showed higher purity, all the characteristic peaks of 1-anti crystal were nearly negligible,
accompanied by an increase in intensity of characteristic peaks of 1-syn crystal. There no peaks
o
indicative of the existence of 1-anti crystal when the temperature reached at 220 C.
The fluorescence changes were recorded by PL spectra in detail. As shown in Figure 5b, the
fluorescence intensity at 580 nm declined with the sublimation temperature increasing. During
o
the process from 180 to 210 C, the emission band at 580 nm of the sublimate gradually
o
expanded toward 650 nm. While heating at 220 C, the sublimate behaved red fluorescence
(Figure S5, Supporting Information) and the sole emission peak at 650 nm had revealed instead
of a broad emission band. The trend of PL spectra changes were well accordance with the red
ACS Paragon Plus Environment
1
0

Page 11 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
shifted emission and low quantum yield of 1-syn crystals. Moreover, the composition of
sublimate were also supported by IR spectra shown in Figure 6. The absorption originated from
-1
-1
C-O-C and C-O stretching of the sublimate at 1161 cm and 1188 cm underwent unperceived
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
shift when the sublimation temperature increased to 180 C. When the sublimation temperature
o
increased to 185 C, the observed absorption intensity of C-O-C and C-O became stronger and
-1
-1
the stretching gradually shifted to low wavenumber, finally, shifted to 1151 cm and 1176 cm
o
o
at 220 C (Figure 6). As described above, the collected sublimate at 170 C adopted the
o
conformation of 1-anti crystal while the sublimate at 220 C was in the conformation of 1-syn. It
was not hard to explain that the orientation of methoxy group toward the longest chain in the
molecule had quite a different effect on the π delocalization of a conjugated system, resulting in
discrepant absorption stretching band. Hence, these results were well accordance with the change
with PXRD patterns, demonstrated that the sublimate collected at different temperatures had
differences both in structural conformation and sample composition, which resulted from the
different temperature dependence of growth kinetics.
o
220 C
o
2
2
2
10 C
o
05 C
o
00 C
o
195 C
o
1
1
1
90 C
o
85 C
o
80 C
o
175 C
o
1
70 C
C-O
C-O-C
1100
1150
1200
1250
-
1
Wavenumber (cm )
Figure 6. C-O-C and C-O stretching of sublimate at each temperature. Dashed lines indicate the
changes of stretching.
ACS Paragon Plus Environment
1
1

Crystal Growth & Design
Page 12 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 7. The sublimate formation and transformation. (a) The mechanism of 1-anti and 1-syn
-1
crystals sublimation formation studied by DFT calculation (unit: kcal mol ). Because of
difficulty in finding transition states, both from 1-anti to 1-antis and from 1-syn to 1-syns, the
potential energy curves were attained by scanning the distance between two monomers based on
the optimized dimers structures. (b) The reversible transformation scheme between 1-anti and 1-
syn crystals.
In order to give deep insight into the process of temperature controlled sublimation
crystallization, the DFT calculations were carried out to explore the mechanism of crystal
formation. Figure 7a presented potential energy profiles for the transformation between 1-anti
and 1-syn molecules. It was found that the transformation from 1-anti to 1-syn molecules was
taken place via two steps, in which the twist of two C-O-C was occurred step by step via two
ACS Paragon Plus Environment
1
2

Page 13 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
transition states (TS1 and TS2). The energy barriers for two steps were 13.74 and 9.45 kcal mol-1
for TS1 and TS2, respectively. And also, the energy of 1-syn was found to be 0.94 kcal mol-1
higher than that of 1-anti, which meant 1-anti was more stable than 1-syn in gas phase, and the
conversion from 1-anti to 1-syn need under certain temperature..
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Because the crystallization process was difficult to simulate by DFT calculation due to too
many atoms, for the convenience of calculation, the dimers was used as simplified model in the
calculation to measure the difference of intermolecular interaction of 1-anti and 1-syn. From
Figure 7a, it was also found that the aggregate of two molecules via intermolecular interaction
-1
both for 1-syn and 1-anti undergo low barrier of 0.2 and 1.44 kcal mol , and released -12.25 and
-1
-14.38 kcal mol energy, to form the dimer 1-syn and 1-anti, respectively. Because of the low
activation energy barrier and large reaction energy, the route from 1-anti to 1-antis (dimer of 1-
anti) would be the fastest and to reach the kinetically favored structure. However, from 1-anti to
1-syns (dimer of 1-syn) via 1-syn, the thermodynamically favored crystal would take longer to
form because the activation barrier was much higher, but it would be more stable because the
final energy state was the lowest. So, in low sublimation temperature, the kinetically favored
crystal would be formed. However, when the sublimation temperature and time is high and long,
the fine product would transfer to thermodynamically favored crystal. This conclusion was well
agreement with the above experimental results that controlling the sublimation temperature may
result in two polymorphs of compound 1 (Figure 7b and Figure S5, Supporting Information).
Crystal-to-Crystal transformation of the polymorphs. Notably, the fluorescence
microscopy images (Figure S5, Supporting Information) witnessed that the fluorescence of the
o
substrates of 1-anti crystal in 160 C was quite different from the origin samples in apparatus but
resemble the fluorescence of 1-syn crystal, while the substrates of 1-syn crystal displayed no
ACS Paragon Plus Environment
1
3

Crystal Growth & Design
Page 14 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
fluorescence change in the heating procedure (Figure S5, Supporting Information), thus leaded to
the proposal that thermal treating may induce crystals transformation. To investigate this
thermochromism, the differential scanning calorimetry (DSC), thermal gravimetric analysis
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(TGA) of the two crystals were performed. In the first and second heating cycle, both 1-anti and
o
1
-syn crystals showed one peak at 217 C (Figure S7 and S8, Supporting Information), which
was the endothermic peak of melting point. Meanwhile, an exothermic peak of 1-anti and 1-syn
o
crystals upon cooling procedure appeared at 192 C was due to solidification. The same DSC and
TGA curves of 1-syn and 1-anti crystals suggested that heating can induce phase transition.
However, due to the small energy barrier resulted from the rotation of methoxy group around the
-1
C-O bond in molecule (0.94 kcal mol , Figure 7a), it was assumed that the phase transition can
be difficult to detect in DSC and TGA analysis.
Figure 8. Powder X-ray diffraction of 1-anti crystal under heating at different temperature.
ACS Paragon Plus Environment
1
4

Page 15 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
1
-anti
1-syn
o
(b)
(
a)
60
C
C
C
C
o
1
60 C
7
0 o
o
o
150 C
140 C
130 C
1
1
1
1
1
20 oC
30 oC
40 oC
50 oC
60 oC
80
90
o
o
00 o
o
1
1
1
C
C
C
C
C
C
C
o
10
o
120 C
500
550
600
650
700
o
20
o
110 C
o
130
o
40 o
100 C
90 C
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
o
50
60
o
o
8
7
6
0 C
0 C
0 C
o
o
1-anti
C-O
C-O-C
450
500
550
600
650
700
1100
1120
1140
1160
1180
1200
1220
1240
-
1
Wavelength (nm)
Wavenumber (cm )
Figure 9. Characterization of 1-anti crystal under thermal treatment. (a) PL spectra of 1-anti
crystal under thermal treatment (λ = 365 nm). (b) IR spectra of polymorphs 1 and change of IR
ex
spectra of 1-anti crystal upon thermal treatment.
As indicated in Figure S9a (Supporting Information), the measured PXRD spectra of pristine
1-anti crystals have preferred orientation dominated by their 4 0 2 reflections (peaks at
9.3o),42.43 while the reflection peaks from 20 to 35 became more distinct and the preferred
o
o
1
orientation of 4 0 2 reflections was significantly weakened for the ground samples. Notably,
grinding at room temperature induced no change in the crystal form. Next, we employed PXRD
analysis to monitor the changes of 1-anti crystal upon thermal treating. These pristine crystals
o
o
o
were heated on a heating platform from 60 C to 160 C at each subsequent 10 C interval with
1
0 minutes stopovered and then collected the crystals in each interval samples for
characterization. The changes of PXRD patterns of 1-anti crystal in the heating procedure were
o
shown in Figure 8. When the temperature increased from 60 to 100 C, there was no large
o
difference in peak position but intensity changed. The intensity of peaks at 10.3 for 1-anti
o
crystal (denoted by circles in Figure 8) decreased to the minimum when heated at 100 C, and the
o
o
peaks finally disappeared when heated at 110 C. Moreover, the peaks at 19.3 corresponded to
ACS Paragon Plus Environment
1
5

Crystal Growth & Design
Page 16 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
o
the 4 0 2 reflection of 1-anti crystal also disappeared when heated at 110 C (denoted by circles
o
o
in Figure 8). At the same time, characteristic peaks corresponding to 1-syn crystal at 11.3 , 14.3 ,
o
o
o
17.4 and 22.6 began to appear when heated to 110 C (denoted as dashed circles in Figure 8).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
Moreover, PXRD patterns of 1-anti crystal upon heating at 160 C was quite different from its
origin state but same with that of 1-syn crystal (Figure S10, Supporting Information), indicating
that heating might induce crystals of 1-anti conversion into the thermodynamical phase, i.e. 1-
syn. This was well agreement with the calculation results (Figure 7a) and evidenced that heat-
induced Crystal-to-Crystal transformation between the two polymorphs had taken place at 100-
o
1
10 C.
This also brings the question of whether the rate of structure transition have differences
o
between crystal state and powder state. Exposed to air at 100 C for 5 minutes, the differences in
PL spectra and PXRD patterns between the pristine crystals and ground samples were monitored.
As shown in Figure S9a (Supporting Information), PXRD patterns of the ground samples
exhibited similar 1-syn-like peaks but there are still 1-anti-like peaks on crystals samples
(
marked as black circles). PL spectra (Figure S9c, Supporting Information) also confirmed that
the crystal transformation is easily to occur in ground samples at a certain temperature. However,
few experimental clues were available for the definition of the easily rotatable C-O bonds and
specific phase transition temperature. Inspired by the above fact, the pristine 1-anti crystals were
o
subjected to PL and IR spectroscopy analyses by heating at intervals of 10 C for 10 minutes
o
during 60 to 160 C. The emission intensity of 1-anti crystal at 580 nm decreased and the
o
emission band exhibited red-shift from 580 nm to 650 nm. When heating at 120 C, it began to
appear a broad emission band centred at 580 nm and continued to raise the heating temperature
caused the original emission peak at 580 nm gradually to disappear so that a new emission peak
ACS Paragon Plus Environment
1
6

Page 17 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
at 650 nm (Figure 9a) similar to the emission of 1-syn appeared. At the meanwhile, an observed
-1
absorption of C-O-C and C-O stretching at 1161 and 1188 cm of 1-anti crystal had no large
o
difference when heating from 60 to 80 C. However, two 1-syn-like absorptions appeared at
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-1
o
o
1
153 and 1178 cm when heated at 90 C and then became more distinct at 110 C (Figure 9b).
Combining PXRD patterns and PL spectra analyses, the heating procedure can not only verified
o
the easily rotatable of the methoxy group but also the occurrence of phase transition at 90 C.
o
The two distinct absorption bands at 110 C also indicated that phase transition mostly took place
at this temperature. In addition, thermal treating of 1-syn caused no vibration changes in the C-
O-C and C-O as indicated in Figure S11a (Supporting Information). We latter carried out heating
o
at 130 C to monitor the emission change over times (Figure S11b, Supporting Information), and
interestingly to find that the phase transition process is step by step for a new emission peak
emerges at 630 nm. It can be concluded that the hardly detected phase transition endothermic
peak in measurements was ascribed to the little energy required process, coinciding with that
theoretical calculation and DSC and TGA experimental analyses.
CONCLUSIONS
In summary, we demonstrated and decoded here an in-air sublimation method suitable for
obtaining and achieving interconversion of two polymorphs of 5-methoxy-salicylaldhyde azine
(compound 1) by controlling the sublimation temperature. The sublimed rodlike crystals can be
o
o
obtained at 170 C while lamellar crystals can be attained at 220 C, accompanying with
emission color change from orange yellow to red. Single crystal X-ray analysis revealed the two
polymorphs were rotational isomers, antiperiplanar (1-anti) and synperiplanar (1-syn)
configurations toward the longest chain in the molecule, respectively. Both the experimental
analysis and DFT calculation on the dynamic formation process validated the existence of
ACS Paragon Plus Environment
1
7

Crystal Growth & Design
Page 18 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
alternative conformations for 1 in the gas phase because of the temperature-sensitive structure
arrangement. Furthermore, an occurrence of Crystal-to-Crystal transformation from 1-anti to 1-
syn caused by the easily rotatable C-O bonds was observed under thermal treatment. Therefore,
the controllable sublimation process can guide the detection and growth of polymorphic
materials in regular shapes and good crystallinities.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
EXPERIMENTAL SECTION
Materials. The reagents used in this research were purchased from Energy Chemical
(China). Unless otherwise noted, all the solvents used in this experiment were obtained from
Sinopharm Chemical Reagent (China) and were used without further purification
1
Instrumentation. H NMR was recorded on Agilent NMR Systems 400 MHz Spectrometer
13
(
Agilent, USA). C NMR was determined on Agilent NMR Systems 100 MHz Spectrometer
using tetramethylsilane as internal standard. PL spectra were collected on a Horiba FluoroMax-4
luminescence spectrometer. The absolute fluorescence quantum efficiencies were measured
using a Horiba FL-3018 Integrating Sphere. The lifetime was measured by a time-correlated
single-photon counting (TCSPC) system coupled with an interchangeable NanoLEDs and a
microchannel plate detection system. All excitation wavelengths were 365 nm. The solid UV/Vis
diffuse reflectance spectrum was determined on Agilent Cary 60 spectrophotometer. UV-visible
absorption spectra were recorded on a Lambda 750 spectrophotometer. Single crystal X-ray
diffraction were collected by BRUKER SMART APEX II CCD diffractometer (Billerica, USA)
operating at room temperature and their the structures were resolved and analyzed with the
assistance of shelx-97 software. Powder X-ray diffraction data were collected using a XD-2
Purkinje multi crystal X-ray diffractometer in parallel beam geometry employing CuKα radiation
o
at 40 kV and 30 mA. The diffraction data were collected in the 2 Ɵ range from 4 to 40 at a
ACS Paragon Plus Environment
1
8

Page 19 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
-1
o
sacning speed of 1.54 s step with a 2 Ɵ step inof 0.02 . IR analysis was performed in BRUKER
TENSOR II FTIR Spectrometer at room temperature. DSC analysis was performed in Dimand
o
-1
DSC (PerkinElmer) under argon atmosphere at a heating and cooling rate of 8 C min . TG-
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
DTA analyses were performed on Dimand TG/DTA under a dry nitrogen atmosphere at a
o
-1
heating rate of 5 C min . Optical fluorescence images were taken by using UOP0500CC
microscope at the excitation of UV (365 nm) light.
Computational method. All calculations were performed using Gaussian 09 package.54
Theoretical calculations for the geometrical optimizations was performed by density functional
theory (DFT) and time-dependent DFT (TD-DFT) using B3LYP method.55,56 The -311G+(d,p)
basis sets were employed for C, H, O and N atoms. We ascertained that all the transition states
have only one imaginary frequency through vibrational analysis. Intrinsic reaction coordinate
(
IRC) calculations were performed to ensure that the transition states led to the expected
reactants and products. The vibrational frequency was calculated at the same level to characterize
the nature of the stationary points as true minima (with no imaginary frequency) or transition
states (with unique imaginary frequency). The zero-point vibrational energy (ZPE) and thermal
corrections was also obtained by frequency calculations.
ASSOCIATED CONTENT
Supporting Information.
Crystallographic data for 1-anti and 1-syn crystals including ORTEP drawings, selected bond
lengths and angles for 1-anti and 1-syn, UV absorption spectra, fluorescence decay profiles,
TDDFT energy gaps calculation, fluorescence microscopy images of the sample under thermal
treatment, powder X-ray diffraction of simulated samples and measured samples, DSC curves for
ACS Paragon Plus Environment
1
9

Crystal Growth & Design
Page 20 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
-anti and 1-syn crystals, changes in PXRD patterns after samples processing, fluorescence and
1
13
IR spectra under thermal treatment, and H NMR and C NMR spectra for 1-anti and 1-syn
crystals. These materials are available free of charge via the internet at http://pubs.acs.org. Full
crystallographic data (CCDC 1841532 for 1-anti crystal) has been deposited at Cambridge
Crystallographic Database Center and is available free of charge via the internet at
www.ccdc.cam.ac.uk/data_request/cif.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
AUTHOR INFORMATION
Corresponding Author
*
E-mail: (H. W.) hongmingwang@ncu.edu.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
We are grateful to the support of the National Natural Science Foundation of China (21363014
and 21103082). This work was also supported by the Natural Science Foundation of the Jiangxi
Province of China (Grant No. 20142BCB23003 and 20143ACB21021)
REFERENCES
(1). Galer, P.; Korosec, R. C.; Vidmar, M.; Š ket, B. Crystal Structures and Emission
Properties of the BF(2) Complex 1-Phenyl-3-(3,5-dimethoxyphenyl)-propane-1,3-dione:
Multiple Chromisms, Aggregation- or Crystallization-Induced Emission, and the Self-Assembly
Effect. J. Am. Chem. Soc. 2014, 136, 7383-7394.
ACS Paragon Plus Environment
2
0

Page 21 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(
2). Liu, H.; Yao, L.; Li, B.; Chen, X.; Gao, Y.; Zhang, S.; Li, W.; Lu, P.; Yang, B.; Ma, Y.
Excimer-induced high-efficiency fluorescence due to pairwise anthracene stacking in a crystal
with long lifetime. Chem. Commun. 2016, 52, 7356-7359.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(3). Davis, R.; Rath, N. P.; Das, S. Thermally reversible fluorescent polymorphs of alkoxy-
cyano-substituted diphenylbutadienes: role of crystal packing in solid state fluorescence. Chem.
Commun. 2004, 74-75.
(4). Yuan, M.-S.; Wang, D.-E.; Xue, P.; Wang, W.; Wang, J.-C.; Tu, Q.; Liu, Z.; Liu, Y.;
Zhang, Y.; Wang, J. Fluorenone Organic Crystals: Two-Color Luminescence Switching and
Reversible Phase Transformations between π–π Stacking-Directed Packing and Hydrogen Bond-
Directed Packing. Chem. Mater. 2014, 26, 2467-2477.
(5). Chen, P.-Z.; Zhang, H.; Niu, L.-Y.; Zhang, Y.; Chen, Y.-Z.; Fu, H.-B.; Yang, Q.-Z. A
Solid-State Fluorescent Material Based on Carbazole-Containing Difluoroboron β-Diketonate:
Multiple Chromisms, the Self-Assembly Behavior, and Optical Waveguides. Adv. Funct. Mater.
2
017, 27, 1700332.
(6). Hinoue, T.; Shigenoi, Y.; Sugino, M.; Mizobe, Y.; Hisaki, I.; Miyata, M.; Tohnai, N.
Regulation of π-stacked Anthracene Arrangement for Fluorescence Modulation of Organic Solid
from Monomer to Excited Oligomer Emission. Chem. Eur. J. 2012, 18, 4634-4643.
(
7). Yang, Z.; Mao, Z.; Xie, Z.; Zhang, Y.; Liu, S.; Zhao, J.; Xu, J.; Chi, Z; Aldred, M. P.
Recent advances in organic thermally activated delayed fluorescence materials. Chem. Soc. Rev.
017, 46, 915-1016.
2
ACS Paragon Plus Environment
2
1

Crystal Growth & Design
Page 22 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
8). Chi, Z.; Zhang, X.; Xu, B.; Zhou, X.; Ma, C.; Zhang, Y.; Liu, S.; Xu, J. Recent advances
in organic mechanofluorochromic materials. Chem. Soc. Rev. 2012, 41, 3878-3896.
(9). Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Highly efficient organic
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
light-emitting diodes from delayed fluorescence. Nature 2012, 492, 234-238.
(10). Li, Y.; Li, X.-L.; Chen, D.; Cai, X.; Xie, G.; He, Z.; Wu, Y.-C.; Lien, A.; Cao, Y.; Su, S.-
J. Design Strategy of Blue and Yellow Thermally Activated Delayed Fluorescence Emitters and
Their All-Fluorescence White OLEDs with External Quantum Efficiency beyond 20%. Adv.
Funct. Mater. 2016, 26, 6904-6912.
(11). Chen, C. T. Evolution of Red Organic Light-Emitting Diodes: Materials and Devices.
Chem. Mater. 2004, 16, 4389-4400.
(12). Sirringhaus, H. 25th Anniversary Article: Organic Field-Effect Transistors: The Path
Beyond Amorphous Silicon. Adv. Mater. 2014, 26, 1319-1335.
(
13). Reineke, S.; Lindner, F.; Schwartz, G.; Seidler, N.; Walzer, K.; Lüssem, B.; Leo, K.
White organic light-emitting diodes with fluorescent tube efficiency. Nature 2009, 1212, 234-
38.
2
(14). Wu, J.; Li, Q.; Xue, G.; Chen, H.; Li, H. Preparation of Single-Crystalline
Heterojunctions for Organic Electronics. Adv. Mater. 2017, 29, 1606101.
(15). Nakamura, M.; Sanji, T.; Tanaka, M. Fluorometric Sensing of Biogenic Amines with
Aggregation-Induced Emission-Active Tetraphenylethenes. Chem. Eur. J. 2011, 17, 5344-5349.
(16). Liu, B.; Dan, T. T. T.; Bazan, G. C. Collective Response from a Cationic Tetrahedral
Fluorene for Label-Free DNA Detection. Adv. Funct. Mater. 2007, 17, 2432-2438.
ACS Paragon Plus Environment
2
2

Page 23 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(
17). Li, K.; Jiang, Y.; Ding, D.; Zhang, X.; Liu, Y.; Hua, J.; Feng, S. S.; Liu, B. Folic acid-
functionalized two-photon absorbing nanoparticles for targeted MCF-7 cancer cell imaging.
Chem. Commun. 2011, 47, 7323-7325.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(18). Wei, R.; Song, P.; Tong, A. Reversible Thermochromism of Aggregation-Induced
Emission-Active Benzophenone Azine Based on Polymorph-Dependent Excited-State
Intramolecular Proton Transfer Fluorescence. J. Phys. Chem. C 2013, 117, 3467-3474.
(19). Mutai, T.; Tomoda, H.; Ohkawa, T.; Yabe, Y.; Araki, K., Switching of Polymorph-
Dependent ESIPT Luminescence of an Imidazo[1,2-a]pyridine Derivative. Angew. Chem. Int.
Ed. 2008, 47, 9522-9524.
(20). Zhao, Y.; Gao, H.; Fan, Y.; Zhou, T.; Su, Z.; Liu, Y.; Wang, Y. Thermally Induced
Reversible Phase Transformations Accompanied by Emission Switching Between Different
Colors of Two Aromatic-Amine Compounds. Adv. Mater. 2009, 21, 3165-3169.
(21). Zhang, Y.; Song, Q.; Wang, K.; Mao, W.; Cao, F.; Sun, J.; Zhan, L.; Lv, Y.; Ma, Y.; Zou,
B.; Zhang, C. Polymorphic crystals and their luminescence switching of triphenylacrylonitrile
derivatives upon solvent vapour, mechanical, and thermal stimuli. J. Mater. Chem. C 2015, 3,
3
049-3054.
(22). Green, D. C.; Ihli, J.; Thornton, P. D.; Holden, M. A.; Marzec, B.; Kim, Y. Y.; Kulak, A.
N.; Levenstein, M. A.; Tang, C.; Lynch, C.; Webb, S. E.; Tynan, C. J.; Meldrum, F. C. 3D
visualization of additive occlusion and tunable full-spectrum fluorescence in calcite. Nat.
Commun. 2016, 7, 13524.
ACS Paragon Plus Environment
2
3

Crystal Growth & Design
Page 24 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
23). Xia, G.; Shen, S.; Hu, X. M.; Xu, K.; Jiang, Z.; Wang, M.; Wang, H. Controlling Crystal
Structures and Multiple Thermo-/Vapochromic Behaviors of Benzimidazole-based Squaraine
Dyes by Molecular Design and Solvent Adjustment. Chem. Eur. J. 2018, 24, 13205-13212.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(24). Chen, X. Principles and practices of single crystal structure analysis. Science Press:
2
007.
(25). Ramya, K.; Saraswathip, N. T.; Raja, C. R. Studies on the growth and characterization of
organic crystal l-Arginine glutarate by liquid diffusion technique. Optik, 2017, 130, 1408-1413.
(26). Sun, C. Y.; Wang, X. L.; Zhang, X.; Qin, C.; Li, P.; Su, Z. M.; Zhu, D. X.; Shan, G. G.;
Shao, K. Z.; Wu, H.; Li, J. Efficient and tunable white-light emission of metal-organic
frameworks by iridium-complex encapsulation. Nat. Commun. 2013, 4, 2717.
(27). Demazeau, G.; Largeteau, A. ChemInform Abstract: Hydrothermal/Solvothermal Crystal
Growth: An Old but Adaptable Process. Cheminform 2015, 46, 159-163.
(28). Nangia, A.; Desiraju, G. R. Pseudopolymorphism: occurrences of hydrogen bonding
organic solvents in molecular crystals. Chem. Commun., 1999, 7, 605-606.
(29). Fujii, K.; Sakon, A.; Sekine, A.; Uekusa, H. Reversible Color Switching of an Organic
Crystal Induced by Organic Solvent Vapors. Cryst. Growth Des. 2011, 11, 4305-4308.
(30). Tedesco, C.; Erra, L.; Immediata, I.; Gaeta, C.; Brunelli, M.; Merlini, M.; Meneghini, C.;
Pattison, P.; Neri, P. Solvent Induced Pseudopolymorphism in a Calixarene-Based Porous Host
Framework. Cryst. Growth Des. 2010, 10, 1527-1533.
ACS Paragon Plus Environment
2
4

Page 25 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(
31). Mukherjee, A.; Desiraju, G. R. Synthon polymorphism and pseudopolymorphism in co-
crystals.The 4,4’-bipyridine–4-hydroxybenzoic acid structural landscape. Chem. Commun. 2011,
47, 4090-4092.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(32). Barbour, L. J. Crystal porosity and the burden of proof. Chem. Commun. 2006, 11, 1163-
1
168.
(
33). Ye, X.; Liu, Y.; Han, Q.; Ge, C.; Cui, S.; Zhang, L.; Zheng, X.; Liu, G.; Liu, J.; Liu, D.;
Tao, X. Microspacing In-Air Sublimation Growth of Organic Crystals. Chem. Mater. 2018, 30,
12-420.
4
(34). Karpinska, J.; Erxleben, A.; McArdle, P. Applications of Low Temperature Gradient
Sublimation in Vacuo: Rapid Production of High Quality Crystals. The First Solvent-Free
Crystals of Ethinyl Estradiol. Cryst. Growth Des. 2013, 13, 1122-1130.
(35). Barsky, I.; Bernstein, J. Crystal structures and characterization of the polymorphs of (2-
furyl)oxoacetamide. CrystEngComm. 2008, 10, 669.
(36). Kettner, F.; Huter, L.; Schafer, J.; Roder, K.; Purgahn, U.; Krautscheid, H. Selective
crystallization of indigo B by a modified sublimation method and its redetermined structure. Acta
Crystallogr. Sect E: Struct. Rep. Online 2011, 67, 02867.
(37). Harada, N.; Abe, Y.; Karasawa, S.; Koga, N. Polymorphic Equilibrium Responsive
Thermal and Mechanical Stimuli in Light-emitting Crystals of N-Methylaminonaphthyridine.
Org. Lett. 2012, 14, 6282-6285.
ACS Paragon Plus Environment
2
5

Crystal Growth & Design
Page 26 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
38). He, T.; Stolte, M.; Burschka, C.; Hansen, N. H.; Musiol, T.; Kalblein, D.; Pflaum, J.;
Tao, X.; Brill, J.; Würthner, F. Single-crystal field-effect transistors of new Cl(2)-NDI
polymorph processed by sublimation in air. Nat. Commun. 2015, 6, 5954.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(39). Brillante, A.; Bilotti, I.; Valle, R. G. D.; Venuti, E.; Milita, S.; Dionigi, C.; Borgatti, F.;
Lazar, A. N.; Biscarini, F.; Mas-Torrent, M.; Oxtoby, N. S.; Crivillers, N.; Veciana, J.; Rovira,
C.; Leufgen, M.; Schmidt, G.; Molenkamp, L. W. The four polymorphic modifications of the
semiconductor dibenzo-tetrathiafulvalene. CrystEngComm 2008, 10, 1899-1909.
(40). Tripathi, A. K.; Pflaum, J., Correlation between ambipolar transport and structural phase
transition in diindenoperylene single crystals. Applied Physics Letters 2006, 89, 283-2.
(41). Kamali, N.; Erxleben, A.; Mcardle, P. Unexpected Effects of Catalytic Amounts of
Additives on Crystallization from the Gas Phase: Depression of the Sublimation Temperature
and Polymorph Control. Cryst. Growth Des. 2016, 2492-2495.
(42). Sarma, B.; Roy, S.; Nangia, A. Polymorphs of 1,1-bis(4-hydroxyphenyl)cyclohexane and
multiple Z' crystal structures by melt and sublimation crystallization. Chem. Commun. 2006,
4918-4920.
(43). Karpinska, J.; Erxleben, A.; McArdle, P. 17β-Hydroxy-17α-methylandrostano[3,2-
c]pyrazole, Stanozolol: The Crystal Structures of Polymorphs 1 and 2 and 10 Solvates. Cryst.
Growth Des. 2011, 2829-2838.
(44). Taha, M.; Shah, S. A.; Sultan, S.; Ismail, N. H.; Yousuf, S. 2-{[2-(2-Hydroxy-5-
methoxybenzylidene)hydrazin-1-ylidene]methyl}-4-methoxyphenol. Acta Crystallogr Sect E
Struct Rep Online 2014, 70, 0131.
ACS Paragon Plus Environment
2
6

Page 27 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(
45). Mijanuddin, M.; Sheldrick, W. S.; Mayer-Figge, H.; Ali, M.; Chattopadhyay, N. Crystal
structure and feasibility of intramolecular proton transfer reaction of salicylaldazine. J. Mol.
Struct. 2004, 693, 161-165.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(46). Xiao, H.; Chen, K.; Cui, D.; Jiang, N.; Yin, G.; Wang, J.; Wang, R. Two novel
aggregation-induced emission active coumarin-based Schiff bases and their applications in cell
imaging. New J. Chem. 2014, 38, 2386-2393.
(47). Wang, Z.; Zhou, F.; Wang, J.; Zhao, Z.; Qin, A.; Yu, Z.; Tang, B. Z. Electronic effect on
the optical properties and sensing ability of AIEgens with ESIPT process based on
salicylaldehyde azine. Sci. China Chem. 2018, 61, 76-87.
(
48). Tomin, V. I.; Demchenko, A. P.; Chou, P.-T. Thermodynamic vs. kinetic control of
excited-state proton transfer reactions. J. Photochem. Photobiol. C: Photochem. Rev. 2015, 22,
-18.
1
(49). Lakowicz, J. R. Principles of Fluorescence Spectroscopy, third ed., Science Press,
Beijing, 2008.
(50). Peng, C. Y.; Shen, J. Y.; Chen, Y. T.; Wu, P. J.; Hung, W. Y.; Hu, W. P.; Chou, P. T.
Optically Triggered Stepwise Double-Proton Transfer in an Intramolecular Proton Relay: A Case
Study of 1,8-Dihydroxy-2-naphthaldehyde. J. Am. Chem. Soc. 2015, 137, 14349-14357.
(51). Li, S.; He L.; Xiong, F.; Li, Y.; Yang, G. Enhanced Fluorescent Emission of Organic
Nanoparticles of an Intramolecular Proton Transfer Compound and Spontaneous Formation of
One-Dimensional Nanostructures. J. Phys. Chem. B 2004, 108, 10887-10892.
ACS Paragon Plus Environment
2
7

Crystal Growth & Design
Page 28 of 30
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
52). Chen, H.; Farahat, M. S.; Law, K.-Y.; Whitten, D. G. Aggregation of Surfactant
Squaraine Dyes in Aqueous Solution and Microheterogeneous Media: Correlation of
Aggregation Behavior with Molecular Structure. J. Am. Chem. Soc. 1996, 118, 2584-2594.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(53). Kumar, N. S. S.; Varghese, S.; Suresh, C. H.; Rath, N. P.; Das, S. Correlation between
Solid-State Photophysical Properties and Molecular Packing in a Series of Indane-1,3-dione
Containing Butadiene Derivatives. J.Phys. Chem. C 2009, 113, 11927-11935.
(54). Frisch, M.; Trucks, G.; Schlegel, H.; Scuseria, G.; Robb, M.; Cheeseman, J.;
Montgomery, J.; Vreven, T.; Kudin, K.; Burant, J.; Millam, J.; Iyengar, S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.; Nakatsuji, H.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J.; Hratchian, H.; Cross, J.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R.; Yazyev, O.; Austin, A.; Cammi, R.; Pomelli, C.;
Ochterski, J.; Ayala, P.; Morokuma, K.; Voth, G.; Salvador, P.; Dannenberg, J.; Zakrzewski, V.;
Dapprich, S.; Daniels, A.; Strain, M.; Farkas, O.; Malick, D.; Rabuck, A.; Raghavachari, K.;
Foresman, J.; Ortiz, J.; Cui, Q.; Baboul, A.; Clifford, S.; Cioslowski, J.; Stefanov, B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R.; Fox, D.; Keith, T.; Al-Laham, M.; Peng,
C.; Nanayakkara, A.; Challacombe, M.; Gill, P.; Johnson, B.; Chen, W.; Wong, M.; Gonzalez,
C.; Pople, J. Gaussian, Inc., Wallingford CT, 2009.
(
55). Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy
formula into a functional of the electron density. Phys. Rev. B: Condens. Matter 1988, 37, 785-
89.
7
ACS Paragon Plus Environment
2
8

Page 29 of 30
Crystal Growth & Design
1
2
3
4
5
6
7
8
9
(
56). Becke, A. D. Density-functional thermochemistry. Abstracts of Papers of the American
Chemical Society 1993, 212.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ACS Paragon Plus Environment
2
9