548
F. Ito
31.4 Summary
Research on the crystal formation process of organic fluorescent materials is important to elucidate the photoresponse behavior of structures involving one or more
molecules. In addition, the crystal formation process is important for the development of organic solid-state light-emitting materials that exhibit dramatic changes in
emission behavior caused by slight differences in molecular aggregation structures
and phase changes and is essential for establishing not only molecular design but
also crystal engineering molecular assembly design guidelines. Based on the fluorescence visualization of the crystal formation process, the two-step nucleation model
was clearly confirmed based on fluorescence color changes. An intermediate state,
such as liquid-like clusters, is important in not only the crystal nuclei formation
process but also polymorphic expression. The origin of the polymorphic expression
is the key to understanding the crystallization conditions that can selectively generate
crystals with the desired structure, the molecular dynamics in the initial process of
crystal nucleation, and for elucidating the mechanism of crystal polymorphism. The
present method has low requirements because crystal formation can be observed
with a conventional optical detection system in the ambient atmosphere, especially
for control of polymorphism of organic emissive materials with multiple emissive
states or colors depending on the phase, such as mechanofluorochromic molecules.
This approach can be used to provide a comprehensive picture of crystallization by
combination with other observation techniques.
Acknowledgements The authors thank Mr. Jun-ichi Fujimori, Ms. Yukino Suzuki, Ms. Mai
Saigusa, and Ms. Narumi Oka (Shinshu University), Dr. Mitsuo Hara and Prof. Takahiro Seki
(Nagoya University), Dr. Ryohei Yasukuni and Prof. Marc Lamy de la Chapelle (Paris 13 University), Dr. Yohei Haketa and Prof. Hiromitsu Maeda (Ritsumeikan University), Dr. Tetsuya Miyano,
Prof. Norimitsu Tohnai, Dr. Syoji Ito, and Prof. Hiroshi Miyasaka (Osaka University) for their
support with the experiments and useful discussions. This work was partly supported by the
Nanotechnology Platform Program, JSPS KAKENHI (Grants Numbers JP21750021, JP15H01081,
JP17H05253, and JP19H02686), the Iketani Science and Technology Foundation, and the JGC-S
Scholarship Foundation.
References
1. Erdemir D, Lee AY, Myerson AS (2009) Nucleation of crystals from solution: classical and
two-step models. Acc Chem Res 42:621–629
2. Knezic D, Zaccaro J, Myerson AS (2004) Nucleation induction time in levitated droplets. J
Phys Chem B 108:10672–10677
3. Hughes CE, Williams PA, Keast VL, Charalampopoulos VG, Edwards-Gau GR, Harris KDM
(2015) New in situ solid-state NMR techniques for probing the evolution of crystallization
processes: pre-nucleation, nucleation and growth. Faraday Discuss 179:115–140
4. Hughes CE, Harris KDM (2008) A technique for in situ monitoring of crystallization from
solution by solid-state C-13 CPMAS NMR spectroscopy. J Phys Chem A 112:6808–6810
F. Ito
31.4 Summary
Research on the crystal formation process of organic fluorescent materials is important to elucidate the photoresponse behavior of structures involving one or more
molecules. In addition, the crystal formation process is important for the development of organic solid-state light-emitting materials that exhibit dramatic changes in
emission behavior caused by slight differences in molecular aggregation structures
and phase changes and is essential for establishing not only molecular design but
also crystal engineering molecular assembly design guidelines. Based on the fluorescence visualization of the crystal formation process, the two-step nucleation model
was clearly confirmed based on fluorescence color changes. An intermediate state,
such as liquid-like clusters, is important in not only the crystal nuclei formation
process but also polymorphic expression. The origin of the polymorphic expression
is the key to understanding the crystallization conditions that can selectively generate
crystals with the desired structure, the molecular dynamics in the initial process of
crystal nucleation, and for elucidating the mechanism of crystal polymorphism. The
present method has low requirements because crystal formation can be observed
with a conventional optical detection system in the ambient atmosphere, especially
for control of polymorphism of organic emissive materials with multiple emissive
states or colors depending on the phase, such as mechanofluorochromic molecules.
This approach can be used to provide a comprehensive picture of crystallization by
combination with other observation techniques.
Acknowledgements The authors thank Mr. Jun-ichi Fujimori, Ms. Yukino Suzuki, Ms. Mai
Saigusa, and Ms. Narumi Oka (Shinshu University), Dr. Mitsuo Hara and Prof. Takahiro Seki
(Nagoya University), Dr. Ryohei Yasukuni and Prof. Marc Lamy de la Chapelle (Paris 13 University), Dr. Yohei Haketa and Prof. Hiromitsu Maeda (Ritsumeikan University), Dr. Tetsuya Miyano,
Prof. Norimitsu Tohnai, Dr. Syoji Ito, and Prof. Hiroshi Miyasaka (Osaka University) for their
support with the experiments and useful discussions. This work was partly supported by the
Nanotechnology Platform Program, JSPS KAKENHI (Grants Numbers JP21750021, JP15H01081,
JP17H05253, and JP19H02686), the Iketani Science and Technology Foundation, and the JGC-S
Scholarship Foundation.
References
1. Erdemir D, Lee AY, Myerson AS (2009) Nucleation of crystals from solution: classical and
two-step models. Acc Chem Res 42:621–629
2. Knezic D, Zaccaro J, Myerson AS (2004) Nucleation induction time in levitated droplets. J
Phys Chem B 108:10672–10677
3. Hughes CE, Williams PA, Keast VL, Charalampopoulos VG, Edwards-Gau GR, Harris KDM
(2015) New in situ solid-state NMR techniques for probing the evolution of crystallization
processes: pre-nucleation, nucleation and growth. Faraday Discuss 179:115–140
4. Hughes CE, Harris KDM (2008) A technique for in situ monitoring of crystallization from
solution by solid-state C-13 CPMAS NMR spectroscopy. J Phys Chem A 112:6808–6810