Chapter 2
Direct Visualization of Crystal Formation
and Growth Probed by the Organic
Fluorescent Molecules
Fuyuki Ito
Abstract In this chapter, the direct visualization of crystal formation and growth
probed by organic fluorescent molecules exhibiting mechanofluorochromism and
displaying aggregation-induced emission (AIE) is discussed. The fluorescence
observations of the evaporative crystallization can reveal a two-step nucleation model
for nuclei formation. The fluorescence from the droplets showed dramatic changes
depending on the molecular state, such as monomer, amorphous, and crystal polymorph. The quartz crystal microbalance (QCM) measurement also revealed the
changes in the mechanical properties during the solvent evaporation. These methods
provide a useful and convenient fluorescence tool for in situ crystal analysis, from
which detailed experimental evidence and mechanistic insights into crystal formation and transformation can be obtained through direct fluorescence visualization
with real-time, on-site, and nondestructive methods.
Keywords Evaporative crystallization · Fluorescence color changes ·
Mechanofluorochromism · Aggregation-induced emission (AIE) · Quartz crystal
microbalance (QCM) · Two-step nucleation model · Liquid-like cluster
2.1 Introduction
Crystal formation from solution is essential in fundamental science as well as in the
fabrication of pharmaceuticals, food, polymers, and organic solid materials; however,
it remains poorly understood. In solution crystallization, the formation of crystal
nuclei plays an important role in determining the crystal structure, size, and polymorph, controlling crystallization and crystal quality. In classical nucleation theory,
molecules are added one-by-one to extend the crystal lattice and form an embryonic nucleus in a one-step process. The classical model for crystallization visualizes
the formation of a metastable crystalline nucleus that reaches a critical size through
F. Ito (B)
Department of Chemistry, Institute of Education, Shinshu University, 6-ro, Nishinagano, Nagano
380-8544, Japan
e-mail: fito@shinshu-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
M. Sakamoto and H. Uekusa (eds.), Advances in Organic Crystal Chemistry,
https://doi.org/10.1007/978-981-15-5085-0_2
29
Direct Visualization of Crystal Formation
and Growth Probed by the Organic
Fluorescent Molecules
Fuyuki Ito
Abstract In this chapter, the direct visualization of crystal formation and growth
probed by organic fluorescent molecules exhibiting mechanofluorochromism and
displaying aggregation-induced emission (AIE) is discussed. The fluorescence
observations of the evaporative crystallization can reveal a two-step nucleation model
for nuclei formation. The fluorescence from the droplets showed dramatic changes
depending on the molecular state, such as monomer, amorphous, and crystal polymorph. The quartz crystal microbalance (QCM) measurement also revealed the
changes in the mechanical properties during the solvent evaporation. These methods
provide a useful and convenient fluorescence tool for in situ crystal analysis, from
which detailed experimental evidence and mechanistic insights into crystal formation and transformation can be obtained through direct fluorescence visualization
with real-time, on-site, and nondestructive methods.
Keywords Evaporative crystallization · Fluorescence color changes ·
Mechanofluorochromism · Aggregation-induced emission (AIE) · Quartz crystal
microbalance (QCM) · Two-step nucleation model · Liquid-like cluster
2.1 Introduction
Crystal formation from solution is essential in fundamental science as well as in the
fabrication of pharmaceuticals, food, polymers, and organic solid materials; however,
it remains poorly understood. In solution crystallization, the formation of crystal
nuclei plays an important role in determining the crystal structure, size, and polymorph, controlling crystallization and crystal quality. In classical nucleation theory,
molecules are added one-by-one to extend the crystal lattice and form an embryonic nucleus in a one-step process. The classical model for crystallization visualizes
the formation of a metastable crystalline nucleus that reaches a critical size through
F. Ito (B)
Department of Chemistry, Institute of Education, Shinshu University, 6-ro, Nishinagano, Nagano
380-8544, Japan
e-mail: fito@shinshu-u.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
M. Sakamoto and H. Uekusa (eds.), Advances in Organic Crystal Chemistry,
https://doi.org/10.1007/978-981-15-5085-0_2
29