Chapter 6
Molecular and Crystal Structures
of Polymorphic Organic Dyes
and Coloured Organic Compounds
Shinya Matsumoto and Jiyong Hwang
Abstract Molecular and crystal structures were reviewed on several dyes and
coloured organic compounds with four or more polymorphic forms whose structural data are available from the online database. The difference in the molecular and
crystal structures between polymorphs of the target compounds was briefly described.
The result indicated that rigid dye chromophores, structural flexibility and weak
intermolecular interactions such as hydrogen bonding and halogen interactions are
important in terms of the occurrence of the polymorphs of organic dyes.
Keywords Polymorphs · Molecular structure · Crystal structure
6.1 Introduction
Polymorphism, a phenomenon in which the same molecule or chemical composite
exhibits two or more different crystal structures (Bernstein 2002; Hilfiker 2006;
Threlfal 1995; Dunitz and Bernstein 1995; Bernstein et al. 1999; Nangia 2008;
Price 2013; Cruz-Cabeza and Bernstein 2014), is essential in several industries,
such as pharmaceutics (Hilfiker 2006) and dyes, particularly for pigments and functional dye applications (Zollinger 2003; Faulkner and Schwartz 2009; Hunger and
Schmidt 2018; Whitaker 1977, 1995; Erk and Hengelsberg 2003; Engel 2003; Law
1993). This is reflected by numerous patents involving polymorphs and their crystallisation methods. Many research endeavours have been devoted to understanding
polymorphism in terms of crystal growth, polymorphic occurrence and structure–
property relationships. In particular, the prediction of polymorphic crystal structures
has been considered a challenging research subject (Price 2014; Reilly et al. 2016;
Gavezzotti 2007). Polymorphs can generally be categorised into two types, namely
conformational polymorphs and packing polymorphs (Nangia 2008; Cruz-Cabeza
and Bernstein 2014), both of which are commonly observed in dye polymorphs.
S. Matsumoto (B) · J. Hwang
Graduate School of Environment and Information Sciences, Yokohama National University,
Yokohama, Japan
e-mail: matsumoto-shinya-py@ynu.ac.jp
© Springer Nature Singapore Pte Ltd. 2021
Y. Ooyama and S. Yagi (eds.), Progress in the Science of Functional Dyes,
https://doi.org/10.1007/978-981-33-4392-4_6
223
Molecular and Crystal Structures
of Polymorphic Organic Dyes
and Coloured Organic Compounds
Shinya Matsumoto and Jiyong Hwang
Abstract Molecular and crystal structures were reviewed on several dyes and
coloured organic compounds with four or more polymorphic forms whose structural data are available from the online database. The difference in the molecular and
crystal structures between polymorphs of the target compounds was briefly described.
The result indicated that rigid dye chromophores, structural flexibility and weak
intermolecular interactions such as hydrogen bonding and halogen interactions are
important in terms of the occurrence of the polymorphs of organic dyes.
Keywords Polymorphs · Molecular structure · Crystal structure
6.1 Introduction
Polymorphism, a phenomenon in which the same molecule or chemical composite
exhibits two or more different crystal structures (Bernstein 2002; Hilfiker 2006;
Threlfal 1995; Dunitz and Bernstein 1995; Bernstein et al. 1999; Nangia 2008;
Price 2013; Cruz-Cabeza and Bernstein 2014), is essential in several industries,
such as pharmaceutics (Hilfiker 2006) and dyes, particularly for pigments and functional dye applications (Zollinger 2003; Faulkner and Schwartz 2009; Hunger and
Schmidt 2018; Whitaker 1977, 1995; Erk and Hengelsberg 2003; Engel 2003; Law
1993). This is reflected by numerous patents involving polymorphs and their crystallisation methods. Many research endeavours have been devoted to understanding
polymorphism in terms of crystal growth, polymorphic occurrence and structure–
property relationships. In particular, the prediction of polymorphic crystal structures
has been considered a challenging research subject (Price 2014; Reilly et al. 2016;
Gavezzotti 2007). Polymorphs can generally be categorised into two types, namely
conformational polymorphs and packing polymorphs (Nangia 2008; Cruz-Cabeza
and Bernstein 2014), both of which are commonly observed in dye polymorphs.
S. Matsumoto (B) · J. Hwang
Graduate School of Environment and Information Sciences, Yokohama National University,
Yokohama, Japan
e-mail: matsumoto-shinya-py@ynu.ac.jp
© Springer Nature Singapore Pte Ltd. 2021
Y. Ooyama and S. Yagi (eds.), Progress in the Science of Functional Dyes,
https://doi.org/10.1007/978-981-33-4392-4_6
223