Photochromic materials, molecular glasses

Applications or potential applications for these molecules have been demonstrated. Molecular switches can be built using supramolecular or LC photochromic materials.1 Photochromic polymers can be used in phototropic glasses or as a basis for information recording. IR-sensitive materials have been made using biphoto-chromic molecules. Light sensitive dental materials have been developed. 

In order to obtain stable amorphous states of organic materials, the glass transition temperature (Tg) of the materials should be higher than room temperature. Molecular motion is frozen at temperatures below Tg, and crystal growth is suppressed. The Tg of la was found to be lower than room temperature. Although several photochromic amorphous materials containing azobenzene unit have been synthesized, the practical use of amorphous azobenzenes is limited because of thermal instability of the cis-isomer and low reactivity in the solid state. Figure 17.3 shows some molecular structures... 

Tanino T, Yoshikawa S, Ujike T, Nagahama D, Moriwaki K, Takahashi T, Kotani Y, Nakano H, Shirota Y. 2007. Creation of azobenzene based photochromic amorphous molecular materials synthesis, glass forming properties, and photochromic response. J Mater Chem 17 4953 4963. 

---