Diamantane, one of the diamondoid family molecules, was introduced to thermally reversible photochromic heliofulgides. They exhibited good thermally reversible photochromism. A chiral photochromic indolylfulgide derivative was used to control the pitch length of cholesteric liquid crystalline state by photoirradiation. However, as the indolylfulgide derivative has absorption in the visible light region, it is not a suitable agent to control the selective
reflection wavelength. Chiral benzofurylfulgide derivative, possessing shorter absorption maximum wavelength, was employed for this purpose. Diamantane has a long barrel-like C<sub>3</sub>-symmetric structure with the corresponding symmetric axis. Several derivatives, with long alkyl or related substituents on the carbon atoms at both ends of the molecule, showed liquid crystalline properties. Thus, diamantane worked as a thread stitching up photochromism and liquid
Molecular photonics, information processing based on strong interactions of photons and molecules, has attracted much attention, since it can fully utilize many superior properties of both photons and molecules. We have been developing materials showing ultrafast absorption changes in the visible to near infrared regions by photoinduced electron transfer and reverse reactions or by excited electronic state formation. Guided wave mode (GWM) geometry composed of a prism, a metal thin film, and a photoresponsive polymer film successfully achieved sensitive, all optical, and very fast control of reflectance by transient or persistent changes of GWM conditions by means of photoinduced complex refractive index changes upon nanosecond to femtosecond laser excitation. All-optical parallel control of reflected probe light by pump (writing) light was demonstrated by photochromic spiropyran or fulgide, and various metallophthalocyanines dispersed in appropriate polymers.