Photochromic molecules provide a unique opportunity for the practical application of theoretical chemistry, molecular modeling, and molecular simulation, since their molecular properties directly determine the function of devices. 1 Recent remarkable developments of computer hardware and software have opened a new horizon in material design, namely, the combination of computational studies and experimental approaches to offer an understanding of function on a molecular level. 2 This does well for the future design of functional materials.The requirements for the design of photochromic compounds are, among others, the adjustment of absorption wavelength and intensity, the attainment of thermal stability, clarification of reaction mechanism, and enhancement of quantum yield. The purpose of this chapter is to review recent computational studies in consideration of these requirements.
ABSORPTION WAVELENGTH AND INTENSITYThe first event of the photochromic reaction is light absorption. Therefore, how efficiently the molecules of a photochromic compound absorb a given wavelength of light is the first concern. Practical applications often require the use of a limited range of wavelengths of the light source, and, as a result, molecules must be adjusted to the light source. We will include some work on organic functional dyes in this section, since most important studies are on organic dyes. The pioneering work reported in this area has used the Pariser-Parr-Pople