3. Optimizing photochromic properties

It goes without saying that photochromic researchers and engineers from a wide range of fields (organic chemistry, physical chemistry, materials science, etc.) seek to optimize their molecules to obtain "the best" photochromes: high extinction coefficients, the highest possible quantum yields, good fatigue resistance, very fast or very slow thermal recovery, depending on the intended application. The aim is therefore to rationalize the photophysical properties of photochromes in terms of the reaction mechanism and the excited states involved (figure 12 ). Thanks to this in-depth understanding, involving "time-resolved" experimental techniques or theoretical calculations, and to collaboration between photochemists and synthetic chemists, it will then be possible...