Seminarium Optyczne

Photochromic compounds, such as 3H-naphthopyrans, have been applied in commercially available photochromic lenses, for which one of the serious issue is a residual color. 3H-naphthopyrans generate the transoid-cis (TC) form and the transoid-trans (TT) form by UV light irradiation. Typically thermal back reaction of TC form takes from several seconds to tens of seconds while TT form needs much more time. Recently, the suppression of the generation of the TT form was achieved simply by substituting a bulky substituent to the 2-position of the naphthopyrans [1]. However, there are still open questions whether the bulky substituent may also interfere the ring-opening reaction and, as a result, decrease the photochromic reaction efficiency. Herein, naphthopyrans with various aryl substituents at the 2-position were studied. Time-resolved UV-vis and mid-IR optical spectroscopies were applied to detect the transient species involved in the photoreaction over time-scale from subpicosecond to hundreds of microseconds.On the other hand it is important to answer the question whether the TT form is completely suppressed or the lifetime of the TT form is accelerated faster than microseconds. It is crucial not only for fundamental photochemistry but also to demonstrate the potential of these molecular designs for developing optimal photofunctional materials.[1] K. Arai, Y. Kobayashi, J. Abe, Rational Molecular Designs for Drastic Acceleration of the Color-Fading Speed of Photochromic Naphthopyrans, Chem. Commun. 51, 3057-3060 (2015)