Photochromic Radical Complexes That Show Heterolytic Bond Dissociation

Photochromic
materials have been widely used in various research
fields because of their variety of photoswitching properties based
on various molecular frameworks and bond breaking processes, such
as homolysis and heterolysis. However, while a number of photochromic
molecular frameworks have been reported so far, there are few reports
on photochromic molecular frameworks that show both homolysis and
heterolysis depending on the substituents with high durability. The
biradicals and zwitterions generated by homolysis and heterolysis
have different physical and chemical properties and different potential
applications. Therefore, the rational photochromic molecular design
to control the bond dissociation in the excited state on demand expands
the versatility for photoswitch materials beyond the conventional
photochromic molecular frameworks. In this study, we synthesized novel
photochromic molecules based on the framework of a radical-dissociation-type
photochromic molecule: phenoxyl-imidazolyl radical complex (PIC).
While the conventional PIC shows the photoinduced homolysis, the substitution
of a strong electron-donating moiety to the phenoxyl moiety enables
the bond dissociation process to be switched from homolysis to heterolysis.
This study gives a strategy for controlling the bond dissociation
process of the excited state of photochromic systems, and the strategy
enables us to develop further novel radical and zwitterionic photoswitches.