A photoswitchable bichromophoric oxazine with fast switching speeds and excellent fatigue resistance

In search of strategies to regulate the photochemical and photophysical properties of photochromic oxazines, we designed a multichromophoric compound incorporating 3H-indole, benzooxazine, and 2-(4-dimethylaminophenyl)ethynyl fragments. We synthesized this molecule in two steps in an overall yield of 51%, starting from commercial precursors. The ultraviolet irradiation of this photochrome opens a [1,3]oxazine ring in less than 6 ns to generate a zwitterionic isomer with a quantum yield of 0.10. In particular, the photoinduced ring opening generates a 4-nitrophenolate anion and a 3H-indolium cation. Additionally, this process brings the 2-(4-dimethylaminophenyl)ethynyl appendage into conjugation with the 3H-indolium cation. As a result, two distinct bands for the anionic and cationic fragments of the photogenerated zwitterion appear in the visible region of the absorption spectrum. The photogenerated isomer has a lifetime of 2 mu s and switches back to the original form with first-order kinetics. Furthermore, this bichromophoric photochrome tolerates hundreds of switching cycles with no sign of degradation and can be operated within rigid polymer matrices. Thus, this particular structural design can lead to the development of a new family of bichromophoric photochromes and photoresponsive materials with microsecond switching times and excellent fatigue resistances. RI Sortino, Salvatore/E-4684-2011; deniz, erhan/B-6994-2009