A chiroptical binaphthopyran switch: amplified CD response in a polystyrene film

Enantiopure 10,10′-bi(naphtho[2,3-b]pyran) (5a) has been prepared from (R)-BINOL by using the attachment of 1,1-diphenylallyl alcohol to positions 3 and 3′ of the binaphthalene via Heck coupling as a key step. The irradiation of 5a in solution with UV light at 313 nm caused photochemical opening of only one of the pyran rings, accompanied by minor changes in the CD spectrum. Thermal ring closure occurred spontaneously with an activation barrier of 74 kJ mol−1. When 5a was immobilised in a polystyrene film, an improved switching performance, both in terms of fatigue resistance (>10 cycles) and CD signal amplitude (>100 mdeg, >6:1 signal ratio of open/closed forms), was observed.