Hole transfer equilibrium in rigidly linked bichromophoric molecules

Two bichromophoric molecules consisting of anthracene and diphenylpolyene m oieties Linked by two fused norbornyl bridges undergo photoionization upon ultraviolet (UV) pulsed laser irradiation. The simultaneous observation of the cation radicals of both anthracene and polyene groups points to a rapid (nanosecond or faster) intramolecular hole transfer equilibrium between th e two chromophores. The existence of an equilibrium is supported by the res ults of one- and two-laser transient absorption and electrochemical experim ents. Equilibrium constants (293 K) were determined:by both transient absor ption and cyclic voltammetry measurements and were independent of the metho d used within experimental error. For A-sp-VB, which contains anthracene an d vinyldiphenylbutadiene chromophores, K-eq = 4.0 +/- 2 (transient absorpti on) and 3.2 +/- 2 (electrochemical), favoring the anthracene cation radical . For A-sp-VS, containing anthracene and vinylstilbene groups, K-eq 70 +/- 30 (transient absorption) and 105 +/- 50 (electrochemical), favoring the an thracene cation radical.