INTRAMOLECULAR CHARGE-TRANSFER STATES IN SYMMETRICAL BIARYLS - THE UNUSUAL CASE OF BIPERYLENYL

The photophysical properties of TBBP, an alkyl derivative of 3,3'-biperylenyl (BP), are described and compared to those of 9,9'-bianthryl (BA). Both compounds exhibit a solvent-polarity induced fluorescence redshift indicative of symmetry breaking and charge separation. In TBBP, however, the amount of charge transferred is considerably less than that expected based on the simple Twisted Intramolecular Charge Transfer (TICT) state model. The CT emission is highly allowed, with fluorescence quantum yields exceeding 0.5 in all investigated solvents. An equilibrium between the nonpolar (B*) and the CT state (A*) appears to be established, with A* involving strong coupling between the TICT and excitonic wave-functions.