This photophysical study addresses the general question of how electron transfer in bichromophoric molecules influences the conformational relaxation, which can be toward either more or less pi-conjugation. The effects of photoinduced intramolecular charge transfer on the electronic and molecular properties of a series of differently twisted 4-N,N-dimethylamino-4＇-cyanobiphenyls an investigated by steady-state and time-resolved fluorescence. The dipole moments, radiative rates, and torsional relaxations in the excited stare are analyzed by comparison with the absorption spectra and interannular twist angle (phi)-dependont CNDO/S calculations. Independent of the twist angle phi and solvent polarity, the first excited singlet state of these donor-acceptor (D-A) biphenyls (I-III) is an emissive intramolecular (CT)-C-1 state of the L-1(a)-type transferring charge from the dimethylaminobenzene (D) to the cyanobenzene (A) subunit. Similar to the planar restricted D-B fluorene I, the flexible D-A biphenyl LT shows only a weak dependence of the fluorescence radiative rate constants k(f) (0.4-0.6 ns(-1)) on the solvent polarity, consistent with a planarization in the excited state of II. In contrast, the strongly pretwisted biphenyl III behaves similarly to I and II, only in nonpolar solvents ([k(f)] = 0.3 ns(-1), indicating partial excited-state relaxation toward planarity), whereas with increasing polarity the mean radiative rate (kt) decreases down to 0.03 ns(-1). A fast equilibrium between a more planar and a more twisted rotamer distribution in the (CT)-C-1 state of III explains the appearance for III of additional photophysical effects such as (a) strong decrease of the radiative rates with increasing polarity, (b) two long (>200 ps) fluorescence Lifetimes with precursor-successor relation, and (c) excited-state quenching by protic solvents.