Nonradiative twisted intramolecular charge transfer state in polar stilbenes: Photophysical study of 4-perfluorooctylsulfonyl-4'-N,N-dimethylamino stilbene and two bridged derivatives

Photoinduced intramolecular electron transfer has been studied in 4-perfluorooctylsulfonyl-4'-N,N-dimethylamino stilbene (PFSDS) and its bridged derivatives (PFSDS-023(2) and PFSDS-N34(2))where the central double bond is rigidized by a heteroatom Excited-state dipole moments have been obtained from the solvatochromic behavior of the fluorescence. The decrease in the fluorescence quantum yields and the shortening of the fluorescence lifetimes in polar solvents have been analyzed. Semiempirical calculations suggest that the twisted intramolecular charge transfer (TICT) states A(4)* (S-7) for PFSDS, A(4)* (S-7) for PFSDS-023 and A(2)* (S-18) for PFSDS-N34 are sufficiently low lying to become the lowest excited states in polar solvents because of their high dipole moments. The photophysical results suggest non-radiative properties for most of the TICT states and the accessibility of a higher energy emissive TICT state for PFSDS only.