Inner sphere reorganization dynamics accompanying charge transfer in cyanoterphenyl

Picosecond transient absorption studies of 4′-n-pentyl-4-cyanoterphenyl (CTP) suggest that the first excited singlet (S₁) state exhibits a solvent-dependent dynamic Stokes shift, attributed to intramolecular charge-transfer in the S₁ state (in polar solvents) followed by outer sphere reorganization. The degree of charge-transfer character attained by the CTP S₁ state is signaled in picosecond time-resolved resonance Raman (TR³) measurements by a frequency shift of the CN-stretch band. No dynamics are observed for this mode frequency within the time resolution of the experiment (less than 1 ps). However, one of the bands in the 1200-1800 cm^-1 region of the spectrum is reported to exhibit a solvent-dependent dynamic shift. Analysis of a spectral shift correlation function for this band reveals time constants of 45 ps in methanol, 36 ps in butanol, 21 ps in pentanol, and 18 ps in octanol. The evidence suggests that energy dissipation from the inner sphere coordinate to the solvent bath is affected by the dynamic Stokes shift (i.e., the outer sphere coordinate).