Stark absorption spectroscopy of peridinin and allene-modified analogues

Stark absorption spectra of peridinin (Per) and five allene-modified analogues and their angular dependence as a function of an externally applied electric field were measured in methyl methacrylate polymer at 77 K. In all cases, the energetically lowest absorption band has a significant change of static dipole-moment upon photoexcitation (Δμ). In particular, Per has the largest value of |Δμ|. The angles between Δμ and the transition dipole-moment of all the analogues were determined. It is suggested that the allene group in Per plays a key role as the electron donor in the charge transfer process following photoexcitation. The results of MNDO-PSDCI calculations support this idea.