UV RESONANCE RAMAN EVIDENCE FOR VIBRATIONALLY INDEPENDENT PROTOPORPHYRIN-IX VINYL GROUPS

We have examined the protoporphyrin IX (PP) peripheral vinyl C=C stretching 220-nm-excited resonance Raman cross sections, depolarization ratios, and vinyl stretching frequencies. The depolarization ratio of 0.33 observed for the bis(cyanide) complexes of both PP and a monovinylporphyrin derivative indicates that the enhancement of the vinyl vibration is likely in both cases to be dominated by a single tensor component in a manner similar to that for the C=C stretch of simpler olefins. The data suggest that the two peripheral vinyl groups are vibrationally uncoupled.