Resonance Raman Studies of Copper Pheophytinate
In recent years there has been considerable interest in the spectroscopic properties of chlorophyll molecules. Among the techniques employed is resonance Raman spectroscopy which can provide vibrational spectra with high selectivity, from chlorophyll a present in intact chloroplasts or cells.1 However, detecting resonance Raman scattering from chlorophyll a is hindered when excitation in the red region is used, owing to the strong fluorescence of the molecule near 670 nm. Copper pheophytinate, on the other hand, is largely non-fluorescent and thus lends itself to resonance Raman study in the red region. (The mechanism for fluorescence quenching in copper pheophytinate is believed to involve charge transfer from the porpnyrin ring to the Cu2+ ion upon excitation, although direct experimental evidence is still lacking.) we felt that it would be of interest to carry out a resonance Raman study to copper pheophytinate in the red region and compare the results with what is already known about the resonance raman sperctrum of chlorophy 11 a. An advantage of exciting in the red region is that athe QX and Qy bamus in the red region are better resolved than the BX and By bands in the blue region, 2 thus making it easier to observe different vibronic coupling in the red.