Regioselective Deuteration and Resonance Raman Spectroscopic Characterization of Biliverdin and Phycocyanobilin

5-Deuteriophycocyanobilin (4), 5,15,182,182-tetradeuteriobiliverdin IXα dimethyl ester (6), and 5,15-dideuteriomesobiliverdin IXα dimethyl ester (8) have been prepared and analyzed by resonance Raman spectroscopy in the C–H out-of-plane region, based on a previous normal-mode analysis of biliverdin XI α dimethyl ester (5). In this way most of the modes containing out-of-plane vibrations of the methine bridges could be assigned unambiguously. These results are of special relevance with regard to the interpretation of the resonance Raman spectra of the chromoprotein phytochrome.