Spectroscopic properties of selectively deuterium-substituted retinal homologues

A set of retinal homologue molecules (C 15 aldehyde, C 17 aldehyde, C 18 ketone, C20 aldehyde) in which I I H or 15H atom of their olefinic parts was selectively substituted by a deuterium (11D or 15D) was synthesized. Their spectroscopic properties were investigated by means of optical absorption and FT-IR spectroscopies. Normal coordinate calculations were performed for all the set of molecules in order to establish the assignment of vibrational modes. Upon deuterium substitution of the 11H or 15H atom, apparent decrease of the oscillator-intensity of the absorption transition was observed in the case of shorter polyene molecules (C15 and Cl7aldehydes and C18ketone), while the decrease of the oscillator strength was negligible in the case of C20 aldehyde. Vibrational analysis suggested that the selective deuterium substitution induced the shift of electron distribution from double-bond site to single-bond site resulting in the decrease and increase in the bond orders of the former and the latter, respectively.