Synthesis of chlorophyll-a derivatives possessing various amides as potential sensitizers for photovoltaic cells

Abstract

3[Formula: see text]-Carboxy-pyropheophorbides-[Formula: see text] possessing a variety of [Formula: see text]-substituted carbamoyl groups at the 17[Formula: see text]-position were prepared by modifying naturally occurring chlorophyll-[Formula: see text]. 3[Formula: see text]-Methoxycarbonyl-pyropheophorbide-[Formula: see text] was obtained via the protection of the 17[Formula: see text]-carboxy group with an allyl group, and amidated with various primary and secondary amines at the free 17-propionate residue, followed by the acidic hydrolysis of the methyl ester in the 3-substituent to give the desired pyropheophorbide-[Formula: see text] secondary and tertiary amides, respectively, bearing the trans-3[Formula: see text]-COOH. The synthetic pigments potentially usable for dye-sensitized solar cells gave almost the same optical properties in a solution.