Preparation of a squaraine-bounded cellulose derivative for photocurrent generation system

A regio-selectively squaraine (SQ)-bounded cellulose derivative (4) with a degree of substitution of SQ (DSSQ) of 0.55 was prepared from 6-O-(4-methoxytrityl) cellulose (1) by three reaction steps in 77% total yield. Lauryl SQ carboxylate (8) was also prepared as a reference sample. The photostability of SQ moieties of compound 4 in CHCl3 was not improved when compared with SQ-COOH (7), but that of SQ moiety of compound 8 was improved unexpectedly. The Langmuir-Blodgett monolayer films 4B and 8B on an indium tin oxide (ITO) electrode were successfully prepared from compounds 4 and 8 by a vertical dipping method, respectively. The films 4B and 8B showed photocurrent generation performances in the region of 550-680 nm. The quantum yield at 650 nm of film 4B was higher than that of film 8B. These results showed that the cellulose backbone of compound 4 acts as an effective scaffold for the good photocurrent generation performances and that compound 4 was a promising complementary material of the porphyrin-bounded cellulose derivatives (for photocurrent generation at 400-420 nm) for effective utilization of solar light, as well as the phthalocyanine-bounded cellulose derivatives (for photocurrent generation at 650-720 nm).