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

• Squaraine (SQ)-bounded cellulose derivative (4) was prepared.
• Langmuir–Blodgett monolayer film of compound 4 was prepared.
• The LB film of compound 4 showed high photocurrent generation performance.

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).

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