Synthesis of new-type donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole fluorescent dyes and their photovoltaic performances of dye-sensitized solar cells

New-type donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole fluorescent dyes with various lengths of non-conjugated alkyl chains containing a carboxyl group at the end position have been developed and their photovoltaic performances of dye-sensitized solar cells are investigated. It is found that in spite of the lengths of the alkyl chains, due to flexibility of alkyl chain, the cyano group of the dyes is located in close proximity to TiO2 surface and thus a good electron communication between the dyes and TiO2 surface is established.