Squarilium dyes, their infrared and resonance Raman spectra and possible use in redox reactions for solar-energy conversion

Abstract

Infrared and resonance Raman spectra of squarilium dyes I–VI of the type [graphic omitted] are presented and some vibrational modes of the central 4-membered ring are assigned. Methyl viologen dication (MV²⁺) is reduced photocatalytically by IV in DMSO + H₂O (95/5, v/v) with a quantum yield ϕ of (1.8 ± 0.4)× 10^–3 at 406.7 nm, if EDTA is present. Oxidation products of MV²⁺ behave similarly with ϕ=(4.7 ± 0.6)× 10^–2 at 457.9 nm in DMF + H₂O (2/1, v/v). IV^˙+ seems to oxidize H₂O nearly reversibly.