Conformational Switching of π-Conjugated Junctions from Merocyanine to Cyanine States by Solvent Polarity.

Directed by the solvent polarity, the prevalent conformation of a polymethine dye bearing a branched π-conjugated junction can be switched from a heptamethine donor-acceptor (DA) merocyanine-type π-conjugated system to a nonamethine DAD cyanine-type π-conjugated scaffold. Concomitantly the absorption maximum shifts from 585 nm in dichloromethane to 748 nm in methanol solution.