Folding-induced exciton coupling in homo- and heterodimers of merocyanine dyes

Two identical or different merocyanine dyes were tethered by a rigid diphenylacetylene spacer unit that enables the folding of the two dyes into co-facially p-stacked structures in solvents of low polarity. Whilst the solvent-dependent absorption spectra of homodimers of identical dyes are easily interpreted as H-aggregates by exciton theory, the spectra of the heterodimers constitute a novel and more interesting case.