Peculiar photophysical properties of a conformationally proximal pyrene-pair

The mode of interaction of two pyrenylalanine residues which are introduced at positions 1 and 3′ into gramicidine S, [Pya1,3′]GS, was investigated through absorption, CD, and steady-state and time-resolved fluorescence spectroscopy in organic and buffer solutions. CD spectra showed that the pyrene moieties could adopt an orientation to form a sandwich-type close pair on the two strands in a typical antiparallel β-structure in trifluoroethanol. Other spectroscopic studies demonstrated that the pyrenes of [Pya1,3′]GS in trifluoroethanol formed specific intramolecular association on the pyrene pair, a ‘sandwich-type dimer’, in the ground state.