Luminescence and excitation energy transfer in monolayer assemblies incorporating organic dye molecules. I

Abstract

Excitation energy transfer between organic dye molecules in monolayer assemblies is studied. Typical cyanine dyes: N, N′-dioctadecyl-oxacyanine perchlorate and N,N′-dioctadecyl-thiacyanine perchlorate are employed as a donor and acceptor, respectively. Inclusion of the acceptor into the monolayer composed of isolated donor and matrix molecules induces quenching of monomer fluorescence of the donor and consequent sensitization of acceptor fluorescence. Quenching of donor fluorescence by the acceptor obeys the Stern–Volmer relation with a weakly temperature-dependent Stern–Volmer constant. Lowering the temperature from T=293 to 77 K brings about the increase of both the Stern–Volmer constant and the intensity ratio of the sensitized fluorescence to the donor fluorescence. These observations indicate that the rate of thermal deactivation of the excited donor molecule is proportional to temperature in spite of temperature-insensitive energy-transfer rate. Energy transfer between donor and acceptor molecules occurs via a direct dipole-dipole mechanism.