Resonance Energy Transfer from Alkylbenzene Substrates to Naphthalene and Biphenyl Overlayers on Al₂O₃

Abstract

In an ultrahigh vacuum chamber, an alkylbenzene was deposited from the vapor phase onto a cryogenically cooled Al 2 O 3 surface. An additional layer with a fluorophore of naphthalene or methylnaphthalene was deposited, and the bilayer was optically pumped. Vapor-deposited naphthalene and methyl-substituted naphthalene molecules on the surface of Al 2 O 3 are amorphously arranged and exhibit a characteristic excimeric fluorescence that is spectrally broad, featureless, and redshifted relative to the monomer fluorescence. When the bilayer was heated in a temperature-programmed desorption (TPD) experiment, the ordering in the alkylbenzene substrate caused the overlayer of naphthalenes to crystalize due to heteroepitaxy. Finally, the two layers mixed when the surface temperature was nearly at the desorption temperature and resonance energy transfer was observed from the alkylbenzene to naphthalene and methylnaphthalenes when the alkylbenzene percolated through the naphthalene and methylnaphthalene adlayers. The wavelength-resolved TPD and laser-induced fluorescence of the bilayer are reported. Reformation of the excimer after the passage of the alkylbenzene occurred for weak alkylbenzene−naphthalene interaction, whereas for strong interaction, the naphthalene monomer emission persisted after desorption of the alkylbenzene.