Light Emitting Properties of Molecular Thin Films with Epitaxially Oriented and Confined Structures

Abstract One-dimensional needlelike crystals of energy-band-tuned thiophene/p-phenylene co-oligomers were epitaxially grown by vapor-deposition onto the KCl (001) surface. Fluorescence spectroscopy and microscopy elucidated various emission color depending on their frontier orbital energies which were changed by the coplanar or twisted molecular structures. The emitted light was confined within the co-oligomer crystals and self-waveguided along the needle axis, then radiated from the tips of the needles. When the co-oligomer needles were confined in a heterostructure within a thin film of a wide-bandgap p-sexiphenyl oligomer, the self-waveguided emission from the co-oligomer was also observed due to the confinement of excitons and emitted light in the crystal.