EPITAXIAL STRUCTURING OF BLUE-LIGHT-EMITTING P-PHENYLENE OLIGOMERS

Epitaxial structuring of blue light-emitting molecules, p-phenylene ol igomers (p-nP, n = 3,4,5,6), was investigated in thin crystals vapor d eposited on the (001) surface of a KCl single crystal. Their molecular orientation and morphology changed depending on the molecular length and substrate temperatures during deposition. As the length of p-nP wa s longer and the substrate temperature was lower, the orientation of t he molecular axis changed from standing to lying on the KCl surface du e to an increase of molecule-substrate interactions. p-terphenyl (3P) hardly adsorbed on the KCl (001) surface, but a portion of the standin g molecules stuck along the step edge of KCl and formed a walllike str ucture. Long needlelike crystals of p-hexaphenyl (6P) epitaxially grew in two orthogonal KCI [110] directions taking lying orientation even at a higher substrate temperature. In these epitaxial needles, the tra nsition dipoles parallel to the molecular axis gave rise to blue fluor escence sharply polarized along the KCI [110] directions. (C) 1998 Ame rican Institute of Physics.