In this paper, we report the synthesis of a new rigid compound, 4,4'-dicyano-(3,4-dibutyl-2-thienylethynyl)biphenyl (1), as well as the preparation and spectroscopic characterizations of its Langmuir-Blodgett (LB) films. Absorption and emission spectra have shown molecular aggregation of 1 in LB films. An unexpected irradiation-induced luminescence enhancement (IILE) was observed when these LB films were exposed under ultraviolet (UV) irradiation. Because no difference could be observed in UV-visible (UV-vis), fluorescence bands, infrared and Xray diffraction spectra of these LB films before and after UV irradiations, changes of the molecular structure could be ruled out. But aggregates obtained with other methods, such as from water-tetrahydrofuran binary solution and solution casting films or dispersed microcrystals, did not show this IILE effect. This suggested that the IILE effect should be resulted from the special aggregation manner of 1 in the LB films. (c) 2006 Elsevier B.V. All rights reserved.