Photophysical properties of hexamethoxytriphenylene mixed with stearic acid assembled in Langmuir-Blodgett films

Excellent Langmuir-Blodgett (LB) films of 2,3,6,7,10,11-hexamethoxytriphenylene (HMT) have been prepared by mixing with stearic acid (SA). Surface pressure versus area/molecule (pi-A) isotherms at different compositions are measured. Stability of the mixed Langmuir monolayer and the collapse pressure are found to be higher in comparison to that for pure HMT. The absorbance versus number of layers curve reveals uniform film transfer onto the solid substrate. Spectroscopic properties of HMT in solution and in mixed LB films have been compared by absorption, steady state fluorescence and phosphorescence spectroscopy, and lifetime measurements. Surface morphology of LB films has been examined by scanning electron microscopy (SEM). Bathochromic shift in absorption and emission spectrum, and SEM micrographs suggest the formation of some kind of aggregates in LB film, Excitation and emission spectra, and decay analysis confirms that the red shifted band is not of excimeric origin. Multiexponential decay, decrease in fluorescence and phosphorescence lifetime when compared to that of pure HMT also supports the formation of different sized aggregates in the mixed film and a fast energy transfer between different traps. (C) 2002 Elsevier Science B.V. All rights reserved.