Abstract

Ultrafast transient differential transmission in a wide range of probing energies from 0.8 to 2.5 eV have been measured in films of α-sexithyenil (T6) and para-hexaphenyl (P6) photoexcited at 3 .2 eV at room temperature. These materials are important candidates for molecular electronic and optoelectronic applications because of the good stability and processability, the high quantum yield and the rather high mobility [1,2]. Films were deposited by vacuum evaporation at room temperature and display a polycrystalline morphology with molecules aligned at the normal to the substrate. The experiments were carried out in the usual pump and probe configuration using pulses generated by a Ti-sapphire laser with chirped pulse amplification. Tunability was achieved by supercontinuum generation (450-1100 nm) and parametric conversion (1.1-1.6 µm). The excitation wavelength was the second harmonic of the fundamental beam. Goal of our study was the characterization of the primary steps of photoexcitation. A comparison with doping induced spectra and quasi steady state photomodulation spectra allowed the assignement of the observed transient features.

© 1996 IEEE