| Abstract
| - We report the emission spectra, intensity decays, and anisotropy decay of 2,2‘-dimethyl-p-terphenyl (DMT)with four-photon excitation. When excited with a fs Ti:Sapphire laser the emission intensity of DMT wasfound to depend on the third power of the incident intensity for excitation of 783 nm, and on the fourthpower of the incident intensity for excitation at 882 nm. Surprisingly, at the highest value incident power, theemission intensity for four-photon excitation was about 10-fold less than with three-photon excitation. Theemission spectra, intensity decays and correlation times were found to be identical for three- and four-photonexcitation. However, the fundamental anisotropy (r0) of DMT depended on the mode of excitation. To thebest of our knowledge, the r0 value of 0.70 is the highest ever observed for an isotropic solution. Theseresults suggest that four-photon excitation can be used with red-NIR lasers to obtain excitation of UV-absorbingchromophores.
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