INVESTIGATION OF SPECTRAL DIFFUSION IN PMMA ON TIMESCALES FROM 10(-5)TO 10(4) SECONDS VIA TRANSIENT AND PHOTOPHYSICAL HOLE-BURNING

Spectral diffusion (SD) in PMMA samples, doped with Zn-tetrabenzoporph ine, was investigated via triplet state populational hole burning in t he absorption spectrum of a chromophore on a timescale from 20 mu s to 200 ms and via photophysical persistent hole burning on a timescale f rom 10 to 10(4) a covering the temperature interval 1.7-10 K. The SD r ates on microsecond and on long timescales (t > 10 s) coincide. An ano malous increase of the SD rate was found in the millisecond range whic h cannot be attributed to peculiarities in the relaxation rate distrib ution of the two-level systems in PMMA. The apparent correlation of th e observed anomalous SD region with the time domain of the deactivatio n of the chromophore's triplet state points to other broadening mechan isms connected with triplet state dynamics or photophysical hole burni ng. We perform a careful analysis of the possible influence of such me chanisms on transient hole broadening. We show that the complete exper imental data cannot be explained by mechanisms like chromophore-chromo phore interaction, background persistent hole burning, etc. The nature of the discovered anomaly remains unclear. (C) 1998 Elsevier Science B.V. All rights reserved.