Investigation of spectral diffusion in PMMA on timescales from 10 −5 to 10 4 seconds via transient and photophysical hole burning

Abstract

Spectral diffusion (SD) in PMMA samples, doped with Zn-tetrabenzoporphine, was investigated via triplet state populational hole burning in the absorption spectrum of a chromophore on a timescale from 20 μs to 200 ms and via photophysical persistent hole burning on a timescale from 10 to 10 4 s covering the temperature interval 1.7–10 K. The SD rates on microsecond and on long timescales ( t>10 s) coincide. An anomalous increase of the SD rate was found in the millisecond range which cannot be attributed to peculiarities in the relaxation rate distribution of the two-level systems in PMMA. The apparent correlation of the observed anomalous SD region with the time domain of the deactivation of the chromophore's triplet state points to other broadening mechanisms connected with triplet state dynamics or photophysical hole burning. We perform a careful analysis of the possible influence of such mechanisms on transient hole broadening. We show that the complete experimental data cannot be explained by mechanisms like chromophore–chromophore interaction, background persistent hole burning, etc. The nature of the discovered anomaly remains unclear.