SPECTRAL DIFFUSION-INDUCED BY ENERGY-TRANSFER AND HIGH-PRESSURE EFFECTS IN DOPED ORGANIC GLASSES - A HOLE-BURNING STUDY

Time-resolved hole-burning (HB) experiments have been performed on the S-1 <-- S-0 0-0 transitions of free-base chlorin in polystyrene (H(2) Ch in PS) and bacteriochlorophyll-a in triethylamine (BChl-a in TEA) a s a function of temperature (1.2-4.2 K), excitation wavelength, concen tration, and delay time between burning and probing. At concentrations higher than 5 x 10(-4) M a new type of spectral diffusion process tak es place, even at T --> 0, which is induced by energy transfer. Moreov er, HE-experiments on BChl-a in TEA with delay times between microseco nds and hours at high (Delta(p) approximate to 30 kbar) pressure demon strate that a transition from a glassy- to a locally ordered structure occurs in this sample, suggesting that the number of ''two-level-syst ems'' in the glass responsible for spectral diffusion is reduced by co mpression.