Broadband hole burning: a new technique for the measurement of hole burning kinetics, removing the influence of inhomogeneous broadening

Abstract

Abstract One of the problems associated with measurement of hole burning (HB) kinetics in disordered media is their non-exponential time dependence. There are two sources of non-exponentiality inherent to all glassy systems: random orientation of the chromophores and strong inhomogeneous broadening of their optical spectra. The non-exponentiality caused by the above factors conceals other, more interesting sources of dispersive burning kinetics such as dispersion of burning quantum efficiency and distribution of homogeneous line widths. A modification of the HB method, the broadband hole burning (BHB), is proposed, which eliminates the strongest source of non-exponentiality—the influence of inhomogeneous broadening. The new technique was applied to measurements of BHB kinetics on a simple, well-characterized system: H 2 -tetraphenylporphine (TPP) in polystyrene (PS). Only photochemical HB (i.e., proton tautomerization) with negligible dispersion of burning efficiency was expected in this sample. The BHB technique revealed the existence of a second, previously unknown photoreaction, with quantum efficiency about one order of magnitude lower than proton tautomerization. The ordinary HB technique does not detect this photoreaction because its manifestation in burning kinetics is smeared out by the above-mentioned sources of non-exponentiality.