Spectral diffusion of a photochemical proton transfer system in an amorphous organic host: Quinizarin in alcohol glass

Abstract

Experimental data describing the time evolution of photochemical holes in organic glasses are reported. The photochemical system is 1,4-dihydroxyanthraquinone (quinizarin) in ethanol/methanol glasses; its photochemistry is based on proton or deuteron transfer processes. The experiments show a logarithmic increase of the hole widths in a time domain between minutes and about 104 min. The experimental results yield a pronounced deuteration effect and little variation with temperature between 1.35 and 4.2 K. The data are interpreted in a semiquantitative way using current theories of spectral diffusion in amorphous solids. The fastest measured photochemical rates are on the order of seconds, leaving a ‘‘time independent’’ linewidth of about 0.4 cm−1 at 1.35 K.

Isotope effect in the linewidth distribution of single-molecule spectra in doped toluene at 2K

“…As a consequence, the spectral broadening caused by such TLSs should also decrease and the linewidth distribution of the dopant molecules should become narrower, which is in agreement with our experimental data. A narrowing of the homogeneous linewidth of chromophore molecules upon deuteration of the matrix was also found in other amorphous systems with ensemble techniques: PE (deuteration of ethanol [19][20][21]) and HB (deuteration of an ethanol-methanol mixture [22]). …”

Low-temperature relaxation of polymers around doped dyes studied by persistent spectral hole burning

“…This result is consistent with the previous data, which studies time-dependent spectral diffusion at burning temperature. 13 In our case, however, no hole broadening was observed at the burning temperature (20 K). The extent of spectral diffusion (or hole broadening) at 20 K for TPP-PnPMA is too small to be detected by our apparatus.…”

Spectral diffusion and the energy landscape of a protein

“…Traditionally, spectral diffusion in low-temperature glasses is interpreted within the two-level system (TLS) model (23)(24)(25)(30)(31)(32)(33). In this model the relevant conformational changes in the chromophore's environment are assumed to involve a set of uncoupled double-well potentials, each of which has two low-energy quantum states.…”

“…In the past decade it has mainly been exploited in experiments on glasses (23,24), but several experiments on proteins have appeared as well (6,12,13). Two types of spectral diffusion experiments are common: (i) time-dependent experiments where the width of a hole is monitored as a function of waiting time after burning (25) and (ii) temperature-cycling experiments where the width of a hole immediately after the cycle is monitored as a function of cyclic temperature changes (26,27).…”