Temperature dependence of the recombination fluorescence of photoionized indole and N,N,N',N'-tetramethyl-p-phenylenediamine in organic glasses. Consequences of electron tunneling and diffusion

Abstract

The recombination fluorescence seen when TMPD is photoionized in methylcyclohexane, 3-methylhexane, and 2-methyltetrahydrofuran glasses and when indole is photoionized in 2-propanol and ethanol glasses has been investigated. The initial intensity and decay rate of the recombination fluorescence decreases as the UV irradiation temperature is increased from temperatures below the glass transition temperature T/sub g/ of the matrix. This is interpreted in terms of electron tunneling to the cation in which the tunneling barrier height or electron trap depth increases slightly (0.05 to 0.2 eV) with increasing irradiation temperature. By considering how the matrix polarity affects the degree of electron trap deepening as well as the electron trap depth relative to the excited singlet level of the solute, we are able to understand the difference in magnitudes and their changes for the initial decay rate and the initial recombination fluorescence. At temperatures 10 to 30 K above T/sub g/, depending on the matrix polarity, diffusive recombination dominates tunneling recombination and produces a peak in the recombination fluorescence unless the electron trap depth has dropped below the excited singlet of the solute. Thus, this type of experiment offers a simple diagnostic for distinguishing tunneling and diffusive recombination of electrons with cations inmore » disordered matrices.« less