Singlet-exciton transport and spatial and energetic disorder in dibenzofuran crystals

The trap-depth distribution of dibenzofuran singlet excitons and the temperature-dependent energy migration and energy transfer to anthracene super traps has been studied by time-resolved spectroscopy via synchrotron radiation and two-photon laser excitation. The energy transport in the orientationally disordered dibenzofuran single crystals follows a stretched exponential behavior with β=0.57 at temperatures above 150 K. Below this temperature β approaches zero. Spatial (fractal) disorder has been experimentally separated from energetic (temporal) disorder by applying the subordination principle. Spatial disorder indicates an aggregation of orientationally disordered molecules. The aggregates are described by the spectral (fracton) dimension ${\mathit{d}}_{\mathit{s}}$=1.14 over the characteristic diffusion length.