First Observation of the Urbach Tail in a Multicomponent Organic System

Abstract

The exponential attenuation of electronic absorption in spectral regions removed from the absorption maxima, the “Urbach tail,” has been observed in a variety of materials and has been ascribed to thermal and structural disorder. Here, we report, to our knowledge, the first observation of the Urbach tail in a multicomponent organic system (the asphaltenes) which is due, in part, to the overlapping absorption spectra of the diverse component chromophores within the tail spectral region. The distribution of chromophores produces an unusually large, nonthermal width in the Urbach tail.