Comparison of the optical spectra of single crystal and crystalline films of α-sexithiophene

Optical spectra of thin crystalline films of alpha -sexithiophene differ significantly from those of single crystals, particularly in the region of the strong Davydov component. The much broader absorption peak of films is shifted significantly to higher energy and the electroabsorption spectrum shows in the same. range a series of strong features which seem not correlated to the absorption spectrum or to the electroabsorption spectrum of a single crystal which results from a quadratic Stark shift and field broadening of the weak and strong Davydov component, respectively. It is shown that the difference arises from polariton effects of the strong transition and a random orientation of crystallites. (C) 2001 Elsevier Science B.V. All rights reserved.