Revealing Order and Disorder in Films and Single Crystals of a Thiophene-Based Oligomer by Optical Spectroscopy

Depending on processing conditions, ordered microstructures of conjugated oligomers or polymers exhibit variable amounts of grain boundaries, lattice disorder, and amorphous (disordered) regions. These structural details can be determined very precisely. Their correlations with optical or electronic properties, however, are very difficult to establish, because, for example, optical spectra are usually averaged over regions with different degrees of disorder. In an attempt to facilitate the interpretation of optical spectra, we performed systematic studies on thin films and μm-sized single crystals of thiophene-based conjugated molecules, which allowed identifying the relative contributions of ordered and disordered regions in optical emission spectra. A detailed multipeak analysis of the emission spectra showed that the peak positions, the energies of the emitted photons, showed only minor changes, independent if highly ordered or rather disordered samples were examined. However, the relative emission int...