Emission and charge transport properties of thiophene-terminated thiophene/phenylene co-oligomer crystals

We have grown the crystals of two thiophene/phenylene co-oligomers (TPCOs) composed of in-line five and seven alternating thiophene and benzene rings. These TPCOs are characterized by thiophenes located at both molecular terminals. The grown crystals had several pairs of parallel crystal faces that function as optical resonators. These produced interference fringes in their emission and reflectance spectra. We measured the emission spectra in both weak broadband excitation and intense laser excitation regimes. From these spectra we determined the phase refractive index dispersion and the anisotropic group refractive indices. We made field-effect transistor devices using the above TPCO crystals and carried out their electrical measurements. These optical and charge transport properties are compared with those of crystals of other alternating TPCOs with phenylenes located at both molecular terminals.