We have developed a novel and convenient method of crystal growth in a liquid phase. This method produces directly onto a substrate well-defined polygon organic thin crystals with uniform thickness. The thin crystals are found to be single crystals of high quality. We show various illustrations including thiophene/phenylene co-oligomers and an oligophenylene. The organic crystal transistors based on these crystals showed good device performance. These thin single crystals are expected to be suitably applied to electronic devices.

We have determined a refractive index of an organic single crystal of a thiophene/phenylene co-oligomer in its laser oscillation wavenumbers. We estimated the refractive index to be 4.0 on the basis of the mode intervals of the well-resolved longitudinal multimodes that are highly polarized along the normal to the ͑001͒ plane of the single crystal. This large number is in good agreement with that obtained by the quantum chemical calculations at semiempirical levels. This is also consistent with the high Q factor ͑ϳ24 500͒ obtained from the line shape analysis.

We have measured and determined the anisotropic refractive indices of thiophene/phenylene co-oligomer (TPCO) crystals. The refractive indices were calculated from the crystal thicknesses and optical path lengths on the basis of the interference of the reflectance spectra measured along the crystal axes by a polarizing microscope with a white light source. The higher refractive indices were observed along the crystal short axis and this was attributed to a denser molecular packing along that axis.

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Polarized emissions have been investigated for single crystals of thiophene/phenylene co-oligomers by microspectroscopic measurements. We measured polarized emissions from two distinct parts on the single-crystal surface (the ab-plane) that were produced by the polarized UV excitation light. At the defect-free part of the crystals, the largest emissions are observed at both the excitation and the emission polarization directions along the crystal short axis on the ab-plane. At the crystal edge, on the other hand, the emissions are strongly polarized along another axis (that is normal to the crystal short axis). For the latter feature, the reflected emission at the crystal edge plays an important role.