The authors demonstrated that N , NЈ-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide ͑PTCDI-C13͒ thin-film transistors ͑TFTs͒ exhibited high field-effect electron mobility of 2.1 cm 2 / V s by just annealing at an adequate temperature ͑140°C͒ after the TFT fabrications. While PTCDI-C13 formed c-axis oriented thin films, the thermal treatments improved crystallinity of the thin films as revealed by x-ray diffraction. The thermal treatment also affected thin-film morphologies; the morphologies changed from oval ball-like grains to flat and large tilelike grains, which had molecular height steps and whose size reached several micrometers.
We have determined crystallographic structures of four thiophene/phenylene co-oligomers with different molecular shapes. The compounds consist of the molecules straight, bent, or zigzag. All the crystals are monoclinic with space group either P21/c or P21/n, Z = 4, and the unique axis of b. The crystals are characterized by the presence of the molecular layered structure in which the molecules form the well-known herringbone structure laterally spreading along the ab-plane. We investigate the molecular disposition in the crystals and present its peculiarity in relation to those comprising nonstraight molecules (e.g., bent or zigzag). The specific effects upon optical characteristics produced by this peculiarity are mentioned.
Evidence for oscillation in monolithic molecular single crystals of a thiophene/phenylene co‐oligomer is reported. The laser oscillations (see Figure) are characterized by naturally formed crystal facet cavities with molecular‐scale flatness. The multimode laser oscillation in a Fabry–Pérot resonator is characterized by sharply resolved spectroscopic lines with their full width at half maximum down to only 38 pm. The laser oscillation is characterized by the presence of a well‐defined threshold.
Emission gain narrowing has been observed for single crystals of a thiophene/phenylene co-oligomer. The hexagon flake crystals were placed on a quartz substrate with the crystals' face in close contact with the substrate plane. These crystals were irradiated with a N 2 laser with a 337.1 nm wavelength at a repetition rate 10 Hz that tuned its intensity to 100-1150 J/cm 2 . The emission gain narrowing takes place at 21490 ͑465.4 nm͒ and 20220 cm Ϫ1 ͑494.5 nm͒ with increased intensities, with their half width at half maxima reaching ϳ50 cm Ϫ1 . On the basis of the nonlinear relationship between the emission peak intensities and the laser light intensity, the gain narrowing has been attributed to the amplified spontaneous emission. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1435797͔ Conjugated semiconducting polymers and oligomers are currently attracting great attention as potentially useful materials for optoelectronic devices such as thin-film transistors and light-emitting diodes. 1 Solid-state lasing and amplified spontaneous emission ͑ASE͒ have been observed in these materials. 2 Since excitation through photopumping is a facile way to attain lasing and ASE, this method has long been used. [3][4][5] The earliest examples can be found for anthracene molecules embedded in host matrices of, e.g., fluorene. 6 Later this approach was more widely applied to dye-doped systems and polymer thin films. 7 Very recently solid-state injection lasing was achieved using a tetracene single crystal, vouching for the high practicality of organic semiconductors. 8 In view of current injection, crystals of high quality are more advantageous than any other systems that involve defects which may well act as carrier traps. Reported observation of lasing or ASE of the crystals, however, remains scarce even in the case of photopumping. This is partly because the photoluminescent efficiency of chromophores is decreased by higher concentrations, 9 even though their efficiency is high at dilution. Yet a typical examples for the ASE haves been verified by Fichou et al. 10 and by Horowitz et al. 11 using single crystals of octithiophene and sexithiophene, respectively.Yanagi and Morikawa 12 showed that self-waveguided emission takes place along the crystals' long axis of needleshaped crystals of p-sexiphenyl that are epitaxially grown on top of a single crystal substrate of potassium chloride. The molecular axes of p-sexiphenyl align perpendicular to the crystals' needle axis so that the propagation of the polarized emission can be enhanced with the transverse electric mode along that needle. The uniaxially aligned transition dipoles in the p-sexiphenyl crystals are responsible for the selfwaveguided emission. Recent progress demonstrated that this is analogous to the case of a newly emerging class of semiconducting molecular crystals, thiophene/phenylene co-oligomers. 13 These materials were developed by Hotta and co-workers 14 and are characterized by a variety of extensions of conjugation along the backbone. The conjugation ...
Large plate‐like single crystals of several millimeters to ∼ 1 cm in size of organic semiconducting materials are prepared via an improved crystal‐growth technique. The crystals (see Figure) exhibit self‐waveguided amplified spontaneous emission with a relatively small threshold resulting from the excellent optical properties of the crystals, such as high transparency and low light scattering.
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