ИСТИНА

Single-crystal thiophene-phenylene (TPCO) and furan-phenylene co-oligomers (FPCO) are in strong demand in organic optoelectronics for various light-emitting devices, since they can combine high luminescence and efficient charge transport. Doping with highly luminescent molecules is a promising way to control the luminescent properties of organic semiconductor crystals. Recently, we have found that luminescent self-dopants appear as minor byproducts in the course of TPCO chemical synthesis . In this work, we report on photothermal deflection spectroscopy technique (Fig. 1a) to control small concentration (<<1%) of molecular dopants in TPCO and FPCO single crystals. We detected dopants absorption features in single-crystal grown from vapor and solution. Using reference samples of single crystals self-doped with a longer co-oligomer and assuming that the dopant absorption is linearly dependent on the dopant content, we estimated the dopant concentration in various self-doped samples (Fig. 1b). It was observed that dopant distribution may be nonuniform in the presented materials. We compare luminescent and photothermal techniques for control of doping in organic semiconductor crystals by the lower-bandgap molecules with the sensitivity in the ppm range.