ИСТИНА

Single crystals of thiophene-phenylene co-oligomers (TPCO) are promising materials for organic optoelectronics as they demonstrate high photoluminescence (PL) efficiency and charge carrier mobilities. PL external quantum yield (QY) of TPCO was found to be about 60 %, and charge mobilities in the range 0.1–1.0 cm2/(V*s) were reported. In this work, we investigate PL and its QY in two similar types of solution-grown TPCO single crystals: 5,5'-bis(4-(trimethylsilyl)phenyl)-2,2'-bithiophene (TMS-PTTP-TMS) and 5,5'-bis(4-(trifluoromethyl)phenyl)-2,2'-bithiophene (CF3-PTTP-CF3). The single crystalline TPCO films have sizes of 1-3 mm with thickness of some um. In the studied crystals, PL reabsorption is noticeable due to absorption and emission spectra overlap. To avoid reabsorption and increase PL QY, we milled the single crystals. PL spectra of single crystals and their milled samples showed that milling decreases the reabsorption effect. However, we found that the larger CF3-PTTP-CF3 films show lower PL QY, whereas the larger TMS-PTTP-TMS demonstrates higher PL QY. The possible reasons of different PL features of the two types of TPCO crystals are discussed.