ИСТИНА

Single crystals of thiophene-phenylene co-oligomers (TPCO) have already shown their high potential for organic optoelectronics as they combine efficient charge transport with high photoluminescence (PL) quantum yield (QY). However, the origin of this unique combination is yet unclear. Here we report on PL dynamics from novel TPCOs single crystals with the identical conjugated core (5,5’-diphenyl-2,2’-bithiophene, PTTP) and different terminal substituents that have strong effect on the crystal packing. The PL QY from crystals is a factor of 2-3 higher than that in diluted solutions. The maximum QY exceeds 60% (re-absorption corrected) which is the highest among the insofar reported for the TPCOs. The single-exponential PL decay with a lifetime of ~1 ns is very close to the radiative lifetime which suggests low concentration of exciton traps. We also observed noticeable (especially at 77 K) spectral dynamics in the PL spectrum at ~100 ps time scale which are thought to indicate strong energy exchange between excitonic sub-ensembles in the TPCO crystals. This highlights extremely rich photophysics that could be harnessed in advanced organic light-emitting devices.