Low-Threshold Red Lasing in Diketopyrrolopyrrole-Based Organic Semiconductor Films

Achieving low-lasing threshold organic semiconductor lasers (OSLs) in the red to deep-red region remains challenging due to the intrinsic trade-off between long-wavelength emission and high optical gain. Extended π-conjugation required for red-shifted emission typically enhances nonradiative decay and aggregation-induced quenching, resulting in reduced radiative rate constants (k_r) and increased lasing thresholds (E_th). Here, we report molecular design strategies based on a diketopyrrolopyrrole (DPP) scaffold that independently address high radiative decay and advanced molecular orientation control aimed at low-threshold red OSLs. For solution-processed architectures, donor rigidification using hexamethylazatriangulene (HMAT) combined with DPP cores enables precise modulation of excited-state dynamics, suppressing nonradiative pathways while maintaining high oscillator strength. This strategy affords efficient deep-red emission and reduced lasing thresholds in distributed feedback (DFB) structures. Further, a miniaturized DPP framework with improved thermal evaporation compatibility enables stable vacuum deposition and promotes preferential horizontal molecular orientation, leading to efficient red DFB lasing with low thresholds. These results establish complementary molecular design strategies for controlling the photophysical properties and molecular orientation of DPP-based gain media, providing a versatile platform for low-threshold red OSLs across both solution-processed and vacuum-deposited architectures.