Highly Stable Red Emissive Organic Semiconductor Materials with Low Amplified Spontaneous Emission Thresholds.

Excited‐state intramolecular proton transfer (ESIPT) chromophores have attracted considerable attention as promising gain media for organic lasers, particularly in amplified spontaneous emission (ASE) due to their advantageous characteristics. These include an intrinsic four‐level photocycle, significant separation between absorption and emission spectra, and enhanced emission efficiency facilitated by aggregate‐induced emission. This study investigates the amplification of π‐conjugation in hydroxyphenyl‐benzothiazole (HBT)‐based ESIPT materials via dimerization to intensify ESIPT processes, surge absorption cross‐section, enhance optical gain, and induce a redshift in emission spectra. Computational study shows that the ESIPT processes of the new dimers proceed through single proton transfer where the second proton transfer is not accessible. While the ESIPT photocycle does not extend to both HBT moieties of the dimers, the dimers foster more efficient ESIPT processes in both solution and solid states than their parent HBT, resulting in substantial Stokes shifts (>233 nm). Moreover, both dimers exhibit enhanced solid‐state photoluminescence quantum yields, reaching up to ≈55%, and low solid‐state ASE threshold values (≈6.8 µJ cm−2) in the red region. Remarkably, the new dimers demonstrate excellent thermal and photostability with notably reduced spectral overlap compared to their parent, highlighting the potential utility of the approaches to developing new organic solid‐state laser materials. [ABSTRACT FROM AUTHOR]