Efficient UV Organic Solid‐State Lasers with Ultra‐Short Wavelengths Based on Dispirofluorene‐Indenofluorene Isomers

Abstract The development of efficient UV organic solid‐state lasers (OSLs) remains a significant challenge, yet it is crucial for enabling advanced photonic technologies. This study investigates two dispirofluorene‐indenofluorene regioisomers, (2,1‐a)‐DSF(tBu) 4 ‐IF ( DSFIF‐syn ) and (1,2‐b)‐DSF(tBu) 4 ‐IF ( DSFIF‐anti ), to elucidate the impact of subtle structural differences on their solid‐state photophysical and lasing properties. Through a combination of experimental techniques and theoretical approaches, including comprehensive optical characterization and molecular dynamics simulations, it is demonstrated that DSFIF‐syn exhibits significantly reduced intermolecular aggregation compared to DSFIF‐anti , resulting in enhanced optical performance in solid‐state thin films. Remarkably, amplified spontaneous emission (ASE) is achieved at a record‐short wavelength of 365 nm with a low threshold of 4.5 µJ cm −2 (5000 W cm − 2 ) in a PMMA blend film. Moreover, distributed feedback (DFB) laser devices incorporating a blend film of DSFIF‐syn dispersed in polystyrene (PS) enabled lasing at an unprecedentedly short wavelength of 358.5 nm, as well as a low lasing threshold of 0.7 µJ cm − 2 (780 W cm − 2 ) at 363.3 nm. These results demonstrate that dispirofluorene‐indenofluorene derivatives are highly promising UV laser dyes, highlighting isomeric control as a valuable molecular design strategy for advancing high‐performance organic lasers.