Addressing the critical challenge of simultaneous high solid-state photoluminescence and efficient analyte mass transport for vapor sensors, a steric hindrance-engineered boron difluoride complex film, BODIQU-tBuCZ, is reported for ultrasensitive detection of nerve agent simulant DCP. Strategic incorporation of bulky tert-butyl groups suppresses detrimental π-π stacking, and creates a porous 3D network (38.76% free volume) for rapid mass transport. Comprehensive structural and spectroscopic analyses validate this design principle and its impact on photophysics and sensing kinetics. The resulting BODIQU-tBuCZ sensor achieves exceptional performance: an ultra-low LOD of 0.001 ppt, ultra-fast ~3-second response, and remarkable stability over >50 cycles. Quantitative comparison confirms its superiority over state-of-the-art sensors. This work presents a generalizable steric engineering strategy for high-performance fluorescent films, offering a promising platform for real-time neurotoxic threat monitoring.
