Millisecond-Delayed Fluorescence in Heavy-Halogen-Substituted TADF Emitters for Air-Pressure Sensing

Designing luminescent materials with controllable responses to external stimuli is important for optical sensing applications. Here, two heavy-halogen-substituted donor-acceptor emitters based on a dibenzo[a,c]phenazine-3,6-dicarbonitrile scaffold were synthesized and investigated as low-pressure optical sensors under UV excitation (365 nm). In Zeonex films, both compounds exhibit thermally activated delayed fluorescence (TADF), where the emission intensity strongly depends on oxygen concentration, enabling pressure-dependent luminescence. Reduced pressure suppresses oxygen-induced triplet quenching, resulting in enhanced delayed fluorescence. Halogen substitution modulates the photophysical processes and leads to different sensing performances. The brominated derivative shows a maximum pressure sensitivity of 6.8% mbar^-1 in the range of 0.1-100 mbar, while the iodinated analogue reaches 1.8% mbar^-1 between 1 and 700 mbar. The weak temperature dependence allows reliable pressure readout within the investigated temperature range. These results demonstrate that heavy-halogen substitution provides an effective strategy for developing oxygen-regulated TADF materials for optical pressure sensing.