Beyond Molecular Design: Cocrystallization in Hydrogen-Bonded Organic Frameworks for Energy-Conserving Dehydration and Real-Time Luminescent Humidity Detection

Abstract

Luminescent probes attract increasing attentions for the unique superiorities like visually real-time detecting. However, for optical humidity sensing, it is still quite challenging to attain facile dehydration/activation in sensing materials, due to the high polarity of water molecules, which limits their applications in real-time detection and energy-conserving applications. Here, we report two fluorescent hydrogen-bonded organic frameworks (HOFs), HPISF-H₂O and TPISF. HPISF-H₂O achieves water absorption in low humidity, but needs an energy-intensive step (heating to ∼92°C in air) to dehydrate. Conversely, despite only a hydroxyl group being replaced, TPISF cannot bind to H₂O at all. In other words, real-time detection is not readily achieved through straightforward molecular design. Therefore, we propose a cocrystallization strategy to adjust their water-binding capacity. As a result, the HOF cocrystals are adjusted to have both good H₂O absorptivity and very gentle desorbing operation without heating (dry gas blowing or vacuuming). Benefiting from this strategy, appreciable advantages for an effective humidity sensor are realized, including real-time detection (second-scale response/recovery) and distinguishing fluorescence variation. Efficient sensing across a broad relative humidity (RH) range (10.0%–80.0%) was further achieved. Moreover, the mechanistic insight of fluorescent sensing was ascertained through detailed analyses of structural transformation, spectroscopic data, and theoretical approach.