Hierarchical Self‐Assembly of Tetrakis(1‐pyrenyl)porphyrins into Microscopic Petals and Flowers with Ultrasensitive Room‐Temperature NO₂ Sensing in a Broad Humidity Range

Abstract A metal free meso‐tetrakis(1‐pyrenyl)porphyrin H₂T[(Pyr)₄]P (1) and its cobalt congener CoT[(Pyr)₄]P (2) are firstly fabricated into the hierarchical nanopetals and micro‐ball‐flowers, respectively, by a simple solution‐based method. Unexpectedly highly sensitive, stable, selective and reproducible responses to 50–400 ppb NO₂ gas are obtained at room temperature for the aggregates of both 1 and 2, within 2 min dynamic exposure period at a broad relative humidity (RH) range of 0%‐75%. In particular, the micro‐ball‐flowers of 2 achieve a sensitivity of 91.4 and 214% ppm⁻¹ at 45% RH and 75% RH, respectively, demonstrating the potentials as chemical sensors operating in real‐world atmospheres. Furthermore, the sensitivity of 1 and 2 remains almost unchanged under 0%–75% RH after 6 months. The present work represents one of the best results among organic‐based ppb‐level NO₂ sensors operating under a broad RH range in terms of sensitivity and stability to humidity variations at room temperature.