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

Graphical Moisture-resistant : Remarkably specific sensors for NO 2 have been developed based on hierarchical self-assembly of porphyrin devices. They are effective sensors over a broad humidity range. A metal free meso -tetrakis(1-pyrenyl)porphyrin H 2 T[(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 NO 2 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 NO 2 sensors operating under a broad RH range in terms of sensitivity and stability to humidity variations at room temperature.