Orthogonal effect on Pyrene-Porphyrin conjugates towards the detection of Volatile Organic Compounds under UV and Visible light illumination through Surface Photovoltage

Abstract

In this work, we have developed two modular compounds encompassed with pyrene at meso position of the freebase porphyrin (H2PyP) and its complex with Zn (ZnPyP). Both compounds exhibited to show a unique energy transfer process due to the orthogonal pyrene units and reveal that appreciable electronic interactions exist between peripheral units to the porphyrin π-system and behave like strong donor materials in solid-state thin films. Detailed photophysical and excited state gas phase interactions were modulated through surface photovoltage using Scanning Kelvin Probe (SKP) technique and explored towards detection of different Volatile organic compounds (VOCs) (Ethanol, Acetone, 1-Hexanol, Triethylamine, Nonanal, and Acetonitrile) in dark, UV and visible light illuminations. H2PyP and ZnPyP show n-type behaviour with high selectivity towards 1-hexanol under UV light illumination while ZnPyP exhibits n-type behaviour and H2PyP show p-type behaviour under visible light exposure. The response and recovery studies demonstrate that H2PyP and ZnPyP show unprecedented selectivity towards 1-hexanol by altering it p and n type behaviour. H2PyP exhibits a high photovoltage response of 93% for an exposure of 17 s with a recovery rate of 23% in 5 s, while ZnPyP show 97% in 2 s with a recovery rate of 55% in 116 s under UV light. The unique response of H2PyP and ZnPyP to 1-hexanol could be attributed to donor-donor interaction and intermolecular hydrogen bonding at central core and Zn(II)metal centre and variations in the energy transfer process. Further, density functional theory study reveals that binding interactions of H2PyP and ZnPyP with VOCs show greater affinity for alcohols in comparison to other compounds.