Triphenylamine-porphyrin conjugates as antenna modular systems towards the detection of 1-hexanol through surface photovoltage under UV and visible light illumination using the scanning Kelvin probe

Abstract

Two modular porphyrin systems containing triphenylamine (TPA) unit at meso position of freebase porphyrin (H₂TPAP) and its metalation with Zn(II) as ZnTPAP is developed to ascertain the role of antenna effect on the photo induced energy transfer process. H₂TPAP and ZnTPAP exhibited a significant electronic overlap between peripheral TPA and porphyrin π-system to demonstrate its strong donor behaviour in solid-state thin films. Porphyrin ensembles change their surface photovoltages towards recognition of various VOCs (like ethanol, acetone, 1-hexanol, triethylamine, nonanal, and acetonitrile) as observed through photophysical and excited-state gas-phase interaction studies using Scanning Kelvin Probe (SKP). The chemical sensitivity towards the surface potential is monitored under dark, UV and visible light illuminations. Both H₂TPAP and ZnTPAP exhibited to show different behaviour with high selectivity towards 1-hexanol vapours. Under UV light illumination at 365 nm, ZnTPAP exhibited a rapid response (99 %) within 1 s and good recovery (54 %) within 96 s. Under visible light (QTH), the response and recovery decreased due to sequential photo-induced energy and electron transfer processes. Further, density functional theory results confirm that both H₂TPAP and ZnTPAP show more affinity towards alcohol vapours compared to other VOCs. Molecular interactions including donor-donor and hydrogen bonding interactions in tandem contribute to the intriguing response to 1-hexanol and enhance the photo response of ZnTPAP over H₂TPAP.