Exploitation on the organic semiconductors nitro ethynylated-thiourea molecular framework as efficient sensing materials in the detection of carbon dioxide (CO<inf>2</inf>) by electron donating groups (EDGs) alteration

Organic semiconductors of nitro ethynylated-thiourea derivatives of D-π-A (1a-1d) with different donating groups were studied as active materials in the sensing layer, to evaluate their role in enhancing the sensing response (%) towards carbon dioxide (CO2) at ambient temperature. The fabricated 1a-1d on interdigitated electrodes (IDEs) indicate a significant increase in sensing response after exposure to CO2 (10–1000 mg/L) in relative humidity 65–70% RH. The reaction occurs between CO2 gas and water vapour in the designated environment produced two different ions of carbamates and bicarbonates. The increment in the resistivity values of 1a-1d is accredited to the interaction occurred between 1a-1d and the bicarbonate ion at the amide-carbonyl (NH-C[dbnd]O) reactive site. The role of difference donating groups anchored to the molecular framework of ethynylated-thioureas is to stabilize the electron conjugation and fluctuation in the molecular system of D-π-A. The highest sensing response (%) is attributed to 1c with strong activating electron donor group (15.99%−38.57%). 1a and 1b bearing moderate activating electron donor groups possess moderate sensing response towards CO2 (14.05%−36.15%), while 1d contains weak activating electron donor group exhibited the lowest sensing response of 7.82%−24.91%. All the synthesised compounds exhibited moderate response (τres) within 60 s and recovery (τrec) time 180 s significantly for absorption and desorption of CO2. Additionally, the theoretical mechanistic approach to the detection of CO2 was calculated via computational calculation at B3LYP/6-31G (d, p) level of theory to address the correlation between experimental and theoretical approach.