The design of portable devices by immobilization of sensory probes using donor−acceptor (D−A) architectures enables the visual detection and onsite analysis of volatile organic compounds (VOCs). In this work, we have reported on the synthesis of different D−A architectures of 2-thiohydantoin (2TH) derivatives by extending the conjugation with phenyl (Ph-2TH), naphthalene (Naptha-2TH), and anthracene (Anthra-2TH) moieties at the C 5 position. Single-crystal X-ray analysis reveals that extending the conjugation leads to variation in the molecular arrangement in the crystal lattice. Ph-2TH and Naptha-2TH show ribbon-like self-assembled layered arrangements, whereas Anthra-2TH crystallized in herringbone packing in the crystal lattice. The C−S•••H interactions were varied with interatomic distances of 2.67, 2.63, and 2.27 Å, respectively, for phenyl, naphthalene, and anthracene. The photophysical and excited-state gas-phase interactions using scanning kelvin probe studies reveal that 2TH ensembles alter their surface photovoltages toward recognition of different VOCs (like ethanol, acetone, toluene, triethylamine, nonanal, and chloroform) depending on their donor and acceptor nature. All three 2TH derivatives showed n-type behavior with high selectivity toward nonanal, and Anthra-2TH exhibited high response (91.02%) within 278 s as well as recovery (92.83%) in surface photovoltages in 647 s. Combined experimental and computational studies demonstrate that the aromatic moieties appended 2TH ensembles would be an efficient D−A ensemble for the detection of VOCs containing carbonyl and alcohol functionalities aiding strong intermolecular interactions.

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Volatile organic compounds (VOCs), namely, acetone, ethanol, acetonitrile, 2-propanol, isoprene, and toluene exhaled in human breath act as potential biomarkers for the identification of certain physiological disorders. This work investigates the sensing capability of two-dimensional Sc2CO2 MXene nanosheets toward these VOCs using first-principles density functional theory calculations. Since carbon dioxide and water vapor persist in the exhaled breath, their interaction with Sc2CO2 as interferent species is examined too. It is found that 2-propanol (−0.63 eV), ethanol (−0.59 eV), and acetonitrile (−0.51 eV) show higher interaction with the Sc2CO2. Meanwhile, the chemiresistive sensorial behavior has been examined, and it is revealed that Sc2CO2 is highly sensitive to acetonitrile (50.20%). Both ethanol (1.03 × 10–3 s) and 2-propanol (5.24 × 10–3 s) have a fast recovery at room temperature. Alternatively, the change in work function of Sc2CO2 nanosheets on adsorption of VOC biomarkers has been examined. The corresponding results have proved that the work function-based Sc2CO2 sensor is sensitive to physisorbed species like toluene (47.62%) and isoprene (37.83%) that are not quantifiable using the chemiresistive sensing mechanism. Overall, our research predicts that the Sc2CO2 MXene nanosheet can be utilized as a dual-mode sensor to detect potential VOC biomarkers in the exhaled breath. Also, our results will assist the experimentalists in designing MXene nanosheet-based room-temperature sensors as point-of-care breathalyzers for disease diagnosis.

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