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.

Tuning the π-conjugation and varying the functional units can improve the response behavior with superior sensitivity and selectivity. Herein, we report on five novel donor–acceptor (D–A) molecular ensembles developed through C5 substitution on 2-thiohydantoin (2TH) with π-conjugation having different electron-donating groups. The structure–property relationships were investigated by single-crystal X-ray diffraction (SC-XRD) analysis, photophysical, electrochemical, and computational studies. The structural influence of 2TH derivatives on surface interactions with volatile organic compounds (VOCs) were analyzed by binding affinities, kinetics, and other intrinsic parameters (work function, surface photovoltages (SPVs), and response and recovery times). N,N-diMeAPh-2TH exhibits mechanochromic and vapochromic behavior, shows red-shifted emission at ∼554 nm upon exposure to nonanal vapors with a visual color change from orange-red to brown, and shows vivid color variations with different VOCs. N,N-diMeAPh-2TH shows reversible vapochromic behavior as well. Ph-2TH, 4-OMePh-2TH, and 2,4-diOMePh-2TH exhibit n-type behavior with the greater SPV response achieved for Ph-2TH (90%), but good recovery (58%) in SPV in 439 s is observed in the case of 2,4-diOMePh-2TH. In contrast, 3,4-diOMePh-2TH and N,N-diMeAPh-2TH exhibit p-type behavior toward nonanal vapors with a high SPV response obtained for N,N-diMeAPh-2TH (94%) within 293 s as well as recovery (87%) in surface PVT in 692 s. The results demonstrate that electron-donating substituents −N(CH3)2 can improve sensing performance by increasing electron density, whereas steric hindrance on the phenyl unit can modulate sensing performance.

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