Substituent Effect on Stimuli-Responsive Donor-Acceptor Framework-Based 2-Thiohydantoins for Monitoring Nonanal Vapors

Tuning the pi-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 pi-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 similar to 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 2,4diOMePh-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.