Tuning the π‑Conjugation of 2‑Thiohydantoins toward a Rigorously Defined Detection of Volatile Organic Compounds by Surface Photovoltage

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 C5 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.