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It is generally accepted that while efficient suppression of molecular vibration is inevitable for purely organic phosphors due to their long emission lifetime in the regime of 1 ms or longer, fluorophores having a lifetime in the nanoseconds regime are not sensitive to collisional quenching. Here, however, we demonstrate that a fluorophore, 2,5-bis(hexyloxy)terephthaldehyde (BHTA), capable of having hydrogen bonding (H bonding) via its two aldehyde groups can have a largely enhanced (450%) fluorescence quantum yield (QY) in amorphous poly(acrylic acid) (PAA) matrix compared to its crystalline powder. We ascribe this enhanced QY to the efficient suppression of molecular vibrations via intermolecular H bonding. We confirm this feasibility by conducting temperature-dependent fluorescence emission intensity measurement. As gaseous phenol can intervene with the H bonding between BHTA and PAA, interestingly, BHTA embedded in PAA can selectively detect gaseous phenol by a sharp fluorescence emission intensity drop that is visibly recognizable by the naked eye. The results provide an insightful molecular design strategy for a fluorophore and fluorometric sensory system design for enhanced photoluminescence QY and convenient detection of various volatile organic compounds.

Transition metal dichalcogenide-based quantum dots are promising materials for applications in diverse fields, such as sensors, electronics, catalysis, and biomedicine, because of their outstanding physicochemical properties. In this study, we propose bio-imaging characteristics through utilizing water-soluble MoS2 quantum dots (MoS2-QDs) with two different sizes (i.e., ~5 and ~10 nm). The structural and optical properties of the fabricated metallic phase MoS2-QDs (m-MoS2-QDs) were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, UV–vis absorption spectroscopy, and photoluminescence. The synthesized m-MoS2-QDs showed clear photophysical characteristic peaks derived from the quantum confinement effect and defect sites, such as oxygen functional groups. When the diameter of the synthesized m-MoS2-QD was decreased, the emission peak was blue-shifted from 436 to 486 nm under excitation by a He-Cd laser (325 nm). Density functional theory calculations confirmed that the size decrease of m-MoS2-QDs led to an increase in the bandgap because of quantum confinement effects. In addition, when incorporated into the bio-imaging of HeLa cells, m-MoS2-QDs were quite biocompatible with bright luminescence and exhibited low toxicity. Our results are commercially applicable for achieving high-performance bio-imaging probes.

The design of photoactive materials and interface engineering between organic/inorganic layers play a critical role in achieving enhanced performance in energy-harvesting devices. Two-dimensional transitional dichalcogenides (TMDs) with excellent optical and electronic properties are promising candidates in this regard. In this study, we demonstrate the fabrication of size-controlled MoS2 quantum dots (QDs) and present fundamental studies of their optical properties and their application as a hole-transport layer (HTL) in organic solar cells (OSCs). Optical and structural analyses reveal that the as-prepared MoS2 QDs show a fluorescence mechanism with respect to the quantum confinement effect and intrinsic/extrinsic states. Moreover, when incorporated into a photovoltaic device, the MoS2 QDs exhibit a significantly enhanced performance (5/10-nanometer QDs: 8.30%/7.80% for PTB7 and 10.40%/10.17% for PTB7-Th, respectively) compared to those of the reference device (7.24% for PTB7 and 9.49% for PTB7-Th). We confirm that the MoS2 QDs clearly offer enhanced transport characteristics ascribed to higher hole-mobility and smoother root mean square (Rq) as a hole-extraction material. This approach can enable significant advances and facilitate a new avenue for realizing high-performance optoelectronic devices.