Charge Trapping in Semiconductor Photocatalysts: A Time- and Space-Domain Perspective.

Harnessing solar energy to produce value-added fuels and chemicals through photocatalysis techniques holds promise for establishing a sustainable and environmentally friendly energy economy. The intricate dynamics of photogenerated charge carriers lies at the core of the photocatalysis. The balance between charge trapping and band-edge recombination has a crucial influence on the activity of semiconductor photocatalysts. Consequently, the regulation of traps in photocatalysts becomes the key to optimizing their activities. Nevertheless, our comprehension of charge trapping, compared to that of well-studied charge recombination, remains somewhat limited. This limitation stems from the inherently heterogeneous nature of traps at both temporal and spatial scales, which renders the characterization of charge trapping a formidable challenge. Fortunately, recent advancements in both time-resolved spectroscopy and space-resolved microscopy have paved the way for considerable progress in the investigation and manipulation of charge trapping. In this Perspective, we focus on charge trapping in photocatalysts with the aim of establishing a direct link to their photocatalytic activities. To achieve this, we begin by elucidating the principles of advanced time-resolved spectroscopic techniques such as femtosecond time-resolved transient absorption spectroscopy and space-resolved microscopic methods, such as single-molecule fluorescence microscopy and surface photovoltage microscopy. Additionally, we provide an overview of noteworthy research endeavors dedicated to probing charge trapping using time- and space-resolved techniques. Our attention is then directed toward recent achievements in the manipulation of charge trapping in photocatalysts through defect engineering. Finally, we summarize this Perspective and discuss the future challenges and opportunities that lie ahead in the field.

Electron beam-induced white emission from iridium complexes-doped polymer dots.

Radiation detection plays an important role in diverse applications, including medical imaging, security, and display technologies. Scintillators, materials that emit light upon exposure to radiation, have garnered significant attention due to their exceptional sensitivity. Previous research explored polymer dots (P-dots) doped with iridium complexes as nano-sized scintillators for radiation detection, but these were constrained to emitting specific colors like red, green, and blue, limiting their utility. Recently, there has been a breakthrough in the development of white light emitters stimulated by UV-visible light. These emitters exhibit a broad spectral range in the visible wavelength, enhancing contrast and simplifying detection by visible-light sensors. Consequently, the quest for white color scintillators in radiation detection has emerged as a promising avenue for enhancing scintillation efficiency. In this study, we present a novel approach by applying P-dots doped with two iridium complexes to create white light-emitting nano-sized scintillators. These scintillators offer a wider spectral coverage within the visible-light wavelength range. Under UV light (365 nm) excitation, our synthesized P-dots exhibited remarkable white light emission. Moreover, when excited by electron beam irradiation, we observed the clear emission close to white emission which is valuable for improving the detection of radiation.

Sequential C-F Bond Transformation of the Difluoromethylene Unit in Perfluoroalkyl Groups: A Combination of Fine-Tuned Phenothiazine Photoredox Catalyst and Lewis Acid.

A sequential process via photoredox catalysis and Lewis acid mediation for C-F bond transformation of the CF2 unit in perfluoroalkyl groups has been achieved to transform perfluoroalkylarenes into complex fluoroalkylated compounds. A phenothiazine-based photocatalyst promotes the defluoroaminoxylation of perfluoroalkylarenes with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) under visible light irradiation, affording the corresponding aminoxylated products. These products undergo a further defluorinative transformation with various organosilicon reagents mediated by AlCl3 to provide highly functionalized perfluoroalkyl alcohols. Our novel phenothiazine catalyst works efficiently in the defluoroaminoxylation. Transient absorption spectroscopy revealed that the catalyst regeneration step is crucial for the photocatalytic aminoxylation.

Supramolecular nanosheet formation-induced photosensitisation mechanism change of Rose Bengal dye in aqueous media.

Development of two-dimensional materials and exploration of their functionalities are significant challenges due to their potential. In this study, we successfully fabricated a supramolecular nanosheet composed of amphiphilic Rose Bengal dyes in an aqueous medium. Furthermore, we elucidated a distinct change in the photosensitisation mechanism induced by nanosheet formation.