The intermediacy of alkoxy radicals in ceriumcatalyzed C−H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)−alkoxide complexes have been synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance and transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified alkoxy radicals as the sole heteroatom-centered radical species generated via ligand-tometal charge transfer (LMCT) excitation. Alkoxy-radical-mediated hydrogen atom transfer (HAT) has been verified via kinetic analysis, density functional theory (DFT) calculations, and reactions under strictly chloride-free conditions. These experimental findings unambiguously establish the critical role of alkoxy radicals in Ce-LMCT catalysis and definitively preclude the involvement of chlorine radical. This study has also reinforced the necessity of a high relative ratio of alcohol vs Ce for the selective alkoxy-radical-mediated HAT, as seemingly trivial changes in the relative ratio of alcohol vs Ce can lead to drastically different mechanistic pathways. Importantly, the previously proposed chlorine radical−alcohol complex, postulated to explain alkoxy-radicalenabled selectivities in this system, has been examined under scrutiny and ruled out by regioselectivity studies, transient absorption experiments, and high-level calculations. Moreover, the peculiar selectivity of alkoxy radical generation in the LMCT homolysis of Ce(IV) heteroleptic complexes has been analyzed and back-electron transfer (BET) may have regulated the efficiency and selectivity for the formation of ligand-centered radicals.

Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices. However, judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology, composition, and defect. Herein, we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization. The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX3 perovskite, respectively. The formation of supramolecular structure retard perovskite nucleation, while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth. This judicious control enables a segmented growth, inducing the growth of insular nanocrystal consist of low-dimensional structure. Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%, ranking among the highest efficiency achieved. The homogeneous nano-island structure also enables high-efficiency large area (1 cm2) device up to 21.6%, and a record high value of 13.6% for highly semi-transparent ones.

The anti-Kasha process provides the possibility of using high-energy excited states to develop novel applications. Our previous research (Nature communications, 2020, 11, 793) has demonstrated a dual-emission anti-Kasha-active fluorophore for bioimaging application, which exhibits near-infrared emissions from the S 1 state and visible anti-Kasha emissions from the S 2 state. Here, we applied tunable blue-side femtosecond stimulated Raman spectroscopy (FSRS) and transient absorption spectroscopy, assisted by quantum calculations, to reveal the anti-Kasha dual emission mechanism, in which the emergence of two fluorescing states is due to the retardation of internal conversion from the S 2 state to the S 1 state. It has been demonstrated that the facts of anti-Kasha high-energy emission are commonly attributed to a large energy gap between the two excited states, leading to a decrease in the internal conversion rate due to a poor Franck−Condon factor. In this study, analysis of the calculation and FSRS experimental results provide us further insight into the dual-emission anti-Kasha mechanism, where the observation of hydrogen out-of-plane Raman modes from FSRS suggested that, in addition to the energy-gap law, the initial photoinduced molecular conformational change plays a key role in influencing the rate of internal conversion.

The van der Waals heterojunction involving graphene (Gr) with transition metal dichalcogenides (TMDs) is regarded as a promising structure for its outstanding performance in optoelectronic response. The electron–hole thermalization has been deemed to be the main reason for the subband gap excitation charge transfer from Gr to TMDs. However, the role of the intricate interlayer interaction of Gr and TMDs still requires intensive investigation. Here, we have investigated the photocarrier dynamics in a five-layer PtSe2/Gr heterojunction by using time-resolved optical pump and terahertz probe spectroscopy. Interestingly, after photoexcitation, electron transfer from PtSe2 to Gr has been demonstrated successfully in the PtSe2/Gr/substrate heterojunction; by contrast, no observable charge transfer occurs in the Gr/PtSe2/substrate heterostructure. The prominent difference for the different stacking sequences between Gr and PtSe2 can be ascribed to the effective electric field introduced by the fused silica substrate. A physical picture accounting for the effective electric field introduced by the substrate has been proposed to interpret the charge transfer process in the TMD/Gr heterostructure. More importantly, the electric field induced by the substrate plays a dominant role in controlling the charge transfer pathway in the TMDs/Gr heterojunction. This study not only sheds light on the substrate engineering of the van der Waals heterojunction but also provides new insight into the layer interaction dynamics in the Gr/TMD heterojunction.

Heterostructures constructed from graphene and transition metal dichalcogenides (TMDs) have established a new platform for optoelectronic applications. After a large number of studies, one intriguing debate is the existence of the interfacial exciton in graphene/ TMDs. Hereby, by combined optical pump−terahertz probe spectroscopy and transient absorption spectroscopy, we report the observation of the interfacial exciton in graphene/MoS 2 heterostructure. With the photon energy well below the band gap of monolayer MoS 2 , the hot electrons of graphene are transferred to MoS 2 within 0.5 ps; subsequently, the relaxation of the holes in graphene and electrons in MoS 2 shows an identical time scale of 15−18 ps, which manifests the formation and relaxation of the interfacial exciton in the heterostructure following photoexcitation. Moreover, a model of the carrier heating and photogating effect in graphene is proposed to estimate the amount of transferred charge, which agrees well with the experimental results. Our study provides insights into the dynamics of graphene-based heterostructure interfacial non-equilibrium carriers.