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Graphitic carbon nitride (g-CN), composed of heptazines, holds promise as a photocatalyst for hydrogen evolution. But its suboptimal visible light absorption and poor electrical conductivity limit photocurrent density and catalytic activity. Carbon atom doping, specifically carbon-modified g-CN (C/g-CN), enhances photocatalytic performance. This study investigates the impact of carbon dopants at the three-coordinated nitrogen atom (N3C) and the two-coordinated nitrogen atom (N2C) sites on the reaction mechanism of water-splitting in the ground and excited states. Nonadiabatic dynamics simulations are employed on water hydrogen-bonded to C-doped heptazines (H 2 O⋯C/heptazine) to unveil the molecular-level decomposition mechanism in the excited states. The simulations reveal that the C dopants at N2C improve the activity for water-splitting in the ground state. The C dopants at N3C improve the H atom detachment from H 2 O via the electron-driven proton transfer (EDPT) process. The synergistic effect of carbon dopants on enhanced catalytic activity of C/g-CN is elucidated. [Display omitted] • The reaction mechanism for water-splitting is studied on the C-doped g-CN. • The C dopants at the N2C site improve the activity in the ground state. • The C dopants at the N3C site improve light adsorption and photoinduced reactions. • The synergistic effect of carbon dopants on enhanced catalytic activity is reported. [ABSTRACT FROM AUTHOR]

Studying the excited‐state decay process is crucial for materials research because what happens to the excited states determines how effective the materials are for many applications, such as photoluminescence and photocatalysis. The high computational cost, however, limits the use of high‐accuracy theoretical approaches for analyzing research systems containing a significant number of atoms. Time‐dependent density functional theory is a practical approach to investigate the photorelaxation processes in these systems, as demonstrated in the studies of the excited‐state decays of heptazine‐water clusters and adenine in water described in this review. Here, we highlight the importance of conical intersections in the excited‐state decay processes of these systems using the aforementioned examples. In the heptazine‐water and adenine‐water systems, these intersections are associated with the photocatalytic water splitting reaction, caused by a barrierless reaction called water to adenine electron‐driven proton transfer. We expect the result would be helpful for researching the excited‐state decays of graphitic carbon nitride materials and DNA nucleotides. [ABSTRACT FROM AUTHOR]

Molecular photothermal conversion materials are recently attracting increasing attention for phototherapy applications. Herein we investigate the excitation and de-excitation processes of a photothermal molecule (C1TI) that is among the recently developed class of small-molecule-based photothermal imines with superb photothermal conversion efficiencies (PTCEs) up to 90% and a molecule (M2) that is constructed by replacing the amino group of C1TI with an H atom, via excited-state dynamics simulations based on the time-dependent density functional theory (TD-DFT). The simulations reveal fast (<150 fs of average time) nonradiative decays of the lowest excited singlet (S1) state to a conical intersection (CI) with the ground (S0) state in high yields (C1TI: 93.9% and M2: 87.1%). The fast decays, driven by C=N bond rotation to a perpendicular structural configuration, are found to be barrierless. The slight structural difference between C1TI and M2 leads to drastically different S0-S1 energy surfaces, especially M2 features a relatively much lower CI (0.8 eV in energy) and much more decay energy (1.0 eV) to approach the CI. This work provides insights into the de-excitation mechanisms and the performance tuning of C=N enabled photothermal materials. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (CN) materials have drawn remarkable research attention due to their extraordinary optical properties, which are especially promising for metal-free photocatalysis and photoluminescence. Herein we theoretically study the light absorption, electronic, and excitonic characteristics of covalently hybrid structures of CN quantum dots (CNQDs) and graphene quantum dots (GQDs). Density functional theory (DFT) and time-dependent DFT (TD-DFT) reveal that the relative size of CNQDs and GQDs and chemical modification to GQDs or CNQDs surface are critical determining the absorption and photocatalytic/photoluminescent performances of the as-studied structures. Importantly, the distribution position of the photoexcited electron–hole pair is found to depend on the relative size of CNQDs and GQDs, and chemical groups such as epoxy group may lead to distinct exciton distributions in the CNQD–GQD hybrid structures after attaching them to GQD or CNQD surface as compared to the case of pristine GQD and CNQD, indicating a non-negligible influence of unintended chemical reactions to CNQDs and/or GQDs under working conditions on the efficiencies of the materials for photocatalytic and photoluminescent applications. [ABSTRACT FROM AUTHOR]