2D transition metal carbides or nitrides, known as MXenes, are a new family of 2D materials with close to 30 members experimentally synthesized and dozens more theoretically investigated. Because of the abundant surface terminations, MXenes have been compounded with various materials by multi-interactions. In addition to the prevented aggregation and oxidation of MXene flakes, the MXene/polymer membranes exhibit outstanding mechanical, thermal, and electrical properties due to the synergistic effects. However, relatively little is currently known about the MXene/polymer membranes and a special review on the progress of the synthesis, properties, and applications of MXene/polymer membranes has not been reported to date. Herein, this Review starts with an introduction of the synthesis and properties of MXenes. Then the development of MXene/polymer membranes will be discussed, which aims to summarize various approaches of fabricating MXene/polymer membranes and their fascinating properties. The focus then turns to their exciting potential applications in various fields such as filtration, electromagnetic interference (EMI) shielding, energy storage devices, wearable electronics, etc. Finally, outlooks and perspectives for the future challenges and prospects of MXene/polymer membranes are provided.

Inspired by the formulation of quantum-electrodynamical time-dependent density functional theory (QED-TDDFT) by Rubio and co-workers [Flick et al., ACS Photonics 6, 2757-2778 (2019)], we propose an implementation that uses dimensionless amplitudes for describing the photonic contributions to QED-TDDFT electron–photon eigenstates. This leads to a Hermitian QED-TDDFT coupling matrix that is expected to facilitate the future development of analytic derivatives. Through a Gaussian atomic basis implementation of the QED-TDDFT method, we examined the effect of dipole self-energy, rotating-wave approximation, and the Tamm–Dancoff approximation on the QED-TDDFT eigenstates of model compounds (ethene, formaldehyde, and benzaldehyde) in an optical cavity. We highlight, in the strong coupling regime, the role of higher-energy and off-resonance excited states with large transition dipole moments in the direction of the photonic field, which are automatically accounted for in our QED-TDDFT calculations and might substantially affect the energies and compositions of polaritons associated with lower-energy electronic states.

Here, we design and synthesize an organic laser molecule, 2,7-diphenyl-9H-fluorene (LD-1), which has state-of-the-art integrated optoelectronic properties with a high mobility of 0.25 cm2 V–1 s–1, a high photoluminescence quantum yield of 60.3%, and superior deep-blue laser characteristics (low threshold of P th = 71 μJ cm–2 and P th = 53 μJ cm–2 and high quality factor (Q) of ∼3100 and ∼2700 at emission peaks of 390 and 410 nm, respectively). Organic light-emitting transistors based on LD-1 are for the first time demonstrated with obvious electroluminescent emission and gate tunable features. This work opens the door for a new class of organic semiconductor laser molecules and is critical for deep-blue optical and laser applications.

The photophysics of benzaldehyde are analyzed through the lens of TD-DFT adiabatic excited states and Boys or Edmiston−Ruedenberg localized diabatic states. We predict rate constants for two processes in excited benzaldehyde: (i) the intersystem crossing from S 1 → T 2 and (ii) the phosphorescence from T 1 → S 0 . We also study (iii) the conical intersection between T 2 and T 1 that is putatively responsible for an ultrafast internal conversion process, T 2 → T 1 . In agreement with Ohmori et al. (J. Phys. Chem. 1988, 92 (5), 1086−1093), our results suggest that the S 1 → T 2 intersystem crossing in benzaldehyde is rapid not only because of a large spin−orbit matrix element (i.e., El-Sayed's rule) but also because of a fortuitously small energy barrier. Furthermore, when studying the T 2 → T 1 internal conversion, we find that both Boys and Edmiston−Ruedenberg localization give remarkably stable and accurate diabatic states which will be useful for ongoing studies of dynamics near conical intersections. To our knowledge, this is the first example whereby localized diabatization techniques have been tested and have successfully recovered the topology of a conical intersection.

We present a complete derivation of derivative couplings between excited states in the framework of adiabatic time-dependent density functional response theory. Explicit working equations are given and the resulting derivative couplings are compared with derivative couplings from a pseudo-wavefunction ansatz. For degenerate excited states, i.e., close to a conical intersection (CI), the two approaches are identical apart from an antisymmetric overlap term. However, if the difference between two excitation energies equals another excitation energy, the couplings from response theory exhibit an unphysical divergence. This spurious behavior is a result of the adiabatic or static kernel approximation of time-dependent density functional theory leading to an incorrect analytical structure of the quadratic response function. Numerical examples for couplings close to a CI and for well-separated electronic states are given.