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Two‐coordinate Carbene−Metal−Amide (CMA) complexes with thermally activated delayed fluorescence (TADF) have attracted much attention owing to their excellent luminescence properties and potential applications in organic light‐emitting devices. However, the luminescence mechanism remains unclear. Herein, we took one CMA Au(I) complex as an example and investigate its relevant photophysics using both density functional theory (DFT) and time‐dependent DFT methods with a polarizable continuum model. The calculated absorption and emission spectra agree with the experimental data and the S1and T1states show mixed ligand to ligand charge transfer (CT) and ligand to metal CT characters. Small spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) minimizes the energy difference between the S1and T1states (ΔEST). Properly large spin‐orbit coupling promotes the reverse intersystem crossing (rISC) process. At 300 K, the rISC process is much more efficient than the T1phosphorescent emission, which leads to the TADF emission. The initially populated S1state first hops to the T1state via intersystem crossing (ISC). At 300 K, the reverse ISC (rISC) process from T1to S1is much more efficient than the T1phosphorescence emission enabling thermally activated delayed fluorescence. Small energy gap between S1and T1, proper spin‐orbit coupling value, and certain thermal energy facilitate rISC.

Self−assemble donor−acceptor chromophores have extensive applications in photofunctional devices owing to their unique charge transport properties. To explore the possibility of improving nonlinear optical (NLO) properties by self-assembling to multilayer complexes, we theoretically investigated the geometric and electronic structures, interlayer weak interactions, absorption spectra, charge transfer properties, polarizabilities (α) and first hyperpolarizabilities (β) of naphthalimide, -phenyl and -naphthyl monomers, dimers and trimers by increasing the layer number n (n = 1, 2, 3). Different stacking patterns of their dimers were also taken into account. It shows that parallel stacking patterns are conducive to maximizing overlap with respect to antiparallel ones due to the concept of optimal π-orbital overlap is more vast than purely maximizing cofacial overlap to improve charge transport. The decreases in band gap for the di/trimeric vs monomeric naphthalimide, -phenyl and -naphthyl monomers indicate the possibility of more favorable photoinduced electron transition in the aggregate when compared to the monomer. The linear and second order NLO properties of these complexes are investigated in detail. The α values increase linearly as the increase number n of layer (n=1, 2 and 3), providing a new kind of tendency forecast method for the linear optical properties. Along with the increasing electron donating ability of the donor, the βtot values of monomers increased, revealing the general rule of designing NLO moleculars. The dependence of βtot value on the layer number shows that the βtot value increased with the increased number of layer, which can be rationalized by considering the enhancement of interlayer electronic transition and two-dimensional NLO character with the two charge transfer axes. We hope this work may evoke one’s attention to design new, highly efficient second-order NLO materials with excellent building blocks: multilayer complexes.

Owing to the potential application in the development of new nonlinear optical (NLO) materials, metallomacrocycles have currently attracted considerable attention. The unusual 24 atoms {C16B8} cobaltacarborane ring 4, [Cp*Co(2,3-Et2C2B4H3-5-CC-7-CC)]4(Cp* = η5-C5Me5), featured highly symmetrical, 2D planar, tetratruncated square architectures have been investigated and characterized compared to its 1D rod-like dinuclear building blocks 2a, [Cp*Co(2,3-Et2C2B4H3-7-CC)]2, 2b, [Cp*Co(2,3-Et2C2B4H3-5-CC)]2, and the 0D sandwich monomer 1, Cp*Co(Et2C2B4H4), by density functional theory. Calculations of geometric and electronic structures, UV–vis absorption spectra, polarizabilities (αave), and second hyperpolarizabilities (γtot) have been performed herein with the aim of rationalizing the structure–property relationship and providing a novel high-performance NLO molecular materials. It is found that the tetranuclear species present long-range bidirectional charge transfer behaviors, leading to an excellent 2D NLO character along with a very large γtotvalue approached 639.8 × 10–36esu. Furthermore, because of the multipath of redox process, related molecules can also be used as efficient multistate controlled cubic NLO switches. Overall, we envision that the fascinating architectures introduced in the present work will paves the way toward the rational design of such kind metallomacrocycles for novel functional NLO materials.

In view of the experimental observation of (H2)2@C70and (H2O)2@C70, it has been suggested that hydrogen fluoride (HF) dimer can be completely localized within the sub-nanospace inside the fullerene C70cage. With the aim of quantum chemical prospective of (HF)2@C70, electronic structure calculations of C60hosting H2, HF, and H2O monomers, as well as C70hosting H2, HF, and H2O monomers and dimers, were performed by using the density functional theory, together with the quantum theory of atoms in molecules, the natural population, and interaction energy calculation. The F–H···F bonding energy inside C70was estimated at −13.25 kcal/mol, which is smaller than that of free dimer in the gas phase (−8.37 kcal/mol). Exploration of various featured properties suggests that (HF)2@C70may be also regarded as a unique system composed of both inter- and intramolecular interactions like (H2)2@C70and (H2O)2@C70. In addition, absorption spectroscopy and linear and nonlinear optical coefficients of C60hosting H2, HF, and H2O monomers, as well as C70hosting H2, HF, and H2O monomers and dimers, have also been forecasted. The results show that there is almost no influence of embedded H2, HF, and H2O monomers and dimers on the peak wavelength of absorption spectra for C60and C70. Endohedral C70possesses the larger second hyperpolarizabilities with respect to that of endohedral C60, indicating that the effect of cage size is effective in the second hyperpolarizabilities of endohedral fullerenes. The study will benefit not only the designation and the syntheses of the novel molecular (HF)2@C70but also the understanding of the structures and properties of endohedral fullerenes.