The excited state properties of dibenzothiophene-benzoyl-9,9-dimethyl-9,10-dihydroacridine (DBT-BZ-DMAC) in the solid phase are theoretically studied through a combined quantum mechanics and molecular mechanics (QM/MM) method. The results indicate that the non-radiative decay rate of the molecule in the solid phase is significantly decreased due to the suppression of the rotation of the DMAC and DBT units in the molecule, while the radiative rate is greatly increased owing to the enhancement of the transition dipole moment. Moreover, the fluorescence efficiency in the solid phase (20.5%) is shown to be much larger than that in the gas phase (0.01‰), which confirms that DBT-BZ-DMAC is a typical aggregation-induced emission (AIE) system. The results further display that both the intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes take place between the first singlet excited state (S1) and the lowest degenerate triplet excited states (T1 and T2). In addition, the charge transfer rate is studied using the Marcus theory and the intrinsic charge mobility is calculated by performing the kinetic Monte Carlo method. The results show that the DBT-BZ-DMAC crystal is a p-type semiconductor with a hole mobility of 0.14 cm² V⁻¹ s⁻¹ at room temperature. Our investigation elucidates the experimental measurements and helps one to understand the AIE mechanisms of the DBT-BZ-DMAC fluorescence emitter, which is beneficial for developing new TADF emitters.

Based on the elastic-scattering Green's function theory, we have developed an approach to characterize the electron transport process in molecular devices, thereby allowing descriptions of the couplings between the molecule and metals at the hybrid density functional theory level. Two molecular devices with benzene-1,4-dithiol and α,α′-xylyl dithiol molecules embedded between two gold electrodes have been studied at the correlated hybrid density functional theory level. The calculated current–voltage characteristics are in very good agreement with existing experimental results, indicating the vital importance of the electron correlation effects in the electron transport. We have also examined the existence of one electron reduction and its effects on the current–voltage characteristics.

We have shown an accurate theoretical description for electronic transport properties of molecular junctions. By applying the elastic scattering Green’s function theory approach in combination with the frontier molecular orbital theory for describing the surface–molecule coupling and the hybrid density-functional theory for geometrical and electronic structures calculations, reliable predictions are obtained about the chemical and physical modifications on the current–voltage characteristics of molecular junctions, due to molecular geometrical relaxation, the choice of terminal atoms, the effect of donor/acceptor substitutions, as well as their thermal rotations.

Formalisms for current–voltage $\mathrm{(I–V)}$ characteristics of a single molecular junction with electrodes possessing one-, two-, and three-dimensional energy distributions are derived and compared in the framework of elastic scattering theory. Model calculations on a device constituted of 1,4 benzene-dithiolate molecule chemically bonded to two gold electrodes are carried out using hybrid density functional theory. It is shown that the dimensionality of metal contacts has a strong effect on the $\mathrm{I–V}$ characteristics of the molecular junction, in particular the shape of the conductance curves. Good agreement with experimental $\mathrm{I–V}$ curves has been found for the case of the three-dimensional electron system.

Rigid electron donors (D) and acceptors (A) have been widely used in recent years for the construction of D–A type thermally activated delayed fluorescence (TADF) materials. However, the chromophore robustness does not always make a positive contribution to the high efficiency of TADF materials. Here, the comparison study of two D–A type red TADF compounds (PT-TPA and PT-Az) demonstrated, for the first time, the positive impact of chromophore flexibility on the efficiency of TADF materials. In PT-Az, the rotation of terminal phenyl groups is restrained by an ethylene linker, leading to its inferior photoluminescence quantum yield (PLQY). In contrast, PT-TPA with free rotation of the phenyl groups showed a low reorganization energy and a large transition dipole moment for the S₁ → S₀ transition, which resulted in a high fluorescence radiative decay rate. As a result, the optimized devices based on PT-TPA gave a maximum external quantum efficiency (EQE) of 29.7% (632 nm) when doped in a single host and an EQE of 28.8% (648 nm) in an exciplex host. This study provided an insight into the impact of chromophore flexibility on the photophysical properties and device efficiency of TADF materials, and these results may provide valuable guidance for the molecular design of efficient emitters.