Theoretical Insight Into the Ultralong Room-Temperature Phosphorescence of Nonplanar Aromatic Hydrocarbon

Abstract

Purely aromatic hydrocarbon materials with ultralong room-temperature phosphorescence (RTP) were reported recently, but which is universally recognized as unobservable. To reveal the inherent luminescent mechanism, two compounds, i.e., PT with a faint RTP and HD with strong RTP featured by nonplanar geometry, were chosen as a prototype to study their excited-state electronic structures by using quantum mechanics/molecular mechanics (QM/MM) model. It is demonstrated that the nonplanar ethylene brides can offer σ-electron to strengthen spin-orbit coupling (SOC) between singlet and triplet excited states, which can not only promote intersystem crossing (ISC) of S1→Tn to increase the population of triplet excitons, but also accelerate the radiative decay rate of T1→S0, and thus improving RTP. Impressively, the nonradiative decay rate only has a small increase, owing to the synergistic effect between the increase of SOC and the reduction of reorganization energy of T1→S0 caused by the restricted torsional motions of aromatic rings. Therefore, a bright and long-lived RTP was obtained in aromatic hydrocarbon materials with twisted structure. This work provided a new insight into the ultralong RTP in pure organic materials.

Ultrapure Blue Phosphorescent Organic Light-Emitting Diodes Employing a Twisted Pt(II) Complex

“…16,19 (Figure 2a, Table S1) The dihedral angles of ψPz-Py1 and ψPz-Py2 are 57.24°a nd 15.95°, respectively, both of which are about 14°larger when compared to Pt(pzpyOczpy-iPr), 27 2b). Density functional theory (DFT) calculations reveal that Pt(mpzpyOczpy-mesi) has more stabilized frontier molecular orbitals than its analog, PtON1, due to the high electronegativity of the Py2 group 28,29 (Figure S2). The lowest unoccupied molecular orbital (LUMO) primarily localizes on the Py1 moiety, whereas the highest occupied molecular orbital (HOMO) predominantly resides on the aryloxy platinum circle comprising a Pt atom, Py2, oxide bridge, and carbazolyl (cz).…”

Multiscale QM/MM modelling of catalytic systems with ChemShell

“…Liu et al used QM/MM methods to investigate the structure and stability of vanadium-doped active sites in Al-MCM-41, and their potential use as heterogeneous catalysts for the oxidation of furans. 210 Besides catalysis applications, covalent QM/MM embedding methods in ChemShell have also been recently applied to the excited state properties of organic materials [211][212][213][214][215][216] and the adsorption of hydrogen onto amorphous solid water. 217 The ionic QM/MM embedded cluster approach can be used to model both bulk defects and surface reactivity.…”

Role of halogen effects and cyclic imide groups in constructing red and near-infrared room temperature phosphorescence molecules: theoretical perspective and molecular design

“…The use of nonplanar ethylene films to provide s-electrons could promote the intersystem crossing (ISC) of S 1 -T n and increase the radiative decay rate of T 1 -S 0 , thus increasing the RTP efficiencies, while the relationship between RTP and the nonplanar conformation was revealed. 21 In addition, based on density functional theory (DFT) and TD-DFT methods, Fang and Cui illustrated the inner double emission mechanism of RTP and thermally activated delayed fluorescence (TADF) emissions. 22 Zhao et al studied the influence of the heteroatom effect on RTP emission by DFT and TD-DFT methods, and proved that the change of heteroatoms and their positions could achieve coordinated photophysical properties.…”