Manipulation of the emission properties of pure organic room-temperature phosphors through molecular design is attractive but challenging. Tremendous efforts have been made to modulate their aggregation behaviors to suppress nonradiative decay in order to achieve efficient light emission and long lifetimes. However, success has been limited. To attain such a goal, here we present a rational design principle based on intrinsic molecular-structure engineering. Comprehensive investigations on the molecular orbitals revealed that an excited state with hybrid (n,p*) and (p,p*) configurations in appreciable proportion is desired. Tailoring the aromatic subunits in arylphenones can effectively tune the energy level and the orbital feature of the triplet exciton. Our experimental data reveal that a series of full-color pure organic phosphors with a balanced lifetime (up to 0.23 s) and efficiency (up to 36.0%) can be realized under ambient conditions, demonstrating the validity of our instructive design principle.

Room temperature phosphorescence (RTP) from pure organic material is rare due to the low phosphorescence quantum efficiency. That is why the recent discovery of crystallization induced RTP for several organic molecules aroused strong interests. Through a combined quantum and molecular mechanics CASPT2/AMBER scheme taking terephthalic acid (TPA) as example, we found that electrostatic interaction not only can induce an enhanced radiative decay T1 → S0 through the dipole-allowed S1 intermediate state, but also can hinder the nonradiative decay process upon crystallization. From gas phase to crystal, the nature of S1 state is converted to (1)(π,π*) from (1)(n,π*) character, enhancing transition dipole moment and serving as an efficient intermediate radiative pathway for T1 → S0 transition, and eventually leading to a boosted RTP. The intermolecular packing also blocks the nonradiative decay channel of the high-frequency C═O stretching vibration with large vibronic coupling, rather than the conventional low-frequency aromatic rotation in crystal. This mechanism also holds for other organic compounds that contain both ketones and aromatic rings.

Efficient quantum dynamical and electronic structure approaches are presented to calculate resonance Raman spectroscopy (RRS) with inclusion of Herzberg-Teller (HT) contribution and mode-mixing (Duschinsky) effect. In the dynamical method, an analytical expression for RRS in the time domain is proposed to avoid summation over the large number of intermediate vibrational states. In the electronic structure calculations, the analytic energy-derivative approaches for the excited states within the time-dependent density functional theory (TDDFT), developed by us, are adopted to overcome the computational bottleneck of excited-state gradient and Hessian calculations. In addition, an analytic calculation to the geometrical derivatives of the transition dipole moment, entering the HT term, is also adopted. The proposed approaches are implemented to calculate RR spectra of a few of conjugated systems, phenoxyl radical, 2-thiopyridone in water solution, and free-base porphyrin. The calculated RR spectra show the evident HT effect in those π-conjugated systems, and their relative intensities are consistent with experimental measurements.

It has been suggested that the exotic aggregation-induced emission (AIE) phenomenon was caused by the restriction on the nonradiative decay through intramolecular vibrational/rotational relaxation. There have been other proposed mechanisms such as J-aggregation or excimer formation, etc. Through computational studies, we propose a direct approach to verify the AIE process, namely, using resonance Raman spectroscopy (RRS) to explore the microscopic mechanism of AIE. Taking examples of AIE-active 1,2-diphenyl-3,4-bis(diphenylmethylene)-1-cyclobutene (HPDMCb) and AIE-inactive 2,3-dicyanopyrazino phenanthrene (DCPP) for comparison, we found that for the AIEgen, after aggregation into cluster, the intensities of low-frequency peaks in RRS are evidently reduced relative to the high-frequency peaks, along with a remarkable blueshift. However, the RRS of non-AIEgen remains almost unaffected upon aggregation. Such distinctive spectroscopic characteristics can be ascribed to the intramolecular vibrational relaxation which is hindered for AIEgen, especially for the low-frequency ring-twisting motions, because the RRS amplitude is proportional to the mode vibrational relaxation energy times frequency λ j ω j . Thus, RRS is a direct way to clarify the recent dispute on the AIE mechanism. If such predictions are true, it will clearly validate the earlier proposed restriction on the nonradiative decay through an intramolecular vibration/rotation relaxation mechanism.

The increasing demand for high-performance organic light-emitting devices (OLEDs) based on thermally-activated delayed fluorescence (TADF) principle urgently requires to establish an efficient preparation strategy of highperformance TADF materials. Although considerable progress has been made in molecular design approaches for TADF materials, it still remains an unaddressed issue how molecular aggregated states or supramolecular structures determine the TADF property of organic solids. Herein, we present an organic molecule 3-(10Hphenoxazin-10-yl)-9H-xanthen-9-one (3-PXZ-XO) with TADF and polymorph characteristics. Three kinds of 3-PXZ-XO based crystals A, B, and C with different TADF properties were obtained. The three crystals display obviously different emission maxima (λ em,max : 535 nm for A, 555 nm for B, and 576 nm for C), photoluminescence (PL) quantum yields (Φ: 51% for A, 28% for B, and 39% for C), and delayed lifetimes of excited states (τ TADF : 914 ns for A, 774 ns for B, and 994 ns for C). Single-crystal X-ray diffraction analyses revealed that in A, B, and C there are different intermolecular π•••π stacking interaction modes between the adjacent donor planes or acceptor planes. The different TADF properties of the three polymorphs are mainly attributed to their different supramolecular structures. Appropriate donor•••donor and acceptor•••acceptor stacking interactions inducing aggregation structures can strongly enhance TADF property of organic solids.

Conspectus Organic phosphorescence is defined as a radiative transition between the different spin multiplicities of an organic molecule after excitation; here, we refer to the photoexcitation. Unlike fluorescence, it shows a long emission lifetime (∼μs), large Stokes shift, and rich excited state properties, attracting considerable attention in organic electronics during the past years. Ultralong organic phosphorescence (UOP), a type of persistent luminescence in organic phosphors, shows an emission lifetime of over 100 ms normally according to the resolution limit of the naked eye. According to the Jablonski energy diagram, two prerequisites are necessary for UOP generation and enhancement. One is to promote intersystem crossing (ISC) of the excitons from the excited singlet to triplet states by enhancing the spin–orbit coupling (SOC); the other is to suppress the nonradiative transitions of the excitons from the excited triplet states. In this Account, we will give a summary of our research on ultralong organic phosphorescence, including the design of materials, manipulation of properties, fabrication of nano/microstructures, and function applications. First, we give a brief introduction to the UOP development. Then, we discuss the constructed methods of UOP materials from the inter/intramolecular interaction types, including π–π interactions, intermolecular hydrogen bonds, halogen bonds, ionic bonds, covalent bonds, and so on. These effective interactions can build a rigid environment to restrain the nonradiative transitions from the molecular motions or external quenching by oxygen, moisture, or heat, and thus enhance the UOP performance. Next, the manipulation of UOP properties, containing excitation wavelength, emission colors, lifetimes, and quantum efficiency (QE), through molecular or crystal engineering will be summarized. Recently, the excitation wavelengths of the materials for UOP can be regulated in different regions, such as UV, visible light, and X-ray; the emission colors of UOP can cover the whole visible-light region, from deep blue to red; the phosphorescence lifetime of UOP materials can reach 2.5 s, and the quantum efficiency can be achieved up to 96.5%. Moreover, we will present the fabrication of micro/nanoscale UOP materials, including the preparation of micro/nanostructure, optical performance, and device fabrication. Afterward, we will review the potential applications of UOP materials in organic/bio-optoelectronics, such as information encryption, bioimaging, sensing, afterglow display, etc. Finally, an outlook on the development of UOP materials and applications will be proposed.

A time-dependent approach is presented to simulate the two-photon absorption (TPA) and resonance hyper-Raman scattering (RHRS) spectra including Duschinsky rotation (mode-mixing) and Herzberg-Teller (HT) vibronic coupling effects. The computational obstacles for the excited-state geometries, vibrational frequencies, and nuclear derivatives of transition dipole moments, which enter the expressions of TPA and RHRS cross sections, are further overcome by the recently developed analytical excited-state energy derivative approaches in the framework of time-dependent density functional theory. The excited-state potential curvatures are evaluated at different levels of approximation to inspect the effects of frequency differences, mode-mixing and HT on TPA and RHRS spectra. Two types of molecules, one with high symmetry (formaldehyde, p-difluorobenzene, and benzotrifluoride) and the other with non-centrosymmetry (cis-hydroxybenzylidene-2,3-dimethylimidazolinone in the deprotonated anion state (HDBI(-))), are used as test systems. The calculated results reveal that it is crucial to adopt the exact excited-state potential curvatures in the calculations of TPA and RHRS spectra even for the high-symmetric molecules, and that the vertical gradient approximation leads to a large deviation. Furthermore, it is found that the HT contribution is evident in the TPA and RHRS spectra of HDBI(-) although its one- and two-photon transitions are strongly allowed, and its effect results in an obvious blueshift of the TPA maximum with respect to the one-photon absorption maximum. With the HT and solvent effects getting involved, the simulated blueshift of 1291 cm(-1) agrees well with the experimental measurement.

High-spin states in 138 Nd were investigated by using the 48 Ca + 94 Zr reaction and γ -ray coincidences were acquired with the GASP spectrometer. A rich level scheme was developed including 14 new bands of quadrupole transitions at very high spins. Linking transitions connecting 11 high-spin bands to low-energy states have been observed. Calculations based on the cranked Nilsson-Strutinsky formalism have been used to assign configurations to the observed bands. The main result of these calculations is that all 14 bands exhibit a stable triaxial deformation up to the highest observed spins, giving strong support to the existence of a triaxial minimum with normal deformation and positive asymmetry parameter in nuclei with a few holes in the N = 82 shell closure.