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A new diabatization scheme is proposed to calculate the electronic couplings for the singlet fission process in multichromophoric systems. In this approach, a robust descriptor that treats single and multiple excitations on an equal footing is adopted to quantify the localization degree of the particle and hole densities of the electronic states. By maximally localizing the particles and holes in terms of predefined molecular fragments, quasi-diabatic states with well-defined characters (locally excited, charge transfer, correlated triplet pair, etc.) can be automatically constructed as the linear combinations of the adiabatic ones, and the electronic couplings can be directly obtained. This approach is very general in that it applies to electronic states with various spin multiplicities and can be combined with various kinds of preliminary electronic structure calculations. Due to the high numerical efficiency, it is able to manipulate more than 100 electronic states in diabatization. The applications to the tetracene dimer and trimer reveal that high-lying multiply excited charge transfer states have significant influences on both the formation and separation of the correlated triplet pair and can even enlarge the coupling for the latter process by 1 order of magnitude.

pH buffer plays versatile roles in both biology and chemistry. In this study, we unravel the critical role of pH buffer in accelerating degradation of the lignin substrate in lignin peroxidase (LiP) using QM/MM MD simulations and the nonadiabatic electron transfer (ET) and proton-coupled electron transfer (PCET) theories. As a key enzyme involved in lignin degradation, LiP accomplishes the oxidation of lignin via two consecutive ET reactions and the subsequent C–C cleavage of the lignin cation radical. The first one involves ET from Trp171 to the active species of Compound I, while the second one involves ET from the lignin substrate to the Trp171 radical. Differing from the common view that pH = 3 may enhance the oxidizing power of Cpd I via protonation of the protein environment, our study shows that the intrinsic electric fields have minor effects on the first ET step. Instead, our study shows that the pH buffer of tartaric acid plays key roles during the second ET step. Our study shows that the pH buffer of tartaric acid can form a strong H-bond with Glu250, which can prevent the proton transfer from the Trp171-H•+cation radical to Glu250, thereby stabilizing the Trp171-H•+cation radical for the lignin oxidation. In addition, the pH buffer of tartaric acid can enhance the oxidizing power of the Trp171-H•+cation radical via both the protonation of the proximal Asp264 and the second-sphere H-bond with Glu250. Such synergistic effects of pH buffer facilitate the thermodynamics of the second ET step and reduce the overall barrier of lignin degradation by ∼4.3 kcal/mol, which corresponds to a rate acceleration of 103-fold that agrees with experiments. These findings not only expand our understanding on pH-dependent redox reactions in both biology and chemistry but also provide valuable insights into tryptophan-mediated biological ET reactions.

The variational quantum eigensolver (VQE) algorithm can simulate the chemical systems such as molecules in the noisy-intermediate-scale quantum devices and shows promising applications in quantum chemistry simulations. The accuracy and computational cost of the VQE simulations are determined by the underlying ansatz. Therefore, the most important issue is to generate a compact and accurate ansatz, which requires a shallower parametric quantum circuit and can achieve an acceptable accuracy. The newly developed adaptive algorithms (AAs) such as the adaptive derivative-assembled pseudo-Trotter VQE (ADAPT-VQE) can solve this issue via generating compact and accurate ansatzes. However, these AAs show very low computational efficiency because they require a large number of additional measurements. Here we propose an amplitude reordering (AR) strategy to accelerate the promising but expensive AAs by adding operators in a “batched” fashion in a way that their order is still quasi-optimal. We first introduce the AR method into ADAPT-VQE and build the AR-ADAPT-VQE algorithm. We then endow the energy-sorting VQE (ES-VQE) algorithm with the adaptive feature and introduce the AR into AES-VQE to form the AR-AES-VQE algorithm. To demonstrate the performance of these algorithms, we calculate the dissociation curves of three small molecules, LiH, linear BeH2, and linear H6, by using (AR-)ADAPT-VQE and (AR-)AES-VQE algorithms. It is found that all of the AR-equipped AAs (AR-AAs) can significantly reduce the number of iterations and subsequently accelerate the calculations with a speedup of up to more than ten times without the obvious loss of accuracy. The final ansatz generated by the AR-AAs not only avoids extra circuit depth but also maintains the computational accuracy; sometimes the AR-AAs even outperforms their original counterparts.

Lead-free halide double perovskites (LFDPs) arouse great interest as environmentally friendly substitutes to the state-of-the-art lead halide perovskites. However, most halide LFDPs feature large bandgaps that afford weak visible-light absorption. Herein, we synthesized and systemically studied the single-crystallographic, physical–chemical, band structural, and electronic properties of a series of multidimensional Au-based lead-free hybrid polymorphs, [(NH3CH3)2(AuI4)(AuI2)], [(NH2CHNH2)(AuI4)(AuI2)], [NH3(CH2)nNH3][(AuI4)2] (n= 2, 3), [NH3(CH2)nNH3][(AuI4)(I3)] (n= 4, 5, 6), and [NH3(CH2)nNH3]2[(AuI4)(AuI2)(I3)2] (n= 7, 8, 9). Among these two-dimensional (2D) perovskite-related and zero-dimensional nonperovskite polymorphs, we found an abnormal variation of structural dimensionality with increasing the size of A-site cations. These polymorphs displayed ultrabroad absorption ranges (200–1300 nm) and tunable low indirect bandgaps (0.93–1.18 eV). Combined single-crystallography and Hall effect measurements demonstrate that the I3–conduces to the formation of 2D perovskite structures related by connecting with the (AuI4)−sheets and also the charge transport properties. Consequently, [NH3(CH2)5NH3][(AuI4)I3] and [NH3(CH2)8NH3]2[(AuI4)(AuI2)(I3)2] showed high spectroscopic limited maximum efficiencies of 28.4 and 20.5%, respectively, with a film thickness of 500 nm. Our findings bring the Au-based polymorphs to the forefront of study on lead-free low-bandgap perovskites for optoelectronics and reveal the unique rule of dimensionality engineering in such materials.

Thermally activated delayed fluorescence (TADF) emitters have become a hot topic in organic light-emitting diode materials due to their advantages of high efficiency, long lifespan and low cost. Many investigations have shown that TADF efficiency is determined by the reverse intersystem crossing (ISC) rate from the triplet to singlet excited state where the direct spin-obit coupling (SOC) is a pivoted factor. This study demonstrates that nonadiabatic coupling (NAC) is critical in enhancing TADF efficiency, as elucidated through second-order perturbation theory. We start from the time-dependent correlation function approach for calculating ISC rate to incorporate SOC and NAC as well as the Herzberg-Teller-like vibronic coupling. From three typological molecular model simulations, we find that the NAC can even reach to 32.6% contribution to ISC rate, and these contributions are sensitive to the motions of vibrational modes. This finding may provide important reference and guidance for further optimizing material properties and designing new TADF emitters.

Tin-based perovskites are one of the most promising candidates for the development of lead-free perovskite solar cells (PSCs) and have attracted lots of attention. Despite the extensive research efforts, the performance of tin-based PSCs (Sn-PSCs) still lags far behind the lead containing counterparts due to the poor stability and self-p-doping. Here, we perform first-principles density functional theory calculations combined with non-adiabatic molecular dynamics simulations to unveil the origins of the instability of tin iodine perovskite when exposed to O2. It is found that O2is more thermally favorable to be adsorbed on iodine-vacancy (VI) defect sites in the defective surface rather than the pristine surface, and the generation of peroxide species on the VIsites dramatically accelerates the structural decomposition. The presence of VIdefects on the surface of CsSnI3decreases the band gap by inducing a local shallow state around conduction band minimum, significantly accelerating the electron–hole recombination. The adsorption of O2on VIsite slightly increases the band gap compared to that of the pristine one and decreases the influence of VIon the surface’s optoelectronic properties and the electron–hole recombination rate but significantly accelerates structural decomposition by weakening the defect tolerance ability of the [SnI6]4–octahedra as well as the carriers’ relaxation. The increased structural instability in combined VIand O2points to the surface VIdefect passivation as the main optimization scheme for efficient and stable Sn-PSCs.

Dipyrrolonaphthyridinedione (DPND) thin films exhibit interesting photophysical properties and singlet fission (SF) processes. A recent experimental work found that the alkyl substitution in the DPND skeleton has the remarkable influence on the characteristics of electronic absorption spectra and SF rates. Here, we theoretically elucidate the microscopic mechanism of the substituent effect on the optical properties and exciton dynamics of materials by combining the electronic structure calculations and the quantum dynamics simulations. The results show that the alkyl substituent has a minor effect on the single molecular properties but dramatically changes those of DPND aggregates via varying the intermolecular interactions. The aggregates of DPND with and without alkyl side chains exhibit the more likely characters of H-type aggregations. In the former (DPND6), the weak degree of mixing of intramolecular localized excited (LE) states and intermolecular charge transfer (CT) states makes the low-energy absorption band possess the predominant optical absorption, while in the latter (DPND), the CT and LE states are close in energy, together with their strong interaction, resulting in the substantial state-mixing, so that its two low-energy absorption bands have nearly equal oscillator strengths and a wide energy spacing of more than 0.5 eV. The simulation of exciton dynamics elucidates that the photoinitiated states in both aggregates cannot generate the free charge carrier because of the lack of enough driving forces. However, the population exchanges between LE and CT states in DPND aggregates are much faster than in DPND6 aggregates, indicating the different SF behaviors, consistent with the experimental observation.

Assessing and improving the performance of organic light-emitting diode (OLED) materials require quantitative prediction of rate coefficients for the intersystem crossing (ISC) and reverse ISC (RISC) processes, which are determined not only by the energy gap and the direct spin–orbit coupling (SOC) between the first singlet and triplet excited-states at a thermal equilibrium position of the initial electronic state but also by the non-Condon effects such as the Herzberg–Teller-like vibronic coupling (HTVC) and the spin-vibronic coupling (SVC). Here we apply the time-dependent correlation function approaches to quantitatively calculate the vibrationally resolved absorption and fluorescence spectra and ISC/RISC rates of a newly synthesized multiple-resonance-type (MR-type) thermally activated delayed fluorescence (TADF) emitter, 7-phenylquinolino[3,2,1-de]acridine-5,9-dione (7-PhQAD), with the inclusion of the Franck–Condon (FC), HTVC, and Duschinsky rotation (DR) effects. The SVC effect on the rates has also been approximately evaluated. We find that the experimentally measured ISC rates of 7-PhQAD originate predominantly from the vibronic coupling, consistent with the previous reports on other MR-type TADF emitters. The SVC effect on ISC rates is about 10 times larger than the HTVC effect, and the latter increases the ISC rates by more than 1 order of magnitude while it slightly affects the vibrationally resolved absorption and fluorescence spectra. The discrepancy between the theoretical and experimental results is attributed to inaccurately describing excited-states calculated by the time-dependent density functional theory as well as to not fully accounting for the complex experimental conditions. This work provides a demonstration of what proportion of ISC and RISC rate coefficients of a MR-type TADF emitter can be covered by the HTVC effect, and it opens design routes that go beyond the FC approximation for the future development of high-performance OLED devices.