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The position at which the second gold(i)-phosphine group is attached was experimentally found to play a noticeable role in intersystem crossing rates of gold(i) naphthalene derivatives. However, the physical origin is ambiguous. Herein we have employed generalized trajectory-based surface-hopping dynamics simulations to simulate the excited-state relaxation dynamics of these gold(i) naphthalene compounds including both the intersystem crossing process from the initially populated first excited singlet states S1 to triplet manifolds and internal conversion processes within these triplet states. Our predicted intersystem crossing rates are consistent with experiments very well. On the basis of the present results, we have found that (1) ultrafast and subpicosecond intersystem crossing processes are mainly caused by small energy gaps and large spin-orbit couplings between S1 and Tn; (2) adding the second gold(i)-phosphine group does not increase spin-orbit couplings between S1 and Tn but decrease their values remarkably, which implies that heavy-atom effects are state-specific, not stateuniversal; (3) the position at which the second gold(i)-phosphine group is attached has a remarkable influence on the electronic structures of S1 and Tn and their relative energies, which affect energy gaps and spin-orbit couplings between S1 and Tn and eventually modulate intersystem crossing rates from S1 to Tn. These new insights are very useful for the design of gold-containing compounds with excellent photoluminescence properties. Finally, this work also exemplifies that different isomers of a compound could have distinct excited-state relaxation dynamics. [ABSTRACT FROM AUTHOR]

The five lowest electronic stages that control the UV photodissociation of formanilide and benzamide are defined using the complete active space self-consistent field theory. The photodissociation patterns in formanilide and benzamide were found to be considerably different from that for aliphatic amides.

A density functional theory investigation of the chemical reactivity of the S=C=S...C1 complex toward 2,3-dimethylbutane (DMB) has been reported and compared to the related reaction of a C1 atom with DMB. The DFT calculations indicate that the reaction of C1 atom with DMB would have little tertiary selectivity toward chlorination consistent with experimental results for photochlorination of alkanes in invert solvents.

Hybrid organic—inorganic perovskites are currently considered the most promising next-generation photovoltaic material. However, poor stability, arising from structural degradation under exposure to moisture, heat, and strong current, remains a critical challenge for their device applications. Using ab initio nonadiabatic molecular dynamics, we demonstrate that methylamine fragments deriving from the dissociation of the methylammonium cation can undermine structural stability, produce deep hole traps, and decrease charge carrier lifetimes by 1–3 orders of magnitude. Both stability and charge lifetime can be restored by methylamine passivation with chlorines, which withdraw electrons from the lone electron pair of methylamine and bring the trap levels down into the valence band. The charge lifetime of the passivated system is even longer than that of the pristine perovskite. The simulations reveal the detailed microscopic mechanism underlying deterioration of perovskite performance due to molecular defects, and demonstrate an effective defect passivation strategy to obtain highly efficient and stable perovskite solar cells. [ABSTRACT FROM AUTHOR]

MAPbBr3 (MA = CH3NH3+) doping with bismuth increases electric conductivity, charge carrier density and photostability, reduces toxicity, and expands light absorption. However, Bi doping shortens excited-state lifetimes due to formation of DY− charge recombination centers. Using nonadiabatic molecular dynamics and time-domain density functional theory, we demonstrate that the DY− center forms a deep, highly localized hole trap, which accelerates nonradiative relaxation ten-fold and is responsible for 90% of carrier losses. Hole trapping occurs by coupling between the valence band and the trap state, facilitated by the Br atoms surrounding the Bi dopant. Passivation of the DY− center with chlorines heals the local geometry distortion, eliminates the trap state, and makes the carrier lifetimes longer than even in pristine MAPbBr3. The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time, due to diminished electron-hole overlap around the passivated defect. Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr3, suggests a strategy for defect passivation and reduction of nonradiative energy losses, and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices. [ABSTRACT FROM AUTHOR]