A better understanding of the photophysical processes occurring within organic semiconductors is important for designing and fabricating organic solar cells (OSCs). In this paper, we investigated the triplet‒triplet annihilation process in CuPc thin films with different molecular stacking configurations. The ultrafast transient absorption measurements indicate that the primary annihilation mechanism is one-dimensional exciton diffusion collision destruction. The decay kinetics shows a clearly time-dependent annihilation rate constant with γ ∝ t−1/2. Annihilation rate constants were determined to be γ0 = (2.87 ± 0.02) × 10−20 and (1.42 ± 0.02) × 10−20 cm3·s−1/2 for upright and lying-down configurations, respectively. Compared to the CuPc thin film with an upright configuration, the thin film with a lying-down configuration shows a longer exciton lifetime and a higher absorbance, which are beneficial for OSCs. The results in this paper have important implications on the design and mechanistic understanding of organic optoelectronic devices.
Catalytic hydrolysis of ammonia borane for dehydrogenation is a promising way for generation and storage of hydrogen energy. Catalysts with reduced utilization of costly noble metals while high activity and stability are highly desired. Herein we show that the catalytic activity of the prototypical Pt/SiO2 catalysts towards ammonia borane hydrolysis could be significantly improved by the presence of a layer of Co(OH)2 beneath the supported Pt nanoparticles. By changing the Pt:Co molar ratio in the Pt-Co(OH)2/SiO2 catalysts, the hydrogen generation rates from ammonia borane hydrolysis show a volcano-type curve, with the maximum catalytic activity at the Pt:Co molar ratio of 1:11. The highest turnover frequency value of 829 molH2·molPt−1·min−1 at room temperature outperforms most of the reported Pt-based catalysts, and the apparent activation energy is drastically decreased to 36.2 kJ/mol from 61.6 kJ/mol for Pt/SiO2. The enhanced catalytic performance of Pt-Co(OH)2/SiO2 is attributed to the electrons donation from Co atoms on Co(OH)2 to Pt occurring at the metal-hydroxide interface, which is beneficial for optimizing the oxidation cleavage of the O−H bond of attacked H2O.
The vacuum ultraviolet (VUV) photodissociation of OCS via the F 31Π Rydberg states was investigated in the range of 134–140 nm, by means of the time-sliced velocity map ion imaging technique. The images of S (1D2) products from the CO (X1Σ+) + S (1D2) dissociation channel were acquired at five photolysis wavelengths, corresponding to a series of symmetric stretching vibrational excitations in OCS (F 31Π, v1=0-4). The total translational energy distributions, vibrational populations and angular distributions of CO (X1Σ+, v) coproducts were derived. The analysis of experimental results suggests that the excited OCS molecules dissociate to CO (X1Σ+) and S (1D2) products via non-adiabatic couplings between the upper F 31Π states and the lower-lying states both in the C∞v and Cs symmetry. Furthermore, strong wavelength dependent behavior has been observed: the greatly distinct vibrational populations and angular distributions of CO (X1Σ+, v) products from the lower (v1=0-2) and higher (v1=3,4) vibrational states of the excited OCS (F 31Π, v1) demonstrate that very different mechanisms are involved in the dissociation processes. This study provides evidence for the possible contribution of vibronic coupling and the crucial role of vibronic coupling on the VUV photodissociation dynamics.
Theoretical study was carried out with OX2 (X = Halogen) molecules and calculation results showed that delocalized π36 bonds exists in their electronic structures and O atoms adopt the sp2 type of hybridization, which violated the VSEPR theory’s prediction of sp3 type. Delocalization stabilization energy (DSE) was proposed to measure delocalized π36 bond’s contribution to energy decrease and proved that it brings extra-stability to the molecule. According to our analyses, these phenomena can be summarized as a kind of coordinating effect.
A fundamental study on C?C coupling that is the crucial step in the Fischer-Tropsch synthesis (FTS) process to obtain multi-carbon products is of great importance to tailor catalysts and then guide a more promising pathway. It has been demonstrated that the coupling of CO with the metal carbide can represent the early stage in the FTS process, while the related mechanism is elusive. Herein, the reactions of the CuC3H– and CuC3– cluster anions with CO have been studied by using mass spectrometry and theoretical calculations. The experimental results showed that the coupling of CO with the C3H– moiety of CuC3H– can generate the exclusive ion product COC3H–. The reactivity and selectivity of this reaction are greatly higher than that on the reaction of CuC3– with CO, and this H-assisted C?C coupling process was rationalized by theoretical calculations.