The exciton dissociations and charge recombinations to a triplet state in the donor−acceptor heterojunction solar cells of [2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-b;3,4-b]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) blended with ten different fullerene derivatives are theoretically investigated by using electronic structure calculations together with a Marcus formula. The detailed discussions of available accuracy in the evaluation of all quantities entering the rate expression (driving force, electronic coupling, and internal and external reorganization energies) are provided. The results reveal that the exciton dissociations in most blends are barrierless reactions because the corresponding values of driving forces and reorganization energies are very close; however, the recombinations from the charge transfer states to the triplet state of PCPDTBT occur in the Marcus normal regime. The predicted rates for both the exciton dissociation and charge recombination are in quite good agreement with experimental measurements. In addition, as the triplet charge transfer states are formed, their recombination rates become two orders larger than those for the singlet ones and have orders similar to the exciton dissociations. It is thus expected that the triplet charge recombinations are dominant channels, whereas the singlet charge recombinations can be safely neglected because of quite small rates compared to exciton dissociation ones.

A recently synthesized novel molecule (named CAT-1) exhibits intriguing near-infrared (NIR) thermally activated delayed fluorescence (TADF) close to 1000 nm wavelength; however, the mechanism behind these intrinsic properties is not fully understood. Herein, we unravel that the fluorescence emission spectrum with a broad wavelength range (770–950 nm) of CAT-1 is primarily induced by hydrogen bond steric hindrance based on density functional theory and Marcus theory. It is found that the hydrogen bond steric hindrance plays a critical role in inhibiting the twist of the configuration of different excited states, which leads to the minor driving force for fast electron trapping between the excited states, as well as small internal reorganization energy caused by less changed geometric configuration. Furthermore, such steric hindrance will cause a more distorted plane, resulting in a less favorable electron delocalization. A faster reverse intersystem crossing (RISC) rate is then obtained due to the nearly unchanged conformation between excited states caused by steric hindrance, although the spin–orbit coupling is small. Consequently, the NIR TADF with a longer wavelength can be emitted in CAT-1. This work shows that the hydrogen bond steric hindrance can fine-tune the electronic interactions of the donor and acceptor units to control the TADF.

The heating and low temperature thermite reactions of the Al/SiO 2 sandwich nanostructure are investigated by molecular dynamics simulations in combination with the reactive force field, ReaxFF. In this paper, the initial atomistic processes, thermal stability and energetic reaction properties of Al and SiO 2 are presented. The results show that the melting temperature of the Al/SiO 2 sandwich structure is $1400 K. The thermite reaction self-heating rates are determined by the thickness of the interfacial diffusion barrier at the interface in the nanoparticle.

Derived from the most abundant natural polymer, cellulose nanocrystal materials have attracted attention in recent decades due to their chemical and mechanical properties. However, still unclear is the influence of different exposed facets of the cellulose nanocrystals on the physicochemical properties. Herein, we first designed cellulose II nanocrystals with different exposed facets, the hydroxymethyl conformations distribution, hydrogen bond (HB) analysis, as well as the relative structural stability of these models (including crystal facets {A, B, O} and Type-A models vary in size) are theoretically investigated. The results reveal that the HB network of terminal anhydroglucose depends on the adjacent chain’s contact sites in nanocrystals exposed with different facets. Compared to nanocrystals exposed with inclined facet, these exposed with flat facet tend to be the most stable. Therefore, the strategy of tuning exposed crystal facets will guide the design of novel cellulose nanocrystals with various physicochemical properties.