To rationalize the marked difference in the energy conversion efficiency of dye sensitized solar cells (DSSCs) based on organic dyes 1 and 2 different only in their p spacer, density functional theory (DFT) and time-dependent DFT calculations of the geometries, electronic structures and absorption spectra of the organic dyes before and after binding to titanium oxide were carried out. These enable us to determine factors such as dipole moments associated with the open-circuit photovoltage (V oc ), and to quantify parameters such as the light harvesting efficiency, the electron injection efficiency associated with the short-circuit photocurrent density (J sc ). The results reveal that compared to 2 with a thiazole spacer, 1 with a thiophene spacer could cause a red shift of the absorption spectrum, increase the oscillator strength and improve the driving force for electron injection, thus leading to the larger J sc , in good agreement with experimental data. As for V oc , our results stress that apart from the generally emphasized vertical dipole moment of the dyes pointing outward from the semiconductor surface, the number of photoinjected electrons from the dye to the semiconductor is also crucial to obtain high performance dyes with high V oc . After justifying the reliability of the quantum-chemical methods, we designed another four dyes with different p spacers to screen more efficient organic dyes. Fortunately, taking 1 as reference, we find that dye 4 with a thienothiophene spacer displays an enhanced J sc and V oc , indicating that it will be a more efficient diarylamine-fluorene-based organic dye used in DSSCs, which will play a theoretical guiding role in the design and synthesis of new organic dyes.

The quantum entropy is usually defined using von Neumann's formula, which measures lack of information and vanishes for pure states. In contrast, we obtain a formula for the entropy of a pure state as it is measured from thermodynamic experiments, solely from the self-entanglement of the wave function, and find strong numerical evidence that the two are in agreement for nonintegrable systems, both for energy eigenstates and for states that are obtained at long times under the evolution of more general initial conditions. This is an extension of Boltzmann's hypothesis for classical systems, relating microscopic motion to thermodynamics.

No abstract

A few rice (Oryza sativa L.) varieties or rice straw produce and release allelochemicals into soil in which interfere with the growth of neighboring or successive plants. Allelopathic rice PI312777 and Huagan-1 at their early growth stages released momilactone B, 3-isopropyl-5-acetoxycyclohexene-2-one-1, and 5,7,4¢-trihydroxy-3¢,5¢-dimethoxyflavone into soil at phytotoxic levels, but non-allelopathic rice Huajingxian did not. Both allelopathic and non-allelopathic rice residues released momilactone B and ligninrelated phenolic acids (p-hydroxybenzoic, p-coumaric, ferulic, syringic and vanillic acids) into the soil during residue decomposition to inhibit successive plants. The results indicated that allelochemicals involved in rice allelopathy from living and dead plants are substantially different. Interestingly, the concentrations of the allelochemicals released from the allelopathic rice seedlings in soil increased dramatically when they were surrounded with Echinochloa crus-galli. The concentrations of the allelochemicals were over 3-fold higher in the presence of E. crus-galli than in the absence of E. crus-galli. However, the same case did not occur in non-allelopathic Huajingxian seedlings surrounded with E. crus-galli. In addition to allelochemical exudation being promoted by the presence of E. crus-galli, allelopathic rice seedlings also increased allelochemical exudation in response to exudates of germinated E. crus-galli seeds or lepidimoide, an uronic acid derivative exuded from E. crus-galli seeds. These results imply that allelopathic rice seedlings can sense certain allelochemicals released by E. crus-galli into the soil, and respond by increased production of allelochemicals inhibitory to E. crus-galli. This study suggests that rice residues of both allelopathic and non-allelopathic varieties release similar concentrations and types of allelochemicals to inhibit successive plants. In contrast, living rice plants of certain allelopathic varieties appear to be able to detect the presence of interspecific neighbors and respond by increased allelochemicals.

No abstract

To seek for high-performance small molecule donor materials used in heterojunction solar cell, six acceptor-donor-acceptor small molecules based on naphtho[2,3-b:6,7-b']dithiophene (NDT) units with different acceptor units were designed and characterized using density functional theory and time-dependent density functional theory. Their geometries, electronic structures, photophysical, and charge transport properties have been scrutinized comparing with the reported donor material NDT(TDPP)2 (TDPP  =  thiophene-capped diketopyrrolopyrrole). The open circuit voltage (V(oc)), energetic driving force(ΔE(L-L)), and exciton binding energy (E(b)) were also provided to give an elementary understanding on their cell performance. The results reveal that the frontier molecular orbitals of 3-7 match well with the acceptor material PC61 BM, and compounds 3-5 were found to exhibit the comparable performances to 1 and show promising potential in organic solar cells. In particular, comparing with 1, system 7 with naphthobisthiadiazole acceptor unit displays broader absorption spectrum, higher V(oc), lower E(b), and similar carrier mobility. An in-depth insight into the nature of the involved excited states based on transition density matrix and charge density difference indicates that all S1 states are mainly intramolecular charge transfer states with the charge transfer from central NDT unit to bilateral acceptor units, and also imply that the exciton of 7 can be dissociated easily due to its large extent of the charge transfer. In a word, 7 maybe superior to 1 and may act as a promising donor candidate for organic solar cell.

Perylene diimide (PDI) and its derivatives hold great promise, since they are undeniably considered as an important family of organic n-type semiconductors with both high carrier mobilities and air stabilities comparable to p-type ones, although they traditionally stand out as a class of highperformance dyes and pigments. In this feature article, we summarize the influences of substituents on different positions (imide, ortho, bay) of PDI on their electronic and morphological (packing) properties, which are in close connection with the ability for carrier transport. Then representative molecular packing motifs for PDIs are also classified, with an emphasis on the intricate interplay of intermolecular interactions, packing motifs and electron transport properties of perylene imide related carrier transport materials from a theoretical point of view, towards paving the way for boosting and improving the electron transport mobilities and air stabilities of PDIs-based materials.

No abstract