Torsional angle dependence and switching of inner sphere reorganisation energies for electron and hole charge transfer processes involving phenyl substituted diketopyrrolopyrroles; a density functional study

This document is the Accepted Manuscript version of the following article: Jesus Calvo-Castro, Callum J. McHugh, Andrew J. McLean, ‘Torsional angle dependence and switching of inner sphere reorganisation energies for electron and hole transfer processes involving phenyl substituted diketopyrrolopyrroles; a density functional study’, Dyes and Pigments, Vol. 113, pp. 609-617, February 2015. The Version of Record is available online at doi: https://doi.org/10.1016/j.dyepig.2014.09.031. Published by Elsevier.Determination of inner sphere reorganisation energies is important in the development of organic charge mediating materials and electron transfer reactions. In this study, hole and electron inner sphere reorganisation energies, lambda(h) and lambda(e) respectively, have been computed for the first time for a series of structurally related diketopyrrolopyrrole (DPP) molecular motifs. Inner sphere reorganisation energies for self-exchange electron transfer reactions are calculated as being lower than those associated hole transfer processes in model planar phenyl and thiophenyl substituted DPP systems. It is found that lambda(e) lambda(h).Peer reviewedFinal Accepted Versio

Excimer formation by steric twisting in carbazole and triphenylamine-based host materials

This paper presents a detailed spectroscopic investigation of luminescence properties of 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP) and N,N,N’,N’-tetraphenylbenzidine (TAD) in solutions and neat films. These compounds are compared to their derivatives CDBP and TDAD that contain methyl groups in the 2 and 2’ position of the biphenyl core. We find that whereas steric twisting in CDBP and TDAD leads to a high triplet energy of about 3.0 and 3.1 eV, respectively, these compounds also tend to form triplet excimers in a neat film, in contrast to CBP and TAD. By comparison with N-phenylcarbazole (NPC) and triphenylamine (TPA), on which these compounds are based, as well as with the rigid spiro analogs to CBP and TAD we show that the reduced excimer formation in CBP and TAD can be attributed to a localization of the excitation onto the central biphenyl part of the molecule.We acknowledge support from the Federal Ministry of Education and Research (BMBF) through the project ‘Trip-Q’, the German Science Foundation (DFG) through the Research and Training Group GRK 1640 and the UK Engineering and Physical Sciences Research Council (grant number EP/G060738/1).This is the final published version. It first appeared at http://pubs.acs.org/doi/abs/10.1021/jp512772j

Orientation dependent molecular electrostatics drives efficient charge generation in homojunction organic solar cells

Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-accepting (A) materials to split excitons into charges. However, the use of D-A blends intrinsically limits the photovoltage and introduces morphological instability. Here, we demonstrate that polycrystalline films of chemically identical molecules offer a promising alternative and show that photoexcitation of α-sexithiophene (α-6T) films results in efficient charge generation. This leads to α-6T based homojunction organic solar cells with an external quantum efficiency reaching up to 44% and an open-circuit voltage of 1.61 V. Morphological, photoemission, and modelling studies show that boundaries between α-6T crystalline domains with different orientations generate an electrostatic landscape with an interfacial energy offset of 0.4 eV, which promotes the formation of hybridised exciton/charge-transfer states at the interface, dissociating efficiently into free charges. Our findings open new avenues for organic solar cell design where material energetics are tuned through molecular electrostatic engineering and mesoscale structural control

Cellular dissection of psoriasis for transcriptome analyses and the post-GWAS era

Abstract Background Genome-scale studies of psoriasis have been used to identify genes of potential relevance to disease mechanisms. For many identified genes, however, the cell type mediating disease activity is uncertain, which has limited our ability to design gene functional studies based on genomic findings. Methods We identified differentially expressed genes (DEGs) with altered expression in psoriasis lesions (n = 216 patients), as well as candidate genes near susceptibility loci from psoriasis GWAS studies. These gene sets were characterized based upon their expression across 10 cell types present in psoriasis lesions. Susceptibility-associated variation at intergenic (non-coding) loci was evaluated to identify sites of allele-specific transcription factor binding. Results Half of DEGs showed highest expression in skin cells, although the dominant cell type differed between psoriasis-increased DEGs (keratinocytes, 35%) and psoriasis-decreased DEGs (fibroblasts, 33%). In contrast, psoriasis GWAS candidates tended to have highest expression in immune cells (71%), with a significant fraction showing maximal expression in neutrophils (24%, P < 0.001). By identifying candidate cell types for genes near susceptibility loci, we could identify and prioritize SNPs at which susceptibility variants are predicted to influence transcription factor binding. This led to the identification of potentially causal (non-coding) SNPs for which susceptibility variants influence binding of AP-1, NF-κB, IRF1, STAT3 and STAT4. Conclusions These findings underscore the role of innate immunity in psoriasis and highlight neutrophils as a cell type linked with pathogenetic mechanisms. Assignment of candidate cell types to genes emerging from GWAS studies provides a first step towards functional analysis, and we have proposed an approach for generating hypotheses to explain GWAS hits at intergenic loci.http://deepblue.lib.umich.edu/bitstream/2027.42/109537/1/12920_2013_Article_485.pd

Modelling the shear strength and dilatancy of dry sand in triaxial compression tests

It is well known that density, pressure and soil fabric influence the mechanical behaviour of silica sand. This paper shows how they may be included in a simple constitutive model in which a single set of parameters is sufficient to cover a wide range of initial states. The analysis highlights the different contributions to the mechanical response as well as the calibration procedure. © 2015 Taylor & Francis Group

Shear strength and dilatancy of unsaturated silica sand in triaxial compression tests

It is well known that partial saturation enhances the critical state strength of sand but little is known on the enhancement of the peak strength. A triaxial compression test programme was carried out on a silica sand called in which specimens were tested at different initial densities, water contents and at low stresses. It was found that the enhancement of the peak strength was more significant than the enhancement of the critical state strength. This paper presents a stress-dilatancy analysis in which the enhancement of the peak strength may be explained by the enhancements of the critical state strength and the maximum dilatancy rate. © 2015 Taylor & Francis Group, London