This version is available at https://strathprints.strath.ac.uk/58791/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. Journal Name ARTICLEThis journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 1 The influence of systematic variation of aryl and N-substitution on predicted charge transport behaviour in a series of crystalline diketopyrrolopyrroles is evaluated. A correct combination of substituents is revealed to maximise those properties which dictate device performance in organic single crystals based upon this structural motif. For electron transport, furan and N-alkyl substitution emerge as optimal molecular design strategies, whilst phenyl structures bearing N-benzyl substituents are shown to offer the most significant promise as highly sought after crystalline hole transport materials. IntroductionIn crystalline charge mediating organic materials, control of molecular solid state aggregation -can exert a dramatic impact on intermolecular electronic properties which define delocalised band transport and localised, thermally activated hopping of charge carriers. [1][2][3][4] Electronic coupling, or charge transfer integrals for hole/electron transport, t h/e , describe the extent of wavefunction overlap and are related to the strength of the -and play a significant role in either description. [5][6][7] Inner-sphere reorganisation energy for holes/e h/e , characterises the change in energy between charged and neutral molecular states, owing to geometrical relaxation of the localised molecular environment and can be detrimental to transport behaviour when charge hopping is predominant. Large E CP , are highly desirable in organic semiconductors to preserve the integrity of crystalline intermolecular interactions involving -Thermally--ing domains can result in considerable variation in t h/e , which can ultimately be detrimental to carrier mobility. Regardless of the mechanism of charge transport involved...