Twist and shout: a surprising synergy between aryl and N-substituents defines the computed charge transport properties in a series of crystalline diketopyrrolopyrroles

Abstract

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...

Ground and Excited States of Bis‐4‐Methoxybenzyl‐Substituted Diketopyrrolopyrroles: Spectroscopic and Electrochemical Studies

“…In all molecules the 4MB group is quasi perpendicular to the DPP plane with dihedral angles of 85.8°, 89.5° and 88.7° for ThDPP, OMePhDPP and ThPhDPP respectively. This interesting conformational feature is also seen for benzyl derivatives, and the methoxy substituent does not alter significantly the orientation of the group. In 4MB ThDPP the thiophene rings are arranged in the anti orientation with the sulfur atoms oriented towards the alkyl chain, which is similar to previously reported dialkyated compounds containing this core .…”

“…[11] The planar core of these compounds (Figure 1) consists of a π-conjugated dilactam system which can be substituted with different aromatic groups at the 3-and 6-positions, and with alkyl derivatives as the Nsubstituents. [12,13] Thus, the compounds present a multitude of opportunities for structural and electronic modification via synthetic functionalization, such as end capping of the aromatic sections, [14,15] the addition of conjugated flanking units to extend charge delocalization [16,17] and solubilizing chains of varying polarity at the N position to aid processing. [18] This alkylation of DPP derivatives gives rise to solubility in relatively low polarity organic solvents, [19][20][21] as well as solubility in more polar solvents when heteroatom-containing chains are appended.…”

Exploring structure based charge transport relationships in phenyl diketopyrrolopyrrole single crystals using a 2D π–π dimer model system

“…This contrasts with the significantly larger number of phenyl (77) vs thiophene (28) DPP single crystal structures contained in the Cambridge Structural Database (CSD). Contrary to a popular notion that phenyl-substituted DPPs (PDPPs) are not structurally optimal for OFET applications, 15 we have recently demonstrated that phenyl-based DPP architectures represent a theoretically superior alternative to equivalent thiophene and furan-based systems, 16 particularly in crystalline hole transport environments. Via judicious choice of aryl and Nsubstituents, PDPP single crystal structures can exhibit comparable or even greater charge transfer integrals than rubrene, for which mobilities of 20 cm 2 V -1 s -1 have been reported in the crystalline state.…”

“…We anticipate that PDPP-based architectures may offer a clear potential for the realization of thermally activated reversal of the charge transfer character. PDPP systems are often undervalued as organic semiconductors on account of reduced planarity when compared to thiophene and furan analogues, 16 despite their comparable computed innersphere reorganization energies at torsional angles often observed in crystalline environments. It was therefore of interest to explore the effects of planarity on the intermolecular interactions and charge transfer integrals for fully eclipsed (Δx/Δy of 0.0/0.0 Å) and twodimensional model global minimum (Δx/Δy of 3.3/0.3 Å) dimer pairs by systematically increasing the dihedral angle of the core phenyl rings with respect to the DPP core.…”

“…It should be noted that although other crystal extracted dimer pairs can exhibit large binding energies, such as those with strong H-bonding intermolecular interactions, they do not represent optimal charge transfer propagation channels, on account of their diminished electronic coupling. [8][9][10][11]16 Figure 1. Illustration of long (blue) and short (red) intermonomer displacements in our PDPP dimer model system.…”