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

This document is the Accepted Manuscript version of the following article: Jesus Calvo-Castro, and Callum J. McHugh, ‘Exploring structure based charge transport relationships in phenyl diketopyrrolopyrrole single crystals using a 2D π–π dimer model system’, Journal of Materials Chemistry C, Issue 16, 2017, first published 28 March 2017. The version of record is available online at DOI: http://dx.doi.org/10.1039/C7TC00434F © Royal Society of Chemistry 2017Crystalline phenyl diketopyrrolopyrroles are often overlooked as charge transfer mediating materials in optoelectronic applications. We report an experimentally ratified two dimensional π–π model dimer system dispelling previous misconceptions regarding the potential of these materials as organic semiconductors and that will enable researchers to screen and predict charge transport potential solely on the basis of their single crystal derived π-stacking architectures. In testing our model system versus the available database of phenyl diketopyrrolopyrrole single crystal structures we reveal that these materials are characterised by intrinsically large thermal integrities and in many cases large charge transfer integrals, not solely restricted to dimeric interactions exhibiting close intermonomer arrangements and bearing low torsion of the core phenyl rings. This study will be of significant interest to the increasingly large community engaged in the quest to engineer π-conjugated organic based semiconducting devices and particularly those employing crystalline diketopyrrolopyrroles.Peer reviewe

Understanding the contribution of individual amino acid residues in the binding of psychoactive substances to monoamine transporters

© 2020 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Omega, Vol 5, Iss 28, p.17223–17231, after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsomega.0c01370.The development of point-of-care detection methodologies for biologically relevant analytes that can facilitate rapid and appropriate treatment is at the forefront of current research efforts and interests. Among the various approaches, those exploiting host–guest chemistries where the optoelectronic signals of the chemical sensor can be modulated upon interaction with the target analyte are of particular interest. In aiding their rational development, judicious selection of peripheral functional groups anchored to core motifs with desired properties is critical. Herein, we report an in-depth investigation of the binding of three psychoactive substances, MDAI, mexedrone, and phenibut, to receptors of the monoamine transporters for dopamine, norepinephrine, and serotonin, particularly focusing on the role of individual amino acid residues. We first evaluated the conformational flexibility of the ligands by comparing their experimentally determined crystal structure geometries to those optimized by means of quantum as well as molecular mechanics, observing significant changes in the case of phenibut. Molecular docking studies were employed to identify preferential binding sites by means of calculated docking scores. In all cases, irrespective of the monoamine transporter, psychoactive substances exhibited preferred interaction with the S1 or central site of the proteins, in line with previous studies. However, we observed that experimental trends for their relative potency on the three transporters were only reproduced in the case of mexedrone. Subsequently, to further understand these findings and to pave the way for the rational development of superior chemical sensors for these substances, we computed the individual contributions of each nearest neighbor amino acid residue to the binding to the target analytes. Interestingly, these results are now in agreement with those experimental potency trends. In addition, these observations were in all cases associated with key intermolecular interactions with neighboring residues, such as tyrosine and aspartic acid, in the binding of the ligands to the monoamine transporter for dopamine. As a result, we believe this work will be of interest to those engaged in the rational development of chemical sensors for small molecule analytes as well as to those interested in the use of computational approaches to further understand protein–ligand interactions.Peer reviewe

Impact of substituent effects on the Raman spectra of structurally related N-substituted diketopyrrolopyrroles

This document is the Accepted Manuscript version of the following article: Jesus Calvo-Castro, et al, ‘Impact of substituent effects on the Raman spectra of structurally related N-substituted diketopyrrolopyrroles’, Vibrational Spectroscopy, Vol. 83, pp. 8-16, March 2016, doi: https://doi.org/10.1016/j.vibspec.2015.12.004. This manuscript version is made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.Control over vibrational frequency modes is important in optimising the performance and behaviour of conjugated organic materials employed as charge transfer mediators and optical components in optoelectronic devices. Raman spectroscopy represents a powerful technique that can be employed to determine the structural implications of molecular substitution on photophysical properties in such conjugated organic environments. Herein, we report for the first time, the optimised geometries for a series of eight systematically varied N-substituted diketopyrrolopyrroles as well as their experimental and computed Raman spectra, with special emphasis placed upon their spectral band assignments. Clear out-of-plane structural re-arrangements, including pyramidalisation of the lactam nitrogens arising from intramolecular H-bonding interactions were observed upon N-substitution in the reported systems, leading to significant vibrational frequency shifts for ν(Nsingle bondC) and ν(Cdouble bond; length as m-dashO) modes. In addition, mode scaling factors were determined and found to be comparable with those reported previously, employed using the same density functional. The following study addresses the implications of structural variation on the progression of those intense Raman modes which play a key role in tuning the photophysical properties of N-substituted diketopyrrolopyrrole systems and as such should be of broad interest to those developing functional materials based upon this molecular motifPeer reviewe

A Design-of-Experiments Approach to Developing Thermoresponsive Gelators From Complex Polymer Mixtures

© 2020 Royal Society of Chemistry. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1039/D0ME00093K.This study investigated the effects of additives on the properties of poloxamer (P) 407 thermogels, employing a design-of-experiments (DoE) approach. P407 is a thermoresponsive triblock copolymer that exhibits a solution to gel transition at a critical temperature, typically between 15-25 °C, dependant on polymer concentration. This thermoresponsive gelation has made P407 attractive for many applications including drug delivery, cell culture and tissue engineering. However, the gels formed do not have sufficient strength for some applications where the materials will be exposed to shear, such as topical drug delivery. There have been attempts to improve P407 thermogel properties by the addition of other hydrophilic polymers. However, these studies were limited to a small number of polymers, typically in binary mixtures, exploring one variable at a time. In this study, a DoE approach was carried out using a two-level model exploring P407, P188, poly(vinyl alcohol), poly(ethylene glycol), and poly(acrylic acid) as variables, including an exploration of molecular weight of the latter three additives. The variables were given two different levels (concentrations) to generate a total of 16 training formulations. The thermoresponsive gelation of these 16 formulations was studied by rheometry and predictive models built for gel strength (G’) and gelation temperature (Tgel) responses. The model was able to predict the thermoresponsive gelation of complex octonary test blends, significantly streamlining formulation development processes relative to current methods. The model was then able to identify novel thermoresponsive gel formulations with 20 % improved gel strength compared to a standard 20 % P407 solution, which may be used as temperature-responsive materials for advanced healthcare applications.Peer reviewe

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

This is the Accepted Manuscript version of an article accepted for publication in CyrstEngComm. Under embargo. Embargo end date: 22 November 2017. Jesus Calvo-Castrp, Sebastian Macza, Connor Thomson, Graeme Morris, Alan R. Kennedy and Callum J. McHugh, ‘Twist and shout: a surprising synergy between aryl and N-substituents defines the computed charge transport properties in a series of crystalline diketopyrrolopyrroles’, CrysEngComm, Vol 18(48): 9382-9390, first published online 22 November 2016, available at doi: 10.1039/C6CE02261HThe 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.Peer reviewedFinal Accepted Versio

Impact of systematic structural variation on the energetics of π−π stacking interactions and associated computed charge transfer integrals of crystalline diketopyrrolopyrroles

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Crystal Growth & Design, copyright © 2014 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see DOI: https://doi.org/10.1021/cg5010165, or ACS Articles on Request http://pubs.acs.org/page/policy/articlesonrequest/index.html/Control over solid state structure is critical for effective performance in optoelectronic devices bearing π-conjugated charge mediating organic materials. A series of five structurally related N-benzyl-substituted diketopyrrolopyrroles (DPPs) differing ... Novel crystal structures demonstrating long molecular axis, slipped, π−π cofacial stacking motifs and associated semiconductor bands in a series of N-benzylated diketopyrrolopyrroles are reported. Through variation of just 2 atoms from 60, clear crystal structure/(computed) charge transport activity interdependency is observed, with two structures exhibiting hole transport integrals comparable to Rubrene, a highly effective positive charge carrying, organic, crystalline materialPeer reviewedFinal Accepted Versio

Flipped detection of psychoactive substances in complex mixtures using handheld Raman spectroscopy coupled to chemometrics

© 2022 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives. https://creativecommons.org/licenses/by-nc-nd/4.0/New psychoactive substance (NPS) misuse represents a critical social and health problem. Herein, a novel flipped approach is presented for the detection of psychoactive substances in complex mixtures using portable Raman spectroscopy. This consists firstly of evaluating the spectral dissimilarities of an NPS product to its constituent adulterants followed by detection of the NPS by means of key spectral signatures. To demonstrate it, three structurally diverse NPS and four commonly used adulterants were selected. A Design‐of‐Experiments guided approach was employed to determine the composition of simulate street samples, ranging from binary to quinary mixtures of varying concentrations. Spectra were acquired for all mixtures using a portable Raman spectrometer and examined using projection analysis on model systems, developed via principal component analysis using reference materials. For all 21 mixtures investigated, the innovative ‘flipped’ methodology resulted in isolated and unequivocal detection of the NPS. Interestingly, the NPS signatures were consistent across all mixtures investigated and were 1712, 1000, and 777/1022 cm−1 for 5F‐PB‐22, phenibut, and N‐Me‐2‐AI containing samples, respectively. Thus indicating that the developed model systems could be applicable to structural analogs. NPS were detected to concentrations as low as 6.0% w/w. This flipped methodology was benchmarked to the instrument's output algorithms and outperformed these in terms of NPS detection, particularly for low concentration ternary and quinary mixtures. As a result, this study represents a critical change in the conceptualization of novel approaches for the detection of psychoactive substances and further denotes a blueprint for the development of detection methodologies of target analytes in complex mixtures.Peer reviewedFinal Published versio

Intermolecular interactions and energetics in the crystalline π–π stacks and associated model dimer systems of asymmetric halogenated diketopyrrolopyrroles

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Crystal Growth & Design, © 2016 American Chemical Society, after peer review and technical editing by the publisher. To access the final edited and published work see DOI: 10.1021/acs.cgd.5b01656/Four novel structurally analogous asymmetric, halogenated N-benzyl substituted diketopyrrolopyrroles (DPP) have been synthesized, and their crystal structures obtained. All four crystal structures exhibit π–π stacks with very small displacements along their short molecular axes, which based upon our previous studies involving symmetrical DPPs is a characteristic of N-benzyl substitution. Intermolecular interaction energies were computed for extracted crystal π–π dimer pairs by means of M06-2X density functional at the 6-311G(d) level to investigate the most energetically favored position of the halogen atoms in FBDPP and ClBDPP structures. In addition, effective stabilization energies arising from both benzyl and halogen substitution in these derivatives and in BrBDPP and IBDPP π–π dimer pairs were determined in order to probe the impact of these groups on the resulting dimer stability. Effects of the intermonomer displacements along the long molecular axis, which have been shown by us previously to significantly influence wavefunction overlap and effective electronic coupling, were investigated in detail using aligned and anti-aligned model systems of ClDPP and BrDPP. The predictions of these model systems are remarkably consistent with the observed displacements in their crystal derived π–π dimer pair equivalents, offering insight into the effective role of intermolecular contacts in crystal structures involving this molecular motif, particularly with a view toward crystal engineering in these systems. As a result, we believe that this study should be of significant interest to the growing DPP based materials community and in general to those investigating the detailed manner by which substituents can be employed in the supramolecular design of crystalline molecular architectures.Peer reviewedFinal Accepted Versio

True absolute determination of photoluminescence quantum yields by coupling multiwavelength thermal lens and photoluminescence spectroscopies

© Royal Society of Chemistry 2020. This is the accepted manuscript version of an article which has been published in final form at https://dx.doi.org/10.1039/D0CP03794J.Photoluminescence quantum yields denote a critical variable to characterise a fluorophore and its potential performance. Their determination, by means of methodologies employing reference standard materials, innevitably leads to large uncertainties. In response to this, herein we report for the first time an innovative and elegant methodology, whereby the use of neat solvent/reference material required by thermal lens approaches is eliminated by coupling it to photoluminescence spectroscopy, allowing for the discrimination between materials with similar photoluminescence quantum yields. To achieve that, both radiative and non-radiative transitions are simultaneously measured by means of a photoluminescence spectrometer coupled to a multiwavelength thermal lens spectroscopy setup in a mode-mismatched dual-beam configuration, respectively. The absorption factor independent ratio of the thermal lens and photoluminescence signals can then be used to determine the fluorescence quantum yield both accurately and precisely. We validated our reported method by means of rhodamine 6G and further applied in three novel structurally related diketopyrrolopyrrole based materials to, contrary to results obtained by other methods, unveil significant differences in their photoluminescence quantum yields.Peer reviewe

Detection of nitroaromatic and peroxide-based explosives with amine- and phosphine-functionalized diketopyrrolopyrroles

Effective strategies for the detection and identification of explosives are highly desirable. Herein, we illustrate the efficient optoelectronic detection of nitroaromatic and peroxide-based explosives using amine- and phosphine-substituted diketopyrrolopyrroles. Selective quenching and an unprecedented enhancement of thin-film emission in the presence of nitroaromatic vapors are demonstrated via the judicious choice of amine substituents. The modulation of fluorescence emission in each case is shown to be dominated by electronic and thermodynamic effects, the vapor pressure of explosives, and the thin-film morphology. For peroxide detection, we describe an approach exploiting redox-mediated functional group transformation. The rapid oxidation of triphenylphosphine to phosphine oxide with hydrogen peroxide affords a significant increase in fluorescence emission, facilitating the sensitive turn-on detection of an important class of explosives at ppb concentrations