I19-Small Molecule Single Crystal Diffraction
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Jessica L.
Andrews
,
Sten O.
Nilsson Lill
,
Stefanie
Freitag-Pohl
,
David C.
Apperley
,
Dmitry
Yufit
,
Andrei S.
Batsanov
,
Matthew T.
Mulvee
,
Katharina
Edkins
,
James F.
Mccabe
,
David J.
Berry
,
Michael R.
Probert
,
Jonathan W.
Steed
Diamond Proposal Number(s):
[11145]
Abstract: This work presents an updated solid-form discovery approach to the polymorphism of the antiarrhythmic drug mexiletine hydrochloride, in which experimental and computational techniques are combined to provide a rigorous characterization of the solid-form landscape of this compound. The resulting solid forms were characterized by powder and single-crystal X-ray diffraction, IR spectroscopy, differential scanning calorimetry, and 13C solid-state NMR. This approach reveals five solid-form types of mexiletine hydrochloride. Forms 1, 2, and 3 are mutually enantiotropically related anhydrous polymorphs, with Form 1 the room temperature stable form, Form 2 the high-temperature form, and Form 3 the thermodynamically stable polymorph between 148 and 167 °C. The final two forms termed Types A and B comprise two large families of isomorphous channel solvates, including a fourth nonsolvated form isostructural to the Type A solvates. We report 11 modifications of each solvate, in which a diverse range of solvents are included in the channels, without changing the fundamental structure of the drug framework. These experimental results go hand-in-hand with computational crystal structure prediction (using the AstraZeneca crystal structure prediction approach), which together suggest that it is unlikely further nonsolvated forms, at least with Z′ = 1, will be discovered under ambient conditions.
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Oct 2021
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Abstract: The synthetic methodology to covalently link donors to form cyclophane-based thermally activated delayed fluorescence (TADF) molecules is presented. These are the first reported examples of TADF cyclophanes with “electronically innocent” bridges between the donor units. Using a phenothiazine-dibenzothiophene-S,S-dioxide donor–acceptor–donor (D–A–D) system, the two phenothiazine (PTZ) donor units were linked by three different strategies: (i) ester condensation, (ii) ether synthesis, and (iii) ring closing metathesis. Detailed X-ray crystallographic, photophysical and computational analyses show that the cyclophane molecular architecture alters the conformational distribution of the PTZ units, while retaining a certain degree of rotational freedom of the intersegmental D–A axes that is crucial for efficient TADF. Despite their different structures, the cyclophanes and their nonbridged precursors have similar photophysical properties since they emit through similar excited states resulting from the presence of the equatorial conformation of their PTZ donor segments. In particular, the axial–axial conformations, known to be detrimental to the TADF process, are suppressed by linking the PTZ units to form a cyclophane. The work establishes a versatile linking strategy that could be used in further functionalization while retaining the excellent photophysical properties of the parent D–A–D system.
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Nov 2020
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[22240]
Open Access
Abstract: A simple protocol yielding ortho-substituted nitrosophenols from phenols is demonstrated,
in the form of copper(II) bis(nitrosophenolato) complexes. The developed methodology was applied
to a range of substrates, confirming the role of the copper in both the formation and protection of the
challenging 1, 2-substitution pattern. Using polymer supported thiourea, the Cu could be stripped
from the complexes and thus enabled the isolation or identification of the uncoordinated ligands
and their decomposition products, in yields generally low in line with the intrinsic high reactivity of
2-nitrosophenols. The product complexes are useful intermediates as demonstrated in revisiting a
formal [4 + 2] cycloaddition with dimethylacetylene dicarboxylate to synthesise bicyclic products in
variable yields, revealing the product has a novel structure di erent from those previously reported
in the literature.
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Nov 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11145]
Abstract: Three new symmetrical donor–acceptor–donor (D–A–D)-type molecules were prepared with phenothiazine (PTZ) as electron donors and 9,9-dimethylthioxanthene (TX) as the electron acceptor. The PTZ groups are attached at different positions on the acceptor core – ortho or meta to the sulfur of TX. The molecules have been characterized by X-ray crystallography, in-depth photophysical studies and theoretical calculations. This series provides new insights into how molecular functionalization and intramolecular charge transfer determines the singlet-triplet gap ΔEST. Two of the molecules have weak D/A decoupling and a relatively large ΔEST of 0.52 eV which prohibits the upconversion of triplet excitons to the singlet state, showing strong room temperature phosphorescence (RTP). When the TX acceptor strength is enhanced by the attachment of benzoyl substituents a very small ΔEST of <0.01 eV is observed. In this case excitons in the triplet state can be efficiently upconverted to the singlet state via reverse intersystem crossing (RISC) resulting in thermally activated delayed fluorescence (TADF). TADF and RTP are unambiguously assigned by distinctive photophysical data, notably a comparison of degassed and aerated luminescence spectra, temperature-dependent time-resolved fluorescence decays and power dependence of the intensity of delayed emission (for the TADF emitter).
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Oct 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11145]
Open Access
Abstract: In this work we successfully developed a strategy for positively influencing the conformation of thermally activated delayed fluorescence (TADF) molecules containing phenothiazine as the electron donor (D) unit, and dibenzothiophene-S,S-dioxide as the acceptor (A), linked in D–A and D–A–D structures. In this strategy the effect of restricted molecular geometry is explored to maximize TADF emission. The presence of bulky substituents in different positions on the donor unit forces the molecules to adopt an axial conformer where the singlet charge transfer state is shifted to higher energy, resulting in the oscillator strength and luminescence efficiency decreasing. With bulky substituents on the acceptor unit, the molecules adopt an equatorial geometry, where the donor and acceptor units are locked in relative near-orthogonal geometry. In this case the individual signatures of the donor and acceptor units are evident in the absorption spectra, demonstrating that the substituent in the acceptor uncouples the electronic linkage between the donor and acceptor more effectively than with donor substitution. In contrast with the axial conformers that show very weak TADF, even with a small singlet triplet gap, molecules with equatorial geometry show stronger oscillator strength and luminescence efficiency and are excellent TADF emitters. Acceptor-substituted molecules 6 and 7 in particular show extremely high TADF efficiency in solution and solid film, even with a singlet–triplet energy gap around 0.2 eV. This extensive study provides important criteria for the design of novel TADF and room temperature phosphorescence (RTP) emitters with optimized geometry.
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May 2019
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I19-Small Molecule Single Crystal Diffraction
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Marc K.
Etherington
,
Nadzeya A.
Kukhta
,
Heather F.
Higginbotham
,
Andrew
Danos
,
Aisha N.
Bismillah
,
David R.
Graves
,
Paul R.
Mcgonigal
,
Nils
Haase
,
Antonia
Morherr
,
Andrei S.
Batsanov
,
Christof
Pflumm
,
Vandana
Bhalla
,
Martin R.
Bryce
,
Andrew P.
Monkman
Diamond Proposal Number(s):
[11145]
Open Access
Abstract: We expose significant changes in emission color of carbazole-based thermally activated delayed fluorescence (TADF) emitters that arise through the presence of persistent dimer states in thin films and organic light-emitting diodes (OLEDs). Direct photoexcitation of this dimer state in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) reveals the significant influence of dimer species on the color purity of its photoluminescence and electrolumines-cence. The dimer species is sensitive to the sample preparation method and its enduring presence contributes to the widely reported concentration-mediated redshift in the photoluminescence and electroluminescence of evaporated thin films. This discovery has significant implications on the usability of these, and similar, molecules for OLEDs and explains disparate electroluminescence spectra presented in the literature for these compounds. The significant dimer-ization-controlled changes observed in the TADF process and photoluminescence efficiency mean that careful consid-eration of dimer states is imperative in the design of future TADF emitters and the interpretation of previously reported studies of carbazole-based TADF materials.
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Apr 2019
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11145]
Abstract: Four new symmetrical donor–acceptor–donor (D–A–D)-type molecules are reported with diphenylamine (DPA) or 10,11-dihydro-5H-dibenz[b,f]azepine (Az) as electron donors and 9,9-dimethylthioxanthene-S,S-dioxide (TXO2) as the electron acceptor. The donors are attached at different positions on the acceptor core: either para or meta to the sulfone unit. This series provides new insights into the effects of chromophore rigidity/flexibility on the efficiency of thermally activated delayed fluorescence (TADF). The molecules have been characterized by X-ray crystallography, by in-depth photophysical studies, and by theoretical calculations. The clear differences observed in the photophysical properties when using DPA or Az as a donor are shown to originate from different geometries of the donor unit which, in turn, influence the geometry of the nitrogen lone pair and the donating strength of the corresponding fragment. Thus, a para-substituted Az derivative demonstrated blue TADF in polar media, while the compounds with more flexible DPA units did not show delayed fluorescence. To obtain deep-blue emitters, weaker donating units are needed. A more flexible donor unit leads to increased local excited state (donor) LE emission and reduced TADF. However, a certain amount of flexibility has to be present to ensure deep-blue TADF.
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Dec 2018
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[11145]
Open Access
Abstract: In contrast to monoiridium complexes, the study of diiridium complexes as dopants in phosphorescent organic light-emitting devices (PhOLEDs) is largely unexplored. We now describe the syntheses, detailed NMR analyses, X-ray crystal structures and optoelectronic properties of the new cyclometalated diiridium complexes 5 and 6 in which the iridium centres are bridged by oxamidato ligands. These complexes contain diastereomers – the meso form (ΔΛ) and the racemic form consisting of two enantiomers (ΔΔ and ΛΛ) – with anti-oxamidato bridges. The precursor μ-dichloro-bridged complex 4 is very weakly emissive in solution, whereas the oxamidato bridged complexes 5 and 6 are highly emissive (ΦPL 73% and 63%) with short excited state lifetimes of τP 0.84 and 1.16 μs, respectively. Cyclic voltammetry studies demonstrate that the oxamidato bridging ligand plays a role in mediating intramolecular interactions between the iridium centres. Density functional theory (DFT) calculations and time dependent-DFT (TD-DFT) calculations provide further insights into the structural, electronic, and photophysical properties of the complexes in their ground and excited states. Phosphorescent organic light-emitting diodes (PhOLEDs) using complexes 5 and 6 as the emissive dopants in a simple architecture using a solution-processed active layer give bright green electroluminescence with remarkably high luminance (Lmax > 25[thin space (1/6-em)]000 cd m−2) for diiridium complexes.
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Jun 2017
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[8682]
Abstract: Bio-isosteric replacement is a frequently used tool in medicinal chemistry. While the pharmacological activity is not influenced by the exchange of substituents, the solid-state characteristics and formation of different crystal forms may well be altered dramatically, jeopardizing the processability and safety of the drug compound. In this study we investigate a series of triphenylimidazole (TPI) derivatives as model compounds with the bio-isosteric exchange of only one halogen position (F, Cl, Br, I). Crystallization from two industrially used solvents (methanol and acetonitrile) reveals solvate formation of all TPIs, for which the basic hydrogen bonded motif does not change. The three-dimensional packing depends on the size of the substituent and changes from fluoro- to chloro- and bromo-substitution but remains the same for the larger iodo-substituent. From acetonitrile, only F-TPI and Cl-TPI form an isomorphic channel solvate, which in both cases desolvates reversibly to an isomorphic crystal form. Due to the halogen atom lining of the channels, bromine and iodine are too large to generate a stable packing. This study illustrates the importance of understanding the influence of bio-isosteric substitution on the solid state, in order to best utilize this common tool.
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Jul 2016
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I19-Small Molecule Single Crystal Diffraction
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Diamond Proposal Number(s):
[6749]
Abstract: The synthesis is reported of a new series of oligo(aryleneethynylene) (OAE) derivatives of up to ca. 6 nm in molecular length (OAE9) using iterative Pd-mediated Sonogashira cross-coupling methodology. The oligo-p-phenyleneethynylene cores of the molecular wires are functionalized at both termini with pyridyl units for attachment to gold leads. The molecular structures determined by single-crystal X-ray analysis are reported for OAE4, OAE5, OAE7, and OAE8a. The charge transport characteristics of derivatives OAE3–OAE9 in single-molecular junctions have been studied using the mechanically controlled break junction technique. The data demonstrate that the junction conductance decreases with increasing molecular length. A transition from coherent transport via tunneling to a hopping mechanism is found for OAE wires longer than ca. 3 nm.
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Nov 2013
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