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David Cordes

University of St Andrews, Chemistry, X-Ray Crystallographer

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Papers by David Cordes

Reducing Efficiency Roll‐Off in Multi‐Resonant Thermally Activated Delayed Fluorescent OLEDs through Modulation of the Energy of the T2 State

Advanced Optical Materials

The S1 state and high‐lying triplet excited states (ΔES1Tn) offer insight into clarifying the mec... more The S1 state and high‐lying triplet excited states (ΔES1Tn) offer insight into clarifying the mechanism of efficiency roll‐off of organic light‐emitting diodes (OLEDs). However, experimental detection of the ΔES1Tn is challenging due to Kasha's rule. Here, two emitters, PhCz‐O‐DiKTa and PhCz‐DiKTa, showing multi‐resonant thermally activated delayed fluorescence (MR‐TADF) are reported. By modulating the conjugation between the MR‐TADF DiKTa emissive center and donor substituent, emission directly from the T2 state is for the first time observed in MR‐TADF emitters. Single crystal and reduced density gradient analyses reveal the origin of the reduced observed concentration‐quenching results from weak CH···π and slipped π···π stacking interactions, which suppress nonradiative transitions. Theoretical and photophysical investigations reveal that the ΔES1T2 difference influences the reverse intersystem crossing rate. The OLEDs employing PhCz‐O‐DiKTa and PhCz‐DiKTa as emitters show ma...

Donor Influence on the Optoelectronic Properties of N‐Substituted Tetraphenylimidazole Derivatives

ChemistrySelect

Bulky Iridium NHC Complexes for Bright, Efficient Deep‐Blue OLEDs

Advanced Optical Materials

Four new deep‐blue‐emitting iridium(III) NHC complexes containing sterically demanding ligands ar... more Four new deep‐blue‐emitting iridium(III) NHC complexes containing sterically demanding ligands are synthesized. The four complexes show bright, deep‐blue emission, with emission maxima between 420 and 427 nm in both acetonitrile solution and 30 wt% doped films in TSPO1; the two meridional isomers showing photoluminescence quantum yields, ΦPL, in doped films of 80% and 89%. The two meridional isomers are used to assess the impact of emitters containing bulky, sterically demanding ligands on the performance of organic light‐emitting diodes (OLEDs). OLEDs employing a stepped doping profile with mer‐Ir(tfpi_tmBn)3 as the emitter produce the highest performing devices in this study, with these devices exhibiting deep‐blue [λEL = 429 nm, CIE = (0.16, 0.08)] emission and a maximum external quantum efficiency (EQEmax) of 14.9%, which decreases to 11.7% at 100 cd m−2. The performance of the OLEDs shows very good efficiencies and moderate efficiency roll‐offs in comparison to reported phospho...

Phospholane‐Phosphite Ligands for Rh Catalyzed Enantioselective Conjugate Addition: Unusually Reactive Catalysts for Challenging Couplings

European Journal of Organic Chemistry

The use of Rh catalysts derived from a phospholane‐phosphite ligand were found to be more product... more The use of Rh catalysts derived from a phospholane‐phosphite ligand were found to be more productive than the classic rhodium/BINAP system in enantioselective conjugate additions. These catalysts enable the use of lower amounts of aryl boronic acid in an asymmetric arylation reaction that required an impractical excess of nucleophile. This catalyst was also found to enable the coupling of a poorly reactive Michael acceptor, N‐CBz‐2‐3‐dehydro‐4‐piperidone, or the coupling of poorly reactive 2‐furyl boronic acids at ambient or near temperatures.

Nitric oxide and the Kagome lattice

Acta Crystallographica, May 26, 2017

Kagome lattices derived from 5-substituted isophthalic acids (I, below) have been used as gas sto... more Kagome lattices derived from 5-substituted isophthalic acids (I, below) have been used as gas storage materials for CO and NO. 1 The NO storage capacity of six previously unreported Kagome frameworks of composition Cu(Rip)(H 2 O) (R = Me, MeO, EtO, n PrO, n BuO or i BuO) has been investigated. Unsurprisingly, the length of the substituent alkyl or alkoxy chain was found to influence the NO release capacity of these materials, however the shorter substituent chain derivatives displayed the highest surface area and the lowest NO release capacity. In situ dehydration studies on single crystals of Cu(EtOip)(H 2 O) and Cu( n PrOip)(H 2 O) were conducted and revealed that Cu(EtOip)(H 2 O) undergoes a single-crystal-to-single-crystal transformation upon evacuation at room temperature. These 6 Cu(Rip)(H 2 O) materials have also been investigated for catalytic conversion of NO 2 -to NO.

A single crystal study of CPO-27 and UTSA-74 for nitric oxide storage and release

CrystEngComm, 2019

Single crystal CPO-27-Mg, -Zn and its structural isomer UTSA-74 have been prepared through use of... more Single crystal CPO-27-Mg, -Zn and its structural isomer UTSA-74 have been prepared through use of acid modulators; salicylic acid and benzoic acid, respectively. Salicylic acid directed the synthesis of CPO-27-Mg/Zn whereas benzoic acid the synthesis of UTSA-74. Through "in-house" SCXRD, DMF was seen to bind to the Zn 2+ and water to the Mg 2+ metal sites in CPO-27-M. Although the synthesis conditions were analogous for UTSA-74, DMF is too large to bind due to the proximity of the binding sites. A dissolutionrecrystallisation transformation was examined from UTSA-74 to CPO-27-Zn. The release of nitric oxide was measured for each material.

Room-Temperature Multiple Phosphorescence from Functionalized Corannulenes: Temperature Sensing and Afterglow Organic Light-Emitting Diode

Corannulene-derived materials have been extensively explored in energy storage and solar cells, b... more Corannulene-derived materials have been extensively explored in energy storage and solar cells, but, however, are rarely documented as emitters in light-emitting sensors and organic light-emitting diodes (OLEDs), due to low exciton utilization. Here, we report a family of multi-donor and acceptor (multi-D-A) motifs, TCzPhCor, TDMACPhCor, and TPXZPhCor, using corannulene as the acceptor and carbazole (Cz), 9,10-dihydro-9,10-dimethylacridine (DMAC), and phenoxazine (PXZ) as the donor, respectively. By decorating corannulene with different donors, multiple phosphorescence is realized. Theoretical and photophysical investigations reveal that TCzPhCor shows room-temperature phosphorescence (RTP) from the lowest-lying T1; however, for TDMACPhCor, dual RTP originating from a higher-lying T1 (T1 H ) and a lower-lying T1 (T1 L ) can be observed, while for TPXZPhCor, T1 Hdominated RTP occurs resulting from a stabilized high-energy T1 geometry. Benefiting from the hightemperature sensitivity of TPXZPhCor, high color-resolution temperature sensing is achieved. Besides, due to degenerate S1 and T1 H states of TPXZPhCor, the first corannulene-based solutionprocessed afterglow organic light-emitting diodes (OLEDs) is investigated. The afterglow OLED with TPXZPhCor shows a maximum external quantum efficiency (EQEmax) and a luminance (Lmax) of 3.3% and 5167 cd m -2 , respectively, which is one of the most efficient afterglow RTP OLEDs reported to date.

Janus All‐ <i>Cis</i> 2,3,4,5,6‐Pentafluorocyclohexyl Building Blocks Applied to Medicinal Chemistry and Bioactives Discovery Chemistry

Chemistry: A European Journal, Oct 6, 2021

Monoalkylated derivatives of the unusually polar all-cis 2,3,4,5,6-pentafluorocyclohexyl (Janus f... more Monoalkylated derivatives of the unusually polar all-cis 2,3,4,5,6-pentafluorocyclohexyl (Janus face) motif are prepared starting from an aryl hydrogenation of 2,3,4,5,6pentafluorophenylacetate methyl ester 15. The method used Zeng's Rh(CAAC) carbene catalyst 4 in the hydrogenation following the protocol developed by Glorius. The resultant Janus pentafluorocyclohexylacetate methyl ester 16 was converted to the corresponding alcohol 18, aldehyde 13, bromide 29 and azide 14 through functional group manipulations, and some of these building blocks were used in Ugimulticomponent and Cu-catalysed click reactions. NBoc protected pentafluoroarylphenylalanine methyl ester 35 was also subject to an aryl hydrogenation, and then deprotection to generate the Janus face β-pentafluorocyclohexyl-alanine amino acid 15, which was incorporated into representative members of an emerging class of candidate antiviral compounds. Log P measurements demonstrate that the all-cis 2,3,4,5,6-pentafluorocyclohexyl ring system is more polar than a phenyl ring. In overview the paper introduces new building blocks containing this Janus ring and demonstrates their progression to molecules typically used in bioactives discovery programmes.

Highly Efficient Green and Red Narrowband Emissive Organic Light‐Emitting Diodes Employing Multi‐Resonant Thermally Activated Delayed Fluorescence Emitters**

Angewandte Chemie, Nov 23, 2022

Herein, we demonstrate how judicious selection of the donor decorating a central multi-resonant t... more Herein, we demonstrate how judicious selection of the donor decorating a central multi-resonant thermally activated delayed fluorescence (MR-TADF) core based on DiKTa can lead to very high-performance OLEDs. By decorating the DiKTa core with triphenylamine (TPA) and diphenylamine (DPA), 3TPA-DiKTa and 3DPA-DiKTa exhibit bright, narrowband green and red emission in doped films, respectively. The OLEDs based on these emitters showed record-high performance for this family of emitters with maximum external quantum efficiencies (EQE max ) of 30.8 % for 3TPA-DiKTa at λ EL of 551 nm and 16.7 % for 3DPA-DiKTa at λ EL = 613 nm. The efficiency roll-off in the OLEDs was improved significantly by using 4CzIPN as an assistant dopant in hyperfluorescence (HF) devices. The outstanding device performance has been attributed to preferential horizontal orientation of the transition dipole moments of 3TPA-DiKTa and 3DPA-DiKTa.

Synthesis and crystallographic characterisation of Mg(H 2 dhtp)(H 2 O) 5 ·H 2 O

Inorganic Chemistry Communications, Mar 1, 2016

Coordination polymers and metal-organic frameworks (MOFs) are currently of much interest as gas s... more Coordination polymers and metal-organic frameworks (MOFs) are currently of much interest as gas storage and release materials. One series that has received particular attention is the CPO-27-M (M = Mg,[3] Mn,[4] Fe, Co, [6] Ni [7] or Cu ) or M-MOF-74 (M = Zn [9]) family of materials, due to their high stability to solvent loss, comparatively large pore sizes, and ability to maintain structural integrity upon removal of coordinated solvent molecules. The desolvation of this family of compounds generates metal centres with vacant coordination sites, onto which gas adsorbents such as NO,[11] CO,[12] CO 2 ,[13,14] H 2 S, H 2 and C 2 H 2 may be bound. The CPO-27-Mg structure has particularly good properties for the adsorption of CO 2. The excellent gas adsorption and gas storage properties of CPO-27 MOFs, has led to a rise in interest in the details of their synthesis. A particular goal of these studies is to understand the conditions required to get consistent crystallisation of the target materials and has to minimise potential impurity phases.[18] For example, it is known that, under solvothermal conditions, increasing the pH of the CPO-27-M (M = Mg [3] or Mn [4]) reaction mixture affords a separate, non-porous coordination framework of composition M(H 2 dhtp)(H 2 O) 2 (M = Mg [3] or Mn ) that the authors denote as CPO-26-M. A recent study on the effect of pH on the one-pot reflux synthesis of CPO-27-M describes attempts to prepare CPO-27-Mg using a 2:1 ratio of NaOH:H 4 dhtp, however they report that no solid product could be obtained from this reaction system.[20] Herein we report the synthesis of a crystalline material of composition Mg(H 2 dhtp)(H 2 O) 5 •H 2 O that may be obtained by lowering the amount of NaOH in reaction mixtures that is normally used to prepare CPO-27-Mg by the reflux method. All reagents were obtained from commercial sources and were used without further purification. A solution of Mg(NO 3 ) 2 •6H 2 O (11.4 g, 44.4 mmol) in water (49 mL) and ethanol (24 mL) was added dropwise to a stirred solution of 2,5-dihydroxyterephthalic acid (3.83 g, 19.3 mmol) in aqueous sodium hydroxide (0.5 M, 77.4 mL, 38.7 mmol) over a period of four minutes. The resulting solution was heated to reflux for 24 hours. The solution was cooled to room temperature and an initial yellow solid collected via filtration, washed with hot ethanol and allowed to dry overnight yielding a yellow powder (CPO-27-Mg, 0.846 g, 2.0 mmol, 10%). The brown mother liquor was allowed to stand at room temperature for a further 3 days, over which time brown crystals (4.145 g, 12.6 mmol, 65% yield) formed as the solvent slowly evaporated. Elemental Analysis

Bipyridine‐Containing Host Materials for High Performance Yellow Thermally Activated Delayed Fluorescence‐Based Organic Light Emitting Diodes with Very Low Efficiency Roll‐Off

Advanced Optical Materials, Nov 21, 2019

Two bipolar host materials 3-CBPy and 4-mCBPy are reported. These hosts are structural analogs of... more Two bipolar host materials 3-CBPy and 4-mCBPy are reported. These hosts are structural analogs of the common host materials CBP and mCBP wherein the phenyl rings have been replaced with pyridines. The two materials possess deep HOMO and shallow LUMO levels along with sufficiently high energy S1 and T1 states that make them suitable hosts for yellow emitters in electroluminescent devices. Yellow-emitting thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) were fabricated using 2,4,6-tris(4-(10H-phenoxazin-10-yl)phenyl)-1,3,5-triazine (tri-PXZ-TRZ) as the dopant emitter with either 3-CBPy or 4-mCBPy employed as the host. Their device performance was compared to analogous devices using CBP and mCBP as host materials. The pyridine-containing host devices showed markedly improved external quantum efficiencies (EQE) and decreased roll-off. The 7 wt% tri-PXZ-TRZ-doped device exhibited very low turn-on voltage (2.5 V for both 3-CBPy and 4-mCBPy) along with maximum external quantum efficiencies (EQEmax) reaching 15.6% (for 3-CBPy) and 19.4% (for 4-mCBPy). The device using 4-mCBPy also exhibited very low efficiency roll-off with an EQE of 16.0% at a luminance of 10,000 cd m -2 .

Fluorine containing cyclopropanes: synthesis of aryl substituted all-<i>cis</i> 1,2,3-trifluorocyclopropanes, a facially polar motif

Chemical Communications, 2019

Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.

Enhanced thermally activated delayed fluorescence through bridge modification in sulfone-based emitters employed in deep blue organic light-emitting diodes

Journal of Materials Chemistry C, 2019

Two thermally activated delayed fluorescence (TADF) emitters bearing a new dipyridyl sulfone core... more Two thermally activated delayed fluorescence (TADF) emitters bearing a new dipyridyl sulfone core as the electron-accepting unit and di-tert-butyl carbazoles as electron-donating units are reported. The two emitters, pDTCz-2DPyS and pDTCz-3DPyS, differ in the regiochemistry of the substitution about the pyridine rings [pDTCz-2DPyS = 9,9'-(sulfonylbis(pyridine-6,3diyl))bis(3,6-di-tert-butyl-9H-carbazole); pDTCz-3DPyS = 9,9'-(sulfonylbis(pyridine-5,2-diyl))bis( ,6-di-tert-butyl-9Hcarbazole)]. Both compounds show blue emission in the range of 450-465 nm, which is in line with theoretical calculations. They have very similar singlet-triplet energy (DEST) gaps (DEST = 0.22 eV and 0.21 eV for pDTCz-3DPyS and pDTCz-2DPyS, respectively). pDTCz-2DPyS has a much larger proportion of delayed emission (26.2%) than pDTCz-3DPyS (1.2%)]. The two compounds show comparable photoluminescence quantum yields of 60% in 2,8bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) doped films. The performance of organic light-emitting diodes (OLEDs) depends on the host used. The maximum external quantum efficiency (EQE) in the PPT host of pDTCz-3DPyS is 7.0%, whilst for pDTCz-2DPyS it is 12.4%. High performance is obtained for both materials when bis[2-(diphenylphosphino)phenyl] ether oxide (DPEPO) is used as the host, with a maximum EQE of 13.4% for pDTCz-3DPyS and 11.4% for pDTCz-2DPyS. In addition, pDTCz-3DPyS shows pure blue electroluminescence with CIE color coordinates of (0.15, 0.12) compared to pDTCz-2DPyS with coordinates of (0.15, 0.19).

Improving Processability and Efficiency of Resonant TADF Emitters: A Design Strategy

Advanced Optical Materials, Dec 3, 2019

Tuning the Emission and Exciton Utilization Mechanisms of Pyrazine-Based Multi-Carbazole Emitters and their use in Organic Light-Emitting Diodes

Thermally activated delayed fluorescence (TADF) and hot excitons are two distinct exciton harvest... more Thermally activated delayed fluorescence (TADF) and hot excitons are two distinct exciton harvesting mechanisms that can lead to 100% internal quantum efficiency in organic light-emitting diodes (OLEDs). Herein, we show that with judicious molecular engineering, the resulting structurally similar compounds emit via distinct photophysical mechanisms, which has a direct consequence on the OLED efficiency. When the pyrazine core is substituted with four carbazoles, the molecule 4CzPyz shows TADF in doped PPT film, with ΦPL of 75%, ΔEST of 0.23 eV and τd of 150 µs. The device based on 4CzPyz emits in the sky-blue (λEL = 486 nm) with an EQEmax of 24.1%. When one carbazole is replaced by an ortho-biphenyl, the ΔEST of 3CzBPz increases to 0.29 eV, the ΦPL decreases to 56%, and the TADF character is largely suppressed in the PPT film. However, a RISC process between higher-lying triplet excited states and the S1 state is hypothesized to be operational, supported by a combined photophysical and DFT study, to rationalize how the device with 3CzBPz shows an EQEmax of 9.6% (λEL = 464 nm), reflecting that greater than 86% of the excitons are converted into light in the OLED. When two ortho-biphenyl groups are connected to the pyrazine core, the ΔEST of 2CzBPz is further increased to 0.34 eV while the ΦPL is reduced to 45% in the PPT film. The DFT and photophysical studies indicate that 2CzBPz should act as a traditional blue

Janus faced fluorocyclohexanes for supramolecular assembly: synthesis and solid state structures of equatorial mono-, di- and tri alkylated cyclohexanes and with tri-axial C–F bonds to impart polarity

Chemical Communications, 2022

Concise and general synthesis protocols are reported to generate all-syn mono-, di-and tri-alkyla... more Concise and general synthesis protocols are reported to generate all-syn mono-, di-and tri-alkylated cyclohexanes where a single fluorine is located on the remaining carbons of the ring. The alkyl groups are positioned to lie equatorially and to have triaxial C-F bonds imparting polarity to these ring systems. Intermolecular electrostatic interactions in the solid-state structure of the trialkylated systems are explored and the resultant supramolecular order opens up prospects for design in soft materials.

Highly Efficient Green &amp; Red Narrowband Emissive Organic Light-Emitting Diodes Employing Multi-Resonant Thermally Activated Delayed Fluorescence Emitters

Herein, we demonstrate how judicious selection of donor decorating a central multi-resonant therm... more Herein, we demonstrate how judicious selection of donor decorating a central multi-resonant thermally activated delayed fluorescence (MR-TADF) core based on quinolino[3,2,1de]acridine-5,9-dione (DiKTa) can lead to very high-performance organic light-emitting diodes (OLEDs). Decorating the DiKTa core with triphenylamine (TPA) and diphenylamine (DPA) in 3TPA-DiKTa and 3DPA-DiKTa resulted in compounds showing bright, narrowband green/red emission in doped films, respectively. The OLEDs based on these emitters showed excellent performance with record-high maximum external quantum efficiencies (EQEmax) for this family of emitters, with a EQEmax of 30.8% for the device with 3TPA-DiKTa (lEL = 551 nm) and 16.7% for the device with 3DPA-DiKTa (lEL = 613 nm). The outstanding device performance with 3TPA-DikTa was attributed to preferential horizontal orientation of the transition dipole moment, with anisotropy factor (a) of 0.189. These results demonstrate that the careful selection of the substituents in MR-TADF emitter can tune the color of OLEDs and significantly enhance device performance.

Synthesis and characterization of novel organic heteroatom compounds from reaction of Woollins' reagent with various organic substrates

Phosphorus Sulfur and Silicon and The Related Elements, Mar 3, 2016

Exciton efficiency beyond the spin statistical limit in organic light emitting diodes based on anthracene derivatives

Journal of Materials Chemistry C, 2020

We report two donor-acceptor (D-A) materials based on a cyanoanthracene acceptor paired with diph... more We report two donor-acceptor (D-A) materials based on a cyanoanthracene acceptor paired with diphenylamine (DPAAnCN) and carbazole (CzAnCN) donor moieties. These compounds show hybrid locally excited (LE) charge-transfer (CT) excited states (HLCT), which we demonstrated through a combined photophysical and computational study. Vacuumdeposited organic light emitting diodes (OLEDs) using these HLCT emitters exhibit maximum external quantum efficiencies (EQE max ) close to 6%, with impressive exciton utilization efficiency (Φ s ) of >50%, far exceeding the spin statistic limit of 25%. We rule out triplet-triplet annihilation and thermally activated delayed fluorescence as triplet harvesting mechanisms

Progressive Polytypism and Bandgap Tuning in Azetidinium Lead Halide Perovskites

Inorganic Chemistry, Jul 28, 2021

Mixed halide azetidinium lead perovskites AzPbBr3-xXx (X = Cl or I) were obtained by mechanosynth... more Mixed halide azetidinium lead perovskites AzPbBr3-xXx (X = Cl or I) were obtained by mechanosynthesis. With varying halide composition from Cl -to Br -to I -; the chloride and bromide analogs both form in the hexagonal 6H polytype while the iodide adopts the 9R polytype. An intermediate 4H polytype is observed for mixed Br/I compositions. Overall, the structure progresses from 6H to 4H to 9R perovskite polytype with varying halide composition. Rietveld refinement of the powder X-ray diffraction patterns revealed a linear variation in unit cell volume as a function of the average radius of the anion, which is not only observed within the solid solution of each polytype (according to Vegard's law) but extends uniformly across all three polytypes. This is correlated with a progressive (linear) tuning of the bandgap from 3.43 to 2.00 eV. Regardless of halide, the family of azetidinium halide perovskite polytypes are highly stable, with no discernible change in properties over more than 6 months under ambient conditions.