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1.
Nanoscale ; 2020 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-32902546

RESUMO

We report the synthesis and the single-molecule transport properties of three new oligo(phenyleneethynylene) (OPE3) derivatives possessing terminal dihydrobenzo[b]thiophene (DHBT) anchoring groups and various core substituents (phenylene, 2,5-dimethoxyphenylene and 9,10-anthracenyl). Their electronic conductance and their Seebeck coefficient have been determined using scanning tunneling microscopy-based break junction (STM-BJ) experiments between gold electrodes. The transport properties of the molecular junctions have been modelled using DFT-based computational methods which reveal a specific binding of the sulfur atom of the DHBT anchor to the electrodes. The experimentally determined Seebeck coefficient varies between -7.9 and -11.4 µV K-1 in the series and the negative sign is consistent with charge transport through the LUMO levels of the molecules.

2.
Chempluschem ; 85(8): 1905-1911, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32845079

RESUMO

Detonation-produced nanodiamond, both as a powder (with adsorbed water) and especially when suspended in an aqueous colloid, can support the growth (both aerobic and anaerobic) of bacteria and fungi. These were isolated and identified by microbiological methods, optical and electron microscopy, as species of Penicillium, Purpureocillium, Beaveria, Trichoderma and Aspergillus genera. The C : N molar ratio of the developing fibers (comprising fungal mycelia with attached bacteria and entrapped nanodiamond) decreased from 25 to 11 between the 1st and 10th week of incubation (cf. 40 in initial nanodiamond, 4.6 typical for bacteria and 8.3 for fungi), and from 4 to <1 after the 12th week, as the lysis of microorganisms releases carbon as CO2 and nitrogen as NH4 + or NO3 - . The nitrogen content of the colloid increased by an order of magnitude and more, due to fixation of N2 by nanodiamond under ambient conditions.The process requires water but not necessarily oxygen present.

3.
Dalton Trans ; 49(7): 2190-2208, 2020 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-32003389

RESUMO

Five new neutral heteroleptic iridium(iii) complexes IrL2(pic) (2-6) based on the archetypical blue emitter FIrpic have been synthesised. The cyclometallating ligands L are derived from 2-(2,6-F2-3-pyridyl)-4-mesitylpyridine (7), 2-(3-cyano-2,6-F2-phenyl)-4-mesitylpyridine (8), 2-(2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (9), 2-(2,6-F2-3-pyridyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (10) and 2-(3-cyano-2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (11) for complexes 2, 3, 4, 5 and 6, respectively. The carbazole-functionalised ligands 9-11 show weak thermally activated delayed fluorescence (TADF) in solution. Complexes 5 and 6 reveal dual emission in polar solvents. A broad charge transfer (CT) band appears and increases in intensity relative to the higher energy emission band as solvent polarity is increased. The dual emission occurs when the energy of the ligand 3CT state is comparable to that of the 3MLCT state of the complex, resulting in fast interconversion between the two. Assignment of the ligand TADF and dual emission properties is supported by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) calculations. Phosphorescent organic light emitting devices (PhOLEDs) have been fabricated using these complexes as sky-blue emitters, and their performance is compared to devices using FIrpic and the previously reported complex IrL2(pic) 1 (L from the 2-(2,6-F2-phenyl)-4-mesitylpyridine ligand). For identical device structures, the device containing the carbazole complex 4 performs best out of the seven complexes. The dual emission observed in solution for complexes 5 and 6 is not observed in their devices.

4.
Angew Chem Int Ed Engl ; 59(2): 882-889, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31714641

RESUMO

As the field of molecular-scale electronics matures and the prospect of devices incorporating molecular wires becomes more feasible, it is necessary to progress from the simple anchor groups used in fundamental conductance studies to more elaborate anchors designed with device stability in mind. This study presents a series of oligo(phenylene-ethynylene) wires with one tetrapodal anchor and a phenyl or pyridyl head group. The new anchors are designed to bind strongly to gold surfaces without disrupting the conductance pathway of the wires. Conductive probe atomic force microscopy (cAFM) was used to determine the conductance of self-assembled monolayers (SAMs) of the wires in Au-SAM-Pt and Au-SAM-graphene junctions, from which the conductance per molecule was derived. For tolane-type wires, mean conductances per molecule of up to 10-4.37  G0 (Pt) and 10-3.78  G0 (graphene) were measured, despite limited electronic coupling to the Au electrode, demonstrating the potential of this approach. Computational studies of the surface binding geometry and transport properties rationalise and support the experimental results.

6.
Molecules ; 24(22)2019 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-31744074

RESUMO

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 different from those previously reported in the literature.


Assuntos
Cobre/química , Nitrosação , Compostos Organometálicos/química , Compostos Heterocíclicos/química , Ligantes , Modelos Moleculares , Estrutura Molecular
7.
Chem Commun (Camb) ; 55(94): 14115-14118, 2019 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-31697292

RESUMO

The enantiomers of [EuL3]·3Cl, an analogue of Eu:BPEPC with a lowered energy excitation wavelength, serve as effective reference complexes for the calibration of circularly polarised luminescence (CPL) spectrometers.

8.
ACS Omega ; 4(5): 8731-8738, 2019 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-31459962

RESUMO

The present article deals with an one-to-one structure-property correspondence of a dinuclear iron complex, [Dipic(H2O)FeOH]2·H2O (1) (Dipic = pyridine-2,6-dicarboxylic acid). Variable-temperature X-ray single-crystal structural analysis confirms a phase transition of complex 1 to complex 2 ([Dipic(H2O)FeOH]2) at 120 °C. Further, single-crystal-to-single-crystal (SCSC) transformation was monitored by temperature-dependent single crystal X-ray diffraction, powder X-ray diffraction, time-dependent Fourier-transform infrared spectroscopy, and differential scanning calorimetry. SCSC transformation brings the change in space group of single crystal. Complex 1 crystallizes in the C2/c space group, whereas complex 2 crystallizes in the Pi̅ space group. SCSC transformation brings the change in packing diagram as well. Complex 1 shows two-dimensional network through H-bonding, whereas the packing diagram of complex 2 shows a zigzag-like arrangement. Phase transformation not only fetches structural changes but also in the magnetic properties. Difference in Fe-O-Fe bond angles of two complexes creates notable variation in their antiferromagnetic interactions with adjacent metal centers.

9.
ACS Appl Mater Interfaces ; 11(30): 27125-27133, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31314484

RESUMO

New thermally activated delayed fluorescence (TADF) blue emitter molecules based on the known donor-acceptor-donor (D-A-D)-type TADF molecule, 2,7-bis(9,9-dimethylacridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2), are reported. The motivation for the present investigation is via the use of rational molecular design, based on DDMA-TXO2, to elevate the organic light emitting diode (OLED) performance and obtain deeper blue color coordinates. To achieve this goal, the strength of the donor (D) unit and acceptor (A) units have been tuned with methyl substituents. The methyl functionality on the acceptor was also expected to modulate the D-A torsion angle in order to obtain a blue shift in the electroluminescence. The effect of regioisomeric structures has also been investigated. Herein, we report the photophysical, electrochemical, and single-crystal X-ray crystallography data to assist with the successful OLED design. The methyl substituents on the DDMA-TXO2 framework have profound effects on the photophysics and color coordinates of the emitters. The weak electron-donating methyl groups alter the redox properties of the D and A units and consequently affect the singlet and triplet levels but not the energy gap (ΔEST). By systematically manipulating all of the aforementioned factors, devices have been obtained with acceptor-substituted III with a maximum external quantum efficiency of 22.6% and Commission Internationale de l'Éclairage coordinates of (0.15, 0.18) at 1000 cd m-2.

10.
Angew Chem Int Ed Engl ; 58(30): 10290-10294, 2019 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-31140711

RESUMO

In two closely related series of eight-coordinate lanthanide complexes, a switch in the sign of the dominant ligand field parameter and striking variations in the sign, amplitude and orientation of the main component of the magnetic susceptibility tensor as the Ln3+ ion is permuted conspire to mask modest changes in NMR paramagnetic shifts, but are evident in Yb EPR and Eu emission spectra.

11.
J Phys Chem C Nanomater Interfaces ; 123(17): 11109-11117, 2019 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-31080540

RESUMO

We expose significant changes in the emission color of carbazole-based thermally activated delayed fluorescence (TADF) emitters that arise from 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 electroluminescence. The dimer species is sensitive to the sample preparation method, and its enduring presence contributes to the widely reported concentration-mediated red shift in the photoluminescence and electroluminescence of evaporated thin films. This discovery has implications on the usability of these, and similar, molecules for OLEDs and explains disparate electroluminescence spectra presented in the literature for these compounds. The dimerization-controlled changes observed in the TADF process and photoluminescence efficiency mean that careful consideration of dimer states is imperative in the design of future TADF emitters and the interpretation of previously reported studies of carbazole-based TADF materials.

12.
J Org Chem ; 84(7): 3801-3816, 2019 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-30912439

RESUMO

Thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) are known to occur in organic D-A-D and D-A systems where the donor group contains the phenothiazine unit and the acceptor is dibenzothiophene- S, S-dioxide. This study reports the synthesis and characterization of one new D-A and four new D-A-D systems with methoxy groups on the phenothiazine to examine their effect on emission properties in the zeonex matrix. X-ray analysis and highly specialized NMR techniques were used to characterize asymmetric methoxy-substituted derivative 3b, which is chiral at N because of an extremely high flipping barrier at the phenothiazine N atom. Based on hybrid-density functional theory computations, the methoxy substituents tune the relative stabilities of the axial conformers with respect to equatorial conformers of the phenothiazine units, depending on their substitution position. This conformational effect significantly influences both TADF and RTP contributions compared to the parent D-A-D system. It is also demonstrated that the equatorial forms of D-A-D and D-A systems in zeonex exhibit TADF. Additionally, the methoxy groups promote luminescence in D-A-D systems where only axial conformers exist. This work reveals further design opportunities for more efficient TADF and RTP molecules.

13.
Chemistry ; 25(24): 6212-6225, 2019 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-30861590

RESUMO

A zinc-selective probe based on a set of rare earth complexes of a modified DO3A macrocyclic ligand incorporating a tris-pyridylamine (TPA) moiety has been structurally characterised in solution and in the solid-state. One pyridine group possesses a tert-butyl substituent to serve as an NMR reporter group. The mono-capped square-antiprismatic Dy complex has a long bond (2.83 Å) to an apical N atom (pKa 5.70 Eu) and binds to one water molecule on zinc binding. Zinc binding is reversible and involves all of the exocyclic ligand N donors; it is signalled by large (ratiometric) changes in Eu emission intensity, and by dramatic changes in the size (>50 ppm) and sign of the chemical shift of the paramagnetically shifted tBu resonances in Tb, Dy and Tm complexes. Slow trans-metallation was observed, leading to formation of an unusual di-zinc species in which one zinc ion is seven-coordinate and the other is six-coordinate.

14.
Chemistry ; 25(16): 4017-4024, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30680824

RESUMO

To study pnictogen bonding involving bismuth, flexible accordion-like molecular complexes of the composition [P(C6 H4 -o-CH2 SCH3 )3 BiX3 ], (X=Cl, Br, I) have been synthesised and characterised. The strength of the weak and mainly electrostatic interaction between the Bi and P centres strongly depends on the character of the halogen substituent on bismuth, which is confirmed by single-crystal X-ray diffraction analyses, DFT and ab initio computations. Significantly, 209 Bi-31 P through-space coupling (J=2560 Hz) is observed in solid-state 31 P NMR spectra, which is so far unprecedented in the literature, delivering direct information on the magnitude of this pnictogen interaction.

15.
J Org Chem ; 83(23): 14431-14442, 2018 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-30376712

RESUMO

The synthesis of 1-methylphenoxazine via CO2-directed lithiation chemistry is reported. This electron donor was coupled with 2,8-dibromodibenzothiophene- S, S-dioxide with Buchwald-Hartwig chemistry to give a new donor-acceptor-donor charge-transfer fluorescent molecule 1b. X-ray crystal structures and calculations show that the phenoxazinyl groups are coplanar and equatorial (eq) to the acceptor plane in nonmethylated 1a but are pyramidal and axial (ax) in 1b. The bond rotation energy barriers between donor and acceptor groups for 1a and 1b are only 0.13 and 0.19 eV, respectively, from hybrid-DFT computations at the CAM-B3LYP/6-31G(d) level. Many possible conformers are present in solutions and in zeonex. In zeonex, the methyl groups in 1b shift the emission band 0.13 eV higher in energy compared to 1a. Excited state eq-eq and ax-ax geometries were identified with DFT calculations with charge transfer (CT) emission assigned as 1CT(eq) and 1CT(ax) dominating. The lower energy 1CT(eq) contributes to thermally activated delayed fluorescence, whereas the higher energy 1CT(ax) does not. Phenothiazine analogues 2a and 2b also have major fluorescence emissions assigned as 1CT(eq) and 1CT(ax), respectively. 2a and 2b have substantial room temperature phosphorescence (RTP), whereas 1a and 1b do not, highlighting the importance of the sulfur atom in 2a and 2b to obtain RTP emission.

16.
Dalton Trans ; 47(46): 16524-16533, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30411748

RESUMO

While a number of highly emissive dinuclear Ir(iii) complexes have been reported, they have generally been restricted to structures based on 2-phenylpyridine (Hppy) cyclometalates. We now present a series of new hydrazide-bridged diiridium complexes (5-8) which incorporate bulky 1,2-diarylimidazole cyclometalating ligands in the place of Hppy. Complexes 6-8 are strongly emissive when doped into poly(methyl methacrylate) (PMMA), displaying the highest PLQYs yet reported for ppy-free diiridium emitters (ΦPL = 47-55 ± 10%). Notably, complex 8 has an emission peak at 452 nm and CIExy colour coordinates in the sky-blue region (0.18, 0.27), which is competitive with state-of-the-art monoiridium analogues. X-ray crystallography and solution-state 19F NMR spectra reveal the presence of rigidifying intramolecular π-π interactions for complexes 6-8, which explains their improved photophysical performance compared to 5 which does not have these interactions. Structure-property relationships are further rationalised through density functional theory (DFT) and cyclic voltammetry (CV) data. All the complexes studied in this work display aggregation induced phosphorescent emission (AIPE). This series of compounds increases the structural diversity of highly luminescent dinuclear Ir(iii) complexes to include luminophoric ligands that are not restricted to Hppy-type fragments. The colour range accessible to AIPE-active diiridum complexes has also been substantially broadened.

17.
Angew Chem Int Ed Engl ; 57(50): 16407-16411, 2018 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-30339314

RESUMO

Chemical modification of phenothiazine-benzophenone derivatives tunes the emission behavior from triplet states by selecting the geometry of the intramolecular charge transfer (ICT) state. A fundamental principle of planar ICT (PICT) and twisted ICT (TICT) is demonstrated to obtain selectively either room temperature phosphorescence (RTP) or thermally activated delayed fluorescence (TADF), respectively. Time-resolved spectroscopy and time-dependent density functional theory (TD-DFT) investigations on polymorphic single crystals demonstrate the roles of PICT and TICT states in the underlying photophysics. This has resulted in a RTP molecule OPM, where the triplet states contribute with 89 % of the luminescence, and an isomeric TADF molecule OMP, where the triplet states contribute with 95 % of the luminescence.

18.
J Org Chem ; 83(19): 12320-12326, 2018 10 05.
Artigo em Inglês | MEDLINE | ID: mdl-30247912

RESUMO

Triply fused 1,3-diazepine derivatives have been obtained by acidic reduction of rotationally locked and sterically hindered nitro groups in the presence of an aldehyde or ketone. The nitro groups are sited on adjacent rings of a dicyanodibenzothiophene-5,5-dioxide, which also displays fully reversible two-electron-accepting behavior. The synthesis, crystallographically determined molecular structures, and aspects of the electronic properties of these new molecules are presented.

19.
Inorg Chem ; 57(20): 12836-12849, 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-30256097

RESUMO

The application of a chiral auxiliary ligand to control the diastereoselectivity in the synthesis of a cyclometalated iridium(III) complex is presented. The diastereomeric iridium(III) complexes 1a and 1b are reported, in which a phenoxyoxazoline auxiliary ligand incorporates a chiral center functionalized with a pendant pentafluorophenyl group. The diastereomers were readily separated, and their structural, electrochemical and photophysical properties are discussed. Solution-state NMR data and X-ray crystal structures establish that the pentafluorophenyl group engages in intramolecular π-π interactions. The X-ray analysis reveals that the two diastereomers display very different modes of intramolecular stacking. The variable-temperature 19F NMR data indicate that rotation of the pendant pentafluorophenyl rings in 1b and 1a is a temperature-dependent process and that there is a smaller energy barrier to rotation in 1b in comparison to 1a. This correlates with variable-temperature photoluminescence data, which show that upon heating the integrated emission intensity is reduced substantially more for 1b than for 1a, which is ascribed to the enhanced rotation in 1b, providing a more easily populated nonradiative pathway in comparison to 1a. These experimental data are supported by computational calculations. Phosphorescent organic light-emitting devices (PhOLEDs) using 1a as the dopant complex give blue-green emission with a high maximum external quantum efficiency (EQEmax) of 25.8% (at ca. 270 cd m-2) and with a low efficiency roll-off to 24.9% at 1000 cd m-2. Our results extend the scope of ligand design for cyclometalated iridium complexes which possess interesting structural and emission properties.

20.
Chem Commun (Camb) ; 54(61): 8486-8489, 2018 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-30003200

RESUMO

Crystallographic, emission and NMR studies of a series of C3-symmetric, nine-coordinate substituted pyridyl triazacyclononane Yb(iii) and Eu(iii) complexes reveal the impact of local solvation and ligand dipolar polarisability on ligand field strength, leading to dramatic variations in pseudocontact NMR shifts and emission spectral profiles, giving new guidance for responsive NMR and spectral probe design.

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