Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells

A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-centred transitions) which are red-shifted on going from X = H to X = I, and a broad metal-to-ligand charge transfer band with λmax in the range 387–395 nm. The ten complexes are yellow emitters in solution and yellow or yellow-orange emitters in the solid-state. For a given N^N ligand, the solution photoluminescence (PL) spectra show no significant change on going from [Cu(N^N)(POP)]+ to [Cu(N^N)(xantphos)]+; introducing the iodo-functionality into the N^N domain leads to a red-shift in λmaxem compared to the complexes with the benchmark N^N ligand 5. In the solid state, [Cu(1)(POP)][PF6] and [Cu(1)(xantphos)][PF6] (fluoro-substituent) exhibit the highest PL quantum yields (74 and 25%, respectively) with values of τ1/2 = 11.1 and 5.8 μs, respectively. Light-emitting electrochemical cells (LECs) with [Cu(N^N)(P^P)][PF6] complexes in the emissive layer have been tested. Using a block-wave pulsed current driving mode, the best performing device employed [Cu(1)(xantphos)]+ and this showed a maximum luminance (Lummax) of 129 cd m−2 and a device lifetime (t1/2) of 54 h; however, the turn-on time (time to reach Lummax) was 4.1 h. Trends in performance data reveal that the introduction of fluoro-groups is beneficial, but that the incorporation of heavier halo-substituents leads to poor devices, probably due to a detrimental effect on charge transport; LECs with the iodo-functionalized N^N ligand 4 failed to show any electroluminescence after 50 h

Self-explaining AI as an alternative to interpretable AI

The ability to explain decisions made by AI systems is highly sought after, especially in domains where human lives are at stake such as medicine or autonomous vehicles. While it is often possible to approximate the input-output relations of deep neural networks with a few human-understandable rules, the discovery of the double descent phenomena suggests that such approximations do not accurately capture the mechanism by which deep neural networks work. Double descent indicates that deep neural networks typically operate by smoothly interpolating between data points rather than by extracting a few high level rules. As a result, neural networks trained on complex real world data are inherently hard to interpret and prone to failure if asked to extrapolate. To show how we might be able to trust AI despite these problems we introduce the concept of self-explaining AI. Self-explaining AIs are capable of providing a human-understandable explanation of each decision along with confidence levels for both the decision and explanation. For this approach to work, it is important that the explanation actually be related to the decision, ideally capturing the mechanism used to arrive at the explanation. Finally, we argue it is important that deep learning based systems include a "warning light" based on techniques from applicability domain analysis to warn the user if a model is asked to extrapolate outside its training distribution. For a video presentation of this talk see https://www.youtube.com/watch?v=Py7PVdcu7WY& .Comment: 10pgs, 2 column forma

Characterizing genomic alterations in cancer by complementary functional associations.

Systematic efforts to sequence the cancer genome have identified large numbers of mutations and copy number alterations in human cancers. However, elucidating the functional consequences of these variants, and their interactions to drive or maintain oncogenic states, remains a challenge in cancer research. We developed REVEALER, a computational method that identifies combinations of mutually exclusive genomic alterations correlated with functional phenotypes, such as the activation or gene dependency of oncogenic pathways or sensitivity to a drug treatment. We used REVEALER to uncover complementary genomic alterations associated with the transcriptional activation of β-catenin and NRF2, MEK-inhibitor sensitivity, and KRAS dependency. REVEALER successfully identified both known and new associations, demonstrating the power of combining functional profiles with extensive characterization of genomic alterations in cancer genomes

Phosphane tuning in heteroleptic [Cu(N^N)(P^P)]+ complexes for light-emitting electrochemical cells

The synthesis and characterization of five [Cu(P^P)(N^N)][PF6] complexes in which P^P = 2,7-bis(tert-butyl)-4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (tBu2xantphos) or the chiral 4,5-bis(mesitylphenylphosphino)-9,9-dimethylxanthene (xantphosMes2) and N^N = 2,2'-bipyridine (bpy), 6-methyl-2,2'-bipyridine (6-Mebpy) or 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me2bpy) are reported. Single crystal structures of four of the compounds confirm that the copper(I) centre is in a distorted tetrahedral environment. In [Cu(xantphosMes2)(6-Mebpy)][PF6], the 6-Mebpy unit is disordered over two equally populated orientations and this disorder parallels a combination of two dynamic processes which we propose for [Cu(xantphosMes2)(N^N)]+ cations in solution. Density functional theory (DFT) calculations reveal that the energy difference between the two conformers observed in the solid-state structure of [Cu(xantphosMes2)(6-Mebpy)][PF6] differ in energy by only 0.28 kcal mol‒1. Upon excitation into the MLCT region (λexc = 365 nm), the [Cu(P^P)(N^N)][PF6] compounds are yellow to orange emitters. Increasing the number of Me groups in the bpy unit shifts the emission to higher energies, and moves the Cu+/Cu2+ oxidation to higher potentials. Photoluminescence quantum yields (PLQYs) of the compounds are low in solution, but in the solid state, PLQYs of up to 59% (for [Cu(tBu2xantphos)(6,6'-Me2bpy)]+) are observed. Greatly increased excited-state lifetimes at low temperature are consistent with the complexes exhibiting thermally activated delayed fluorescence (TADF). This is supported by the small energy difference calculated between the lowest-energy singlet and triplet excited states (0.17-0.25 eV). The compounds were tested in simple bilayer light-emitting electrochemical cells (LECs). The optoelectronic performances of complexes containing xantphosMes2 were generally lower with respect to those with tBu2-xantphos, which led to bright and efficient devices. The best performing LECs were obtained for the complex [Cu(tBu2xantphos)(6,6'-Me2bpy)][PF6] due to the increased steric hindrance at the N^N ligand resulting in higher PLQY

What difference does a thiophene make? Evaluation of a 4,4′-bis(thiophene) functionalised 2,2′-bipyridyl copper(I) complex in a dye-sensitized solar cell

AbstractThe synthesis of a 4,4′-bis(2-thienyl-5-carboxylic acid) functionalised 2,2′-bipyridine ligand and corresponding copper(I) complex is described and its application in a dye-sensitized solar cell (DSSC) is studied. The positioning of the thiophene groups appears favourable from DFT analysis and a best efficiency of 1.41% was obtained with this dye, for a 0.3 cm2 cell area DSSC. Two absorbance bands are observed in the electronic absorption spectrum of the copper(I) complex at 316 nm and 506 nm, with ε values of 50,000 M−1 cm−1 and 9030 M−1 cm−1, respectively. Cyclic voltammetry and electrochemical impedance spectroscopy are also used to provide a detailed analysis of the dye and assess its functionality in a DSSC

Dinuclear [Cu2(N^N)(P^P)2][PF6]2 complexes containing bridging 2,3,5,6-tetra(pyridin-2-yl)pyrazine or 2,4,6-tri(pyridin-2-yl)-1,3,5-triazine ligands

The dinuclear copper(I) complexes [Cu2(1)(POP)2][PF6]2, [Cu2(2)(POP)2][PF6]2, [Cu2(1)(xantphos)2][PF6]2 and [Cu2(2)(xantphos)2][PF6]2 containing bridging 2,3,5,6-tetra(pyridin-2-yl)pyrazine (1) or 2,4,6-tri(pyridin-2-yl)-1,3,5-triazine (2) ligands and the P^P ligands bis(2- (diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) are presented. The single crystal structures of [Cu2(1)(POP)2][PF6]2 and [Cu2(2)(POP)2][PF6]2 confirm that both 1 and 2 act as bis(bidentate) ligands, bridging between two copper(I) centres; in [Cu2(1)(POP)2][PF6]2, two pyridine rings are non-coordinating, and in [Cu2(2)(POP)2][PF6]2, there is one non-coordinating pyridine. In solution and on the NMR timescale at 295 K, the four pyridine rings in coordinated 1 are equivalent; similarly, the three pyridine donors in the [Cu2(2)(P^P)2][PF6]2 complexes are equivalent. The dynamic behaviour of [Cu2(2)(POP)2][PF6]2 and [Cu2(2)(xantphos)2][PF6]2 are investigated using variable temperature 1H NMR spectroscopy. The photophysical properties of the complexes are discussed