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1. Eliminating nonradiative decay in Cu(I) emitters: >99% quantum efficiency and microsecond lifetime

   https://doi.org/10.1126/science.aav2865  

   Hamze, Rasha ; Peltier, Jesse L. ; Sylvinson, Daniel ; Jung, Moonchul ; Cardenas, Jose ; Haiges, Ralf ; Soleilhavoup, Michele ; Jazzar, Rodolphe ; Djurovich, Peter I. ; Bertrand, Guy ; et al ( February 2019 , Science)

   Luminescent complexes of heavy metals such as iridium, platinum, and ruthenium play an important role in photocatalysis and energy conversion applications as well as organic light-emitting diodes (OLEDs). Achieving comparable performance from more–earth-abundant copper requires overcoming the weak spin-orbit coupling of the light metal as well as limiting the high reorganization energies typical in copper(I) [Cu(I)] complexes. Here we report that two-coordinate Cu(I) complexes with redox active ligands in coplanar conformation manifest suppressed nonradiative decay, reduced structural reorganization, and sufficient orbital overlap for efficient charge transfer. We achieve photoluminescence efficiencies >99% and microsecond lifetimes, which lead to an efficient blue-emitting OLED. Photophysical analysis and simulations reveal a temperature-dependent interplay between emissive singlet and triplet charge-transfer states and amide-localized triplet states.
2. Copper( i ) and silver( i ) chemistry of vinyltrifluoroborate supported by a bis(pyrazolyl)methane ligand

   https://doi.org/10.1039/d1dt00974e  

   Zacharias, Adway O. ; Mao, James X. ; Nam, Kwangho ; Dias, H. V. ( June 2021 , Dalton Transactions)

   Although unsaturated organotrifluoroborates are common synthons in metal–organic chemistry, their transition metal complexes have received little attention. [CH 2 (3,5-(CH 3 ) 2 Pz) 2 ]Cu(CH 2 CHBF 3 ), (SIPr)Cu(MeCN)(CH 2 CHBF 3 ) and [CH 2 (3,5-(CH 3 ) 2 Pz) 2 ]Ag(CH 2 CHBF 3 ) represent rare, isolable molecules featuring a vinyltrifluoroborate ligand on coinage metals. The X-ray crystal structures show the presence of three-coordinate metal sites in these complexes. The vinyltrifluoroborate group binds asymmetrically to the metal site in [CH 2 (3,5-(CH 3 ) 2 Pz) 2 ]M(CH 2 CHBF 3 ) (M = Cu, Ag) with relatively closer M–C(H) 2 distances. The computed structures of [CH 2 (3,5-(CH 3 ) 2 Pz) 2 ]M(CH 2 CHBF 3 ) and M(CH 2 CHBF 3 ), however, have shorter M–C(H)BF 3 distances than M–C(H) 2 . These molecules feature various inter- or intra-molecular contacts involving fluorine of the BF 3 group, possibly affecting these M–C distances. The binding energies of [CH 2 CHBF 3 ] − to Cu + , Ag + and Au + have been calculated at the wB97XD/def2-TZVP level of theory, in the presence and absence of the supporting ligand CH 2 (3,5-(CHmore »3 ) 2 Pz) 2 . The calculation shows that Au + has the strongest binding to the [CH 2 CHBF 3 ] − ligand, followed by Cu + and Ag + , irrespective of the presence of the supporting ligand. However, in all three metals, the supporting ligand weakens the binding of olefin to the metal. The same trends were also found from the analysis of the σ-donation and π-backbonding interactions between the metal fragment and the π and π* orbitals of [CH 2 CHBF 3 ] − .« less
3. Coinage metal metallacycles involving a fluorinated 3,5-diarylpyrazolate

   https://doi.org/10.1039/d0nj03744c  

   Lakhi, Jaspreet S. ; Patterson, Monika R. ; Dias, H. V. ( September 2020 , New Journal of Chemistry)

   Copper( i ) and silver( i ) pyrazolate complexes {[3,5-(3,5-(CF 3 ) 2 Ph) 2 Pz]Cu} 3 and {[3,5-(3,5-(CF 3 ) 2 Ph) 2 Pz]Ag} 3 have been synthesized using the fluorinated 3,5-(diaryl)pyrazole 3,5-(3,5-(CF 3 ) 2 Ph) 2 PzH and copper( i ) oxide and silver( i ) oxide, respectively. The gold( i ) analog was obtained from a reaction between Au(THT)Cl and [3,5-(3,5-(CF 3 ) 2 Ph) 2 Pz]H/NaH. The X-ray crystal structures show that the coinage metal complexes {[3,5-(3,5-(CF 3 ) 2 Ph) 2 Pz]M} 3 (M = Cu, Ag, Au) are trinuclear in the solid state. They feature distorted nine-membered M 3 N 6 metallacyclic cores. The M–N distances follow Cu < Au < Ag, which is the trend expected from covalent radii of the corresponding coinage metal ions. The 3,5-(3,5-(CF 3 ) 2 Ph) 2 PzH forms hydrogen bonded trimers in the solid state that are further organized by π-stacking between aryl rings. Solid samples of {[3,5-(3,5-(CF 3 ) 2 Ph) 2 Pz]M} 3 display blue photoluminescence. The copper complex {[3,5-(3,5-(CF 3 ) 2 Ph) 2 Pz]Cu} 3 is an excellent catalyst for mediating azide–alkyne cycloaddition chemistry.
4. Ultrafast spectroscopy of biliverdin dimethyl ester in solution: pathways of excited-state depopulation

   https://doi.org/10.1039/D0CP02971H  

   Liu, Yangyi ; Chen, Zhuang ; Wang, Xueli ; Cao, Simin ; Xu, Jianhua ; Jimenez, Ralph ; Chen, Jinquan ( September 2020 , Physical Chemistry Chemical Physics)

   Biliverdin is a bile pigment that has a very low fluorescence quantum yield in solution, but serves as a chromophore in far-red fluorescent proteins being developed for bio-imaging. In this work, excited-state dynamics of biliverdin dimethyl ether (BVE) in solvents were investigated using femtosecond (fs) and picosecond (ps) time-resolved absorption and fluorescence spectroscopy. This study is the first fs timescale investigation of BVE in solvents, and therefore revealed numerous dynamics that were not resolved in previous, 200 ps time resolution measurements. Viscosity- and isotope-dependent experiments were performed to identify the contributions of isomerization and proton transfer to the excited-state dynamics. In aprotic solvents, a ∼2 ps non-radiative decay accounts for 95% of the excited-state population loss. In addition, a minor ∼30 ps emissive decay pathway is likely associated with an incomplete isomerization process around the C15C16 double bond that results in a flip of the D-ring. In protic solvents, the dynamics are more complex due to hydrogen bond interactions between solute and solvent. In this case, the ∼2 ps decay pathway is a minor channel (15%), whereas ∼70% of the excited-state population decays through an 800 fs emissive pathway. The ∼30 ps timescale associated with isomerization is also observed inmore »protic solvents. The most significant difference in protic solvents is the presence of a >300 ps timescale in which BVE can decay through an emissive state, in parallel with excited-state proton transfer to the solvent. Interestingly, a small fraction of a luminous species, which we designate lumin-BVE (LBVE), is present in protic solvents.« less
5. Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

   https://doi.org/10.1039/D2QI00443G  

   Arras, Janet ; Ugarte Trejo, Omar ; Bhuvanesh, Nattamai ; McMillen, Colin D. ; Stollenz, Michael ( July 2022 , Inorganic Chemistry Frontiers)

   A flexible polydentate bis(amidine) ligand LH 2 , LH 2 = {CH 2 NH( t Bu)CN-2-(6-MePy)} 2 , operates as a molecular lock for various coinage metal fragments and forms the dinuclear complexes [LH 2 (MCl) 2 ], M = Cu (1), Au (2), the coordination polymer [{(LH 2 ) 2 (py) 2 (AgCl) 3 }(py) 3 ] n (3), and the dimesityl-digold complex [LH 2 (AuMes) 2 ] (4) by formal insertion of MR fragments (M = Cu, Ag, Au; R = Cl, Mes) into the N–H⋯N hydrogen bonds of LH 2 in yields of 43–95%. Complexes 1, 2, and 4 adopt C 2 -symmetrical structures in the solid state featuring two interconnected 11-membered rings that are locked by two intramolecular N–H⋯R–M hydrogen bonds. QTAIM analyses of the computational geometry-optimized structures 1a, 2a, and 4a reveal 13, 11, and 22 additional bond critical points, respectively, all of which are related to weak intramolecular attractive interactions, predominantly representing dispersion forces, contributing to the conformational stabilization of the C 2 -symmetrical stereoisomers in the solid state. Variable-temperature 1 H NMR spectroscopy in combination with DFT calculations indicate a dynamic conformational interconversion between two C 2 -symmetrical ground state structures in solutionmore »(Δ G ‡c = 11.1–13.8 kcal mol −1 ), which is accompanied by the formation of an intermediate possessing C i symmetry that retains the hydrogen bonds.« less