Red Phosphorescence from Benzo[2,1,3]thiadiazoles at Room Temperature

We describe the red phosphorescence exhibited by a class of structurally simple benzo[2,1,3]thiadiazoles at room temperature. The photophysical properties of these molecules in deoxygenated cyclohexane, including their absorption spectra, steady-state photoluminescence and excitation spectra, and phosphorescence lifetimes, are presented. Time-dependent density functional theory calculations were carried out to better understand the electronic excited states of these benzo[2,1,3]thiadiazoles and why they are capable of phosphorescence.National Science Foundation (U.S.) (1122374)United States. Dept. of Energy. Office of Basic Energy Sciences (DE-FG02-07ER46474

Reductive Coupling of CO Templated by Iron Bound to the Tris(pyrrolide)ethane Scaffold

The reactivity of the high-spin (S = 2) [(Mestpe)Fe(THF)][Li(THF)4] (1) complex (Mestpe = tris(mesitylpyrrolide)ethane) with isocyanide and CO substrates is explored. Reaction of 1 with excess tBuNC forms a low-spin (S = 0), six-coordinate iron(II) species with three tBuNC ligands bound to iron, producing a notable tautomerization of one of the pyrrolide units from N- to C-ligation to iron. Reaction of 1 with an atmosphere of CO also produces a new diamagnetic complex, wherein two molecules of CO are consecutively reductively coupled, driven by the two-electron oxidation and fragmentation of the tris(pyrrolide)ethane ligand. The product features a six-coordinate Fe(II) species bound to a dipyrromethene ligand (resulting from oxidative fragmentation of the Mestpe ligand), an oxalyl-imino pyrrole fragment from pyrrole coupling to two molecules of CO. The reactions of 1 with tBuNC and CO provide insight into how tautomerization of the tris(pyrrolide) ligand upon substrate binding initiates the contiguous reductive coupling of CO.Chemistry and Chemical Biolog

Co(III) Imidos Exhibiting Spin Crossover and C–H Bond Activation

The reaction of (^ArL)­Co­(py) with ^<i>t</i>BuN₃ afforded the isolable three-coordinate Co–imido complex (^ArL)­Co­(N^<i>t</i>Bu), which is paramagnetic at room temperature. Variable-temperature (VT) ¹H NMR spectroscopy, VT crystallography, and magnetic susceptibility measurements revealed that (^ArL)­Co­(N^<i>t</i>Bu) undergoes a thermally induced spin crossover from an <i>S</i> = 0 ground state to a quintet (<i>S</i> = 2) state. The reaction of (^ArL)­Co­(py) with mesityl azide yielded an isolable <i>S</i> = 1 terminal imido complex that was converted into the metallacycloindoline (^ArL)­Co­(κ²-NHC₆H₂-2,4-Me₂-6-CH₂) via benzylic C–H activation

Co(III) Imidos Exhibiting Spin Crossover and C–H Bond Activation

The reaction of (^ArL)­Co­(py) with ^<i>t</i>BuN₃ afforded the isolable three-coordinate Co–imido complex (^ArL)­Co­(N^<i>t</i>Bu), which is paramagnetic at room temperature. Variable-temperature (VT) ¹H NMR spectroscopy, VT crystallography, and magnetic susceptibility measurements revealed that (^ArL)­Co­(N^<i>t</i>Bu) undergoes a thermally induced spin crossover from an <i>S</i> = 0 ground state to a quintet (<i>S</i> = 2) state. The reaction of (^ArL)­Co­(py) with mesityl azide yielded an isolable <i>S</i> = 1 terminal imido complex that was converted into the metallacycloindoline (^ArL)­Co­(κ²-NHC₆H₂-2,4-Me₂-6-CH₂) via benzylic C–H activation

Lock-and-Key Exciplexes for Thermally Activated Delayed Fluorescence

We combine synthetic supramolecular chemistry and materials science to develop novel exciplexes for thermally activated delayed fluorescence. Our approach starts from a bowl-shaped acceptor molecule for which we synthesize tailor-made donors that bind in a lock-and-key fashion. The donor design is guided by extensive density functional theory calculations of three independent donor families. The investigation of a large number of custom-synthesized donors allows us to derive empirical relationships for the prediction of the exciplex emission color. Incorporated within organic light-emitting devices, the lock-and-key exciplexes yield external quantum efficiencies of up to 5.4%, with potentially tunable emission color across the blue and green visible spectrum.Air Force Office of Scientific Research (Grant FA9550-18-1-0341)Department of Energy (Grant DE-FG02-07ER46474)NIH (Grant GM112272