Aggregation‐induced emission (AIE) is a beneficial strategy for generating highly effective solid‐state molecular luminescence without suffering losses in quantum yield. However, the majority of reported AIE‐active molecules exhibit only strong fluorescence, which is not ideal for electrical excitation in organic light‐emitting diodes (OLEDs). By introducing various substituent groups onto the biscarbazole compound, a series of molecular materials with aggregation‐induced phosphorescence (AIP) is designed, which exhibits two distinctly different phosphorescence bands and an absolute solid‐state room‐temperature phosphorescence quantum yield up to 64%. Taking advantage of the AIE feature, the AIP molecules are fabricated into OLEDs as a homogeneous light‐emitting layer, which allows for relatively small efficiency roll‐off and shows an external electroluminescence quantum yield of up to 5.8%, more than the theoretical limit for purely fluorescent OLED devices. The design showcases a promising strategy for the production of cost‐effective and highly efficient OLED technology.

The nature of the electronic ground state of the tetramethyleneethane (TME) diradical has proven to be a challenge for both experiment and theory. Through the use of quantum Monte Carlo (QMC) methods and multireference perturbation theory, we demonstrate that the lowest singlet state of TME is energetically lower than the lowest triplet state at all values of the torsional angle between the allyl subunits. Moreover, we find that the maximum in the potential energy curve for the singlet state occurs at a torsional angle near 45°, in contrast to previous calculations that placed the planar structure of the singlet state as the highest in energy. We also show that the CASPT2 method when used with a sufficiently large reference space and a sufficiently flexible basis set gives potential energy curves very close to those from the QMC calculations. Our calculations have converged the singlet-triplet gap of TME as a function of methodology and basis set. These results provide insight into the level of theory required to properly model diradicals, in particular disjoint diradicals, and provide guidelines for future studies on more complicated diradical systems.

b S Supporting Information T he formate ion, HCO 2 h , is ubiquitous in aqueous chemistry and biology, and its structural properties have been extensively catalogued over many decades using a wide variety of spectroscopic techniques. 1À5 There is renewed interest, however, in this ion's intrinsic behavior due to its increasingly important role in the chain of events leading to activation of CO 2 to transportable fuels, for example, by reductive addition of hydride. 6,7 The electronic and vibrational level structures of the isolated ion were accurately calculated in 2007 by Botschwina and co-workers, 8 and two aspects of the potential curve describing CH dissociation are nonintuitive. First, the ∼18700 cm À1 bond dissociation energy 5,9,10 is much lower than is typical for CH bonds of closed-shell singlets (e.g., 43370 cm À1 for HCN) 11 and second, the shape of the CH potential does not conform to a Morse form, instead exhibiting a sharp change in slope around a bond length of 2 Å where it flattens toward the low dissociation asymptote. Both these features are consistent with the 2003 experimental observation of the CH stretching (ν CH ) fundamental of formate in a Ne matrix 12 at 2456 cm À1 , which is far below the typical 2950 cm À1 value found for aliphatic hydrocarbons. 13 More interestingly, this value is also much lower than that long known for HCO 2 h in aqueous media (2803 cm À1 ) 4 and in crystals (2830 cm À1 ). 14 In this paper, we explore the mechanism underlying the unusual shape of the CH potential, the low intrinsic ν CH frequency, and its anomalously large solvent dependence. This is accomplished by analyzing the vibrational

This study develops synthetic strategies for N,N-trans and N,N-cis Re(O)(LO-N)2Cl complexes and investigates the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate reduction activities of the corresponding [Re(O)(LO-N)2](+) cations. The 2-(2'-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2'-hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both Re(O)(hoz)2Cl and Re(O)(htz)2Cl and one heteroleptic N,N-trans Re(O)(hoz)(htz)Cl. Selection of hoz/htz ligands determines the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re(O)(LO-N)2](+) cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s(-1) at 25 °C) and different LO-N movement patterns, as influenced by the coordination sphere of Re (trans/cis), the noncoordinating heteroatom on LO-N ligands (O/S), and the combination of the two LO-N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO4(-) by H2 when the Re(O)(LO-N)2Cl complexes are immobilized onto Pd/C. Findings from this study provide novel synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.

Dual-phosphorescence emission can be realized via chemical conjugation between an n–π* type of luminophore and a π–π* one.

No abstract

Recently, N,N-trans Re(O)(L)X (L = monoanionic N-O chelates; X = Cl or Br prior to being replaced by solvents or alkoxides) complexes have been found to be superior to the corresponding N,N-cis isomers in the catalytic reduction of perchlorate via oxygen atom transfer. However, reported methods for Re(O)(L)X synthesis often yield only the N,N-cis complex or a mixture of trans and cis isomers. This study reports a geometry-inspired ligand design rationale that selectively yields N,N-trans Re(O)(L)Cl complexes. Analysis of the crystal structures revealed that the dihedral angles (DAs) between the two L ligands of N,N-cis Re(O)(L)Cl complexes are less than 90°, whereas the DAs in most N,N-trans complexes are greater than 90°. Variably sized alkyl groups (-Me, -CHPh, and -CHCy) were then introduced to the 2-(2'-hydroxyphenyl)-2-oxazoline (Hhoz) ligand to increase steric hindrance in the N,N-cis structure, and it was found that substituents as small as -Me completely eliminate the formation of N,N-cis isomers. The generality of the relationship between N,N-trans/cis isomerism and DAs is further established from a literature survey of 56 crystal structures of Re(O)(L)X, Re(O)(L)X, and Tc(O)(L)X congeners. Density functional theory calculations support the general strategy of introducing ligand steric hindrance to favor synthesis of N,N-trans Re(O)(L)X and Tc(O)(L)X complexes. This study demonstrates the promise of applying rational ligand design for isomeric control of metal complex structures, providing a path forward for innovations in a number of catalytic, environmental, and biomedical applications.

The (HCOOH)(2) anion, formed by electron attachment to the formic acid dimer (FA(2)), is an archetypal system for exploring the mechanics of the electron-induced proton transfer motif that is purported to occur when neutral nucleic acid base-pairs accommodate an excess electron [K. Aflatooni, G. A. Gallup, and P. D. Burrow, J. Phys. Chem. A 102, 6205 (1998); J. H. Hendricks, S. A. Lyapustina, H. L. de Clercq, J. T. Snodgrass, and K. H. Bowen, J. Chem Phys. 104, 7788 (1996); C. Desfrancois, H. Abdoul-Carime, and J. P. Schermann, ibid. 104, 7792 (1996)]. The FA(2) anion and several of its H∕D isotopologues were isolated in the gas phase and characterized using Ar-tagged vibrational predissociation and electron autodetachment spectroscopies. The photoelectron spectrum of the FA(2) anion was also recorded using velocity-map imaging. The resulting spectroscopic information verifies the equilibrium FA(2)(-) geometry predicted by theory which features a symmetrical, double H-bonded bridge effectively linking together constituents that most closely resemble the formate ion and a dihydroxymethyl radical. The spectroscopic signatures of this ion were analyzed with the aid of calculated anharmonic vibrational band patterns.