Ultrafast Luminescence Detection with Selective Adsorption of Carbon Disulfide in a Gold(I) Metal-Organic Framework.

Although a widely used and important industrial chemical, carbon disulfide (CS) poses a number of hazards due to its volatility and toxicity. As such, the development of multifunctional materials for the selective capture and easy recognition of CS is one of the crucial issues. Herein, we demonstrate completely selective CS adsorption among trials involving HO, alcohols, volatile organic compounds (including thiol derivatives), N, H, O, CH, CO, NO, and CO.

Synthesis of substituent-free dioxadiaza[8]circulene to investigate intermolecular interactions and photophysical properties.

Peripherally unsubstituted dioxadiaza[8]circulene, as the first example of structurally identified pristine hetero[8]circulene, was synthesized by the substituent detachment reactions. The solid-state structures and photophysical properties were analysed to elucidate intermolecular interactions. Herzberg-Teller type emission was considered to explain the optical behavior.

Photoexcitation and One-Electron Reduction Processes of a CO Photoreduction Dyad Catalyst Having a Zinc(II) Porphyrin Photosensitizer.

We have explored the photophysical properties and one-electron reduction process in the dyad photocatalyst for CO photoreduction, , in which the catalyst of -[Re(1,10-phenanthoroline)(CO)Br] is directly connected with the photosensitizer of zinc(II) porphyrin (), using time-resolved infrared spectroscopy, transient absorption spectroscopy, and quantum chemical calculations. We revealed the following photophysical properties: (1) the intersystem crossing occurs with a time constant of ∼20 ps, which is much faster than that of a single unit, and (2) the charge density in the excited singlet and triplet states is mainly localized on , which means that the excited state is assignable to the π-π* transition in . The one-electron reduction by 1,3-dimethyl-2-phenyl-2,3-dihydro-1-benzo[]imidazole occurs via the triplet excited state with the time constant of ∼100 ns and directly from the ground state with the time constant of ∼3 μs.

Chirality in Singlet Fission: Controlling Singlet Fission in Aqueous Nanoparticles of Tetracenedicarboxylic Acid Ion Pairs.

The singlet fission characteristics of aqueous nanoparticles, self-assembled from ion pairs of tetracene dicarboxylic acid and various amines with or without chirality, are thoroughly investigated. The structure of the ammonium molecule, the counterion, is found to play a decisive role in determining the molecular orientation of the ion pairs and its regularity, spectroscopic properties, the strength of the intermolecular coupling between the tetracene chromophores, and the consequent singlet fission process. Using chiral amines has led to the formation of crystalline nanosheets and efficient singlet fission with a triplet quantum yield as high as 133% ±20% and a rate constant of 6.

Fast, efficient, narrowband room-temperature phosphorescence from metal-free 1,2-diketones: rational design and the mechanism.

We report metal-free organic 1,2-diketones that exhibit fast and highly efficient room-temperature phosphorescence (RTP) with high colour purity under various conditions, including solutions. RTP quantum yields reached 38.2% in solution under Ar, 54% in a polymer matrix in air, and 50% in crystalline solids in air.

Room-temperature quantum coherence of entangled multiexcitons in a metal-organic framework.

Singlet fission can generate an exchange-coupled quintet triplet pair state TT, which could lead to the realization of quantum computing and quantum sensing using entangled multiple qubits even at room temperature. However, the observation of the quantum coherence of TT has been limited to cryogenic temperatures, and the fundamental question is what kind of material design will enable its room-temperature quantum coherence. Here, we show that the quantum coherence of singlet fission-derived TT in a chromophore-integrated metal-organic framework can be over hundred nanoseconds at room temperature.

Luminescence mechanism analysis of a TADF molecule showing peculiar thermal behavior.

In recent years, much attention has been paid to the development of thermally activated delayed fluorescence (TADF) materials with short delayed-fluorescence lifetimes to improve the device performances of OLEDs. In principle, by reducing the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) overlap, while the energy difference between S-T (Δ) and activation energy () can be reduced, and the reverse intersystem crossing rate constant () can be accelerated, a decrease in the radiative rate constant happens, necessitating an advanced molecular design. Furthermore, a molecule based on heptazine as a parent skeleton has recently been found to have a peculiar temperature dependence of luminescence decay, suggesting a negative gap (NG) material.

Unprecedented highly efficient photoluminescence in a phosphorescent Ag(I) coordination polymer.

A luminescent three-dimensional coordination polymer (CP) of [Cd(pmd){Ag(CN)}] (1; pmd = pyrimidine) comprising two different coordination modes of Ag ions was synthesised herein. 1 exhibited thermochromic luminescence, accompanied by positive thermal elongation of the Ag⋯Ag distance. Moreover, 1 showed a bright phosphorescence with the highest photoluminescence quantum yield (), approximately 60% at room temperature, among previously reported phosphorescent Ag-based CPs or metal-organic frameworks.

Singlet fission as a polarized spin generator for dynamic nuclear polarization.

Singlet fission (SF), converting a singlet excited state into a spin-correlated triplet-pair state, is an effective way to generate a spin quintet state in organic materials. Although its application to photovoltaics as an exciton multiplier has been extensively studied, the use of its unique spin degree of freedom has been largely unexplored. Here, we demonstrate that the spin polarization of the quintet multiexcitons generated by SF improves the sensitivity of magnetic resonance of water molecules through dynamic nuclear polarization (DNP).

Vapor-Induced Conversion of a Centrosymmetric Organic-Inorganic Hybrid Crystal into a Proton-Conducting Second-Harmonic-Generation-Active Material.

Chemical responsivity in materials is essential to build systems with switchable functionalities. However, polarity-switchable materials are still rare because inducing a symmetry breaking of the crystal structure by adsorbing chemical species is difficult. In this study, we demonstrate that a molecular organic-inorganic hybrid crystal of (NEt)[MnN(CN)] () undergoes polarity switching induced by water vapor and transforms into a rare example of proton-conducting second-harmonic-generation-active material.

Mechanistic study of photocatalytic CO reduction using a Ru(ii)-Re(i) supramolecular photocatalyst.

Supramolecular photocatalysts comprising [Ru(diimine)] photosensitiser and -[Re(diimine)(CO){OC(O)OCHNR}] catalyst units can be used to reduce CO to CO with high selectivity, durability and efficiency. In the presence of triethanolamine, the Re catalyst unit efficiently takes up CO to form a carbonate ester complex, and then direct photocatalytic reduction of a low concentration of CO, , 10% CO, can be achieved using this type of supramolecular photocatalyst. In this work, the mechanism of the photocatalytic reduction of CO was investigated applying such a supramolecular photocatalyst, with a carbonate ester ligand, using time-resolved visible and infrared spectroscopies and electrochemical methods.

Guest-Tunable Excited States in a Cyanide-Bridged Luminescent Coordination Polymer.

The excited-state energy was tuned successfully by guest molecules in a cyanide-bridged luminescent coordination polymer (CP). Methanol or ethanol vapor reversibly and significantly changed the luminescent color of the CP between green and yellow (Δλ = 32 nm). These vapors did not significantly affect the environment around the luminophore in the ground state of the CP, whereas they modulated the excited states for the resulting bathochromic shift.

Coordination Geometrical Effect on Ligand-to-Metal Charge Transfer-Dependent Energy Transfer Processes of Luminescent Eu(III) Complexes.

Photophysical properties of europium (Eu(III)) complexes are affected by ligand-to-metal charge transfer (LMCT) states. Two luminescent Eu(III) complexes with three tetramethylheptadionates (tmh) and pyridine (py), [Eu(tmh)(py)] (seven-coordinated monocapped-octahedral structure) and [Eu(tmh)(py)] (eight-coordinated square antiprismatic structure), were synthesized for geometrical-induced LMCT level control. Distances between Eu(III) and oxygen atoms of tmh ligands were estimated using single-crystal X-ray analyses.

Intramolecular-rotation driven triplet-to-singlet upconversion and fluctuation induced fluorescence activation in linearly connected donor-acceptor molecules.

Thermally activated triplet-to-singlet upconversion is attractive from both fundamental science and exciton engineering, but controlling the process from molecular configuration is still unrevealed. In particular, the flexibility of the freedom of molecular geometry is of major importance to understand the kinetics of the phonon-induced upconversion. Here, we focus on two linearly connected donor-acceptor molecules, 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) and hexamethylazatriangulene-2,4,6-triphenyl-1,3,5-triazine (HMAT-TRZ), as the model system.

Vapor switching of the luminescence mechanism in a Re(V) complex.

A ReV complex demonstrates methanol selective luminescent color changes from red to green together with enhancements of the corresponding luminescence quantum yields twenty-three times. These characteristic responses are caused by the switching of the characters of the emissive states from metal-to-ligand charge transfer to d-d transition along with a single-crystal-to-single-crystal ligand exchange reaction.

Dual Energy Transfer Pathways from an Antenna Ligand to Lanthanide Ion in Trivalent Europium Complexes with Phosphine-Oxide Bridges.

Trivalent europium (Eu) complexes are attractive materials for luminescence applications if energy transfer from antenna ligands to the lanthanide ion is efficient. However, the microscopic mechanisms of the transfer remain elusive, and fundamental physical chemistry questions still require answers. We track the energy transfer processes in a luminescent complex Eu(hfa)(DPPTO) (hfa, hexafluoroacetylacetonate; DPPTO, 2-diphenylphosphoryltriphenylene) using time-resolved photoluminescence spectroscopy.