Fast and efficient room-temperature phosphorescence from metal-free organic molecular liquids.

Liquid is the most flexible state of condensed matter and shows promise as a functional soft material. However, these same characteristics make it challenging to achieve efficient room-temperature phosphorescence (RTP) from metal-free organic molecular liquids. Herein, we report efficient RTP from liquefied thienyl diketones bearing one or two dimethyloctylsilyl (DMOS) substituents.

Ultrafast nonradiative decay from higher-lying excited states in azulene-dimers.

The anti-Kasha fluorescence nature of azulene has been explained by the large energy gap between the second excited state and the lowest excited singlet state. While such property is expected to be perturbed in the presence of electronic interchromophore interactions without a change in the S-S energy gap, the study of the excited-state dynamics of azulene assemblies or oligomers remains scarce. In this study, we designed dimers with diverse rigid bridge structures with controlled intermolecular interactions.

Tetracene Inclusion in Boron Nitride Nanotubes for Photoluminescence Property Modulation Based on Aggregated State Control in Their Nanocavity.

Boron nitride nanotubes (BNNTs) are used for the self-assembly of tetracene (Tc) molecules without chemical modification in their one-dimensional nanocavities. The Tc aggregated state can be changed depending on the encapsulated Tc amount that is controlled by the sublimation conditions of Tc molecules for the complexation (Tc@BNNTs). As a result, the photophysical processes, including singlet fission in the Tc assemblies, are varied, which enables the emission mode switching of the aggregation-based fluorescence and the excimer emission for Tc@BNNTs.

Dynamic Excited-State Localization Induced by Jahn-Teller Distortion Observed by Coherent Vibrational Spectroscopy.

Molecular symmetry is a central design element in functional materials, yet its dynamic modulation in the excited state and its consequences for optoelectronic properties remain largely unexplored, particularly in main-group p-block element complexes. We address this knowledge gap by investigating unique Al(III) dinuclear triple-helical complexes that combine high symmetry with twisted π-conjugated systems and achieve exceptional optical properties of unusually large Stokes shifts and high photoluminescence quantum yields. Using transient absorption spectroscopy with a 10 fs pump pulse, we detected coherent vibrational oscillations overlapped with transient absorption/stimulated emission signals.

Common mechanism of dual emission in linearly-linked donor-acceptor-type thermally activated delayed fluorescence molecules.

Linearly-linked donor-acceptor-type (D-A) thermally activated delayed fluorescence molecules have been expected to be used as efficient emitters in organic light emitting diodes. Despite their simple molecular structures, some of these molecules exhibit a complex dual emission mechanism due to their two conformers: quasi-coplanar (q-copl.) and perpendicular (perp.

Temperature dependency of energy shift of excitonic states in a donor-acceptor type TADF molecule.

In recent years, thermally activated delayed fluorescence (TADF) has attracted intense attention owing to its straightforward application to high-efficiency organic light-emitting diodes. Further, to develop high-performance TADF materials, many researchers have designed novel molecules that have a small energy gap between the lowest excited singlet and triplet states ( ), and detailed analysis suggests a significant contribution of higher-lying excited states for spin flipping processes. In this study, we demonstrate a peculiar thermal behaviour of emission decay of a donor-acceptor type TADF molecule, TMCz-BO, which seems like thermal deactivation of delayed fluorescence that can be explained without a negative by comprehensive kinetic analysis across various temperatures and solvents.

Impact of iodine-substitution on the symmetry and room-temperature phosphorescence behavior of thienyl diketone skeleton.

Introducing heavy atoms, or replacing atoms with heavier ones, is a routine approach for accelerating spin-flipping photophysical processes. However, predicting its impact on phosphorescence efficiency is not straightforward. Herein, we report an unexpected consequence of bromine-to-iodine substitution in a bromothienyl diketone derivative, TIPS-BrTn, that exhibits outstanding room-temperature phosphorescence (RTP) in cyclohexane solution.

Charge transfer emission between π- and 4f-orbitals in a trivalent europium complex.

Photoinduced metal-to-ligand (or ligand-to-metal) charge-transfer (CT) states in metal complexes have been extensively studied toward the development of luminescent materials. However, previous studies have mainly focused on CT transitions between d- and π-orbitals. Herein, we report the demonstration of CT emission from 4f- to π-orbitals using a trivalent europium (Eu(III)) complex, supported by both experimental and theoretical analyses.

Light-Harvesting Spin Hyperpolarization of Organic Radicals in a Metal-Organic Framework.

Light-driven spin hyperpolarization of organic molecules is a crucial technique for spin-based applications such as quantum information science (QIS) and dynamic nuclear polarization (DNP). Synthetic chemistry provides the design of spins with atomic precision and enables the scale-up of individual spins to hierarchical structures. The high designability and extended pore structure of metal-organic frameworks (MOFs) can control interactions between spins and guest molecules.

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.