Dong Ryeol Whang

Self-Healing of Molecular Catalyst and Photosensitizer on Metal–Organic Framework: Robust Molecular System for Photocatalytic H2 Evolution from Water

Inspired by self-repair mechanism of PSII in plants, we report a self-healing system which spontaneously repairs molecular catalyst and photosensitizer during photocatalytic H2 evolution. A bipyridine-embedded UiO-type metal-organic framework (MOF), namely Ptn_Ir_BUiO, which incorporated H2-evolving catalyst and photosensitizer, was synthesized and subject to photocatalytic H2 evolution reaction (HER). Impressively, HER with Pt0.1_Ir_BUiO showed very stable molecular photocatalysis without significant decrease in its activity and colloidal formation for 6.5 days at least; in the homogeneous counterpart, the molecular catalyst became a colloid just after 7.5 h. It was revealed that the arrangement of diimine sites which closely and densely surrounded the H2-evolving catalyst and photosensitizer in the MOF enabled such a highly efficient self-healing.

A highly efficient wide-band-gap host material for blue electrophosphorescent light-emitting devices

We report on an efficient wide-band-gap host material for blue electrophosphorescence devices, namely, 1,2-trans-di-9-carbazolylcyclobutane (DCz). Photophysical studies show that lower-energy excimer formation between the carbazole units can be efficiently suppressed in a DCz film, thus maintaining its high triplet-state energy and inducing an exothermic energy transfer from DCz to iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic). Electrophosphorescent devices comprising a FIrpic:DCz emitting layer exhibit a superior performance with a maximum external quantum efficiency of 9.8%, a maximum luminance efficiency of 21.5cd∕A, and a maximum power efficiency of 15.0lm∕W at 0.01mA∕cm2.

Stimuli-Responsive Reversible Fluorescence Switching in a Crystalline Donor-Acceptor Mixture Film: Mixed Stack Charge-Transfer Emission versus Segregated Stack Monomer Emission.

We report on a molecularly tailored 1:1 donor-acceptor (D-A) charge-transfer (CT) cocrystal that manifests strongly red-shifted CT luminescence characteristics, as well as noteworthy reconfigurable self-assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule A1, which gives rise to considerable free volume and weak intermolecular interactions. The stacking features of the CT complex result in an external stimuli-responsive molecular stacking reorganization between the mixed and demixed phases of the D-A pair. Accordingly, high-contrast fluorescence switching (red↔blue) is realized on the basis of the strong alternation of the electronic properties between the mixed and demixed phases. A combination of structural, spectroscopic, and computational studies reveal the underlying mechanism of this stimuli-responsive behavior.

A distyrylbenzene based highly efficient deep red/near-infrared emitting organic solid

A highly efficient deep red/near-infrared emitting organic solid based on a β-dicyanostyrylbenzene derivative was reported. Structural, spectroscopic, and quantum-chemical analysis rationalizes a strategy to achieve bright solid-state emitters.

Dynamic dual stage phosphorescence chromatic change in a diborylated iridium phosphor for fluoride ion sensing with concentration discriminating capability

By adding a strongly electron-accepting B(Mes)2 group to the ppy-type ligand of phosphorescent iridium(III) cyclometalated complexes, more stabilized metal-to-ligand charge-transfer (MLCT) states can be obtained by transferring electron density from the pyridyl moiety to the boron atom of the B(Mes)2 group in the metallophosphors to give red phosphorescence. Taking advantage of the binding effect between boron atom and F− ion, the phosphorescent emission color of the iridium(III) cyclometalated complex can be dynamically changed by the external F− ions sequentially from red to yellow and to green through modulation of the charge-transfer emitting states, representing very unique F− ion sensing behavior. In the first step, destabilization of the MLCT states is caused by the weak binding between boron and F− ion, which is then accompanied by switching of the MLCT process to form high-energy MLCT states as induced by the strong binding between boron and F− ion in the second step. Not only does the dynamic phosphorescence chromatic variation depend significantly on the substitution mode of the B(Mes)2 moiety on the ppy ligands, but the dynamic emission response also would pave the way to the development of a novel F− ion sensor showing a unique concentration discrimination feature in aqueous solution with good color reversibility and optical response to the naked eye, high selectivity and sensitivity. All of these data provide valuable insight into the molecular design of a new generation of F− ion sensors featuring both concentration discriminating capability and good potential for practical applications.

Excited State Features and Dynamics in a Distyrylbenzene-Based Mixed Stack Donor-Acceptor Cocrystal with Luminescent Charge Transfer Characteristics.

Combined structural, photophysical, and quantum-chemical studies at the quantum mechanics/molecular mechanics (QM/MM) level precisely reveal the structure-property relationships in a mixed-stack donor-acceptor cocrystal, which displays vibronically structured fluorescence, strongly red-shifted against the spectra of the parent donor and acceptor, with high quantum yield despite the pronounced CT character of the emitting state. The study elucidates the reasons for this unusual combination, quantifies the ordering and nature of the collective excited singlet and triplet state manifold, and details the deactivation pathways of the initially created Franck-Condon state.

Solid-State Phosphorescence-to-Fluorescence Switching in a Cyclometalated Ir(III) Complex Containing an Acid-Labile Chromophoric Ancillary Ligand: Implication for Multimodal Security Printing

In this study, we have demonstrated the reconstruction of encrypted information by employing photoluminescence spectra and lifetimes of a phosphorescent Ir(III) complex (IrHBT). IrHBT was constructed on the basis of a heteroleptic structure comprising a fluorescent N^O ancillary ligand. From the viewpoint of information security, the transformation of the Ir(III) complex between phosphorescent and fluorescent states can be encoded with chemical/photoirradiation methods. Thin polymer films (poly(methylmethacrylate), PMMA) doped with IrHBT display long-lived emission typical of phosphorescence (λ(max) = 586 nm, τ(obs) = 2.90 μs). Meanwhile, exposure to HCl vapor switches the emission to fluorescence (λ(max) = 514 nm, τ(obs) = 1.53 ns) with drastic changes in both the photoluminescence color and lifetime. Security printing on paper impregnated with IrHBT or on a PMMA film containing IrHBT and photoacid generator (triphenylsulfonium triflate) enables the bimodal readout of photoluminescence color and lifetime.

Self-deprotonation and colorization of 1,3-bis(dicyanomethylidene)indan in polar media: a facile route to a minimal polymethine dye for NIR fluorescence imaging.

Colorless 1,3-bis(dicyanomethylidene)indan is an organic acid (pK(a) ≈3.0) that turns blue in polar media owing to self-deprotonation. Moreover, its colored conjugate base shows potential as a minimal anionic polymethine dye for probing biomolecules in cells and in vivo through noncovalent complexation and near-infrared fluorescence signaling.

Highly Luminescent 2D-Type Slab Crystals Based on a Molecular Charge-Transfer Complex as Promising Organic Light-Emitting Transistor Materials

A new 2:1 donor (D):acceptor (A) mixed-stacked charge-transfer (CT) cocrystal comprising isometrically structured dicyanodistyrylbenzene-based D and A molecules is designed and synthesized. Uniform 2D-type morphology is manifested by the exquisite interplay of intermolecular interactions. In addition to its appealing structural features, unique optoelectronic properties are unveiled. Exceptionally high photoluminescence quantum yield (ΦF ≈ 60%) is realized by non-negligible oscillator strength of the S1 transition, and rigidified 2D-type structure. Moreover, this luminescent 2D-type CT crystal exhibits balanced ambipolar transport (µh and µe of ≈10-4 cm2 V-1 s-1 ). As a consequence of such unique optoelectronic characteristics, the first CT electroluminescence is demonstrated in a single active-layered organic light-emitting transistor (OLET) device. The external quantum efficiency of this OLET is as high as 1.5% to suggest a promising potential of luminescent mixed-stacked CT cocrystals in OLET applications.

Designing Highly Efficient CuI Photosensitizers for Photocatalytic H2 Evolution from Water

A series of CuI photosensitizers was synthesized, characterized, and investigated for photocatalytic H2 evolution from water. A structure-property correlation was established for their catalytic activity and photophysical properties, which was further elaborated by DFT calculations. A new CuI photosensitizer (Cu-TPAPhen) with triphenylamine-substituted phenanthroline ligands showed unprecedentedly high turnover numbers of 19 000 when tested in combination with triethylamine as a sacrificial reagent and colloidal Pt as a H2 evolution catalyst. This work paves the way toward cheap metal-based photosensitizers which can replace noble-metal complexes in photocatalytic systems.