Hok-Lai Wong

A Versatile Photochromic Dithienylethene-Containing β-Diketonate Ligand: Near-Infrared Photochromic Behavior and Photoswitchable Luminescence Properties upon Incorporation of a Boron(III) Center

A versatile dithienylethene-containing β-diketonate ligand and its boron(III) compounds have been successfully synthesized. Upon photocyclization, the ligand shows a new absorption band at 630 nm with good fatigue resistance and high thermal stability. Incorporation of the boron center has been demonstrated to shift the photochromic behavior to the NIR region.

Photochromic alkynes as versatile building blocks for metal alkynyl systems: design, synthesis, and photochromic studies of diarylethene-containing platinum(II) phosphine alkynyl complexes.

The synthesis of newly designed photochromic dithienylethene-containing ethynylthiophene and ethynylthieno[3,2-b]thiophene has been described, and their incorporation as versatile ligands into the platinum(II) phosphine system was demonstrated. All platinum(II) complexes have been successfully characterized by (1)H and (31)P NMR spectroscopies, positive fast atom bombardment (FAB) mass spectrometry, as well as elemental analysis. One of the complexes has been characterized by X-ray crystallography. Their photophysical, photochromic, and electrochemical properties have been studied. Upon photoexcitation, all the photochromic diarylethene-containing alkynes and platinum(II) complexes exhibited reversible photochromism. The thermal bleaching kinetic of complex 6 was studied in toluene at 298 and 313 K. Complexes 1, 3, and 4, which contained the labile chloro- ligand, represent a new class of versatile building blocks for photoswitchable functional materials.

Photochromic thienylpyridine-bis(alkynyl)borane complexes: toward readily tunable fluorescence dyes and photoswitchable materials.

A series of diarylethene-containing N^C chelated thienylpyridine-bis(alkynyl)borane complexes has been designed and synthesized. Their photophysical and photochromic properties have been investigated and presented. The characteristic low-energy absorption band of their closed forms could be readily tuned from the visible range to the near-infrared region.

Synthesis, characterization, and photophysical properties of Bodipy-spirooxazine and -spiropyran conjugates: modulation of fluorescence resonance energy transfer behavior via acidochromic and photochromic switching.

Two series of Bodipy-containing photochromic spirooxazine and spiropyran derivatives have been designed, synthesized and characterized by (1)H NMR, ESI mass spectrometry and elemental analysis. Their electrochemical and photochromic properties were investigated. The photophysical, ultrafast transient absorption, and fluorescence resonance energy transfer (FRET) properties from Bodipy (donor) to the ring-opened merocyanine (acceptor) were also studied. Upon photoexcitation, all the photochromic spirooxazine- and spiropyran-containing compounds exhibited reversible photochromism. Computational studies have been performed to provide further insights into the nature of the electronic transitions for the two classes of compounds. The rate constants and activation parameters for thermal bleaching reactions of compounds SO, SP-alkyne, 1-3, and 8-10 were determined through kinetic studies in acetonitrile. The thermal bleaching reaction rate of the spiropyran-containing compounds is found to be much slower than that of the spirooxazine-containing counterparts.

Tunable Photochromism in the Robust Dithienylethene‐Containing Phospholes: Design, Synthesis, Characterization, Electrochemistry, Photophysics, and Photochromic Studies

A series of dithienylethene-containing phosphole derivatives has been designed, synthesized and characterized. One of the compounds has been characterized by X-ray crystallography. Upon photoexcitation, the compounds exhibit drastic color changes, ascribed to the reversible photochromic behavior. Their photochromic, photophysical and electrochemical properties have been studied. They show photochromic reactivities with high photocyclization quantum yields. Their photophysical and photochromic properties are found to be facilely tuned in this system by substitution at the phosphole backbone, as well as variation on the extent of π-conjugation of the phosphole backbone. Some selected compounds have been demonstrated to exhibit photochromic properties in polymethylmethacrylate (PMMA) films.

Versatile Synthesis of Luminescent Tetradentate Cyclometalated Alkynylgold(III) Complexes and Their Application in Solution-Processable Organic Light-Emitting Devices

A new class of cyclometalated tetradentate alkynylgold(III) complexes has been successfully synthesized by post-synthetic modification. Through the judicious design and choice of pincer ligands, post-synthetic cyclization could be achieved to produce the robust and structurally rigid class of tetradentate gold(III) C^N^C^C complexes with high photoluminescence quantum yields of up to 0.49 in solution and 0.78 in doped thin films at room temperature, at least an order of magnitude higher than those of the structurally related uncyclized tridentate alkynylgold(III) analogues. High-performance yellow to orange-red emitting solution-processable organic light-emitting devices have also been achieved with external quantum efficiency of 11.1 %. This work describes for the first time of the use of post-synthetic ligand modification approach to overcome the synthetic challenge for tetradentate alkynylgold(III) complexes.

A solid state highly emissive Cu(I) metallacycle: promotion of cuprophilic interactions at the excited states

The straightforward synthesis of a new Cu(i) metal-rich small metallacycle is presented. This compound is luminescent in the solid state with an emission quantum yield of 72% at room temperature and displays a pronounced reversible red-shift of its emission spectra upon cooling. Quantum chemical calculations reveal that these properties are governed by important geometrical relaxations that imply the formation of cuprophilic interactions at the excited states.

From spherical to leaf-like morphologies: tunable supramolecular assembly of alkynylgold(I) complexes through variations of the alkyl chain length.

A series of luminescent polynuclear alkynylgold(I) complexes with different lengths of alkyl chains attached at the N-heterocyclic carbene moieties has been synthesised and demonstrated to display intriguing self-assembly behaviours through a cooperative growth mechanism. Variation of the alkyl chain length was found to cause drastic morphological differences in the aggregates and to strongly affect the thermodynamic parameters as revealed by the nucleation-elongation model.

Photochromic dithienylethene-containing triarylborane derivatives: facile approach to modulate photochromic properties with multi-addressable functions

A series of dithienylethene-containing triarylboranes has been designed, synthesized, and characterized. The electrochemistry, photophysics, and photochromic behavior have also been studied. The photophysical and photochromic properties could be facilely tuned in this system by varying the thiophene spacers (thiophene, thienothiophene, and bithiophene) between the dithienylethene and the dimesitylboron (BMes2 ) or the position of the BMes2 substitution in the thiophene spacers. The absorption of closed form has been found to be more sensitive towards the structural modification upon incorporation of the BMes2 unit. Moreover, multi-addressable photochromic reactivity is obtained upon addition of Lewis base (F(-) ), which is due to the formation of boron-Lewis base adduct. The dependence of the photophysical and photochromic properties on the thiophene spacers and the position of the BMes2 substitution has been further supported by computational studies.

A new class of three-dimensional, p-type, spirobifluorene-modified perylene diimide derivatives for small molecular-based bulk heterojunction organic photovoltaic devices

A new class of non-planar and three-dimensional spirobifluorene-modified perylene diimide compounds has been successfully designed and synthesized. The functionalization of the perylene diimide core with different spirobifluorene moieties can alter the molecular geometry as well as extend the spectral coverage into the red region. In addition, these compounds can be utilized as donor materials in combination with fullerene to form bulk heterojunctions, and particularly efficient organic photovoltaic (OPV) devices demonstrating high open-circuit voltages of 0.97 V and a power conversion efficiencies of up to 4% have been prepared. These values are the highest among the cells utilizing p-type perylene diimide as photoactive material in OPV devices. This work opens up a new avenue for the design and synthesis of a new class of p-type perylene diimide compounds that are promising candidates as donor materials in the fabrication of OPV devices.