Jia-Sheng Lu

Formation of Azaborines by Photoelimination of B,N‐Heterocyclic Compounds

Highly fluorescent π-conjugated polycyclic azaborines can be prepared from B,N-heterocyclic compounds with a BR2 -CH2 unit through the elimination of an R-H molecule (see scheme). These clean photoelimination reactions occur both in solution and in polymers doped with the precursors.

Highly efficient blue phosphorescent and electroluminescent Ir(III) compounds

Three new Ir(III) compounds with deep-blue phosphorescence have been synthesized. These molecules have the general formula of Ir(C∧N)2(L∧X), where C∧N = 2′,6′-difluoro-2,3′-bipyridine (dfpypy) and L∧X = ancillary ligand such as 2-picolinate, pic (1), acetylacetonate, acac (2), or dipivaloylmethanoate, dpm (3). The ancillary ligands have been found to significantly destabilize both HOMO and LUMO levels of the Ir(III) complexes, compared to Ir(dfpypy)3, without significantly changing the phosphorescence energy. Compounds 1–3 emit bright blue phosphorescence with λmax = 440–460 nm and quantum efficiencies of 0.60–0.95 in solution and the solid state. Double-layer electroluminescent devices using compounds 1–3 as the dopant, CDBP (4,4′-bis(9-carbazolyl)-2,2′-dimethylbiphenyl) as the host/hole transporting layer, and TPBi (1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene) as the electron transport layer have been fabricated. These EL devices show pure blue colour with high efficiency. The EL device of compound 3 at the doping level of 20 wt% shows the best performance with EQE of 10–15% at the brightness of 10–1000 cd m−2 and the maximum current efficiency of 22 cd A−1.

In Situ Solid-State Generation of (BN)2-Pyrenes and Electroluminescent Devices

New BN-heterocyclic compounds have been found to undergo double arene photoelimination, forming rare yellow fluorescent BN-pyrenes that contain two BN units. Most significant is the discovery that the double arene elimination can also be driven by excitons generated electrically within electroluminescent (EL) devices, enabling the in situ solid-state conversion of BN-heterocycles to BN-pyrenes and the use of BN-pyrenes as emitters for EL devices. The in situ exciton-driven elimination (EDE) phenomenon has also been observed for other BN-heterocycles.

Highly Efficient Dual-Color Electrochemiluminescence from BODIPY-Capped PbS Nanocrystals

Electrochemiluminescence (ECL) of a hybrid system consisting of PbS nanocrystals (NCs) and a BODIPY dye (BDY) capping ligand was discovered to produce highly efficient dual emissions with tri-n-propylamine as a coreactant. By means of spooling ECL spectroscopy, the strong dual ECL emission peaks of 984 and 680 nm were attributed to the PbS and BDY moieties, respectively, and found to be simultaneous during the light evolution and devolution. The ECL of the PbS was enhanced via NC collisions with the electrode and reached an efficiency of 96% relative to that of Ru(bpy)3(2+), which is the highest among the semiconductor NCs.

Single Boryl Isomerization in Silyl-Bridged Photochromic Diboryl Dyes

Silyl-bridged dimers of a ppy-BMes(2) (ppy = 2-phenylpyridine, Mes = mesityl) photochrome were found to undergo photochromic switching involving a single boryl unit only. A through-space intramolecular energy transfer was found to be responsible for the single-chromophore isomerization phenomenon and fluorescence quenching. Steric congestion in the diboryl molecules was found to have an impact on photoisomerization quantum efficiency.

Decorating BODIPY with three- and four-coordinate boron groups.

Two new BODIPY derivative molecules decorated by a Lewis acidic BMes(2)(vinyl) group and a photochromic four-coordinate boryl chromophore, respectively, have been synthesized. Significant mutual influence on photophysical and photochemical properties by the different boron-containing units has been observed.

A Dual Emissive BODIPY Dye and Its Use in Functionalizing Highly Monodispersed PbS Nanoparticles

BODIPY (boron-dipyrromethene) dyes and derivatives are well-known to be very effective in light-harvesting and energy-transfer processes, owing to their high fluorescence quantum yields, large molar absorption coefficients, relatively long excited-state lifetimes, and excellent photochemical stability. Thus, they have frequently been used in lightharvesting molecules, as dye sensitizers, and as probes and labels for biomolecules. One important class of materials for various optoelectronic applications, including solar cells, is the class of semiconductor nanoparticles (NPs). The optical and energetic properties of these nanoparticles can be tuned by varying their shape, size, or surface ligands. Lead sulfide NPs are particularly attractive among NPs owing to their narrow band gap, large exciton Bohr radii, and their absorption and emission in the near-IR region. Several recent reports have shown that PbS NPs are very promising materials for achieving high-performance photovoltaic devices. 5, 6] The most commonly used surface ligand for PbS NPs is oleic acid, which can effectively protect the NPs from oxidation and can facilitate their dispersion in organic solvents. However, because they lack any interesting photophysical properties, oleic acid capping ligands do not engage in any electronic communication or interactions with the NPs and thus have little influence on the properties of the NPs and insulate NPs from each other and the surrounding medium. New surface ligands that can communicate electronically with PbS NPs and enhance their performance in optoelectronic devices are therefore in demand. Based on this consideration and the very attractive photophysical properties of BODIPY dyes, we initiated the investigation of new BODIPY dyes as potential new surface ligands for PbS NPs. Herein, we report the synthesis and photophysical properties of a new BODIPY dye (BDY) and its use in PbS NPs functionalization. The procedure used to synthesize BDY is illustrated in Scheme 1. The bromophenyl-BODIPY starting material 1 was synthesized by using a modified literature procedure.

Chelation-assisted photoelimination of B,N-heterocycles.

Metal-chelation and internal H bonds have been found to greatly enhance the photoelimination quantum efficiency of B,N-heterocycles by 2 orders of magnitude. Green phosphorescent Pt(II)-functionalized 1,2-azaborines have been achieved via photoelimination. A mechanistic pathway for the PE reaction has been established.

Triarylboryl-functionalized dibenzoylmethane and its phosphorescent platinum(II) complexes

An acetylacetonato derivative ligand, dibenzoylmethane (dbm), has been functionalized with a dimesitylboryl group. Phosphorescent N^C-chelate Pt(II) compounds with the new molecule as an ancillary ligand have been achieved and used as effective turn-on phosphorescent sensors for fluoride ions under air.

Tuning the Photoisomerization of a N^C‐Chelate Organoboron Compound with a MetalAcetylide Unit

To examine the impact of metal moieties that have different triplet energies on the photoisomerization of B(ppy)Mes2 compounds (ppy = 2-phenyl pyridine, Mes = mesityl), three metal-functionalized B(ppy)Mes2 compounds, Re-B, Au-B, and Pt-B, have been synthesized and fully characterized. The metal moieties in these three compounds are Re(CO)3(tert-Bu2 bpy)(C≡C), Au(PPh3)(C≡C), and trans-Pt(PPh3)2(C≡C)2, respectively, which are connected to the ppy chelate through the alkyne linker. Our investigation has established that the Re(I) unit completely quenches the photoisomerization of the boron unit because of a low-lying intraligand charge transfer/MLCT triplet state. The Au(I) unit, albeit with a triplet energy that is much higher than that of B(ppy)Mes2 , upon conjugation with the ppy chelate unit, substantially increases the contribution of the π→π* transition, localized on the conjugated chelate backbone in the lowest triplet state, thereby leading to a decrease in the photoisomerization quantum efficiency (QE) of the boron chromophore when excited at 365 nm. At higher excitation energies, the photoisomerization QE of Au-B is comparable to that of the silyl-alkyne-functionalized B(ppy)Mes2 (TIPS-B), which was attributable to a triplet-state-sensitization effect by the Au(I) unit. The Pt(II) unit links two B(ppy)Mes2 together in Pt-B, thereby extending the π-conjugation through both chelate backbones and leading to a very low QE of the photoisomerization. In addition, only one boron unit in Pt-B undergoes photoisomerization. The isomerization of the second boron unit is quenched by an intramolecular energy transfer of the excitation energy to the low-energy absorption band of the isomerized boron unit. TD-DFT computations and spectroscopic studies of the three metal-containing boron compounds confirm that the photoisomerization of the B(ppy)Mes2 chromophore proceeds through a triplet photoactive state and that metal units with suitable triplet energies can be used to tune this system.