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.

Reversible 1,1-hydroboration: boryl insertion into a C-N bond and competitive elimination of HBR2 or R-H.

Boranes with the general formula of HBR2 have been found to undergo a facile 1,1-hydroboration reaction with pyrido[1,2-a]isoindole (A), resulting in insertion of a BR2 unit into a CN bond and the formation of a variety of BN heterocycles. Investigation on the thermal reactivity of the BN heterocycles revealed that these molecules have two distinct and competitive thermal elimination pathways: HBR2 elimination (or retro-hydroboration) versus RH elimination, depending on the R group on the B atom and the chelate backbone. Mechanistic aspects of these highly unusual reactions have been established from both experimental and computational evidence. Adduct formation between HBR2 and A was found to be the key intermediate in 1,1-hydroboration of A.

Tuning the photoisomerization of a N

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.

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.

Bluish-green BMes2-functionalized Pt(II) complexes for high efficiency PhOLEDs: impact of the BMes2 location on emission color.

New phosphorescent Pt(II) compounds based on dimesitylboron (BMes(2))-functionalized 2-phenylpyridyl (ppy) N,C-chelate ligands and an acetylacetonato ancillary ligand have been achieved. We have found that BMes(2) substitution at the 4'-position of the phenyl ring can blue-shift the phosphorescent emission energy of the Pt(II) compound by approximately 50 nm, compared to the 5'-BMes(2) substituted analogue, without substantial loss of luminescent quantum efficiencies. The emission color of the 4'-BMes(2) substituted Pt(II) compound, Pt(Bppy)(acac) (1) can be further tuned by the introduction of a substituent group at the 3'-position of the phenyl ring. A methyl substituent red-shifts the emission energy of 1 by approximately 10 nm whereas a fluoro substituent blue-shifts the emission energy by about 6 nm. Using this strategy, three bright blue-green phosphorescent Pt(II) compounds 1, 2 and 3 with emission energy at 481, 492, and 475 nm and Φ(PL)=0.43, 0.26 and 0.25, respectively, have been achieved. In addition, we have examined the impact of BMes(2) substitution on 3,5-dipyridylbenzene (dpb) N,C,N-chelate Pt(II) compounds by synthesizing compound 4, Pt(Bdpb)Cl, which has a BMes(2) group at the 4'-position of the benzene ring. Compound 4 has a phosphorescent emission band at 485 nm and Φ(PL)=0.70. Highly efficient blue-green electroluminescent (EL) devices with a double-layer structure and compounds 1, 3 or 4 as the phosphorescent dopant have been fabricated. At 100 cd m(-2) luminance, EL devices based on 1, 3 and 4 with an external quantum efficiency of 4.7, 6.5 and 13.4%, respectively, have been achieved.

Triarylboron-functionalized Cu(II) carboxylate paddlewheel complexes.

The assembly of two copper(II)-carboxylate dimer complexes appended with four peripheral triarylborane functionalities has been achieved. Complex stabilities in the presence of fluoride are examined.

Efficient electrochemiluminescence of a boron-dipyrromethene (BODIPY) dye.

Electrochemiluminescence (ECL) of a boron-dipyrromethene dye (BDY) in the presence of tri-n-propylamine as a co-reactant was found to be efficient. The ECL of BDY showed a unique peak wavelength of 707 nm, indicative of the intermolecular electronic transition mechanism.

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.

Impact of a dithienyl unit on photostability of N,C-chelating boron compounds.

A dithienyl unit in a N,C-chelate monoboryl compound has been found to completely stabilize a N,C-chelate boryl chromophore toward photoisomerization. N,C-chelate diboryl compounds that contain a dithienyl unit display a similar high stability toward photoisomerization. This greatly enhanced photostability is attributed to the π → π* transition and luminescence involving the dithienyl unit that competes effectively with photoisomerization of the boryl chromophore.

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.

Ru-Pt and Ru-Pd heterobimetallic complexes based on a new ligand with two distinct chelate sites.

A new ligand p-[N-2-(2'-pyridyl)benzimidazolyl]-[N-2-(2'-pyridyl)indolyl]-benzene (L1) has been synthesized and fully characterized. L1 has two distinct chelating sites: one N,N-chelate site and one N,C-chelate site. This ligand has been found to be very effective in selective binding to two different metal ions. Two new heterobimetallic complexes Ru-Pt and Ru-Pd using L1 as the bridging ligand have been successfully synthesized and fully characterized. To understand the mutual influence of the two metal centers on electronic and photophysical properties, the corresponding monometallic Ru(II), Pt(II) and Pd(II) compounds have also been synthesized and investigated. All Ru(II)-containing complexes have been found to be luminescent. Electronic communication between the two different metal centers in the heterobimetallic compounds was found to be weak. The Pt(II) moiety appears to enhance the phosphorescent efficiency of the Ru(II) unit while the Pd(II) analogue has little influence.

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.

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.