Reduction of 2-(BMes2)pyrene (B1) and 2,7-bis(BMes2)pyrene (B2) gives rise to anions with extensive delocalization over the pyrenylene bridge and between the boron centers at the 2- and 2,7-positions, the typically unconjugated sites in the pyrene framework. One-electron reduction of B2 gives a radical anion with a centrosymmetric semiquinoidal structure, while two-electron reduction produces a quinoidal singlet dianion with biradicaloid character and a relatively large S0-T1 gap. These results have been confirmed by cyclic voltammetry, X-ray crystallography, DFT/CASSCF calculations, NMR, EPR, and UV-vis-NIR spectroscopy.

Abstract:Three water-soluble tetracationic quadrupolar chromophores comprising two three-coordinate boron -acceptor groups bridged by thiophene-containing moieties were synthesised for biological imaging applications. The derivative 3 containing the bulkier 5-(3,5-Me2C6H2)-2,2′-(C4H2S)2-5′-(3,5-Me2C6H2) bridge is stable over a long period of time, exhibits a high fluorescence quantum yield and strong one-(OPA) and two-photon absorption (TPA), with a TPA cross-section of 268 GM at 800 nm in water. Confocal laser scanning fluorescence microscopy studies in live cells indicate localisation of the chromophore at the mitochondria; moreover, cytotoxicity measurements prove biocompatibilty. Thus, chromophore 3 has excellent potential for one-and two-photon excited fluorescence imaging of mitochondrial function in cells.

We show that by judicious choice of substituents at the 2- and 7-positions of pyrene, the frontier orbital order of pyrene can be modified, giving enhanced control over the nature and properties of the photoexcited states and the redox potentials. Specifically, we introduced a julolidine-like moiety and Bmes (mes=2,4,6-Me C H ) as very strong donor (D) and acceptor (A), respectively, giving 2,7-D-π-D- and unsymmetric 2,7-D-π-A-pyrene derivatives, in which the donor destabilizes the HOMO-1 and the acceptor stabilizes the LUMO+1 of the pyrene core. Consequently, for 2,7-substituted pyrene derivatives, unusual properties are obtained. For example, very large bathochromic shifts were observed for all of our compounds, and unprecedented green light emission occurs for the D/D system. In addition, very high radiative rate constants in solution and in the solid state were recorded for the D-π-D- and D-π-A-substituted compounds. All compounds show reversible one-electron oxidations, and Jul Pyr exhibits a second oxidation, with the largest potential splitting (ΔE=440 mV) thus far reported for 2,7-substituted pyrenes. Spectroelectrochemical measurements confirm an unexpectedly strong coupling between the 2,7-substituents in our pyrene derivatives.

. (2015) 'DA triarylboron compounds with tunable pushpull character achieved by modication of both the donor and acceptor moieties.', Chemistry : a European journal., 21 (1). pp. 177-190. Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

Boroles with a fluoromesityl group on the B atom have greatly improved air stability compared to their mesityl analogues.