Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

Abstract

Irrespective of the dielectric constant (ε) or the hydrogen-bonding ability of a pure solvent, the lowest excited singlet state (DBA*) of 9,10-dibromoanthracene (DBA) is quenched by ground-state 2,5-dimethylhexa-2,4-diene (DMHD) giving rise to the appearance of an exciplex emission. By means of sub-picosecond and nanosecond laser photolysis as well as steady-state photolysis, however, the following solvent-dependent results are obtained; (1) in acetonitrile (ε = 37.5) and acetone (ε = 20.7), an exciplex (DBA-DMHD)* formed between DBA* and DMHD generates the DBA radical anion (DBA' -) as an intermediate for formation of 9-bromoanthracene (BA) from DBA; (2) in ethanol (ε = 24.6), 2-propanol (ε = 19.9), 1-octanol (ε = 10.3), diethyl ether (ε = 4.34), and heptane (ε = 1.92)" a neutral radical species (NR') generated by decomposition of (DBA-DMHD)* (or by a reaction of DBA* with DMHD) is an intermediate for formation of a dibenzobicyclo[2.2.2]octadiene-type compound (a [4+2] adduct); (3) both DBA'-and NR' are generated in methanol (ε = 32.7) but the rate (v) of BA formation upon steady-state photolysis of DBA in the presence of 1 M DMHD decreases in the order of v(acetonitrile, ε = 37.5) > v(acetone, ε = 20.7) > methanol, ε = 32.7). It thus can be concluded that the mechanism of exciplex decomposition and the reaction of DBA* with DMHD are affected by not only the dielectric constant of a pure solvent but also its hydrogen -bonding ability.

Dual Functional Full-Color Carbon Dot-Based Organelle Biosensor Array for Visualization of Lipid Droplet Subgroups with Varying Lipid Composition in Living Cells

“…To assess the sensitivity of CDs to the changes of LD lipid composition, the effect of different concentrations of TAG and CE on the luminescence of CDs was investigated. Chloroform, with a dielectric constant (ε) of about 4.8, is often combined with methanol for lipid dissolution. , However, to create an environment closer to the internal polarity of LDs (ε is about 2.1∼6.9) and consider the high polarity of methanol (ε is about 32.7) only chloroform was chosen as the solvent for dissolving TAG and CE. B-CDs and R-CDs show 79 and 77% decrease in fluorescence intensity as the TAG concentration decreases from 190 to 10 mg mL –1 (Figure C), while their fluorescence intensities decrease by 61 and 60% in the test of CE (Figure D).…”