CHEMILUMINESCENSE OF 1,1'-BIISOQUINOLINIUM AND 2,2'-BIQUINOLINIUM SALTS - REACTIONS OF ELECTRON-RICH OLEFINS WITH MOLECULAR-OXYGEN

2,2'-Dialkyl-1,1'-biisoquinolylidenes (BIQ), having been prepared by t wo-electron reduction of the corresponding diquaternary salts BIQ(2+)( X-)(2), react with triplet dioxygen to produce chemiluminescence (CL). In aprotic solvents, the kinetics of the reaction are first-order wit h respect to the concentrations of the substrate and of oxygen. The se cond-order rate constants at 25 degrees C increase in the order DMF < MeCN < DMSO, which correlate:with the free energy change for an electr on-transfer (ET) from BIQ to O-2, although this process is endothermic in all three solvents; In non-polar solvents such as benzene, the rea ction proceeds much more slowly. From these results; a reaction mechan ism is proposed as follows. An ET or partial charge-transfer gives a r adical ion pair {BIQ(.+)... O-2} or a CT complex, in which intersystem crossing takes place from the triplet to the singlet state, and then radical coupling at the 1-position followed by cyclisation yields a 1, 2-dioxetane, the postulated intermediate of the CL reaction; An electr on-rich olefin having a closely related structure, 1,1'-dimethyl-2,2'- bisquinolylidene (BQ), shows a similar redox behaviour to that of BIQ. Reaction of BQ with O-2 produces CL, and the emitter has been identif ied as the singlet excited state of 1-methyl-2(1H)-quinolinone 8a. The effects of substituents in the quinoline ring on the autoxidation rat e have been investigated in MeCN and DMSO. An olefin having the more n egative oxidation potential shows the higher reactivity to O-2, sugges ting that the autoxidation of BQ should take place via a similar react ion pathway as that of BIQ.