Quenching kinetics of the acridine excited state by vinyl monomers in homogeneous and micellar solution

Abstract

The quenching of singlet and triplet electronic excited states of acridine cation by vinyl monomers is investigated in homogeneous (methanol), aqueous, and reverse micelles of sodium dodecyl sulfate (SDS). The fluorescence quenching of the dye by styrene derivatives in methanol as well as in aqueous SDS micelles is very efficient with quenching rate constants of the order of 10 ¹⁰ M ^-1 s ^-1 and 5×10 ⁷ s ^-1 , respectively. However, triplet quenching rate constants in methanol are much lower than the diffusion controlled limit, and no dye photoblenching is observed suggesting that a quenching process follows a reversible photoinduced charge-transfer mechanism. The fluorescence quenching of the dye by styrene derivatives in reverse SDS micelles is a pseudo-first-order process with no micellar quenching transient. It is shown that placing the dye inside a reverse micelle substantially reduces the quenching rate by styrene derivatives. The scope of this effect on photoinitiation efficiency for radical polymerization of styrene derivatives via a photoredox process of cationic dyes in reverse micelles is discussed. Association constants of vinyl monomers to SDS micelles, K, as well as partition coefficients in n-octanol/water have been also determined using the fluorescence quenching method. K is correlated with the boiling points of the vinyl monomers.