Emission characteristics and micellization of cationic 1,4-bis(β-pyridyl-2-vinyl)benzene laser dye

Abstract

Cationic species of the recently reported 1,4-bis(β-pyridyl-2-vinyl)benzene (P2VB) blue laser dye has been generated by direct protonation and identified analytically. The steady state emission and the emission quantum yields have been studied both in aqueous and in micellar media. The hydrochloride derivative (P2VB · HCl) shows a substantial increase in fluorescence quantum yields (ϕ_f) as a result of both cationic and anionic micellization. Micellization also induces weak laser action in P2VB · HCl dye upon pumping with a nitrogen laser.

The photochemical quantum yield of P2VB · HCl(λ_ex= 337 nm) has been evaluated as ϕ_c= 0.003 and contrasted to that of the parent V2VB dye, for which ϕ_c= 0.004.

Both conductometric and surface tension studies reveal a ground-state aggregation of P2VB · HCl at a critical concentration of ca. 7.5 × 10^–3 mol dm^–3. Excited-state molecular aggregation has also been observed in concentrated P2VB · HCl solutions which show excimeric emission at 500 nm. The enthalpy of excited-state photoassociation has been evaluated as ΔH_a=–11.0 kJ mol^–1 indicating that P2VB · HCl molecules in the excimer configuration are bound less tightly.