We report on a series of π-conjugated styryl quinolinium push-pull chromophores and investigate their pH-triggered linear and nonlinear optical properties. Two pH-sensitive functional groups are located at electron acceptor and electron donor, respectively. New styryl quinolinium derivatives with protonated quinolinium group (NHQ) at electron acceptor have dimethylamino, methoxyphenol and phenol group acting as an electron donor for 2-(4-(dimethylamino)styryl)quinolinium 4-methylbenzenesulfonate (DA-NHQ), 2-(4-hydroxy-3-methoxystyryl)quinolinium 4-methylbenzenesulfonate (HM-NHQ), 2-(4-hydroxystyryl)quinolinium 4-methylbenzenesulfonate (OH-NHQ), respectively. These derivatives exist in three different chemical forms that can be interconverted using changes in pH values.
We characterize their optical properties by absorption, fluorescence and hyper-Rayleigh scattering measurements in various pH values. Results show that styryl quinolinium derivatives exhibit three states switching mode of fluorescent (FL) and nonlinear optical (NLO) response with high contrast. Interestingly, these derivatives display different FL/NLO switching modes, and therefore have a high potential for imaging applications.
