Solid-State Structure and Spectroscopy of Chromoionophoric Acridinium Derivatives

Abstract

Abstract A comparative study is presented of the chromoionophoric and fluoroion-ophoric behaviour of 1 and 2, which both consist of an aza-crownether-ionophore integrated with a twisted 9-aryl-acridinium chromophore. In 2 the degree of ground state twisting in the chromophore is enhanced relative to that in 1. While the cation induced spectral shifts (i.e. chromoionophoric effect) in 2 are not significantly different from those in 1, the cation binding properties of 2 are enhanced significantly. This is explained in terms of better preorganisation of 2 and higher charge density of the anilino nitrogen in 2 as supported by X-ray data. In addition to their chromoionophoric properties, the non-fluorescing 1 and 2 show an acridiniumtype of fluorescence upon binding of H+ and Ag+ ions. This fluoroionophoric effect is also significantly enhanced in 2 where restricted internal rotational freedom allows for a higher fluorescence quantum yield of the complex.