Anthrylmethylamines and anthrylmethylazamacrocycles as fluorescent pH sensors—a systematic study of their static and dynamic properties

Abstract

The pH dependent fluorescence of various 9-mono- and 9,10-disubstituded anthracenes is reported. They have a compartmental structure: fluorophore (anthracene)–spacer (methylene)–and ionophore (mono-, polyamines, azamacrocycles). In these n-basic anthrylmethylamines the fluorescence of anthracene is intramolecularly quenched by unprotonated amine groups. The pK_A values have been evaluated by titration in order to calculate the amount (mole fraction) of each of the n + 1 differently charged species and their dependence on the pH. The fluorescence–pH profiles (intensities and lifetime versus pH) have been determined, and interpreted as the formation of differently protonated species with different fluorescence intensities and hence different fluorescence lifetimes. The experimentally determined fluorescence lifetime–pH profiles can be described by three lifetimes. This is corroborated by global analysis. The measurement of the fluorescence quantum yields of the completely protonated species yielded the radiative lifetimes. The rate constants and quantum yields of the photoinduced electron transfer (PET) are calculated for the species with shorter lifetimes and hence smaller fluorescence intensities.