Fluorescent Oligomers Built with Triazole-Based Turn-Motifs: Length- and Solvent-Dependent Photophysical Properties

Abstract

Foldable oligomers can reversibly change their conformations under specific conditions. Among such molecules, fluorescent foldamers could potentially allow for the detection of the folding events by straightforward spectroscopic measurements. We have designed and synthesized foldable oligomers by using N-2-aryl substituted bis(triazolo)benzene motif as a conformationally well-defined and fluorescent repeating unit. These new π-conjugated oligomers were constructed by consecutive reduction, azo coupling, and oxidative cyclization reaction sequences, which facilitated access to a series of fluorescent (F = 81–83%) oligomers from pre-assembled building blocks. Our structure design and synthetic strategy allow for a precise control over both the chain length and interchromophore spatial relationship, which was also confirmed by X-ray crystallographic studies on select systems. In addition, solvent-dependent interchromophore interactions elicited significant changes in fluorescence intensity, which becomes more pronounced with increasing chain length.