Novel butterfly-shaped AIE-active pyrrolopyrrole aza-BODIPYs: synthesis, bioimaging and diamine/polyamine detection

Abstract

Constructing novel near-infrared (NIR) fluorophores with an aggregation-induced emission (AIE) character is of particular interest but remains challenging. In this work, we linked two propeller-shaped alkoxyl-substituted tetraphenylethylene (TPE) to the short axis of a pyrrolopyrrole aza-BODIPY (PPAB) core by a phenylene spacer to form three novel NIR dyes (PPAB-TPE1–PPAB-TPE3). Due to the butterfly-shaped conformation and non-planar molecular structure, three dyes exhibited typical AIE characteristics with up to 390-fold fluorescence enhancement in the aggregated state. The structural effects on their photophysical properties and solvatochromic behavior via experimental and theoretical approaches were studied. The results indicated that attaching an AIE rotor along the short axis of PPAB is an efficient and facile strategy to construct AIE-active NIR dyes. Taking PPAB-TPE1 as an example, the resulting nanoparticles encapsulated by an amphiphilic copolymer F-127 had a small size and NIR emission, which showed potential application to bioimaging in HeLa cells. Moreover, PPAB-TPE1 showed sensitive and selective detection of diamine/polyamine with an over 210 nm hypsochromic shift in the absorption maximum and ratiometric fluorescence “turn on” process. The limit of detection was up to 0.053 μM. Visual putrescine gas detection with colorimetric and ratiometric fluorescent modes was also demonstrated.