Integrating Twisted and Push-Pull Structural Motifs for Efficient Dual-Functioning Near-Infrared BODIPY Photosensitizers

Abstract

Two strategies to achieve high singlet oxygen quantum yields are uniquely combined here into a single BODIPY‐based scaffold for dual‐functioning near‐infrared photosensitizers. A twisted BODIPY core is functionalized with electron‐donating moieties via Knoevenagel condensation with the aim to take advantage of both twist‐induced and spin‐orbit charge‐transfer intersystem crossing and thereby realize efficient triplet generation. All the synthesized molecules exhibit red‐shifted absorption and emission, falling into the phototherapeutic window, and varying ratios of singlet oxygen production and fluorescence emission. In particular, the BODIPY derivative decorated with a dimethylacridine donor displays a favorable balance between singlet oxygen and fluorescence quantum yields (in chloroform medium). Quantum‐chemical analysis suggests that the high singlet oxygen quantum yields primarily result from spin‐orbit charge‐transfer intersystem crossing, with transient absorption spectroscopy confirming the involvement of a charge‐transfer state for the push‐pull dyads. This work hence provides guidance for the rational design and optimization of innovative photosensitizers for image‐guided photodynamic therapy.