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

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.