J- and H-aggregates of heavy-atom-free Aza-BODIPY dyes with high 1O2 generation efficiency and photodynamic therapy potential

Abstract

Aggregation of molecules offers a facile way to tune the optical properties of dyes, thus providing a design platform for organic nano-photosensitizers (PSs) with the potential in photodynamic therapy (PDT). However, it is still a great challenge to control the molecular organization of dye monomers to form a specific aggregation to maximize the efficiency of PDT. Herein, we present a novel supramolecular strategy to build nano-PSs from metastable aggregation of heavy-atom-free Aza-BODIPY dyes (BDP-1 and BDP-2) bearing pyridine units, which represented high singlet oxygen (1O2) generation efficiency (up to 0.85–0.89) to overcome the several intrinsic drawbacks of traditional heavy-atom Aza-BODIPY PSs. X-ray crystallographic analysis and theoretical calculations revealed that multiple intermolecular electrostatic interactions triggered the formation of J- and H-aggregates, which transformed excited state properties of the chromophores and promoted the intersystem crossing (ISC) process by reducing singlet-triplet energy gaps (ΔEST) and radiative decay. This study provides insights for clarifying the relationship between molecular structure and aggregates properties by ingenious molecular design and engineering, which should open up new opportunities to construct functional aggregates for PDT.