Exploring BINOL-O-BODIPY-based dimers as advanced chromophoric platforms enabling triplet state population

The development of chromophoric systems that populate triplet states upon light absorption, i.e. triplet state photosensitizers (TS-PSs), has great interest for many applications in diverse fields beyond Organic Photochemistry, such as Biomedicine (e.g., in singlet-oxygen-based photodynamic therapy, PDT, and phototheranosis) or Sustainable Energy (e.g., in photocatalytic water splitting). Despite the high fluorescence of the BODIPY (boron dipyrromethene) dyes, they can be suitable and valuable candidates as advanced TS-PS scaffolds, owing to their outstanding light-absorption capability and their tuneability by workable organic chemistry, as well as to the existence of well-known designing strategies to promote the required intersystem crossing (ISC) towards the TS. Among these strategies, the use of heavy atoms, such as iodine or heavy metals is one of the most used. However, these dyes usually suffer from the potential toxicity of said heavy atoms, limiting their application in Biomedicine. Another approach is based on the construction of orthogonal (directly-linked) BODIPY dimers, although this strategy is not general and usually requires complex syntheses. Additionally, modulating the population of intramolecular charge transfer (ICT) states in BODIPYs has emerged as a potential tool for designing TS-PSs, since ICT states can serve as runways promoting the ISC. Among these ICT-modulable-BODIPYs, two easily-accessible designs have been studied: meso-meso p-phenylene-bridged BODIPY-BODIPY dimers and BINOL-O-BODIPYs. In this context, we hypothesized that putting both designs together within the same molecule could be a potential strategy to boost triplet population in heavy-atom-free BODIPYs. This communication shows preliminary results related to this investigation, concerning the design, synthesis and photophysical characterization, including fluorescence and singlet oxygen generation, of the new dyes combining both features.