Synthesis and characterization of aryl-substituted BODIPY dyes displaying distinct solvatochromic singlet oxygen photosensitization efficiencies

Three BODIPY derivatives substituted at meso position by aryl (phenyl or N,N-dimethylaminonaphthyl) groups and functionalized at position 2 with electron-withdrawing formyl or electron deficient benzimidazole heterocycle were synthesized and completely characterized by the usual spectroscopic techniques. A comprehensive photophysical study showed a remarkable enhancement of the singlet oxygen sensitization quantum yield for meso-substituted dimethylaminonaphthyl BODIPY with the decrease of the dielectric constant of the solvent (0.02–0.04 for dimethylsulfoxide vs. 0.84 in toluene). In toluene the triplet state formation for the aminonaphthyl substituted BODIPY's was found to be mediated by the intramolecular charge transfer state (ICT), whereas in polar solvents triplet state formation is hindered by fast recombination of the ICT state. Pump-probe transient absorption spectroscopy was used to characterize the photoinduced dynamics of the BODIPY derivatives from the femtosecond to the nanosecond time scale.FCT - Laserlab-Europe(REDE/1517/RMN/2005)This work was supported by the Fundação para a Ciˆencia e a Tec nologia (FCT), Portuguese Agency for Scientific Research, through the Coimbra Chemistry Centre projects UIDB/00313/2020 and UIDP/ 00313/2020 and through the Centro de Química (CQUM), project UID/ QUI/00686/2020. The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Reequipment, contract REDE/ 1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT. Raquel C. R. Gonçalves acknowledges FCT for funding (SFRH/BD/ 05278/2020). The research leading to these results has received funding from Laserlab-Europe (grant agreement no. 284464, EC’s Seventh Framework Programme)