Exploring BODIPY meso-enamines as singlet-oxygen photosensitizers for PDT

We have recently reported on the control of Vilsmeier-Haack processes in meso-methylBODIPYs with activated DMF as the electrophilic reagent.¹ Such a control allows the selective generation of beta-formylBODIPYs, BODIPY meso-enamines or BODIPY meso-iminium/enamine salts, by selecting properly the substitution pattern in the starting BODIPY, the hard (or soft) nature of the activated-DMF reagent, as well as the reaction conditions.¹ It was also shown that meso-enamination deeply alters the photophysical properties of the BODIPY chromophore, quenching efficiently the fluorescence by the activation of non-radiative de-excitation channels, including intramolecular charge transfer (ICT), which in turn enables singlet-oxygen generation.¹

This result, easy generation of a family of BODIPYs with potentiality to act as singlet-oxygen photosensitizers for photodynamic therapy (PDT)² without involving heavy atoms or complex polyBODIPY designs, prompted us to detailed explore the scope of such a possibility. This presentation shows the results obtained from such an exploration, by reporting the most interesting results concerning singlet-oxygen generation in a selected family of BODIPY meso-enamines.

[1] Palao, E.; Montalvillo-Jiménez, L.; Esnal, I.; Prieto-Montero, R.; Agarrabeitia, A. R.; García-Moreno, I.; Bañuelos, J.; López-Arbeloa, I.; de la Moya, S.; Ortiz, M. J., Controlling Vilsmeier-Haack processes in meso-methylBODIPYs: A new way to modulate finely photophysical properties in boron dipyrromethanes. Dyes Pigments. 2017, 141, 286.

[2] a) Kamkaew, A.; Lim, S. H.; Lee, H. B.; Kiew, L. V.; Chung, L. Y.; Burgess, K., BODIPY dyes in photodynamic therapy. Chem. Soc. Rev. 2013, 42, 77. b) Awuah, S. G.; You Y., Boron dipyrromethane (BODIPY)-based photosensitizers for photodynamic therapy. RSC Adv. 2012, 2, 11169.