Chiroptical behavior of BINOL-based spiranic O-BODIPYs. A study on the influence of the structural factors

Spiranic O-BODIPYs bearing a phenol-based bi(polyarene) unit tethered to the boron center through oxygen atoms constitute an interesting family of BINOL-BODIPY dyads useful for the development of photonic applications due to their synthetic accessibility and tunable photonic properties. We found previously that the electron-donor capability of the involved BINOL moiety switched on a non-emissive intramolecular charge transfer (ICT) state, which restricted the fluorescence efficiency of the dyad. We demonstrated that the influence of this non-radiative deactivation channel can be efficiently modulated by the substitution pattern, either at the dipyrrin core or at the polyarene moiety, being possible to diminish or even virtually cancel the ICT probability, and hence achieve bright fluorescence upon dual excitation at far-away spectral regions.¹

Additionally, we demonstrated that this simple structural motif exhibits chiroptical properties (circular dichroism, CD, and circularly polarized luminescence, CPL), as a consequence of the chiral perturbation exerted by the BINOL-based unit over the inherently achiral BODIPY chromophore.²

Based on these previous results, we found interesting to carry out a comprehensive study on the influence of the structure of both the BODIPY chromophore and the BINOL moiety over the chiroptical properties of this family of O-BODIPYs, directed to the improvement of said properties for their use in photonic applications. This communication reports the most important preliminary results obtained from this study, directed to the design of improved BODIPYs for Chiroptics.

[1] Gartzia-Rivero, L.; Sánchez-Carnerero, E. M.; Jiménez, J.; Bañuelos, J.; Moreno, F.; Maroto, B. L.; López-Arbeloa, I.; de la Moya, S. Modulation of ICT probability in bi(polyarene)-based O-BODIPYs: towards the development of low-cost bright arene-BODIPY dyads. Dalton Trans. 2017, 46, 11830.

[2] Sánchez-Carnerero, E. M.; Moreno, F.; Maroto, B. L.; Agarrabeitia, A. R.; Ortiz, M. J.; Vo, B. G.; Muller, G.; de la Moya, S. Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores. J. Am. Chem. Soc. 2014, 136, 3346.