Introducing chiral N-BODIPYs: Promising dyes for chiroptical applications

N-BODIPYs (diaminoborondipyrromethenes) have been recently described by us for the first time as a new family of BODIPY dyes with huge technological potential. This new dyes retain the effective photophysical behavior exhibited by other boron-substituted BODIPYs, such as O-BODIPYs. However, key bonding features of nitrogen compared to those of oxygen (enhanced bond valence and different bond directionality) open up new possibilities for functionalizing BODIPYs, for example the existence of more pendant moieties near the chromophore (from two in O-BODIPYs, up to four in N-BODIPYs). This fact increases the synthetic versatility of the new dyes and, therefore, increases the possibilities for controlling their photophysics.¹

On the other hand, we have also designed a simple new structural motif to achieve circularly polarized luminescence (CPL) from inherently achiral monochromophore systems. This design is based on a spiranic BINOL-derived O-BODIPY dye and provides CPL levels (|g_lum|) in solution falling into the usual range (10⁻⁵ to 10⁻²) of that obtained from other simple organic molecules (SOM).^2,3

With the aim of expanding the up-to-now limited number of structures for CPL-SOMs, we have combined together the two new findings (N-BODIPY and CPL-active monochromophoric spiranic BODIPY) to synthesize a series of chiral spiranic N-BODIPYs. The study of the circular dichroism (CD) of these BODIPYs will provide a first insight into the potential of these new dyes in Chiroptics, including CPL. This communication reports the most important results concerning the conducted study.

[1] Ray, C.; Díaz-Casado, L.; Avellanal-Zaballa, E.; Bañuelos, J.; Cerdán, L.; García-Moreno, I.; Moreno, F.; Maroto, B. L.; López-Arbeloa, Í.; de la Moya, S., N-BODIPYs Come into Play: Smart Dyes for Photonic Materials. Chem. Eur. J. 2017, 23 (39), 9383-9390.

[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 (9), 3346-3349.

[3] Sánchez-Carnerero, E. M.; Agarrabeitia, A. R.; Moreno, F.; Maroto, B. L.; Muller, G.; Ortiz, M. J.; de la Moya, S., Circularly Polarized Luminescence from Simple Organic Molecules. Chem. Eur. J. 2015, 21 (39), 13488-13500.