Molecular recognition of C70-fullerene by meso-phenyl bodipy dye

The ground and excited states interaction of 4,4-difluoro-1,3,5,7-tetramethyl-2,6-diethyl-8-phenyl-4-bora-3a,4a-diaza-s-indacene (2), the meso-phenyl congener of the well-known boradipyrromethene (bodipy) dye PM567 (1) with C60 and C70 (F) was investigated in non-polar (toluene) and polar coordinating (benzonitrile) solvents. This dye 2 can efficiently recognize C70 in both the solvent media. It is the first report of wavelength ratiometric sensing of fullerenes (F) in both the ground and excited state. The dye (2) showed higher binding selectivity with C70 over C60 in both benzonitrile and toluene having selectivity ratio C70/C60~100 and ~6 respectively. Interestingly, the binding preference of the dye 2 with C70/C60 was opposite to that observed with the dye 1 (possessing a meso-methyl group), revealing that the selectivity can be tuned by subtle changes in the bodipy structure. The results were rationalized by 1H NMR and DFT based calculation of the HOMO-LUMO interactions of the adduct.