Synthesis and photophysical properties of a bichromophoric system hosting a disaccharide spacer

The synthesis of an efficient energy donor-acceptor system is reported, together with its photophysical properties. The bichromophoric species has been conceived to show potentialities for biological applications since a biocompatible disaccharide spacer, constituted of D-galactose and D-glucose derivatives, was used in compound 12 to connect two BODIPY units with different absorption/emission properties. The luminescence spectrum in acetonitrile of 12 shows an intense fluorescence band with a maximum at about 770 nm that is almost identical to that of the lowest-energy BODIPY, regardless of the excitation wavelength used. The quantum yield is 0.2 with an excited state lifetime of 2.5 ns. Excitation and ultrafast transient absorption spectroscopy demonstrates that a very efficient energy transfer takes place in 12 from the highest-energy lying BODIPY subunit to the lowest-energy emissive BODIPY moiety, with a time constant of about 31 ps. Noteworthily, the emission of 12 falls in the near infrared window, suitable for potential biological applications.