Synthesis of ternary BODIPY-(Zn-porphyrin) ₂ conjugates aimed at the structure-specific photoresponse

This work aims to design BODIPY-(Zn-porphyrin) 2 conjugates that channel all harvested light energy into one conjugate moiety, providing a specific photoresponse with an extended excitation range. Three BODIPY-porphyrin conjugates have been prepared, and their excitation energy deactivation channels have been established. In two of them, the BODIPY π-conjugation was extended at either the 2,6-positions or the 3,5-positions via Sonogashira coupling. Then the click reaction was applied to conjugate it to two Zn-porphyrins. The π-conjugation extension shifts the BODIPY absorption spectra bathochromically, with the 3,5-substituted BODIPY spectra being more shifted compared to those of the 2,6-substituted ones. These BODIPY-(Zn-porphyrin) 2 conjugates exhibit fluorescence spectra that are almost identical to those of the parent BODIPYs, independently of the excitation wavelength. The Zn-porphyrin transfers its own excitation energy to the BODIPY moiety and simultaneously acts as a BODIPY fluorescence quencher by enhancing the BODIPY radiationless transition rate in the conjugate. The third BODIPY-(Zn-porphyrin) 2 conjugate was prepared by attaching two Zn-porphyrins via click reaction to azide groups in the meta-positions of the phenyl ring at the 8-position of BODIPY. Here, the BODIPY moiety harvests the excitation energy, which ultimately goes to the Zn-porphyrins with no traces of BODIPY emission. Notably, the intramolecular transition rates in the Zn-porphyrins remain unperturbed in the conjugate.