Synthesis and photophysical properties of orthogonal rhodium(iii)–carbon bonded porphyrin–aza-BODIPY conjugates

Abstract

This work reports the facile synthesis and photophysical properties of two novel near infrared (NIR) absorbing conjugates based on orthogonally arranged rhodium(III) tetrakis-4-tolylporphyrin (Rh^III(ttp)) and BF₂-chelated tetraarylazadipyrromethene (aza-BODIPY) linked by a covalent Rh–C(aryl) bond. These conjugates exhibit intense absorption and moderate fluorescence bands around 700 nm, which do not correspond with those of their aza-BODIPY precursors, due to the strong ground-state interaction between the aza-BODIPY and metal porphyrin moieties. DFT calculations predict that the energies of the 4d_xy, 4d_xz and 4d_yz orbitals of the central metal and the highest occupied MO of the aza-BODIPY moiety lie close to one another. Minor changes in the linkage position on the aza-BODIPY moiety can alter the relative energies of these MOs and hence have a significant impact on the optical and photophysical properties.