title: Phosphorus complexes of meso-triaryl-25-oxasmaragdyrins.
abstract: The aromatic PO2 complexes of meso-triaryl-25-oxasmaragdyrins were synthesized by treating the free base 25-oxasmaragdyrins with POCl3 in toluene/triethylamine at refluxing temperature. The complexes are stable and characterized by X-ray and different spectroscopic techniques. In these complexes, the phosphorus(V) ion was bound to two pyrrolic nitrogen atoms of the smaragdyrin macrocycle and two oxygen atoms in tetrahedral geometry. The X-ray structure revealed that the smaragdyrin macrocycle showed significant distortion upon insertion of a PO2 unit, and the phosphorus atom lies 1.339 Å above the mean plane defined by three meso-carbon atoms of the macrocycle. These complexes absorb strongly in the visible region and are 2.5 times more strongly fluorescent than free base 25-oxasmaragdyrins. The smaragdyrin macrocycle becomes electron-deficient upon complexation with a PO2 unit because these complexes are easier to reduce but difficult to oxidize compared to free base smaragdyrins. We designed and synthesized a covalently linked BODIPY-PO2-smaragdyrin dyad and demonstrated efficient energy transfer from the BODIPY unit to the PO2-smaragdyrin unit.
authors.affiliation: Department of Chemistry, Indian Institute of Technology , Powai, Mumbai 400076, India.
authors.forename: Hemanta
authors.initials: H
authors.lastname: Kalita
authors.forename: Way-Zen
authors.initials: WZ
authors.lastname: Lee
authors.forename: Mangalampalli
authors.initials: M
authors.lastname: Ravikanth