Near-infrared luminescent Sn(IV) complexes of N-confused tetraphenylporphyrin: Effect of axial anion coordination

Novel tin(IV) halo complexes of an N-confused tetraphenylporphyrin with different axial ligands have been synthesized and characterized by various spectroscopic methods including X-ray crystallographic analysis. The molecular structures of the dichloro and dibromo derivatives possess perfect octahedral geometries, which are nearly comparable to the corresponding regular porphyrin complexes. In contrast, the iodide/triiodide complex obtained by a same reaction manner, demonstrated that the tin(IV) cation is slightly displaced towards axially coordinated iodide anion, giving rise to the different electronic structure due to the tautomeric form of N-confused porphyrin ligand. These structural differences reflected to the distinct photophysical and electrochemical properties. The Sn(IV) complexes are near IR luminescent, however the unsymmetrical axial coordination of iodide and triiodide anions in the tin(IV) N-confused porphyrin complex allows, in particular, the longer emission lifetimes and a smaller singlet-triplet energy gap, which were investigated by steady-state and time-resolved spectroscopies as well as theoretical calculations.