Synthesis of stannyl porphyrins and porphyrin dimers via Stille coupling and their 119Sn NMR and fluorescence properties

Free base stannyl porphyrins and free base porphyrin dimers have been successfully synthesized via copper-free Stille coupling in 21−67% yields. This approach provides an access to stannyl porphyrin synthons that were previously unavailable. Moreover, variation of the reaction conditions selectively provides access to either stannyl porphyrins or porphyrin dimers. Full 119/117Sn NMR analysis was used for characterization of the stannyl porphyrins and detailed 119Sn-1H-13C NMR analyses were carried out on a series of the starting tin reagents and the stannyl porphyrins. These investigations indicate that significant structural information can be gathered by use of commonly known NMR techniques. Photophysical properties of the novel porphyrins prepared including absorption, emission, and fluorescence lifetimes were investigated. The stannyl porphyrins emitted in the visible region, and in all cases large Stokes shifts were observed. The emission intensities of the stannyl porphyrins were 100-fold higher than those of the starting bromoporphyrins. Measured fluorescence lifetime (S0→S1) of the stannyl and dimeric porphyrins were in the 7.7−12 ns region.