Meso-to-meso Sulfide- and Disulfide-Bridged Subporphyrin Dimers

Treatment of meso-chlorosubporphyrin with controlled equivalents of Na₂S·9H₂O in DMF led to the formation of either meso-to-meso sulfide (S)-bridged dimer 4 or disulfide (SS)-bridged subporphyrin dimer 6. S-bridged dimer 4 displayed a split Soret-like band and a large Stokes shift and became a fully delocalized one-quantum system in the S₁ state, as indicated by femtosecond transient absorption anisotropy measurements and theoretical calculations. Contrastingly, SS-bridged dimer 6 showed a broad but nonsplit Soret-like band, no fluorescence, and very fast S₁ decay with a lifetime of 4 ps, which indicated the presence of a rapid decay channel.