Synthesis and anion binding studies of thiaphlorins and covalently linked thiaphlorin-porphyrin dyads

Abstract

A series of thiaphlorins with N₂S₂ and N₃S cores have been prepared in decent yields from readily available precursors. The thiaphlorins were characterized by all spectroscopic techniques and the structures of two thiaphlorins were solved by X-ray crystallography. The spectral studies indicated that the properties of thiaphlorins were quite different from those of thiaporphyrins. The methodology used for the synthesis of thiaphlorins has been extended to synthesize a series of monofunctionalized thiaphlorins. We also performed functional group transformation of thiaphlorins without decomposition, supporting the conjecture of the stable natures of thiaphlorins. The crystal structure analysis of two thiaphlorins indicated that the macrocycles are not planar and that they each show a marked kink at sp³-hybridised meso carbon. The functionalized thiaphlorins have been used to synthesize several novel porphyrin–thiaphlorin dyads as well as a bis(thiaphlorin) dyad under mild palladium(0) coupling conditions. Preliminary anion-binding studies carried out on thiaphlorins and porphyrin–thiaphlorin dyads indicated that they can bind anions effectively in their protonated forms and that these systems can also be used as optical sensors.