Synthesis and studies of covalently linked porphyrin-expanded heteroporphyrin dyads

Abstract

Mono-functionalized core-modified sapphyrin (with a N₂S₃ core) and smaragdyrin (with a N₄O core) containing a meso-iodophenyl functional group were synthesized by following a [3+2] condensation approach using appropriate precursors. The mono-functionalized sapphyrin and smaragdyrin building blocks were used to synthesize the first examples of diphenyl ethyne bridged porphyrin–sapphyrin and porphyrin/Zn^II porphyrin–smaragdyrin dyads under mild Pd⁰-coupling conditions. The dyads are freely soluble in common organic solvents and were characterized by various spectroscopic techniques. Photophysical studies indicated the possibility of energy transfer from the porphyrin/Zn^II porphyrin sub-unit to the smaragdyrin sub-unit in porphyrin/Zn^II porphyrin–smaragdyrin dyads. The potential of these dyads as fluorescent sensors for anions was explored. The studies indicated that the porphyrin–sapphyrin dyad cannot be used as fluorescent sensors, whereas the porphyrin–smaragdyrin dyad was suitable.