Synthesis and Studies of Covalently Linked Porphyrin-Expanded Heteroporphyrin Dyads

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 Pd-0-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.