Synthesis and properties of cyclophosphazenes appended with covalently linked porphyrin–ferrocene conjugates

Cyclotriphosphazene and cyclotetraphosphazene appended with six and eight covalently linked porphyrin–ferrocene conjugates respectively were synthesized by treating N3P3Cl6 and N4P4Cl8 with appropriate equivalents of ferrocene linked porphyrin containing meso-hydroxyphenyl group in THF in the presence of Cs2CO3 followed by column chromatographic purification. NMR and absorption studies indicated a weak interaction between adjacent porphyrin–ferrocene conjugates. Electrochemical studies supported electrochemical equivalence of ferrocenyl and porphyrinyl moieties in these multi-porphyrin–ferrocene conjugate assemblies. The fluorescence studies showed significant quenching of porphyrin fluorescence due to photo-induced electron transfer from ferrocene to singlet state of porphyrin unit in these assemblies.

Synthesis, spectral and electrochemical properties of cyclophosphazenes appended with porphyrin–ferrocene conjugates are described.Figure optionsDownload as PowerPoint slideHighlights
► Multi-porphyrin–ferrocene conjugate assemblies on cyclophosphazenes were synthesized.
► Cyclophosphazene rings are robust and stable.
►  Absorption studies showed three/four fold intensity enhancement.
► Electrochemical studies supported electrochemical equivalence of ferrocene units.
► Fluorescence quenching was attributed to photo-induced electron transfer.