Synthesis of new porphyrinoid dyads linked with a butenyne bridge via the Sonogashira reaction

Abstract

Conjugated porphyrin dyads have valuable electron-optical properties that make them useful for a variety of applications. Two dyads of palladium(II) β-octaethylporphyrin linked with a butenyne bridge to nickel(II) meso-diphenylporphyrin and methyl pyropheophorbide-a were synthesized using the Sonogashira cross-coupling reaction. Both dyads exhibited optical properties considerably different from their corresponding components, which indicated strong electronic interaction between the units in the dyads in both the ground and excited states, providing fast energy flow between the chromophores. DFT calculations revealed the structural features of the dyads in interconnection with their electronic properties. Conjugation energy gain forced a decrease in the dihedral angle between the porphyrin plane and the linking carbon–carbon double bond, although at the expense of distortion of the diphenylporphyrin ring. Electron transitions upon excitation comprise molecular orbitals centered on both chromophores, and their interaction led to an emerging new bathochromically shifted Soret band component at 460 nm. The palladium porphyrinate–chlorin dyad exhibits luminescence properties in the red visible range at room temperature and phosphorescence in the near-infrared (NIR) range at 77 K. In contrast, the palladium–nickel porphyrinate dyad does not emit light but absorbs light more efficiently across the entire visible spectrum. Both dyads feature broad and strong absorption representing panchromatic-like dyes. These dyads could be useful as potential photosensitizers for solar light conversion devices.