Panchromatic π‐Extended Porphyrins from Conjugation with Quinones

Abstract

Typical porphyrins are coloured compounds due to their characteristic wavelength‐selective visible light absorptions. An exceptional “blackened” ZnII–porphyrin was recently obtained from fusing the β,β′‐positions of the porphyrin core with four quinone units. Here, studies with metal‐free and NiII‐containing analogues are reported. These quinone‐fused porphyrins were prepared from the corresponding β,β′‐tetrasulfolenoporphyrins via thermally generated porphyrindienes, which were trapped by [4+2] cycloaddition as benzoquinone cycloadducts, which were subsequently oxidised. By using this strategy, metal‐free and NiII‐containing porphyrins with one, two, three or four conjugated naphthoquinone moieties were prepared efficiently. The presence of the π‐conjugated naphthoquinone moieties changed the porphyrin chromophores profoundly, giving broadly absorbing “blackened” pigments. The influence of coordinated NiII ions, or of the absence of a metal ion in the modified porphyrin core, on their structural and spectroscopic properties was explored. Blackened quinone‐conjugated porphyrins might be pigments suitable for solar energy conversion. With their unique peripheral functional groups they are also a set of porphyrins “programmed” for further covalent extension. Thus, they are building blocks for the preparation of supra‐porphyrinoid assemblies that might be useful in optoelectronics and in the nanosciences.

Molecular flattening effect to enhance the conductivity of fused porphyrin tape thin films

“…[15][16][17][18] Particularly, the extension of the porphyrin p-system plays an important role in the enhancement of their optical properties yielding NIR absorbers. [19][20][21][22][23] One application of these materials is the production of bulk heterojunction solar cells. 24 The extension of the porphyrin p-conjugation generally increases the absorption in the Q-band region and widens the fraction of the solar spectrum that can be used for the conversion of energy.…”

Grafting Copper and Gallium Corroles onto Zinc Oxide Nanoparticles

“…In order to improve the harvesting of solar energy in a broad spectral region, it is important to extend the corrole energy absorption across the visible spectrum as much as possible. As already documented, β ‐pyrrolic modification and extension of the porphyrin π system significantly broadens and redshifts the light absorption . In this context, very recently, the expansion of corrole aromaticity was reported by our group, affording a number of corrole derivatives in good yields ,,…”

“…As already documented, β-pyrrolic modification and extension of the porphyrin π system significantly broadens and redshifts the light absorption. [10][11][12][13] In this context, very recently, the expansion of corrole aromaticity was reported by our group, affording a number of corrole derivatives in good yields. [8,14,15] Immobilization of the absorbing dye molecules onto the surface of semiconducting metal oxide nanoparticles, which collectively act as the working electrode of a dye-sensitized solar cell (DSSC), is crucial for initiating an electrical current via the injection of electrons from the dye into the conduction band of the metal oxide.…”

Quinone-fused porphyrins as contrast agents for photoacoustic imaging

“…S4 † ). 15 , 16 Porphyrins typically show changes in their photophysical properties with complexed metals in the core, as seen for black porphyrins 3-2H and 3-M (M = Ni and Zn). As the quinone moiety exhibits electron accepting and excited state quenching properties, the dyes do not show 1 O 2 /ROS generation upon excitation with light, which is highly beneficial for purely diagnostic applications.…”

“… 12 , 13 As a basis for the synthesis of NIR chromophores, porphyrins are envisaged with a variety of linkages, 13 in which an anthraquinone as a bridging synthon can be applied. 14 Tetra naphthoquinone-conjugated porphyrins absorb in the whole visible and NIR range, 15 , 16 thus, their appearance in organic solutions (CH 2 Cl 2 /methanol) is black. Therefore, and due to the absence of fluorescence emission, the application of such dyes for biomedical photoacoustic imaging is highly promising ( Fig.…”