Corrole–ferrocene and corrole–anthraquinone dyads: synthesis, spectroscopy and photochemistry

Abstract

Two different donor-acceptor systems based on corrole-ferrocene and corrole-anthraquinone having the 'Olefin Bridge' at the β-pyrrole position have been designed and synthesized. Both the dyads corrole-ferrocene () and corrole-anthraquinone () are characterized by elemental analysis, ESI-MS, (1)H NMR, UV-Visible, fluorescence spectroscopies (steady-state, femtosecond time-resolved), femtosecond transient absorption spectroscopy (fs-TA) and electrochemical methods. (1)H-NMR shows that two doublets at 6.50 and 7.25(δ) ppm belong to vinylic protons, which are characteristic of the formation of dyads. UV-Visible absorption spectra showed that dyads are merely superpositions of their respective constituent monomers and dominated by corrole S1 ← S0 (Q-band) and S2 ← S0 (Soret band) transitions with a systematic red-shift of both Soret and Q-bands along with the broadening of the bands. A prominent splitting of the Soret band for both the dyads is observed due to bulky substitutions at the peripheral position, which deviate from the planarity of the corrole macrocycle. Both the dyads exhibit significant fluorescence emission quenching (95-97%) of corrole emission compared to the free-base corrole monomer. Emission quenching is attributed to the excited-state intramolecular photoinduced electron transfer (PET) from corrole to anthraquinone in the dyad, whereas in the dyad it is reversed. The electron-transfer rates (kET) for and were found to be 3.33 × 10(11) and 2.78 × 10(10) s(-1), respectively. Despite their very different driving forces, charge separation (CS) and charge recombination (CR) are found to be in identical timescales.

Strategies for Corrole Functionalization

“…A complementary strategy was reported by Giribabu and co-workers, , that selected the corrole derivative 199 as the phosphonium salt partner (Figure ). The condensation of this compound with aldehydes allowed the synthesis of the donor–acceptor dyads 200 – 203 .…”

“…All dyads exhibit significant fluorescence emission quenching (higher than 88%) of the corrole emission when compared to the free-base corrole monomer. The authors remarked that depending on the moiety attached to the corrole the corrole unit may act as electron donor or as electron acceptor …”

Pyrene Appended Free‐base, Phosphorus(V) and Gallium(III) Corroles and Their β,β′‐Linked Corrole Dimers: Synthesis, Photophysical and Electrochemical Properties

“…Recently, many corrole conjugates having donor (D) – acceptor (A) units have been reported with a variety of chromophores, possessing various connectivities. For example, corrole‐ BODIPY conjugates, [31–34] PBI‐corrole‐diphenylamine triad, [35] corrole‐fullerene dyad, [36] corrole‐porphyrin conjugates, [37–44] corrole‐anthraquinone dyad, [45] corrole‐ferrocene conjugates, [45,46] and corrole‐fluorene dyad, [47] have been investigated. In most of these examples, the electronic effect of the two chromophores has been probed and their utility for light harvesting applications investigated.…”

Triphenylamine corrole dyads: Synthesis, characterization and substitution effect on photophysical properties

“…21 The potentiality of stable corroles depends on their ability to display within the arrays either efficient energy or electron transfer process following light absorption. In the design of photoactive arrays, corroles can play the role of energy acceptors more easily than that of energy donors, due to their relatively low excited state energy level; examples are triphenylamine-corrole, 21 coumarin-corrole, 22 ferrocene-corrole, 23,24 phenathiazine-corrole, 25 carbazolecorrole, 26 BODIPY-corrole, 27 porphyrin-corrole, 28,29 etc. In addition, they have been employed as electron donors rather than electron acceptors, due to the relative ease of oxidation of their macrocycle, depending on the substitution pattern; as in the case of corrole-fullerene, 30 corrole-napthalimide, 31 corrole-perlynbisimide, 32 corroleanthraquinone, 33 etc.…”