A Panchromatic Supramolecular Fullerene‐Based Donor–Acceptor Assembly Derived from a Peripherally Substituted Bodipy–Zinc Phthalocyanine Dyad

Abstract

A panchromatic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene-zinc phthalocyanine conjugate (Bodipy-ZnPc) 1 was synthesized starting from phthalocyanine aldehyde 4, via dipyrromethane 3 and dipyrromethene 2. Conjugate 1 represents the first example in which a Bodipy unit is tethered to the peripheral position of a phthalocyanine core. Electrochemical and optical measurements provided evidence for strong electronic interactions between the Bodipy and ZnPc constituents in the ground state of 1. When conjugate 1 is subjected to photoexcitation in the spectral region corresponding to the Bodipy absorption, the strong fluorescence characteristic of the latter subunit is effectively quenched (i.e., > or = 97%). Excitation spectral analysis confirmed that the photoexcited Bodipy and the tethered ZnPc subunits interact and that intraconjugate singlet energy transfer occurs with an efficiency of ca. 25%. Treatment of conjugate 1 with N-pyridylfulleropyrrolidine (8), an electron-acceptor system containing a nitrogen ligand, gives rise to the novel electron donor-acceptor hybrid 1<-->8 through ligation to the ZnPc center. Irradiation of the resulting supramolecular ensemble within the visible range leads to a charge-separated Bodipy-ZnPc(*+)-C(60)(*-) radical-ion-pair state, through a sequence of excited-state and charge transfers, characterized by a remarkably long lifetime of 39.9 ns in toluene.

TD-DFT calculations and MCD spectroscopy of porphyrin and phthalocyanine analogues: rational design of photosensitizers for PDT and NIR region sensor applications

“…The trends in the MO energies of the frontier π -MOs and in the HOMO-LUMO gaps of the analogous set of fused-ring-expanded phthalonitriles (39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54), shown in Figure 7, are also broadly similar to those predicted for the corresponding Pc (1-22) and aza-BODIPY (23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38) analogues. The alignments of the nodal planes of the a and s MOs (Figure 8) are similar to those of the corresponding tetraazapophyrin analogues (Figure 3), as would be anticipated based on their radial symmetry and the manner in which the 4 angular nodal planes lie on alternating sets of 8 atoms on the inner perimeter due to the M L = ± 4 properties.…”

A multicomponent molecular approach to artificial photosynthesis – the role of fullerenes and endohedral metallofullerenes

“…In this regard, a particular emphasis has been placed on extending the visible light absorption features of chromophores into the near-infrared region, since the solar spectrum spans over all these regions. [10][11][12][13][14] A rather elegant but, yet, simple approach involves electron donors or acceptors with high extinction coefficients in the visible part of the solar spectrum. The complexity is kept at a comparably simple level.…”

Step-by-step self-assembled hybrids that feature control over energy and charge transfer

“…As another major class of multifunctional molecular materials, fullerenes (27) offer unique opportunities for stabilizing charged entities. Together with the rigid, confined structure of the aromatic π-sphere, these molecules are perfect electron acceptors in artificial photosynthetic reaction centers (28,29).…”