Charge-Transfer Interactions in Face-to-Face Porphyrin-Fullerene Systems: Solvent-Dependent Luminescence in the Infrared Spectral Region
摘要:
The cyclophane-type molecular dyads 1.2H and 1.Zn, in which a doubly bridged porphyrin donor adopts a close, tangential orientation relative to the surface of a fullerene acceptor, were prepared by Bingel macrocylization. The porphyrin derivatives 2.2H and 2.Zn with two appended, singly linked C-60 moieties were also formed as side products. NMR investigations revealed that the latter compounds strongly prefer conformations with one of the carbon spheres nesting on the porphyrin surface, thereby taking a similar orientation to that of the fullerene moiety in the doubly bridged systems. Cyclic voltammetric measurements showed that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa are only small in all four dyads, despite the close proximity of the donor and acceptor components. The steady-state and time-resolved absorption and luminescence properties of 1.Zn and 2.Zn were investigated in toluene solution and it was shown that, upon light excitation, both the porphyrin- and the fullerene-centered excited states are deactivated to a lower-lying CT state, emitting in the IR spectral region (lambda(max) = 890 and 800 nm at 298 and 77 K, respectively). In the more polar solvent benzonitrile, this CT state is still detected but, owing to its very low energy (below 1.4 eV), is not luminescent and shorter-lived than in toluene. The remarkable observation of similar photophysical behavior of 1.Zn and 2.Zn suggests that a tight donor-acceptor distance cannot only be established in doubly bridged cyclophane-type structures but also in singly bridged dyads, by taking advantage of favourable fullerene-porphyrin ground-state interactions.
Charge-Transfer Interactions in Face-to-Face Porphyrin-Fullerene Systems: Solvent-Dependent Luminescence in the Infrared Spectral Region
摘要:
The cyclophane-type molecular dyads 1.2H and 1.Zn, in which a doubly bridged porphyrin donor adopts a close, tangential orientation relative to the surface of a fullerene acceptor, were prepared by Bingel macrocylization. The porphyrin derivatives 2.2H and 2.Zn with two appended, singly linked C-60 moieties were also formed as side products. NMR investigations revealed that the latter compounds strongly prefer conformations with one of the carbon spheres nesting on the porphyrin surface, thereby taking a similar orientation to that of the fullerene moiety in the doubly bridged systems. Cyclic voltammetric measurements showed that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa are only small in all four dyads, despite the close proximity of the donor and acceptor components. The steady-state and time-resolved absorption and luminescence properties of 1.Zn and 2.Zn were investigated in toluene solution and it was shown that, upon light excitation, both the porphyrin- and the fullerene-centered excited states are deactivated to a lower-lying CT state, emitting in the IR spectral region (lambda(max) = 890 and 800 nm at 298 and 77 K, respectively). In the more polar solvent benzonitrile, this CT state is still detected but, owing to its very low energy (below 1.4 eV), is not luminescent and shorter-lived than in toluene. The remarkable observation of similar photophysical behavior of 1.Zn and 2.Zn suggests that a tight donor-acceptor distance cannot only be established in doubly bridged cyclophane-type structures but also in singly bridged dyads, by taking advantage of favourable fullerene-porphyrin ground-state interactions.
Synthesis, and Optical and Electrochemical Properties of Cyclophane-Type Molecular Dyads Containing a Porphyrin in Close, Tangential Orientation Relative to the Surface oftrans-1 Functionalized C60. Preliminary Communication
The synthesis of the cyclophane-type molecular dyads I and 1 . Zn was accomplished by Bingel macrocyclization of porphyrin-tethered bis-malonates 5 or 5 . Zn, respectively, with C-60 (Scheme). In these macrocycles, the doubly bridged porphyrin adopts a close, tangential orientation relative to the surface of the C-sphere. The porphyrin derivatives 6 and 6 . Zn with two appended, singly-linked C60 moieties were also formed as side products in the Bingel macrocyclizations The trans-1 addition pattern of the fullerene moiety in 1 and 1 . Zn was unambiguously established by H-1- and C-13-NMR spectroscopy. Due to the close spatial relationship between the fullerene and porphyrin components in 1 and 6 and the corresponding Zn-11 complexes, the porphyrin fluorescence is efficiently quenched as compared to the luminescence emitted by 5 and 5 . Zn, respectively (Fig. 2). Cyclic-voltammetry studies show that the mutual electronic effects exerted by the fullerene on the porphyrin and vice versa in I and 1 . Zn are relatively small despite the close proximity between the porphyrin donor and the fullerene acceptor (Fig. 3).