Construction And Properties Of Donor-acceptor Ensembles Based On Porphyrin Or Phthalocyanine And [60] Fullerene Or Carbon Nanotube

Much attention has been paid to the studies on photoinduced electron transfer (PET) in donor-acceptor systems recently mainly to develop artificial photosynthetic systems, in which porphyrin (Por)/phthalocyanine (Pc) and [60]fullerene (C60)/ carbon nanotube (CNT) are considered as attractive molecular components due to their unique structures and rich photoelectronic properties. The Por/Pc—60/CNT system has been proved to be a potential candidate for solar energy conversion materials and molecular devices. Here, a series of ensembles based on the donor Por/Pc and acceptor C60/CNT were constructed and fully characterized. The photophysical and electrochemical properties of the novel donor-acceptor ensembles were studied, and the long-lived charge separated states have been achieved. The important results obtained are described as follows:1. A new amide-linked phthalocyanine-fullerene dyad (ZnPc-C60) is reported. Steady-state, time-resolved fluorescence and transient absorption measurements showed the occurrence of PET from the singlet excited phthalocyanine to fullerene with large driving force(△GCS).The larger nonlinear absorption of ZnPc-C60,better than fullerene (C60) and the control sample, was observed by the Z-scan experiments, which indicated the synergistic effect of two active moieties in the dyad.2. Ferrocene-phthalocyanine-fullerene supramolecular triads have been constructed with pyridine-or imidazole-appended fulleropyrrolidine and covalently linked zinc phthalocyanine-ferrocene dyad via axial coordination. The stablilities of the triads (Kassoc-8.58×104 mol-1·L) were studied by optical absorption methods. Steady-state and time-resolved fluorescence measurements suggested that the occurrence of efficient PET (kCS-109 s-1) from excited phthalocyanine to fullerene entity in the triads with high charge-separation quantum yields (ΦCS-0.88). The redox potentials were determined by cyclic voltammetric, and the driving forces (△GCS--0.60 eV) were estimated to be exothermic, which favored the forming of charge-separation state.3. Novel covalent-linked ferrocene-porphyrin-SWNTs triads hybrid have been synthesized and fully characterized by IR, Raman, AFM and TEM. The amount of functional groups in the triads hybrid were roughly estimated to be around 51-57% by TGA and XPS analysis. The considerable porphyrin attachment significantly improved the solubility (234 mg-L-1) and dispersion stability of the SWNTs in organic solvents. The UV-Vis absorption and fluorescence spectra of the nanohybrid indicated the weak in ground state and strong in excited state electronic interaction between donors (porphyrin containing ferrocene) and the extendedπ-system of SWNTs acceptors. The PET reactions from porphyrin to C60 in the triads hybrid were observed in fluorescence lifetime and nanosecond laser-flash photolysis experiments, which confirmed to form long-lived (64.5μs) charge separated state (Fc+-H2P)m-x-SWNTs(m-x)·-(Fc-H2P)n-m+x.4. Novel covalently functionalized SWNTs simultaneity with two kinds of chromophores (porphyrin and phthalocyanine) have been synthesized and characterized. The UV-Vis absorption and fluorescence spectra of the nanohybrid indicated the weak in ground state and strong in excited state electronic interaction between donors (porphyrin and phthalocyanine moieties) and the extendedπ-system of SWNTs acceptors. This novel nanohybrid material exhibited wider spectral region and more excellent solubility (309 mg-L-1) compared to those of either porphyrin or phthalocyanine functionalized SWNTs, which was favorable for the good film formation on the electrode and the effective utilization of solar energy, hence the performance of devices might be improved greatly.5. Conjugated polyamides containing porphyrin and C6o in the main chain were prepared and characterized. Gel permeation chromatography (GPC) analysis of the polyamides showed the weight-average molecular weight of about 2.37×104. The temperature at 5% weight loss determined by thermogravimetric analysis (TGA) was above 216℃. Atomic force microscopy (AFM) images displayed the flat round-shaped aggregation structure of the polyamides. The photophysical properties were studied by UV-Visible, fluorescence spectroscopy, and fluorescence lifetime. The PET reactions from porphyrin to C6o in the polyamides were observed in nanosecond laser-flash photolysis experiments, which confirmed to form charge separated state (porphyrin radical cation-C60 radical anion pair) with a lifetime about 100μs. The calculated ratio of kcs/kcR was found to be-10000 indicating the high charge stabilization in the PET process.The results showed that all above donor-acceptor systems were potential solar energy conversion materials.