Synthesis, Electronic Structures And Aggregate States Of Porphyrin-Perylene Arrays

The recent progresses in the field of porphyrin-perylene molecular arrays were summarized in Chapter 1. The review showed the promising applications of these dyad arrays in the fabrication of molecular devices, and outlined two fundamental research trends: (1) the synthetic routes towards porphyrin-perylene arrays are inefficient, as a result, there are few candidates of the arrays for basic studies. (2) There are rare reports on the aggregation states of the porphyrin-perylene arrays and the related electronic structure. A research strategy was accordingly proposed for this thesis: it emphasized on the design of a more efficient route to synthesize porphyrin-perylene arrays, on the investigation of the electronic structure, aggregation states and related charge/energy transfer processes in the derived arrays.A more efficient synthetic route towards porphyrin-perylene arrays was adopted to prepare different arrays in high yield. As an indispensable building block of the molecular arrays, the synthesis of asymmetric mono-(p-amino-phenyl)-triphenyl-porphyrin is considered to be the choke point in determination of the net production of the expected arrays. In the classical synthetic route of mixing condensation-separation-reduction-imidization, the mixing condensation resulted in the low yield of mono-substituted porphyrin and the difficulty to be free from other byproducts, consequently led to the total yield of the arrays no more than 3%. The improved route of homo-condensation-nitrification-reduction-separation-imidization boosted up the total yield of the arrays to about 14%. Through this improved route, three kinds of porphyrin-perylene molecular arrays Por-SBPTCD, Por-SBPTCD-Por and Por-Tetra-PTCD were obtained. The molecular structures were characterized by 1H NMR, FTIR and element analysis.The electronic structures of Por-SBPTCD, Por-PTCD-Por and Por-Tetra-SDPTCD have been comprehensively investigated by absorption spectra, cyclic voltammogrametry (CV) and ultraviolet photoelectron spectroscopy (UPS). Weak electronic interactions between porphyrin and perylene chromophores were indicated by absorption spectra of Por-SBPTCD, Por-PTCD-Por, and optical absorption of Por-Tetra-SDPTCD in organic solvents showed an evident excitonic feature, whichsuggested the aggregation of molecular arrays. Due to the existence of multiple redox centers, the electrochemistry behavior of Por-SBPTCD, Por-PTCD-Por and Por-Tetra-PTCD displayed characteristics distinct from the parental chromopphores and dependent on the aggregation states and media. Compared with UPS of TPP and DBPTCD, molecular arrays showed evident variations near the top of valence band. The HOMO level of Por-SBPTCD localized between l.OeV of TPP's and 2.3eV ofr DBPTCD's HOMO, and the work function of Por-SBPTCD was smallest among the three compounds. ARUPS spectra taken from the sub-monolayer on Ru(0001) surface indicated that the molecular plane of both TPP and DBPTCD are parallel to the substrate surface but porphyrin and perylene chromophores in Por-SBPTCD arrays are not coplanar.Energy-transfer and photoinduced electron-transfer of Por-SBPTCD and Por-PTCD-Por in CF3COOH/CHC13 have been investigated in detail. Compared with the spectra of TPP and DBPTCD, The fluorescence spectra of Por-SBPTCD and Por-PTCD-Por in CHC13 revealed that the emissions of perylene and porphyrin chromophore were both diminished greatly. These results indicated the mechanism of photoinduced charge transfer between perylene and porphyrin chromophores. The quantum yields of electron and hole transfer were both more than 98% when either perylene or porphyrin chromophores were photoexcited. The electronic absorption spectra of Por-SBPTCD and Por-PTCD-Por in CF3COOH/CHC13 exhibited that the B and Q bands of porphyrin chromophore varied with the concentration of CF3COOH range from 0 to 3.26xl0-3M, but the spectra of perylene chromophore did not The emission spectra of Por-SBPTCD and Por-PTCD-Por in CF3COOH /CHC13 with the concentration of CF3COOH from 0 to 3.26xl0-3M indicated...