Synthesis Of Schiff-base Zinc Methoxy Porphyrins And Study On Their Photoelectrochemical Properties

Porphyrin compounds are the key material of dye sensitized solar cells （DSSC）, theirsynthesis and application have become one of the important research direction. In order toenlarge the spectral response of the dye range, five kinds of Schiff-base zinc methoxyporphyrins which never have been reported were synthetized. Through extendÏ€-conjugationof porphyrin dye, the photovoltaic performance was improved.In this paper, 5-（4-nitro） pheny-10,15,20-tris（4-methoxylphenyl） porphyrin product wassynthesized through Adler method in the first step, after the crude product was restored, zincporphyrin was obtaineded. 5-[p-（benzyl idene amino）] pheny-10,15,20-tris（4-methoxylphen-yl） porphyrin zine and other four compounds were synthesized by Zinc porphyrin,benzaldehyde and its derivatives.The factors which effect reaction were discussed in this paper. The results showed theoptimum reaction conditions, the mole ratio of paranitrobenzaldehyde, anisaldehyde, pyrrolewere fixed, which is 1:3:4, that the optimum reaction time is 45 min, the suitable temperatureis 120℃, the optimum amount of propionic acid should control the concentration of pyrroleis 0.27 mol/L; in the second step of the reaction, the optimum mass ratio of nitro porphyrincrude product and SnCl₂·2H₂O is 1.1:1. The results of infrared and mri indicated that the fivecompounds are target product and their melting point are between 76～82℃.In 3×10^-7mol/L concentration, the UV-vis absorption spectra of five kinds of Schiff-basezinc methoxy porphyrins in DMF solution show that the strong Soret band at 428 nm nearby,Q（Ⅰ）band at 603 nm nearby, Q（Ⅱ） band at 562 nm nearby. Compare to other similarSchiff-base zinc porphyrin which don’t have peripheral substituents on porphyrin ring. Soretbands are red-shifted and absorbing intensity are stronger in a certain degree. When theporphyrin dyes absorbed in TiO₂film, the largest absorb band of 5-[p-（4-nitro benzyl idene amino）] pheny-10,15,20- tris （4- methoxylphenyl） porphyrin zine （3） reached 881 nm.The fluorescence spectra show that all Schiff-base zinc methoxy porphyrins have twoemission peaks. The emission peaks around 620 nm are stronger and the emission peaksaround 657 nm are weaker. The emission maxima of 3 are red shifted 6 nm with respect to theother four kinds of compounds. Maximum absorption edge mainly concentrated in the 570 nm.The zerothezeroth energies (E_0-0) are determined between 2.15².19 eV.Their zerothezerothenergies are minished compare to most porphyrin dye （2.4².5 eV）.From cyclic voltammetry, the electrochemical level of five kinds of compounds aredetermined between 1.05¹.17 eV. The electrochemical level of 1, 3 is the least of all ofcompounds and minimal reached 1.05 eV. From the excited states oxidation potential, thedriving forces for electron injection from the excited porphyrin singlet state to the conductionband （CB） of TiO₂（-0.5 V vs NHE） (â–³G_inj) for the Schiff-base zinc methoxy porphyrin dyeswere determined between -0.96 -0.91 eV. The regeneration of porphyrin radical cation by(I/I^3-) （+0.5 V vs NHE） (â–³G_reg) foe the porphyrin dyes were determined between -0.27 ^-0.21 eV. The experimental result show that the processes of electron injection and restorecationic dye are thermodynamically feasible.