POLY(ARYLENEETHYNYLENE) TYPE POLYMERS CONTAINING A FERROCENE UNIT IN THE PI-CONJUGATED MAIN-CHAIN - PREPARATION, OPTICAL-PROPERTIES, REDOX BEHAVIOR, AND MOSSBAUER SPECTROSCOPIC ANALYSIS

Palladium-catalyzed polycondensation between diiodoferrocenes (1,1'-di iodoferrocene and 1,6-diiodo-1',6'-biferrocene) and diethynyl aromatic compounds HC=C-Ar-C=CH (e.g., 2,5-diethynyl-pyridine and 2,5-diethyny l-3-hexylthiophene) gives poly(aryleneethynylene) (PAE) type polymers containing the ferrocene unit in the pi-conjugated main chain. The pre pared polymers include (-Fc-C=C-Ph-C=C-)(n), PAE-Fc-1, (-Fc-C=C-Py-C=C -)(n), PAE-Fc-2, and (-Fc-C=C-hexTh-C=C-)(n) PAE-Fc-3 (Fc = 1,1'-ferro cenylene; Ph = p-phenylene; Py = pyridine-2,5-diyl; hexTh = 3-hexylthi ophene-2,5-diyl). H-1-NMR and IR spectra of the polymers are reasonabl e for their structures. The PAE type polymer containing the pyridine u nit (PAE-Fc-2) is soluble in formic acid, and the polymer containing t he hexylthiophene unit (PAE-Fc-3) is soluble in common organic solvent s such as CHCl3, THF, and benzene. UV-visible spectra of the polymers exhibit a main pi-pi absorption peak at about 330 nm and a d-d absorp tion peak at about 450 nm. The cyclic voltammogram of the polymers in a CH3CN/CH2Cl2 solution shows a reversible Fe(II) reversible arrow Fe( III) redox cycle at about 0.25 V vs Ag/Ag+, and the redox peaks are br oadened compared with those of low-molecular-weight ferrocenes. Exchan ge of electrons along the main chain is considered to be the origin of the broadening. The polymers themselves are insulating, however, they are converted into semiconducting materials with conductivity of 10(- 7) to 10(-4) S cm(-1) by formation of adducts with iodine. Mossbauer s pectra of the polymers reveal oxidation of Fe(II) in the ferrocene uni t of PAE-Fc-1 to Fe(III), and the ease of the oxidation reflects the e lectronic properties of the polymer.