Synthesis, emission and spectro-electrochemical studies of bithienylnaphthalene systems

Abstract

Four new bis(2-thienyl)naphthalene monomers were synthesized and their absorption, emission and redox properties were studied. Thus, 1,5-dimethoxy-2,6-bis(2-thienyl)naphthalene (2,6-BTDMN), 1,5-dimethoxy-4,8-bis(2-thienyl)-naphthalene (4,8-BTDMN), and 1,4,5,8-tetramethoxy-2,6-bis(2-thienyl)naphthalene (2,6-BTTMN) were synthesized by Stille coupling reaction between the respective dibromides and 2-(tributylstannyl)-thiophene while 2,6-bis(2-thienyl)-naphthalene (2,6-BTN, previously prepared from dibromo precursor) and 1,5-bis(2-thienyl)-naphthalene (1,5-BTN) were prepared similarly between the corresponding di-triflates and 2-(tributylstannyl)thiophene. Monomers 1,5-BTN and 4,8-BTDMN reveal only one peak in both absorption and emission spectra, while monomers 2,6-BTN, 2,6-BTDMN, and 2,6-BTTMN show multiple bands for absorption and a single doublet for emission. The oxidation potential values for the monomers range from 0.95 V, for monomer 1,5-BTN to 0.59 V, for monomer 2,6-BTTMN. Electropolymerized monomers, with the exception of 2,6-BTTMN, form good polymeric films on ITO coated glass substrate. They are pale greenish in color in their oxidized states and relatively transmissive and pale yellow in their reduced state. Spectro-optoelelectrochemistry revealed a band gap range of 2.4–2.9 eV. Iodine-doped polymer from chemically polymerized monomer 2,6-BTTMN has a conductivity of 5×10 −2 S/cm.