124 | lcca-2 STUDY OF PHOTONIC AND ELECTROCHEMICAL PROPERTIES OF NEW ELECTROACTIVE MATERIAL Saadeldin. E. Taher * a and Saleh.M. Bofarwa b a Tobruk university- Department of Chemistry -Faculty of Science-Tobruk – Libya b Omar Al-Mukhtar university- Department of Chemistry -Faculty of Science- Al-Beadia– Libya Saadeldinlamin@yahoo.co.uk ABSTRACT: A new conjugated co-compound incorporating the redox-active thiophene-EDTT units has been characterized by using electrochemical and optical techniques. This paper discusses the electrochemical and spectroscopic properties of 5,7-bis(3-hexylthiophen-2-yl)-2,3-dihydrothieno[3,4-b][1,4]dithiine compound. The central core appears as Ethylene3,4-dioxythiophene (EDTT), which has tethered with bis-hexylthiophene units. The redox properties of the material were studied using cyclic voltammetry in acetonitrile as the solvent and tetrabutylammonium hexafluorophosphate (Bu4NPF6) 0.1 M as the supporting electrolyte, and the optical properties of this compound have been achieved by electronic absorption spectroscopy in acetonitrile solution. The electrochemical properties of the monomer have given lower oxidation potential compared to its polymer. The optical band gap of the monomer has shown a big difference compared to the polymer state. Keywords: low band-gap polymer, electro-polymerisation, organic conjugated molecule based on thiophene derivatives. Introduction Organic conjugated polymers are able to display semiconducting ability as they have delocalised π-electrons happening from all the conjugated double bonds and this lets them to exhibit electroactivity in the main chain of the material. 1,2 The extent of π-orbital overlap in the polymer determines the polymers ability to transport charges (electrons and holes) through the backbone. 1,3,4 During the backbone of polythiophene, the conformation of the thiophenes can be appeared in several different forms. The conformer usually depends on the structure of the monomer chosen and any substituents appended, which can influence the structure through intermolecular interactions or steric repulsion. 5 The oxidation of terthiophenes is normally shown in the formation of a cation radical on the end thiophene, and the species is stabilised through resonance with the rest of the unit. 6,7 The oxidation and reduction processes of polythiophene are shown as stable and reversible. The number of electrons that a polythiophene donates is dependent on the substituents attached. 5 8 Polythiophene is a commonly used material in electrochromic and electronic devices, such as organic light emitting diodes (OLEDs), organic field effect transistors (OFETs) and organic solar cells (OSCs), due to its high electrical conductivity in the doped state and high stability. 9 3,4-Ethylenedioxythiophene (EDOT) is excellent example for such a monomer design, where the fused 1,4-dioxane (dithiane) cycle decreases the steric effect and enhances the donor ability. 5,10 The electropolymerisation of EDOT produces poly3,4-ethylenedioxythiophene (PEDOT), which has shown high conductivity and good stability along the polymer chain. 5,11 The polythiophene is usually given the band gaps in region of 2 eV, which is lowering band-gap of parent system. This is often achieved by introducing pendant substituents through the polymer backbone in order to increase the energy of the highest occupied molecular orbital (HOMO) or to reduce the energy of the lowest unoccupied molecular orbital (LUMO). 12,13 This paper discusses the electrochemical and spectroscopic properties of ethylene3,4-diothiathiophene (EDTT)- bis- hexylthiophene compound, where the central core appears as ethylene3,4-dithiathiophene (EDTT) , which has tethered with bis-hexylthiophene units as shown in Figure 1. S S S S S Figure 1. Structure of ,7-bis(3-hexylthiophen-2-yl)-2,3- dihydrothieno[3,4-b][1,4]dithiine compound