Structure properties relationship in organic semiconductor: the case of poly(dispiro[1,3-dioxalane-2,4’(5’h)-benzo[2,1-b:3,4-b’]ditiophene)

Organic π−conjugated compounds have experienced over the last decades a tremendous interest as versatile and highly performing active components in a large variety of devices and applications. Two peculiar characteristics of organic materials are key for their technological exploitation. Firstly, most organic conjugated materials can be manufactured by low cost, solution based deposition techniques. Moreover, the intrinsic flexibility of both their electrochemical and optical properties holds promises for custom designed active materials. On this respect, the formulation of general structure-property relationships is a key requirement. Aim of the present contribution is to present the properties of a new thiophene derivate: the poly(dispiro[1,3-dioxalane-2,4’(5’h)-benzo[2,1-b:3,4-b’]ditiophene (pDTO-B) which can be obtained as thin film by electro-polymerization of the DTO-B (fig.1) monomer by different techniques. The CV of pDTO-B shows two reversible redox waves: a p-type process at oxidative potential (≈0.5V) and a n-type one in the negative potential region (-2 V). When the polymer is in the neutral state, it has a purple coloration due to the absorption in the visible (530nm). At potentials above 0.6V the polymer backbone is oxidized, therefore there is a drop of the absorption in the visible and an increment in the IR region. Similar behavior happens when the polymer is reduced: the film bleaches at -2.3 V and it assumes a purple color when it is oxidized back to the neutral state (-1.8V). It can be noticed the two process, n-type and p-type, are symmetrical and involve the same amount of charge. This particular behavior makes this polymer very interesting for both electrochromic and energy storage applications because can be used as negative and positive electrode in the final device.