Incorporating Cobalt Carbonyl Moieties onto Ethynylthiophene-Based Dithienylcyclopentene Switches. 2. Electro- and Spectroelectrochernical Properties

The redox behavior of dithienyl perhydro- and perfluorocyclopentene photochromic molecular switches, modified with 3-ethynylthiophene and phenyl-3-ethynylthiophene substituents, is explored by cyclic voltammetry and UV/vis-NIR and IR spectroelectrochemistry. The extent of electrochemical oxidation induced cyclization was depedent on whether a perhydro- or perfluorocyclopentene unit was present, with the former favoring ring closure, and on the nature of the substituents on the thienyl ring. The inclusion of a phenyl spacer between the alkynyl and thienyl moieties increased the stability of the molecular switches when addressed electrochemically. Binding of Co-2(CO)(6) and Co-2(CO)(4)dppm moieties to the alkyne units is shown to destabilize the cationic closed form and, in one example, inhibit oxidative cyclization for the 1,2-bis(5'(4 ''-phenyl-3 ''-ethynylthiophene)-2'-methylthien-3'-yl)perfluorocydopentene [Co-2(CO)(6)](2) complex (4Fo). However, the electrochemical cyclization observed for the Co-2(CO)(6) and Co-2(CO)(4) dppm complexes of 1,2-bis(5'-(3 ''-ethynylthiophene)2'-methylthien-3'-yl)cydopentene (3Ho and 5Ho, respectively) was induced following oxidation of the cobalt carbonyl moieties (i.e., at lower potentials than oxidation of the open form of the dithienylethene), possibly via an intramolecular electron transfer mechanism and thereby providing an alternative route to control the electrochromic behavior of the switch.