The photostability of nine ferrocene derivatives of varying functionality was investigated using cyclic voltammetry. Derivatives with carbonyl groups (aldehyde or ketone) directly attached to the cyclopentadiene ring system were found to decompose in aqueous (pH 7.4) solution over a period of 10 min when exposed to light. The kinetics of the photodecomposition process were investigated and the relative values of the rate constants for the photodecomposition tabulated. The implications for biosensor applications are assessed. [5-lo]. Their prevalence in the latter cannot simply be ascribed to their ability to mediate redox protein electrochemistry as this is an attribute possessed by a large number of simpler metal complexes such as ferrocyanide [11][12][13]. The apparent preference for ferrocenes in sensor development, as in numerous other applications, is due to the unrivalled versatility offered by its derivatives. The addition of functional substituents to the basic ferrocene structure can significantly alter the physical and chemical properties of the molecule thereby providing a means for tailoring mediators to their diverse biological and chemical functions encountered in sensor development. Modifications of the solubilities and electrochemical properties of these derivatives by altering such functional substituents were a primary concern in the early development of sensors that relied on solution based mediation. The recent pursuit of reagentless biosensors however has meant that it has been necessary to immobilize the mediator, through the various functionalities offered by such substituents, either onto a polymer [14, 151, the electrode [16], or even the protein itself [17][18][19]. While much information has been obtained on the electrochemical properties of such mediators, their stability, whether in solution or immobilized, is one property that is often overlooked and unfortunately is one that is vital to the success of any sensor relying upon these components. In this communication we have examined the photostability of nine monosubstituted ferrocenes in aqueous solution and shown that carbonyl functionality directly attached to the cyclopentadiene ring can initiate photodecomposition under ambient light and we report the corresponding kinetic factors.
KeywordsAlthough ferrocene is known to be relatively inert in most solvents, with the notable exception of chlorocarbons [20], certain derivatives however have been found to decompose rapidly when exposed to light. Several authors report the photodecomposition of a variety of ferrocenes in a range of solvents including decalin [21], iso-octane [21], acetonitrile [21], methanol [21, 221, DMSO [21, 231, pyridine [21, 231, DMF [21, 231, chloroform [20] and carbon tetrachloride [20]. The relationship between decomposition rate and solvent appears to be complex [21] but it is thought that the presence of water in these solvents, even in trace amounts, is the contributing factor to the decomposition process. These photodecomposition studies have a...
