Monatsh Chem 139, 781–787 (2008) DOI 10.1007/s00706-007-0851-2 Printed in The Netherlands Cyclic voltammetric and computational study of a 4-bromophenyl monolayer on a glassy carbon electrode Maryam Khoshroo, Abbas A. Rostami, Saeed Yeganegi Department of Chemistry, Faculty Basic of Science, University of Mazandaran, Babolsar, Iran Received 7 May 2007; Accepted 9 November 2007; Published online 1 February 2008 # Springer-Verlag 2008 Abstract A glassy carbon (GC) surface modiﬁed with monolayer of 4-bromophenyl was examined as vol- tammetric electrode for some redox systems. The modiﬁed electrode exhibited very slow electron transfer in comparison to the unmodiﬁed surface by factors which varied with the redox systems. How- ever, after scanning the modiﬁed electrode in 0.1 M tetrabutylammonium tetraﬂuoroborate (TBABF 4 ) in acetonitrile from 0.4 to 1.1 V vs. Ag=AgCl for 20–25 cycles, the modiﬁed electrode showed much faster electron transfer kinetics, e.g., the results for FeðCNÞ 6 3=4 were approaching those observed with unmodiﬁed surfaces. The effect is attributed to an ap- parently irreversible structural change in the 4-bromo- phenyl monolayer, which increases the rate of electron tunneling. The transition to the conducting state is as- sociated with electron injection into the monolayer and causes a signiﬁcant decrease in the calculated HOMO- LUMO gap for the monolayer molecule. Once the monolayer is switched to the conducting state, it sup- ports rapid electron exchange with the redox system, but not with dopamine, which requires adsorption to the electrode surface. A conductive surface modiﬁed electrode may have useful properties for electroanalyti- cal applications and possibly in electrocatalysis. Keywords Cyclic voltammetry; Computational study; 4-Bro- mophenyl; Glassy carbon. Introduction Chemically modiﬁed electrodes have been the sub- ject of numerous studies in the last 2 decades since they may ﬁnd applications in electrocatalysis, corro- sion protection, thin ﬁlm optical devices, integrated circuits, information storage, and sensing [1–6]. A recent approach for electrode modiﬁcation involves the spontaneous adsorption of thiols on gold elec- trode surfaces to form the so-called self-assembled monolayers, SAMs [7, 8]. The adsorption of thiol results in the formation of a gold-sulfur bond that is characterized by a partial covalent character [7, 9]. However, recent studies have shown that these monolayers are not totally stable and that they can be oxidatively or reductively desorbed [10]. SAMs are interesting on their own because of their easy preparation and also because this ﬁrst layer can be further modiﬁed to build up more complex chemical structure. On the other hand, carbon electrodes are usually modiﬁed by an oxidative procedure that generates ox- ygen functionalities which can be used to do further chemistries [1, 11]. Since electrochemical or chemi- cal oxidation may damage the carbon surface, a new method involving the electrochemical reduction of a phenyldiazonium derivative was developed [12]. According to Scheme 1, this surface modiﬁcation procedure involves the formation of a diazonium radical followed by the formation of a covalent bond to the glassy carbon electrode. Correspondence: Abbas A. Rostami, Department of Chemis- try, Faculty Basic of Science, University of Mazandaran, Babolsar, Iran. E-mail: rostami@umz.ac.ir