CONICET | Buscador de Institutos y Recursos Humanos

Organic selenium compounds have been suggested to have antioxidant properties due to the rather low one-electron reduction potentials of the corresponding radical cations. Some mechanistic aspects and synthetic potentials of photoinduced electron transfer (PET) activation of organoselenium substrates have been explored by Pandey et al. These interesting studies have been useful in initiating various synthetic reactions. However, direct evidence of the mediation of selenide radical cations or of other electrophilic selenium and carbocations species is further needed. We use PET as a tool for radical cation generation, two examples will be discussed. First, the intramolecular PET reaction in the phthalimide system 1 where selenium containing heterocycles products 2 and 3 are found (eq. 1). In this system, product distribution and photophysical properties of different phthalimides with variable distance between the selenium atom and the phthalimide moiety will be also presented. Second, the generation of radical cations of ArSeR (5) and its derivatives by intermolecular PET in acetonitrile solution, using different photosensitizers will be discussed (eq 2). The nature of the photoinduced step was confirmed by the observation of the semireduced form of the sensitizer. Thus, the PhSeR radical cations were observed for the first time by transient absorption spectroscopy. The monomeric form of PhSeMe.+ shows a maximum at 500 nm; however, another band at 640 nm was observed for the former, attributed to a -dimmer between the selenide radical cation an a neutral molecule, similar to its periodic neighbor PhSMe.+. The influence of electron donating and electron acceptors in the pendant phenyl moiety as well as the steric effect of the alkyl substituent will be discussed in order to explain the experimental observations.