W. Huber

Chain length-dependent polaron (P−) width in phenylenevinylene oligomers: a solid state ENDOR investigation

Abstract We report on the extension of the negative polaron (radical anion) in phenylenevinylene oligomers up to chain length n = 7, where n is the number of phenyl rings. The spin density distribution obtained from solid state pulsed ENDOR spectra is observed to increase with chain length. Local hyperfine interactions as well as the corresponding spin density distribution are reported.

ELECTRON STORAGE AND TRANSFER IN ORGANIC REDOX SYSTEMS WITH MULTIPLE ELECTROPHORES

Publisher Summary The chapter focuses on “dimeric” or (low molecular weight) “oligomeric” redox systems with identical, electronically decoupled electrophores A. The chapter presents the biselectrophore A-1- A, where 1 represents a saturated spacer. Injection of an electron into one subunit A under formation of a radical anion raises the immediate question of whether the electron will tend to localize in the original subunit or whether it will undergo a degenerate electron transfer to the neighboring unit. In the terminology of electron-transfer kinetics such electron hopping between identical redox groups is termed self-exchange. Depending upon the rate of this process, one will observe an “effective delocalization” over two or more units within the timescale of the experiment, or a localization of charge on one unit. The chapter also focuses on the tailoring of the redox behavior of organic compounds— that is, the optimization of such systems for electron storage and electron hopping. While the emphasis is on the reduction and thus on anion formation, it has been shown on many occasions that oxidative cation formation leads to analogous conclusions. It should be emphasized that the approach is a purely empirical one: knowledge of the structural dependence of the charge-storage capacity and of intra-molecular electron-hopping processes might enable us specifically to design dimers, oligomers, and polymers in which the electron-transfer rate, and thus the resulting charge distribution, can be controlled precisely.

The extension of a polaron (radical anion) over oligophenylenevinylene chains

The radical anions obtained from a homologous series of soluble oligophenylenevinylenes have been characterized by ESR and ENDOR spectroscopy in solution; the spin density tends to be localized in a central unit of the chain.

Electron localization and delocalization in biselectrophores

We have performed ESR and pulsed ENDOR experiments on the radical anions of [2.2]-(9,10)-anthracenophane (l1), 1,2-di(9-anthryl)ethane (l2a), 1,3-di(9-anthryl)propane (l2b), 1,2-di-(2-anthryl)ethane (l3), and the doubly layered [14]-annulene (4), both in the liquid and solid state. In the molecules l1, 2 and l4 we have observed that the electron is delocalized over both subunits in the liquid state, whereas it is localized on one aromatic unit in the solid state. The transition from the delocalized to the localized state is observed to occur right at the liquid-to-solid phase transition temperature. For 1,2-di-(2-anthryl)ethane we always observe a localized spin both in the liquid and in the frozen solution.