On the relation between charge‐storage capacity and π‐topology of different oligonaphthylenes

Abstract

Conjugated polymers such as polyacetylene," poly-(p-phenylene)[21 or p~l y p y r r o l e [~~ which can be made conductive by p-or n-doping have been extensively investigated. One of the applications discussed for such electroactive materials is their use as anodic electrodes in secondary lithium battery elements.f3'The most important criterion in the design of polymer electrodes is their charge-storage capacity, which is primarily influenced by i) the number of charges transferred per molecule, ii) the reversibility of the charging and discharging steps, iii) the stability over a number of cycles, and iv) the conductivity of the polymer in the neutral and doped states.In order to optimize conjugated polymers for use in battery elements we have studied the relationship between charge-storage capacity and n-topology. The title compounds are linear (A) and two-dimensional (B) oligonaphthylenes ; their redox behavior has been studied by means of cyclic voltammetry (see scheme 1).Previous cyclovoltammetric experiments on homologous series e.g. of oligo(p-phenylene~inylene)s[~] or oligobphenylene)srsl in solution have suggested that monodisperse oligomeric systems are extremely useful model compounds for elucidating the charging mechanisms of the corresponding polymers.[61 Therefore, we now present a comparative cyclovoltammetric study of the following structurally defined, soluble compounds: i) linear oligo(l,4-naphthylene)s (1-5) and oligo-and poly(l,5-naphthylene)s (6, 7)[71 (Type A); ii) ribbon-type oligo(peri-naphthy1ene)s ("oligorylenes") (8-10) (Type B); and iii) the dimeric biperylenyl ll[*] (see scheme 1).In the cyclic voltammograms of the linear oIigo(l,6naph-thylene)s 1-5I7] the first oxidation potentials appear at an almost identical potential of about 1.3 V. The potentials of higher oxidation states are shifted to less positive values with increasing chain length; from the pentamer 4 onwards, a resolution between the first and second oxidation steps is no