Organic mixed valence compounds with N,N-dihydrodimethylphenazine redox centres
The mixed-valence character of four bis(N,N-dihydrodimethylphenazine) radical cation derivatives with varying π-electron bridges was investigated. The electron transfer (ET) distance within these derivatives varies from ca. 12.5 Å for 1,2-bis[2-(5,10-dihydro-5,10-dimethylphenazinyl)]acetylene (1) to ca. 19.3 Å for 9,10-bis[2-(5,10-dihydro-5,10-dimethylphenazinyl)ethynyl]anthracene (4). All radical cation species show intense intervalence charge-transfer (IV-CT) bands in the NIR. The Mulliken–Hush analysis was used to derive the electronic coupling V, which ranges from 310 to 870 cm−1. Comparisons with analogous ET systems in which the dihydrodimethylphenazine redox centres have been replaced by triarylamine units show that the dihydrodimethylphenazine species have a significantly higher internal reorganisation energy associated with the ET. This behaviour is attributed to C–N stretching and C–C ring modes of the dihydrodimethylphenazine units.