Remarkable homology in the electronic spectra of the mixed-valence cation and anion radicals of a conjugated bis(porphyrinyl)butadiyneElectronic supplementary information (ESI) available: Fig. S1: voltammetry of 1 at 233 K; Fig. S2 and S3: OTTLE-cell progressions of 1 to 1– and 1– to 12–, respectively; Fig. S4: EPR spectra. See http://www.rsc.org/suppdata/cc/b2/b200803n/