Cationic Polaron Delocalization in Porphyrin Nanoribbons

Long-range delocalization of unpaired electrons in organic -conjugated oligomers is an important requirement to achieve high charge carrier mobilities in molecular transistors. We have investigated the polaron delocalization in the radical cations of a series of b,meso,b-edge-fused porphyrin oligomers consisting of up to 18 porphyrin units by a combination of cw-EPR, 1H and 14N ENDOR, HYSCORE and vis-NIR-MIR spectroscopy, supported by DFT simulations. The results demonstrate coherent delocalization of the radical cation over more than ten porphyrin units, which corresponds to an effective coherence length >8.5 nm. We discovered a remarkably non-uniform distribution of the radical spin density and an increase in phase memory time with increasing delocalization length (up to Tm ≈ 4 us at 50 K). This study opens new avenues towards the design of molecular electronic and spintronic materials.