Stepwise reduction of a porphyrin nanowire: minimal structural reorganization up to the open-shell tetraanion
Year: 2026
Type: preprint
Abstract: π-Conjugated porphyrin oligomers serve as molecular wires: they exhibit high single-molecule conductance and excellent cycling kinetics as organic active electrode materials. These applications require systems in which charge/discharge cycles cause minimal changes in molecular geometry. Here, we use a butadiyne-linked porphyrin dimer as a model compound to show that its chemical reduction with alkali metals leads to subtle changes in the bond lengths in the resulting multiply charged anions, as revealed crystallographically. The small structural changes are consistent with a low inner-sphere reorganization energy, as expected for an efficient redox-active molecular wire. π-Bond Delocalization Function (π-BDF) analysis shows that successive reduction increases π-electron delocalization within the porphyrin cores, while the involvement of the butadiyne linker is strongly charge- and spin-state-dependent. The previously unknown, structurally characterized tetraanion has an open-shell singlet diradical ground state with a thermally accessible triplet state, separated by 14.2 kJ mol −1 , as established experimentally by EPR spectroscopy and supported by DFT calculations. The two open-shell states retain nearly identical covalent-delocalization topologies and differ primarily in the organization and coupling of their two unpaired electrons. Prolonged reaction with lithium metal leads to demetallation of these zinc porphyrins and cleavage of the butadiyne, forming an acetylene-appended porphyrin monomer.
Source: ChemRxiv
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7220926405