Symmetric versus asymmetric electron transfer in symmetric molecules
Year: 2026
Type: preprint
Abstract: Photoinduced electron transfer (ET) in symmetric donor-acceptor-donor (D-A-D) or acceptor-donor-acceptor (A-D-A) molecules attracts attention due to applications in advanced materials. It is normally assumed that ET occurs asymmetrically, from one donor to acceptor, thus breaking molecular symmetry and resulting in a dipole moment in the excited state. However, the symmetry can be preserved with symmetric ET from both donors, leading to a nondipolar state with a high quadrupole moment. Here we report on symmetric ET in a D-A-D probe, 5,5'-di(9H-carbazol-9-yl)-2,2'-bipyridine. This probe is weakly solvatochromic in absorption, but highly solvatochromic in emission, revealing a nonlinear spectral shift and strong decay of the oscillator strength in solvents of increasing polarity. We develope a 3-excited-state model that fits the data quite well for symmetric ET, while no reasonable fit is possible for asymmetric ET. The model predicts the symmetric ET to be barrierless and ultrafast, in good agreement with observations.
Source: ChemRxiv
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214342214