Intramolecular electron transfer in multi-redox systems based on cyclic [3]spirobifluorenylne compound

28 March 2023, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Cyclic [3]spirobifluorenylene with bulky alkyl groups at the ends (1) was designed and synthesized to investigate the electron transfer phenomena in a -conjugated system including orthogonal π-conjugated chains. The three bifluorenyl units in 1 are conjugated to each other via spiro-conjugation, resulting in the splitting of the HOMO levels to a small extent. Therefore, the SOMO–HOMO gap of the radical cation species is small, which is considered to allow the facile intramolecular electron transfer. The electronic properties of 1 and its partial structures were characterized by absorption and fluorescence measurements and electrochemical analysis. From the electrochemical oxidation, the interchain Coulombic repulsion was observed. In the TD-DFT calculations for the radical cation species of 1, the geometry-featured interchain electronic transitions were visualized by NTO calculations. The radical cation species of 1 generated by chemical oxidation with SbCl5 exhibited a broadened and lower-energy shifted NIR absorption band compared to those of its partial structures. Considering the results of the TD-DFT calculations, the NIR band of the radical cation of 1 was attributed to the intramolecular electron transfer processes among the bifluorenyl units in the macrocycle. ESR experiments also indicated the delocalization of a spin of 1·+ in the whole molecule. This work demonstrates the usefulness of spiro-conjugation as a bridging unit in molecular wires to facilitate smooth electron transfer.

Keywords

spirobifluorene
electron transfer
redox
spiro-conjugation
shape-persistent macrocyclic compounds

Supplementary materials

Title
Description
Actions
Title
Supporting Information
Description
Synthetic procedures, spectroscopic and computational data, and NMR spectra.
Actions
Title
CIF
Description
Crystallographic data.
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.