Biradicals stabilized by intramolecular charge transfer: Properties of heterosubstituted pentalene and cyclooctatetraene biradicals

Shmuel Zilberg, Yehuda Haas

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

Intramolecular charge transfer can lead to substantial stabilization of singlet ground state and a corresponding increase of the singlet-triplet gap for molecules isoelectronic with the dianions of antiaromatic hydrocarbons. The formal biradicals 2,5-di-heterosubstituted-pentalenes and 1,5-di-heterosubstituted-cyclooctatetraenes are theoretically predicted to have the potential to be stable, persistent non-Kekulé molecules, as supported by high-level quantum chemical calculations. The singlet-triplet energy gaps and the S0-S1 excitation energies of these molecules are similar to those of aromatic molecules rather than standard biradicals. These formal biradicals have a pronounced zwitterionic character, having a singlet ground state. The marked stabilization of the ground-state singlet for these non-Kekulé molecules is accompanied by a significant destabilization of the highest occupied molecular orbital (HOMO), leading to a low ionization potential (IP). This apparent inconsistency is explained by analyzing the electronic structure of the molecules. In the case of di-azapentalene, the energy of the first electronic excited state is only slightly lower than the ionization potential, making it a candidate for molecular autoionization.

Original languageEnglish
Pages (from-to)8397-8400
Number of pages4
JournalJournal of Physical Chemistry A
Volume110
Issue number27
DOIs
StatePublished - 13 Jul 2006
Externally publishedYes

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