TY - JOUR
T1 - Biradicals stabilized by intramolecular charge transfer
T2 - Properties of heterosubstituted pentalene and cyclooctatetraene biradicals
AU - Zilberg, Shmuel
AU - Haas, Yehuda
PY - 2006/7/13
Y1 - 2006/7/13
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=33746336284&partnerID=8YFLogxK
U2 - 10.1021/jp057027v
DO - 10.1021/jp057027v
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AN - SCOPUS:33746336284
SN - 1089-5639
VL - 110
SP - 8397
EP - 8400
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 27
ER -