title: Tuning effects for some cyclic aromatic carbenes bearing remote amino groups.
abstract: Yamamoto and co-workers synthesized two cyclic aromatic carbenes with remote amino groups. Here we theoretically studied related compounds to explore tuning effects on the singlet-triplet splitting by variations of functional groups. For the Yamamoto compound, the lowest singlet state lies 15.7 kcal/mol below the lowest triplet. The singlet-triplet separation is reduced by ∼7 kcal/mol when the dimethylamino groups are replaced by H. In one set of carbenes, when X = O, we substitute S, Se, Te, SO, SeO, and TeO for X; the resulting ΔE(S-T) predictions are 9.9, 7.3, 3.9, 4.3, 2.3, and -0.1 kcal/mol, respectively. A different set of X fragments yields triplet electronic ground states with ΔE(S-T) values of -8.6 (X = BH), -6.8 (X = AlH), -7.2 (X = GaH), -7.5 (X = InH), and -7.0 kcal/mol (X = TlH). We also predicted ΔE(S-T) with N(CH3)2 replaced by PH2, AsH2, SbH2, BiH2, BH2, CH3, OH, and F. Of all the molecules considered, that with N(CH3)2 replaced with BH2 and X = BH most favors the triplet state, lying 13.7 kcal/mol below the singlet. Finally, we have relocated the N(CH3)2 and NH2 groups from the (3, 6) positions to the (4, 5), (2, 7), and (1, 8) terminal ring positions, with very interesting results.
authors.affiliation: Research Center for Advanced Computation, School of Physics and Chemistry, Xihua University , Chengdu, China 610039.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zeng
authors.forename: Hao
authors.initials: H
authors.lastname: Feng
authors.forename: Yaoming
authors.initials: Y
authors.lastname: Xie
authors.forename: Henry F
authors.initials: HF
authors.lastname: Schaefer