TY - JOUR
T1 - Second hyperpolarizabilities of singlet polycyclic diphenalenyl radicals
T2 - Effects of the nature of the central heterocyclic ring and substitution to diphenalenyl rings
AU - Nakano, Masayoshi
AU - Nakagawa, Nozomi
AU - Kishi, Ryohei
AU - Ohta, Suguru
AU - Nate, Masahito
AU - Takahashi, Hideaki
AU - Kubo, Takashi
AU - Kamada, Kenji
AU - Ohta, Koji
AU - Champagne, Benoît
AU - Botek, Edith
AU - Morita, Yasushi
AU - Nakasuji, Kazuhiro
AU - Yamaguchi, Kizashi
PY - 2007/9/20
Y1 - 2007/9/20
N2 - Adopting density functional theory and a hybrid exchange-correlation functional, the relationship between the second hyperpolarizability (γ) and the diradical character has been investigated for diphenalenyl-based compounds containing different heterocyclic five-membered central rings (C 4H4X, where X = NH, PH, O, S, CH2, SiH 2, BH, GaH, C=O, C=S, and C=Se) or substituted by donor (NH 2)/acceptor(NO2) groups. It turns out that these structural modifications can tune the diradical character from 0.0 to 0.968 and lead to variations of γ over more than 1 order of magnitude, demonstrating the controllability of γ in this family of compounds. In particular, when the central ring is strongly aromatic, the diradical character is larger than 0.7, which is associated with pretty large γ values except for almost the pure diradical case (γ ≈ 1). On the other hand, when the aromaticity decreases-or the antiaromaticity increases-the diradical character and the second hyperpolarizability get smaller. These relationships are correlated to structural (bond length alternation) and charge distribution (charge transfer between the phenalenyl rings and the central ring) properties, which account for the relative importance of the resonance diradical, zwitterionic, and quinoid forms. Therefore, the diradical character and the second hyperpolarizability can be controlled by the aromaticity of the ring while the paradigm of the enhancement of γ for intermediate diradical character is globally verified. Then, upon introducing donor groups, the zwitterionic character increases, leading to closed-shell species and small second hyperpolarizabilities. In the case of substitution by acceptor groups, the charge transfer is reduced but the diradical character and the second hyperpolarizability hardly changes.
AB - Adopting density functional theory and a hybrid exchange-correlation functional, the relationship between the second hyperpolarizability (γ) and the diradical character has been investigated for diphenalenyl-based compounds containing different heterocyclic five-membered central rings (C 4H4X, where X = NH, PH, O, S, CH2, SiH 2, BH, GaH, C=O, C=S, and C=Se) or substituted by donor (NH 2)/acceptor(NO2) groups. It turns out that these structural modifications can tune the diradical character from 0.0 to 0.968 and lead to variations of γ over more than 1 order of magnitude, demonstrating the controllability of γ in this family of compounds. In particular, when the central ring is strongly aromatic, the diradical character is larger than 0.7, which is associated with pretty large γ values except for almost the pure diradical case (γ ≈ 1). On the other hand, when the aromaticity decreases-or the antiaromaticity increases-the diradical character and the second hyperpolarizability get smaller. These relationships are correlated to structural (bond length alternation) and charge distribution (charge transfer between the phenalenyl rings and the central ring) properties, which account for the relative importance of the resonance diradical, zwitterionic, and quinoid forms. Therefore, the diradical character and the second hyperpolarizability can be controlled by the aromaticity of the ring while the paradigm of the enhancement of γ for intermediate diradical character is globally verified. Then, upon introducing donor groups, the zwitterionic character increases, leading to closed-shell species and small second hyperpolarizabilities. In the case of substitution by acceptor groups, the charge transfer is reduced but the diradical character and the second hyperpolarizability hardly changes.
UR - http://www.scopus.com/inward/record.url?scp=34948901455&partnerID=8YFLogxK
U2 - 10.1021/jp0734676
DO - 10.1021/jp0734676
M3 - Article
AN - SCOPUS:34948901455
SN - 1089-5639
VL - 111
SP - 9102
EP - 9110
JO - Journal of physical chemistry A
JF - Journal of physical chemistry A
IS - 37
ER -