Second Hyperpolarizabilities of Singlet Polycyclic Diphenalenyl Radicals: Effects of the Nature of the Central Heterocyclic Ring and Substitution to Diphenalenyl Rings

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• 作者：Masayoshi Nakano ; Nozomi Nakagawa ; Ryohei Kishi ; Suguru Ohta ; Masahito Nate ; Hideaki Takahashi ; Takashi Kubo ; Kenji Kamada ; Koji Ohta ; Beno&icirc ; t Champagne ; Edith Botek ; Yasushi Morita ; Kazuhiro Nak
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：September 20, 2007
• 年：2007
• 卷：111
• 期：37
• 页码：9102 - 9110
• 全文大小：715K
• 年卷期：v.111,no.37(September 20, 2007)
• ISSN：1520-5215

文摘

Adopting density functional theory and a hybrid exchange-correlation functional, the relationship betweenthe second hyperpolarizability () and the diradical character has been investigated for diphenalenyl-basedcompounds containing different heterocyclic five-membered central rings (C₄H₄X, where X = NH, PH, O, S,CH₂, SiH₂, BH, GaH, C=O, C=S, and C=Se) or substituted by donor (NH₂)/acceptor(NO₂) groups. It turnsout that these structural modifications can tune the diradical character from 0.0 to 0.968 and lead to variationsof over more than 1 order of magnitude, demonstrating the controllability of in this family of compounds.In particular, when the central ring is strongly aromatic, the diradical character is larger than 0.7, which isassociated with pretty large values except for almost the pure diradical case (y 1). On the other hand,when the aromaticity decreases-or the antiaromaticity increases-the diradical character and the secondhyperpolarizability get smaller. These relationships are correlated to structural (bond length alternation) andcharge distribution (charge transfer between the phenalenyl rings and the central ring) properties, which accountfor the relative importance of the resonance diradical, zwitterionic, and quinoid forms. Therefore, the diradicalcharacter and the second hyperpolarizability can be controlled by the aromaticity of the ring while the paradigmof the enhancement of for intermediate diradical character is globally verified. Then, upon introducingdonor groups, the zwitterionic character increases, leading to closed-shell species and small secondhyperpolarizabilities. In the case of substitution by acceptor groups, the charge transfer is reduced but thediradical character and the second hyperpolarizability hardly changes.