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New Acceptor–Bridge–Donor Strategy for Enhancing NLO Response with Long-Range Excess Electron Transfer from the NH2...M/M3O Donor (M = Li, Na, K) to Inside the Electron Hole Cage C20F19 Acceptor through the Unusual σ Chain Bridge (CH2)4

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journal contribution
posted on 04.04.2013, 00:00 by Yang Bai, Zhong-Jun Zhou, Jia-Jun Wang, Ying Li, Di Wu, Wei Chen, Zhi-Ru Li, Chia-Chung Sun
Using the strong electron hole cage C20F19 acceptor, the NH2...M/M3O (M = Li, Na, and K) complicated donors with excess electron, and the unusual σ chain (CH2)4 bridge, we construct a new kind of electride molecular salt e@C20F19–(CH2)4–NH2...M+/M3O+ (M = Li, Na, and K) with excess electron anion inside the hole cage (to be encapsulated excess electron–hole pair) serving as a new A–B–D strategy for enhancing nonlinear optical (NLO) response. An interesting push–pull mechanism of excess electron generation and its long-range transfer is exhibited. The excess electron is pushed out from the (super)­alkali atom M/M3O by the lone pair of NH2 in the donor and further pulled inside the hole cage C20F19 acceptor through the efficient long σ chain (CH2)4 bridge. Owing to the long-range electron transfer, the new designed electride molecular salts with the excess electron–hole pair exhibit large NLO response. For the e@C20F19–(CH2)4–NH2...Na+, its large first hyperpolarizability (β0) reaches up to 9.5 × 106 au, which is about 2.4 × 104 times the 400 au for the relative e@C20F20...Na+ without the extended chain (CH2)4–NH2. It is shown that the new strategy is considerably efficient in enhancing the NLO response for the salts. In addition, the effects of different bridges and alkali atomic number on β0 are also exhibited. Further, three modulating factors are found for enhancing NLO response. They are the σ chain bridge, bridge-end group with lone pair, and (super)­alkali atom. The new knowledge may be significant for designing new NLO materials and electronic devices with electrons inside the cages. They may also be the basis of establishing potential organic chemistry with electron–hole pair.