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Issue 47, 2017
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Tuning the inter-molecular charge transfer, second-order nonlinear optical and absorption spectra properties of a π-dimer under an external electric field

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Abstract

In this work, we applied an external electric field (F) to a biphenalenyl derivative (BN-PLY2) in the direction of the negative z-axis (Fz) and the positive z-axis (F+z), respectively. The influence of the two directions of F on the molecular structures and electronic properties is investigated, which gives interesting results. Density functional theory (DFT) calculations show that the application of Fz (Fz = 0 to −190 × 10−4) is an advantage toward improving π-dimer stability, which is attributed to an increase in bonding and attractive electrostatic interactions. Interestingly, a large amount of negative charge is induced by applying Fz to the upper layer, resulting in an increase in the electron density in the upper layer, which is the main factor for the formation of a symmetric highest occupied molecular orbital (HOMO) at Fz = −180 × 10−4 au (−9.26 × 109 V m−1). Moreover, when F+z is applied, the HOMO and HOMO−1 undergo orbital interchange in the π-dimer at F+z = 100/110 × 10−4 au. Significantly, the effect of the external electric field effectively regulates the first hyperpolarizabilities (βtot). When the F+z ranges from 0 to 140 × 10−4 au, the βtot values slightly decrease to 0 au. Note that, upon increasing F+z, the βtot values sharply increase to 6.67 × 103 au (F+z = 190 × 10−4 au). Furthermore, the evolutions of the absorption spectra under F might well explain the trend of βtot values. When the F+z ranges from 0 to 140 × 10−4 au, the broad absorption spikes with a low-energy are significantly blue-shifted, while only absorption spikes with a high-energy are significantly red-shifted (F+z = 140 to 190 × 10−4 au). The present work not only provides a deeper understanding of the relationships between the molecular structure and the electronic properties of a π-dimer system, but can also be developed for designing highly efficient nonlinear optical materials through the influence of an external electric field.

Graphical abstract: Tuning the inter-molecular charge transfer, second-order nonlinear optical and absorption spectra properties of a π-dimer under an external electric field

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Article information


Submitted
19 Sep 2017
Accepted
16 Nov 2017
First published
16 Nov 2017

Phys. Chem. Chem. Phys., 2017,19, 31958-31964
Article type
Paper

Tuning the inter-molecular charge transfer, second-order nonlinear optical and absorption spectra properties of a π-dimer under an external electric field

F. Gao, H. Xu and Z. Su, Phys. Chem. Chem. Phys., 2017, 19, 31958
DOI: 10.1039/C7CP06412H

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