Quantum chemical design of nanographenes with remarkable linear and nonlinear optical properties

Our research topic deals with polycyclic aromatic hydrocarbons, also called nanographenes, in order to achieve remarkable linear and nonlinear optical properties

Polycyclic aromatic hydrocarbons are compounds of which the shape and the size tailor their molecular properties. Our research topic deals with such compounds, also called nanographenes, in order to achieve remarkable linear and nonlinear optical properties [1].  Recent investigations have shown that specific chemical modifications can lead to open-shell compounds, i.e. compounds with one or more unpaired electrons [2].  Among these, diradicals or diradicaloids, of which the unpaired electrons can interact more or less strongly over large distances.  If the interaction is weak, the diradical character (a parameter describing the chemical bond nature [3]) is large. If it is strong, these electrons form a bond and the diradical character is small.  The most interesting compounds are those with intermediate diradical character because their excitation energies are small, they can exhibit singlet fission, and their nonlinear optical properties (two-photon absorption, third-harmonic generation) are exalted [3-4].  Within a multidisciplinary approach combining synthesis and characterizations, our research consists in applying quantum chemistry methods to unravel their structure-property relationships (for instance by functionalizing the nanographenes or by substitutions of rings/atoms [5]), to highlight their spectroscopic (vibrational) signatures [6], and to probe the impact of intermolecular interactions [7].  A second part of our research is methodological.  Indeed, the electronic structure and associated properties of open-shell compounds are complex quantities to determine, owing to the large static and dynamic electron correlations [8]. 

 

teranthene

Fig. 1. Design of teranthene derivatives [2] with expected remarkable linear and nonlinear optical properties.

 

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[2]   A. Konishi, Y. Hirao, M. Nakano, A. Shimizu, E. Botek, B. Champagne, D. Shiomi, K. Sato, T. Takui, K. Matsumoto, H. Kurata, and T. Kubo, J. Am. Chem. Soc. 132, 11021 (2010).

[3]   M. Nakano and B. Champagne, J. Phys. Chem. Lett. 6, 3236 (2015).

[4]   M. Nakano, R. Kishi, S. Ohta, H. Takahashi, T. Kubo, K. Kamada, K. Ohta, E. Botek, and B. Champagne, Phys. Rev. Lett. 99, 033001 (2007). 

[5]   M. Nakano and B. Champagne, J. Chem. Phys. 138, 244306 (2013). 

[6]   J. Romanova, V. Liégeois, and B. Champagne, Phys. Chem. Chem. Phys. 16, 21721 (2014).

[7]   K. Yoneda, M. Nakano, K. Fukuda, H. Matsui, S. Takamuku, Y. Hirosaki, T. Kubo, K. Kamada, and B. Champagne, Chem. Eur. J. 20, 11129 (2014).

[8]    W. Mizukami, Y. Kurashige, and T. Yanai, J. Chem. Theor. Comput. 9, 401 (2013); M. de Wergifosse, F. Wautelet, B. Champagne, R. Kishi, K. Fukuda, H. Matsui, M. Nakano, J. Phys. Chem. A 117, 4709 (2013); X. Lopez, M. Piris, M. Nakano, and B. Champagne, J. Phys. B: Mol. Opt. Phys. 47, 015101 (2014).