Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (10): 2215-2220.doi: 10.3866/PKU.WHXB201308141


Nonlinear Optical Properties:Second Harmonic Generation for Aromatic Amino Acids

WEI Jing, CHENG Wen-Dan   

  1. Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, P. R. China; University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2013-04-26 Revised:2013-08-05 Published:2013-09-26
  • Contact: CHENG Wen-Dan
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (21173225, 21101156) and Foundation of Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, China.


The geometrical structures of a series of neutral, protonated, and deprotonated aromatic amino acids (Phe, [Phe―H]-, PheH+, Tyr, [Tyr―H]-, TyrH+, Trp, [Trp―H]-, and TrpH+) were optimized using density functional theory (DFT)-B3LYP with a 6-31G* basis set. Based on the optimized structures, the excited state properties were studied using time-dependent DFT at the B3LYP/6-31G* level. We calculated the second-order polarizabilities for second harmonic generation with the sum-over-states method. We examined the origins of the nonlinear optical responses and determined the cause for the variation in the second-order polarizabilities. Our calculations show that the second-order polarizabilities for protonated, and deprotonated aromatic amino acids are much higher than those for the neutral aromatic amino acids, with the order Phe < PheH+ < [Phe―H]- and Tyr < TyrH+ < [Tyr―H]-. By analyzing their electronic origins, we find that charge transitions in the side chains (benzene, phenol, and indole) make the main contributions to the second-order polarizability for neutral aromatic amino acids. For protonated and deprotonated aromatic amino acids, π→π* charge transfers within indole rings, and charge transfers within amino groups and the carboxyl groups attached to alpha-carbon atoms make almost identical contributions to the second-order polarizability.

Key words: Aromatic amino acid, Second-order polarizability, Protonated and deprotonated molecules, Density functional theory, Sum-over-states method


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