First-order hyperpolarizabilities of H-shape azobenzenes in gas and in THF have been theoretically studied by Hartree-Fock method and basis set sto-3g with Onsager model, including 4,5-bis((E)-(4-nitrophenyl)diazenyl)anthracene-1,8-diol, 4,5-bis((E)-(4-(trifluoromethyl)phenyl)diazenyl)anthracene-1,8-diol, 4,5-bis((E)-(3-chloro-4-fluorophenyl)diazenyl) anthracene-1,8-diol and 4,5-bis((E)-(4-chlorophenyl)diazenyl)anthracene-1,8-diol. Compared with corresponding azobenzene monomers, H-shape azobenzenes had much larger first-order hyperpolarizabilities. There were four factors which could obviously influence their first-order hyperpolarizabilities. Firstly, H-shape azobenzenes possessed dihedral angles of approximate ten degrees caused by coulomb repulsions with weakening dipole's changes between ground states and excited states. Meanwhile, dihedral angle induced energy gap between HOMO and LUMO to increase. Secondly, dipole-dipole interaction was considered as perturbation which caused strong energy splitting of each molecular orbital with the lessening of energy gap. Thirdly, hyper-conjugated effect existed in H-shape azobenzene and it induced energy gap to decline. Fourthly, solvent effects could obviously enhance their first-order hyperpolarizabilities by comparing results in gas with results in THF. These factors competed and affected each other. The latter three factors lastly overcame coulomb repulsion, which explained that H-shape azobenzenes' first-order hyperpolarizabilities were much larger than corresponding monomers'.

Date Published: 4 January 2008
PDF: 6 pages
Proc. SPIE 6839, Nonlinear Optics: Technologies and Applications, 683921 (4 January 2008); doi: 10.1117/12.757559

Published in SPIE Proceedings Vol. 6839:
Nonlinear Optics: Technologies and Applications
Yiping Cui; Qihuang Gong; Yuen-Ron Shen, Editor(s)