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'.