Computer-Aided and Experimental Studies of Conjugation Effect in Azobenzene-Based Compounds towards Nonlinear Optic Application

Diphosphine ligands containing {(-HC=N) imine group} demonstrating aliphatic and aromatic framework such as ethane and azobenzene exhibit different nonlinear optical (NLO) properties. In this study, two different ligands N,N '-Bis-(2-diphenylphosphinobenzyaldehyde)-ethane-1,2-diamine (A) and N,N '-Bis-(2-diphenylphosphinobenzyaldehyde)-4,4 azodianiline (B) have been synthesized with a percentage yield of 60-70 % and further characterized by spectroscopic analysis. Comparative study of computational analysis using Gaussian software with DFT method and hybrid functional B3LYP together with basis set 6-31G++(d,p) has shown good agreement of less than 5 % deviation errors. From previous study, derivatives of these compounds have shown good NLO properties contributing by many factors such as conjugation, electron withdrawing groups (EWG), electron donating groups (EDG), metal mass, highest occupied molecular orbital-lowest unoccupied orbital (HOMO-LUMO) and band gap. The evaluation shows that both ligands have high NLO properties established on the value of beta(tot) at 1064 nm wavelength. Studies indicate that ligand B showed highest NLO property with the beta(tot) value of 11.1534x10(-30) esu followed by ligand A 10.3786x10(-30) esu due to increased conjugation in the system. This is supported by the high dipole moment 5.501404 mu (D) of ligand B. These ligands can be further modified by the addition of the metals to form complexes in order to improve NLO properties with the beta(tot) value of complex A 24.0638x10(-30) esu followed by complex B with the beta(tot) value 526.9826x10(-30) esu.