Synthesis, spectroscopic and DFT characterization of 4 <i>β</i> -(4-<i>tert</i>-butylphenoxy) phthalocyanine positional isomers for non-linear optical absorption

Abstract

In this work the synthesis, spectral characterization and non-linear optical properties of metal-free 4β-(4-tert-butylphenoxy) phthalocyanine isomers are described and compared to the previously reported alpha derivative. The second-order nonlinear optical properties of the phthalocyanine isomers were investigated using the Z-scan technique and compared to the theoretical data obtained from density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations. Z-scan results indicated strong non-linear behaviour, revealing reverse saturable absorption (RSA) profiles for all four isomers. The experimental β_exp values showed the following trend:C_4h (9.31×10^–10mMW^–1)>D_2h (7.89×10^–10mMW^–1)>Cs (7.32× 10^–10 mMW^–1) > C_2v (1.77 × 10^–10 mMW^–1). These results were similar to that obtained with the 4β-(4-tert-butylphenoxy) phthalocyanines as the C_2v and C_s isomers were found to have the lowest β_exp values compared to other symmetries. The 4β-(4-tert-butylphenoxy) phthalocyanine C_4h isomer was found toshowbetter non-linear optical properties compared to all other isomers.

Keywords: Phthalocyanine, non-linear optical absorption, density functional theory, magnetic circular dichroism