Unsymmetrical phthalocyanines containing azo moiety; Synthesis and photophysical properties

Unsymmetrical metal-free phthalocyanine was synthesized through cyclotetramerization of 4-[2,6-dimethyl-4-(4-tert-butyl-phenylazo)phenoxy]phthalonitrile and 4-(hexylthio)phthalonitrile in the presence of lithium in n-pentanol, then metal-free phthalocyanine was obtained by acidification with acetic acid. Finally, metalation was achieved by refluxing metal-free phthalocyanine in n-pentanol in the presence of zinc (II) salt. The structure of synthesized phthalocyanine derivatives were characterized by using proton nuclear magnetic resonance, mass spectrometry, ultraviolet-visible spectroscopy, and Fourier transform infrared spectroscopy. The HOMO-LUMO energies were computed using density functional theory. The HOMO-LUMO energy difference is 2.28 eV. The calculated results were consistent with the experimental data. In addition, aggregation behaviors and general trends for photophysical properties of these phthalocyanine derivatives were studied in tetrahydrofuran. The emission intensities of these phthalocyanine derivatives were strongly quenched by 1,4-benzoquinone in tetrahydrofuran.