Sterically demanding zinc(ii) phthalocyanines: synthesis, optical, electrochemical, nonlinear optical, excited state dynamics studies

Abstract

Two novel sterically demanding zinc phthalocyanines were synthesized and characterized. Their optical and electrochemical properties were investigated in detail. The emission spectra were recorded in different solvents and the fluorescence yields obtained were in the range of 0.2–0.3 while time-resolved fluorescence data revealed radiative lifetimes of typically few ns. Nonlinear optical (NLO) properties were also evaluated at wavelengths of 600, 640, 680, and 800 nm using picosecond (∼1.5 ps) pulses and further studies with femtosecond (∼140 fs) pulses at 800 and 780 nm were also performed. Two-photon absorption (2PA) and saturable absorption (SA) were the dominant nonlinear absorption mechanisms observed with ps/fs excitation at different wavelengths in the visible spectral region. NLO coefficients were extracted from ps/fs closed and open aperture Z-scan measurements. Large two-photon absorption cross-sections of ∼14 000 GM and n₂ values in the range of 1–7 × 10⁻¹⁶ cm² W⁻¹ were retrieved for these molecules from the ps Z-scan data. The excited state decay dynamics were investigated using degenerate pump-probe experiments with ∼70 fs pulses near 600 nm. Double exponential fits of the pump-probe data suggested two decay times for both molecules investigated.