Optical limiting of eight-β-octa-octyloxy-phthalocyanines for picosecond pulses in solution

The optical power limiting performances for eight-beta-octa-octyloxy phthalocyanines with initial linear transmission T-0 = 88-92% at 532 nm in a 0.5 cm spectroscopic cell in toluene have been measured with 35 ps pulses, in which eight-beta-octa-octyloxy phthalocyanine free-base exhibits the strongest optical limiting ability through a reverse saturable absorption from S-1 --> S-n excited singlet states with sigma(S1) = 4.0 x 10(-17) cm(2). The optical limiting thresholds are 50, 130 and 140 mJ/cm(2) at T/T-0 = 0.5 for eight-beta-octa-octyloxy phthalocyanine free base, nickel phthalocyanine, and lead phthalocyanine respectively. The throughput of eight-beta-octa-octyloxy phthalocyanine free base is clamped down to 70 mJ/cm(2) with the limiting nonlinear transmittance T-lim, = 0.18 as the incident fluence reaching to 400 mJ/cm(2). The aggregation behaviors for eight-beta-octa-octyloxy phthalocyanines have been studied, in which the aggregation equilibrium constant k = 5.6 x 10(3) in toluene for eight-beta-octa-octyloxy phthalocyanine free base is larger than in mixed solvent containing acetonitrile (k' = 1.4 x 10(3)). This means that the eight-beta-octa-octyloxy phthalocyanines aggregate more easily in nonpolar solvent than in polar solvent through the pi-pi interaction. (C) 2003 Elsevier B.V. All rights reserved.