Tetrabrominated Lead Naphthalocyanine for Optical Power Limiting

The complex 2,(3)-tetrabromo-3,(2)-tetra[(3,5-di-tert-butyl)phenyloxy]-naphthalocyaninato lead [Br(4)(tBu(2)C(6)H(3)O)(4)NcPb, 1] has been prepared and its optical limiting properties for ns light pulses have been measured. Complex 1 behaves as a reverse saturable absorber within the spectral range 440-720 nm with a limiting threshold of 0.1 J cm(-2) at 532 nm. The lifetime of the absorbing triplet excited state has been evaluated as 3.8 x 10(-7) s and the quantum yield of triplet formation has been measured as 0.07 in toluene. The nonlinear optical transmission properties of complex 1 have also been determined in Plexiglas [naphthalocyanine content: 5.0 x 10(-4) M (0.1% by weight)]. A reversible nonlinear absorption was again observed for a fluence above 0.4 J cm(-2), but through different excited-state dynamics. This may be rationalized in terms of aggregation of the molecule in the polymer matrix.