Reverse saturable absorption of platinum ter/bipyridyl polyphenylacetylide complexes

Abstract

Transition metal poly-ynes are very interesting nonlinear optical materials for optical limiting applications because of their low linear absorption at low intensities, but high nonlinear absorption at high intensities in the entire visible spectral range. The reverse saturable absorption (RSA) of seven platinum ter/bipyridyl polyphenylacetylide complexes has been investigated at 532 nm with nanosecond pulses. In an f/214 geometry, with sample linear transmission of 90% in a 2 mm cell, the reverse saturable absorption thresholds for these complexes are 8–30 mJ/cm2. The maximum output fluence of these complexes are limited to 0.45–1.16 J/cm2 for incident fluence as high as 3.6 J/cm2. The RSA is strongly influenced by the nature of the triaryl coordination ligand and the conjugation length of the polyphenylacetylide ligand in these complexes. This RSA is mainly attributed to the triplet excited state absorption, with a ratio of effective excited state to ground state absorption cross sections as high as ∼20. These results suggest that platinum ter/bipyridyl polyphenylacetylide complexes could be promising candidates for nanosecond optical limiting applications; and it is possible to improve the reverse saturable absorption by appropriate structural modifications.