Substantial non-linear optical response of new polyads based on Ru and Os complexes of modified terpyridines

The third-order non-linear optical behavior of two new series of multicompo nent systems based on coordination compounds of transition metals is report ed. These systems, soluble in acetonitrile, are made of a metal (Ru or Os) bis-terpyridyl (tpy) unit, as photosensitizer P, connected to one or two el ectron acceptor groups, or to both electron donor (D) and electron acceptor (A) groups to form polyads of D-P-A type. The non-linear absorption and no n-linear refraction response was substantial and was examined using the z-s can technique. The results are presented for two different excitation condi tions. For excitation under laser pulses of nanosecond duration the compoun ds with the Ru. center exhibit reverse saturable absorption (RSA). The corr esponding Os samples show saturable absorption (SA) for low incident intens ities that turns to RSA above an intensity threshold that depends on the co ncentration of the solutions. In contrast, under sub-picosecond laser excit ation the Ru and the Os samples each exhibit saturable absorption. The non- linear refraction monitored for nanosecond excitation is negative (self-def ocusing) for both Ru and Os complexes.