Thresholds of optical limiting in solutions of nanoscale compounds of zinc phthalocyanine with galactopyranosyl radicals

The optical limiting (OL) of nanosecond laser pulses in solutions of newly synthesized dyes in dimethyl sulfoxide (DMSO) has been investigated. These dyes are compounds of zinc phthalocyanine (ZnPc) with D-galactopyranosyl radicals (Gal) located in the peripheral ($p$-GalZnPc) and nonperipheral ($n$-GalZnPc) positions with respect to the ZnPc macrocycle. Experiments have been performed using laser radiation with a wavelength of 532 nm, at which the optical absorbance of solutions of ZnPc, $p$-GalZnPc and $n$-GalZnPc dyes is four orders of magnitude lower than the absorbance in the peaks at wavelengths of 671, 680, and 701 nm, respectively. It is established that solutions of $p$-GalZnPc and $n$-GalZnPc in DMSO have a much lower OL threshold in comparison with ZnPc solution; the nonlinearity of $p$-GalZnPc solutions exceeds that of $n$-GalZnPc solutions. OL thresholds for the dyes under study in a wide concentration range are determined.