ISSN 1063-7850, Technical Physics Letters, 2013, Vol. 39, No. 7, pp. 664–668. © Pleiades Publishing, Ltd., 2013. Original Russian Text © G.M. Mikheev, I.P. Angelov, V.N. Mantareva, T.N. Mogileva, K.G. Mikheev, 2013, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2013, Vol. 39, No. 14, pp. 86–94. 664 The interest in the optical and nonlinear optical properties of dye compounds based on phthalocyanine (Pc) is due to their applicability in medicine for pho- todynamic therapy and diagnostics of cancer tumors, as well as in the technology of gas sensors, solar batter- ies, thin-film electronic devices, light-emitting diodes, photovoltaic devices, optical limiting (OL) devices, etc. [1–4]. The flexible chemical structure of phthalocyanine makes it possible to attach various functional groups and radicals (as well as various atoms coordinating phthalocyanine macrocycle) to it. As a result, one can design various metal nanocom- plexes with different optical and nonlinear optical properties based on phthalocyanine. There are many publications devoted to the optical and nonlinear optical properties of solutions and film structures of Pc compounds with various metals and radicals (see, for example, [5–11]). From the point of view of photodynamic therapy, ZnPc compounds, which are characterized by high output of singlet oxy- gen upon photoexcitation [12], are most interesting. However, ZnPc has insufficient selectivity of “attach- ing” to the tumor cells. To overcome this drawback, radicals are attached to ZnPc molecules in order to improve their selective properties and increase their ability to be accumulated on pathological cells, taking into account the metabolism of pathogens [13]. Galactopyranosyl can play the role of such a radical. It is noteworthy that radical Gal can be located in both peripheral (p-GalZnPc) and nonperipheral (n- GalZnPc) positions with respect to the ZnPc macro- cycle (Fig. 1) [14]. Recently, ZnPc dyes with galacto- pyranosyl radicals were synthesized in [15, 16]. Study of their physical, physicochemical, and biochemical properties showed that they depend strongly on the position of the Gal radical in the dye chemical struc- ture. Due to these features, the aforementioned dyes can be used as a functional component of nanocom- plexes designed for theranostics [3]. One must know the optical and nonlinear optical properties of these newly synthesized compounds to use them as diagnos- tic markers. However, to the best of our knowledge, the nonlinear properties (in particular, OL) in solu- tions of these compounds have not been investigated. The purpose of our study is to fill in this gap. The objects of study, p-GalZnPc and n-GaLZnPc dyes with a chemical formula C 80 H 88 N 8 O 24 Zn, were synthesized as a result of the interaction of ZnPc (C 32 H 16 N 8 Zn) with D-galactopyranose (C 12 H 20 O 6 ) in dry argon by the technique described in [14–16]. The thus-prepared compounds were identified and characterized on an NMR spectrometer (AVANCE AV600 II+ NMR), which recorded spectra of 1 H nuclei at a frequency of 600 MHz; an electron- ionization mass spectrometer (Bruker Esquire LC); and an IR spectrometer (BIORAD SPC-3200 FTS7 FT-IR). The diameter of disklike conjugants p- GalZnPc and n-GalZnPc, calculated based on the data of [17], is in the range from 2 to 2.5 nm. Thresholds of Optical Limiting in Solutions of Nanoscale Compounds of Zinc Phthalocyanine with Galactopyranosyl Radicals G. M. Mikheev, I. P. Angelov, V. N. Mantareva, T. N. Mogileva, and K. G. Mikheev Institute of Mechanics, Ural Branch, Russian Academy of Sciences, Izhevsk, Russia Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria e-mail: mikheev@udman.ru Received March 14, 2013 Abstract—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 radi- ation 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 deter- mined. DOI: 10.1134/S1063785013070195