Effects of Purification and Addition of Electron Acceptor Dyes to Solutions of Macrocyclic Dyes
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ABSTRACT This paper will deal with the electronic and physical effects of purification of a macrocyclic dye, 2,3-napthalocyanine bis(trihexylsiloxide) (SiNC), on the optical limiting performance. The changes in optical limiting performance of SiNC, a carbocyanine dye (1,1',3,3,3',3',Hexamethylindocarbocyanine iodide (HITCI) and two metallated porphyrins upon the addition of an electron acceptor material, methyl viologen dichloride (MV) (1,1'-dimethyl-4,4' bipyridinium dichloride), are also shown and the results discussed.
INTRODUCTION Impurities can have detrimental effects on the electronic and optical properties of materials. Although there are an increasing number of open literature publications appearing on optical limiting properties (OPL) of dyes, very few mention the effects of impurities on the non-linear optical limiting performance. In the first part of this paper, we use SiNC as an example to demonstrate the enhancement in OPL performance obtained by purifying the dye. The exclusion of impurities from the optical limiter is desirable for a number of reasons. Quenching of the Si.napthalocyanines excited states by the presence of an impurity is a possibility. This could dramatically effect the non-linear absorption behaviour of the chromophore. Also, chemical degradation of the dye chromophore may occur and, if the impurity absorbs in the visible, may reduce the overall transmission of the limiter, decreasing its efficiency. Linear absorption spectroscopy and fluorescence spectroscopy were used to monitor the relative purity levels. The second part of this paper describes the effects of adding the electron acceptor methyl viologen to HITCI, SiNC, PbPP (2,10,15,20-tetra(trimethylsilylethynyl)porphyrin lead(H))[1] and ZnPP (2,10,15,20-tetra(trimethylsilylethynyl)porphyrin zinc (II)). This work was instigated by reports [2,3,4] that viologens, when mixed in with electron donor dye solution, could undergo one electron reduction to form highly absorbing species. EXPERIMENTAL WORK Purification of SiNC Purification of SiNC (obtained from Aldrich Chemicals -95% purity) was initially performed using flash elution chromatography through a vertical silica (300 mesh) column using 407 Mat. Res. Soc. Symp. Proc. Vol. 597 ©2000 Materials Research Society
chloroform eluent. A bright green, well-defined band travelled down the column, leaving a khaki-green stationary residue indicating the presence of an impurity. Recrystallization of the solution afforded dark green crystals, which were washed with ethanol and dried at 100 0 C.
Analysis and performance of purified SiNC Transmission spectra were recorded using a 2mm spectroscopic cell on a Perkin Elmer UV/Vis/NIR spectrophotometer. Although the linear transmission of the purified and unpurified samples were matched to 39.6 ± 0.2 % at 590nm, slight differences between the two spectra were observed (figure 1), with a clear sharpening of the So to S, transition. The fluorescence spectra, measured in a front-face geometry using weak solutions, showed a small variation betw
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