Synthesis of novel stilbene-alkoxysilane fluorescent brighteners, and their performance on cotton fiber as fluorescent brightening and ultraviolet absorbing agents

Two novel fluorescent brightening agents (compounds 3a-b shown in Figure 1) were synthesized, using a facile three-step synthetic route, from 4,4'-diamino-2,2'-disulfonic-stilbene, cyanuric chloride, and a readily cross-linkable 3-aminopropyltrimethoxy silane. The products contain hydrolytically active trimethoxysilyl, (-Si(OCH)(3)), functional groups that readily hydrolyze in the presence of water, and subsequently generate a water insoluble silicon cross-linked-network (Si-O-Si) via a condensation process. The cross-linked product hydrolyzes on treatment with hot aqueous sodium hydroxide to silanols (-Si(OH)(3)) to form compounds 4a-b which are readily water soluble and produce a clear fluorescent solution. The silanol forms of compounds 4a-b were used for further characterization and performance evaluation. The structures of compounds 4a-b were characterized by H-1-NMR, Fourier-Transform infrared (FT-IR) spectroscopy and negative electrospray ionization mass (-ESI-MS) spectroscopy. Compounds were applied to cotton fiber as fluorescent brightening agents and their performance was evaluated by measuring the degree of whiteness, ultraviolet protection factor (UPF), fluorescence and acid fastness. Results showed that application of 0.25% (o.w.f) of compounds 4a-b impart a high degree of whiteness (CIE WI = 144, 139) as well as good ultraviolet protection factor (UPF = 29, 27) on cotton fiber exhibiting a significant increase in whiteness and UV blocking properties compared to untreated substrate (CIE WI = 81, UPF = 5). Acid fastness tests of both compounds showed a slight change in fluorescence emission intensities as a function of pH. In acidic solutions, a shift in emission maximum occurs at pH 3 from 434 to 453 nm and from 435 to 457 nm, due to the protonation of amino and sulfonic groups of stilbene fluorophore which substantially reduces the quenching process. Published by Elsevier Ltd.