**1. Introduction**

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Triarylmethane (TAM) dyes are organic compounds containing triphenylmethane backbones. TAM compounds are sometimes called leuco-TAMs (LTAMs) or leuco-bases. (Nair et al., 2006) LTAM molecules are the precursors of TAM+ dyes since TAM+ dyes are the oxidized form of LTAM molecules. Backbones of TAM molecules are also known to be an important group in intermediates in the synthesis of various organic functional compounds, including the preparation of polymers and supramolecules. (Bartholome & Klemm, 2006)

TAM+ dyes potentially have numerous applications in the chemical, pharmaceutical, and life science industries, including as staining agents, ink dyes, thermal imaging materials, carbonless copying materials, drugs, leather, ceramics, cotton, and as a cytochemical staining agent. (Balko & Allison, 2000) A number of TAM+ dye molecules are well known, such as malachite green (MG), brilliant green, crystal violet, and pararosanilin, *etc*. The chemical structures of some of these well-known TAM+ dyes are shown in Fig. 1.

© 2012 Keum et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Among them, MG is one of the most commonly used chemicals in dye chemistry. MG is a common green dye but it is absorbed into the human body in its carbinol and leuco forms (see the section on UV-Vis spectroscopy). MG is very active with the fungus *Saprolegnia*, which infects fish eggs in commercial aquaculture, and is known to be good for *Ichthyophthirius* in fresh water aquaria. (Indig et al., 2000) It has been known, however, for MG to be highly toxic to mammalian cells, even at low concentrations.(Plakas et al., 1999; Cho et al., 2003) Because of its low cost, effectiveness as an antifungal agent for commercial fish hatcheries, and ready availability, many people can be exposed to this dye through the consumption of treated fish. Since MG is similar in structure to carcinogenic triphenylmethane dyes, it may be a potential human health hazard.

In addition, in their oxidized form, TAM+ dyes are highly absorbing fluorophores with extinction coefficients of ~2.0 × 105 mol−1cm−1 and high quantum yields. Their absorption maxima can easily be matched with the laser lines by simply changing the length of the conjugated chain and/or the heterocyclic moiety. Thus, TAM+ dyes can be employed as fluorescence labels and sensors of biomolecules *in vivo* because their spectra reach the nearinfrared region. Özer (2002) reported efficient non-photochemical bleaching of a TAM+ dye by chicken ovalbumin and human serum albumin, showing that dye–protein adducts can also form and suggesting that proteins may be primary, rather than indirect, targets of TAM+ action. However, the use of this substance has been banned in many countries because of its toxicity and possible carcinogenicity. Substitutive materials for MG compounds have thus been in considerable demand. Numbers of researchers (Gessner & Mayer, 2005) have been interested in developing TAM+ molecules. We developed Fischer's base (FB) analogs of LTAM molecules (Keum et al., 2008, 2009, 2010, 2011, 2012), whose chemical structures contain a couple of heterocyclic FB rings and a substituted phenyl group on a central carbon of the molecules. The structures and numbering system for the Fischer's base (FB) analogs of LTAMs are shown in Fig. 2.

**Figure 2.** Structures and numbering systems for the FB analogs of symmetric and unsymmetric LTAM molecules.

In this chapter, abbreviations (LTAM and Un-LTAM) will be used to designate the Fischer's base analogs of symmetric and unsymmetric LTAMs, respectively. Note that "the general LTAM" in Section 2.2 denotes the LTAM/TAM+ dyes that contain no FB moieties.

Novel Fischer's Base Analogous of Leuco-TAM and TAM+ Dyes – Synthesis and Spectroscopic Characterization 425
