**2. Preparation**

424 Advanced Aspects of Spectroscopy

health hazard.

molecules.

moieties.

base (FB) analogs of LTAMs are shown in Fig. 2.

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

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

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

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
