By condensing 2‐aminobenzothiazole with 2‐hydroxy‐1‐naphthaldehyde, 2‐hydroxybenzaldehyde, 4‐methoxybenzaldehyde, 4‐hydroxybenzal‐dehyde, benzaldehyde and 4‐dimethylaminobenzaldehyde, and five Schiff bases Ia‐Ie are prepared. Also, two Schiff bases IIa and IIb are prepared by condensation of 2‐amino‐3‐hydroxypyridine with 2‐hydroxy‐1‐naphthaldehyde and 2‐hydroxybenzaldehyde. The 1H NMR, IR and UV/Vis spectra of these seven Schiff bases are investigated. The signals of the 1H NMR spectra as well as the important bands in the IR spectra are considered and discussed in relation to molecular structure. The UV/Vis absorption bands in ethanol are assigned to the corresponding electronic transitions and the electronic absorption spectra of Schiff bases Ib and IIb are studied in organic solvents of different polarities. The UV/Vis absorption spectra of 2‐amino‐3‐hydroxypyridine Schiff bases IIa and IIb are investigated in buffer solutions of different pH values containing 5% (v/v) methanol, and the results are utilized for the determination of pKa and ΔG* of the ionization of the phenolic OH‐groups. The fluorescence spectra of IIa and IIb are studied in organic solvents of different polarities. The obtained spectral results are confirmed by some molecular calculations using the atom super position and electron delocalization molecular orbital theory for the Schiff base IIb.

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Thiazoles belong to the group of azole heterocycles. They are aromatic five-membered heterocycles containing one sulfur and one nitrogen atom. In recent years thiazoles, their derivatives, and isomers have gained considerable attention because of their broad applications in different fields, such as agrochemicals, industrial, and photographic sensitizers. Also, they have pharmaceutical and biological activities that include antimicrobial (sulfazole), antiretroviral (ritonavir), antifungal (abafungin), anticancer (tiazofurin), antidiabetic, anti-inflammatory, anti-Alzheimer, antihypertensive, antioxidant, and hepatoprotective activities. The compounds containing thiazole moieties are a prominent structural feature in a variety of natural products, such as vitamin B and penicillin. Thus, in this chapter several types of thiazole-based heterocyclic scaffolds such as monocyclic or bicyclic systems synthesis and their biological activities studies are presented. Furthermore modification of thiazole-based compounds at different positions to generate new molecules with potent antitumor, antioxidant, and antimicrobial activities is described.