Tine synthesis of three novel benzothiazolyl-derivatives with typical A-π-A' conjugation structures is reported. The influences of the structural modifications on the photophysical properties are studied. Experimental results show that, when the k-conjugation length of organic molecule is short, heteroatom in the π- conjugation structure (sulfur atom in our experiments) gives significant effects on the emission characteristics of the molecules; however, with the extension of the %-conjugation structure, such effects will be decreased and finally disappear. Experimental results also show that, although two-photon absorption cross-section is generally dependent on both the length of π-conjugation structure and the strength of acceptor (or donor), when the π-conjugation structure is long enough, the effect from π-conjugation length will play a dominant role. The results above will be beneficial to the design and synthesis of effective two-photon induced fluorescence molecules. Additionally, a new organic'molecule, named 2-(2-{4-[2-(4-nitro-phenyl )-vinyl]-phenyl}-vinyl )-benzothiazole (NSSBT), has a large two-photon absorption cross-section (181 GM) and a high two-photon induced fluorescent efficiency (the quantum yield is 13.8%) , which implies that this molecule is a promising candidate for an application such as two-photon microscopy and imaging.

Key words: BENZOTHIAZOLE P, TWO PHOTON ABSORPTION, FLUORIMETRIC ANALYSIS, STRUCTURE AND PROPERTY CORRELATION