Heterocyclic Polymethine Dyes Synthesis, Properties and Applications
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ynthesis of Cyanine Dyes Mariusz Mojzych1 · Maged Henary2 (u) 1 Department
of Chemistry, University of Podlasie, 08-110 Siedlce, Poland
2 Department
of Chemistry, Georgia State University, Atlanta, Georgia 30302-4098, USA [email protected]
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Synthesis . . . . . . . . Monomethine Cyanines Trimethine Cyanines . Pentamethine Cyanines Heptamethine Cyanines
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Abstract Recent developments in the general synthesis of cyanine dyes are reviewed. This short chapter provides a background to the subsequent reviews of applications of cyanines. Keywords Heptamethine cyanines · Monomethine cyanines · Pentamethine cyanines · Synthesis · Trimethine cyanines
1 Introduction Classical cyanine dyes are cationic molecules in which two terminal nitrogen heterocyclic subunits are linked by a polymethine bridge as shown by the general structure 1. Their common names denote the number of methine groups in the polyene chain. For example, compounds 1 with n = 0 and n = 3 are referred to as monomethine and heptamethine cyanines, respectively. The end subunits containing a nitrogen atom may be identical or different. Hemicyanines may be represented by a general structure 2, and particular derivatives with the shortest bridge (n = 1) are often called styryl dyes. The first member of cyanine compounds was synthesized in 1856. Several cyanine dyes are natural products [1]. The monomethine and trimethine cyanines generally show absorption in the visible region, and each extension of the chromophore by one vinylene moiety (CH = CH) causes a bathochromic shift of about 100 nm [2]. Depending on substituents, absorption of pentamethine derivatives can reach a near-infrared region (>700 nm), and heptamethine cyanines may show absorption beyond 1000 nm. Cyanine dyes have narrow absorption bands and
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M. Mojzych · M. Henary
extremely high extinction coefficients, often reaching 200 000 M–1 cm–1 . Cyanine dyes are mildly fluorescent in solution and the fluorescence quantum yield decreases with increasing length of the polymethine chain [3]. The fluorescence efficiency is greatly increased upon binding of the dyes with nucleic acids or proteins as a result of the rigidization of the fluorophore. A large number of cyanine dyes have been synthesized and reviewed [1– 10]. The most recent synthetic methodologies are briefly summarized in this chapter and an additional recent synthetic work is described in the chapters Cyanine Dye – Based Compounds for Tumor Imaging With and Without Photodynamic Therapy and Stability and Reactivity of Poly
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