Fluorescence sensing of cations, anions and neutral molecules towards information processing at molecular level

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2002
Baytekin, H. Tarık
Chromo and fluoro ionophores based on donor (D)-acceptor (A) system in which the ligand is part of the n system of the chromophores have received considerable attention over the last years. Perturbation of the % system by metal in complexation leads to spectral shifts and changes of the emissive properties. Because the aza groups responsible for metal cation binding are also directly involved with the formation of the charge-transfer excited state complexes, metal binding by perylene crown should have a dramatic influence upon the fluorescence emission from both the locally excited (LE) and charge transfer (CT) states. In the first part of the study, a new class of fluorescent cation sensors; a series of crowned perylenediimides (2 to 9) have been synthesized. The photophysical mbehaviour of a newly synthesized azacrown substituted perylenediimides dyes have been extensively investigated. Some of the derivatives of this dye were found to be highly solvatochromic. Solvatochromic properties were analysed using Et(30) polarity scale. Complexation of the crowned perylene with alkali and alkaline earth metal ions (Li+, Na+, K+, Mg2+, Ca2+) and with transition and heavy metal ions (Cu2+, Zn2+, Cd2+) and a lanthanide (Eu34) ion in acetone have been studied with UV-Vis and fluorescence spectroscopy. The photophysical changes in the spectra have been correlated with both size and charge density of the cation. In the second part of the study, Metal-Ligand Complex (MLC) type probe, typified by [Ru(L)(bpy)2]2+ (18) have been prepared. This complex was designed for recognition of group IA and IIA metal cations. A chemical linker, or spacer, that connects the recognition site and the luminophore to one another have been constructed in this probe. Here, the amine group of the macrocyclic ring coordinates to the metal cations and hence photoinduced electron transfer (PET) from the side chain amine group to the Ru(II) moiety enhances the metal-to-ligand charge transfer (MLCT) emission. The emission intensity increased on the addition of NaC104, and the response is weaker in the presence of the same concentration of KCIO4 as expected, both due to larger Kd and smaller charge/size ratio. In acetone, K<i was determined to be lxlO"5 M for Na+, and 5x1ü"4 M for K+. In the last part, a base-pairing interactions in nucleic acids a DAPI based system is described as a logic gate design in which hydrogen-bonding interactions have been utilized. The base inputs are introduced as deoxynucleotides, i.e., 5'- monophosphates, in this way, once the base pairing is established according to Watson-Crick rules. The signal changes at that wavelength are in accordance with a NAND logic gate behaviour.

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Citation Formats
H. T. Baytekin, “Fluorescence sensing of cations, anions and neutral molecules towards information processing at molecular level,” Ph.D. - Doctoral Program, Middle East Technical University, 2002.