Molecular sensors and switches have made important contributions to biomedical devices and molecular computational operations. There are numerous molecular designs using a fluorophore linked through a spacer group to a receptor(s), with a wide dynamic range, directional precision, target specificity, and molecular logic capability. Tb(III) and Eu(III) metal ions have natural luminescence lifetimes in the order of milliseconds. As a result they have been used as probes that allow discrimination between probe emission and background fluorescence using time- resolved techniques. Unfortunately the free ions themselves absorb light poorly so cannot provide the sensitivity often required of a probe or a sensor. Their performance however can be improved dra.matically by the coordination of the metal ions to organic chelate ligands containing appropriate organic fluorophores. This project is based on the design and synthesis of Tb(lU) and Eu(III) complexes of phthalimide and phthalamate derivatives as responsive lanthanide complexes. Phthalimide and phthalamate compounds are organic chromophores. Four acyclic phthalimide derivatives, Ll, L3, LS and V, were prepared through condensation reaction of phthalic anhydride and the corresponding amine derivatives in glacial acetic acid. These phthalimide derivatives, Ll, L3, LS and V, were then hydrolysed under basic conditions to yield the desired phthalamate compounds, L2, L4, L6 and L8. The yields of these phthalamate derivatives (L2, L 4, L6 and L8) were 50%-70%. They are fully characterised by lH and 13C NMR spectroscopy, elemental analysis, mass spectrometer, IR and melting point analysis. A series of macrocycles with N-substituted phthalimide pendant arm(s) L9-12were synthesised. The macrocyclic phthalimide derivatives were prepared by incorporating N-bromoalkyl phthalimide onto tri-tert-butyl-1,4,7,10- tetraazacyclododecane-1,4,7 -triacetate, di-tert-butyl-1,4,7,10- tetraazacyclododecane-1,4-diacetate and mono-tert-butyl-1,4,7,10- tetraazacyclododecane-monoacetate through nucleophilic substitution reactions. Removal of t-butyl functions and retention of phthalimide was achieved in trifluoroacetic acid to yield the final products (6%-14%). 1,4,7,10- Tetraazacyclododecane was alkylated on its 4 nitrogen sites by phthalimide function with a propyl bridge to yield L13 (10%). L9-13 were fully characterized by lH and 13C NMR spectroscopy, elemental analysis, mass spectrometer, IR and melting point analysis. Apart from Ll, L3, L4, LS and LlO all the phthalimide and phthalamate derivatives synthesised in this thesis are new. The optimal metal-to-ligand ratio of 1:2 was established for acyclic phthalamate- based terbium complexes, whereby the best antennae effects on the luminescence properties of these complexes were observed. The highest luminescence level of [Tb(L2)2J-, [Tb(L4)2J-, [Tb(L6)2P- and [Tb(LB)2]- was observed at pH ea. 6, but it was quenched at pH> 7. These four terbium complexes exhibited long emission lifetimes of the order of sub-milliseconds. Luminescence features of [TbL9], [TbLlO], [J'bLll]+ and [TbLl2)2+ showed rather weak luminescence under acidic conditions. The luminescence was enhanced under basic conditions while phthalimide functions were hydrolysed to phthalamates. Their phthalamate-based macrocyclic terbium complexes ([TbL9H]-, [TbLlOH]-, [TbLllHJ-, [TbLl2H]-, and [TbL13H]-) exhibited high quantum yields (cp) and long lifetimes (T) of the order of milliseconds at pH ea. 6. The values of <P and T were 46% and 2.4 ms respectively for [TbL9H]-, which was one of the top three terbium complexes benefiting from the macrocyclic architecture. Eu3+ complexes gave luminescence, but a rather weak antennae effect was observed. The results showing different number of chromophores appended on the macrocycle and the size of linkers have a significant effect on Φ The high efficiency of energy transfer could be quenched in the presence of particular metal ions (such as Cu2+, Fe2+, C02+, Ni2+ and Fe3+) for these terbium complexes, [Tb(L2)2J-, [TbL9H]- and [TbLl3H]-. [Tb(L2)2]- and [TbL13H]- were responsive to Cu2+ and Fe3+, while [TbL9H]- was responsive to Cu2+ and C02+. Quenching rate constants (kq) of these complexes in the presence of quenchers showed that Cu2+ has the most significant quenching effect on the luminescence of [Tb(L2)2]-. An NOR mode molecular logic gate system is devised on the basis of using these three terbium complexes, [Tb(V)2]-, [TbL9H]- and [TbL13HJ-, in the presence of responsive metal ions. In [Tb(V)2]- and [TbL13H]-, their luminescence was switched
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:571268 |
| Date | January 2012 |
| Creators | Chen, Gaoyum |
| Publisher | London Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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