Synthesis, Properties Of Polypyridyls And Their Complexes

Imidazo[4,5-f][1,10]phenanthroline is a versatile and multi-purpose ligand of polypyridyls. It not only shows the properties ofσdonor /Ï€acceptor of 1,10-phenanthrline, but also extends the N-heterocyclic aromatic ring and lower the energy ofÏ€conjugation system. Interesting changes of properties will occur when the thiophene ring attaches into imidazo[4,5-f][1,10]phenanthroline. In this paper, a series of 2-(5-substitued-2-thiophene)- imidazo[4,5-f][1,10]-phenanthroline with electron-donating and electron-withdrawing substituents are synthesized. Their properties and Ru (II) complexes are fully discussed. Bulky substituents at 2,9 position of 1,10-phenanthroline will be favourable for the enhancement of flourescence. An important intermediate of 2,9-dichloro-1,10-phenanthroline is synthezied.The first part of the paper states the synthesis of a series of 2-(5-substitued-2-thiophene)- imidazo[4,5-f][1,10]-phenanthroline ligands. With yields beyond 70%, these compounds are characterized with 1H-NMR, element analysis, FT-IR and melting-point test. The result of UV-Vis absorption and emission in DMF reveals that the substituents have influence on the absorption and emission properties for these compounds. Comparing to 2-(2-thiophene)imidazo [4,5-f][1,10]phenanthroline ( L ), bathochromic shift in theπ→π* and n→π* transition absorption maxima and emission maxima occur due to the electron-donating substituent of -OCH₃ in L-OCH₃. While slightly blue shift occurs with the electron-withdrawing substituent of -NO₂ in L-NO₂.The second part of the paper describes the synthesis and photoelectronic properties of Ru(II) complexes. These complexes are easy to prepare and purify in good yields. They have been characterized with FT-IR, element analysis. UV-Vis spectra were collected in methanol and acetonitrile. The LC, L'C, MLCT, ML'CT bands of the spectra have been discussed and assigned. The bands at about 460 nm can be attributed to the MLCT. The ML'CT bands are close to MLCT, but there is some difference in the band position, which agrees with the electronic properties of the substituent on the ligands. The UV-Vis spectra show solvent-dependency of Ru(II) complexes, but there is not significantly influence on the mole extinction coefficients. Excitated at MLCT and ML'CT, Ru(II) complexes give out light at about 600 nm. The electrochemical investigation suggests that the Ru(II) complexes are irreversible in methanol with TBAPF6 as the supporting electrolyte.The third part introduces the synthesis of 2,9-Dichloro-1,10-phenanthroline. It has been synthezied in low yield, and further investigation should be made to improve the yields. Cl4phen Zn(II) complex has been synhesis which showed obvious solvent-depandancy.