Improving Visible Light Sensitization of Luminescent Europium Complexes

Abstract

The synthesis and characterization of the new ligands L(1), L(2) and L(4) are described with the series of four europium complexes of formula [EuL(n)(TTA)(3)] in which TTA refers to 2-thenoyltrifluoroacetonate and L(n) to tridentate ligands with nitrogen containing heterocyclic structure, such as a 2,6-bis(3-methyl-pyrazolyl)-4-(p-toluyl-ethynyl)-triazine for L(1), or terpyridines functionalized at the 4' position by a phenyl-vinylene for L(2), a p-dimethylamino-phenylene for L(3), or a p-aminophenyl-ethynylene for L(4). The spectroscopic properties of the ligands and of the complexes are studied by means of UV-Vis absorption spectroscopy, as well as steady-state and time-resolved luminescence spectroscopy. All complexes display europium centred luminescence upon ligand excitation. Careful examination of the excitation spectra revealed differences in the ligand based sensitization efficiencies. For complexes of L(1) and L(2), excitation of europium is mainly achieved through the TTA moieties and the photo-physical studies on [EuL(1)(TTA)(3)] evidenced a weaker coordination of the bispyrazolyltriazine tridentate ligand, resulting from a partial decomplexation upon dilution. Complexes of L(3) and L(4) display intense excitation through the tridentate units, which extend down to 460 nm in the visible region. In the case of L(3), selective excitation reveals the presence of a ligand-centred emission band at 520 nm which is likely ascribed to a L(3) centred charge transfer state.

Remarkable Tuning of the Coordination and Photophysical Properties of Lanthanide Ions in a Series of Tetrazole‐Based Complexes

“…Although other mechanisms can play an important role, several photophysical studies on series of analogous compounds have delineated an empirical correlation between the efficiency of lanthanide luminescence quantum yield and the energy of the lowest triplet state with a fast and irreversible energy transfer occurring when the triplet energy of the ligand is located at least 3 500 cm À1 above the main luminescence state of the lanthanide ion. [8,10,23,50,51] Accordingly, we have investigated if such a correlation is verified for the series of ligands prepared in this work.…”

“…[16] Bipyridine and terpyridine were chosen as suitable building blocks because their chemistry is well known and the coordination properties of bipyridine-carboxylate and terpyridine-carboxylate ligands and the luminescent properties of their lanthanide complexes have been extensively investigated. [10,[23][24][25] This should allow for a facile comparison of the effect of tetrazolate substitution with respect to carboxylate on the excitation wavelength and luminescence quantum yields of isostructural lanthanide complexes. Accordingly, we have prepared a series of terpyridine-tetrazolate and bipyridine-tetrazolate ligands and structurally characterized their homoleptic lanthanide complexes.…”

Highly Versatile Synthetic Approach to Oligopyridines and Derivatives by Kröhnke-type Ring-closure Reactions

“…The following chalcones and bispyridinium salts were synthesized according to the literature: bisphenyl chalcone (ch), 2-pyridyl-2'-thienyl chalcone (2N,2S'-ch), 2-pyridyl-3'-thienyl chalcone (2N,3S'-ch), 3-pyridyl-3'-thienyl chalcone (3N,3S'-ch), 2-thienyl-2'-thienyl chalcone (2S,2S'-ch), and 2-thienyl-3'-thienyl chalcone (2S,3S'-ch), [8] 2-pyridyl-2'-pyridyl chalcone (2,2'-ch), 2-pyridyl-phenyl chalcone (2N,Ph'-ch), and phenyl-3'-pyridyl chalcone (Ph,3N'-ch), [9] 2-pyridyl-3'-pyridyl chalcone (2,3'-ch), 2-pyridyl-4'-pyridyl chalcone (2,4'-ch), 3-pyridyl-3'-pyridyl chalcone (3,3'-ch), and 4-pyridyl-3'-pyridyl chalcone (4,3'-ch), [10] 3-thienyl-2'-pyridyl chalcone (3S,2N'-ch), 3-thienyl-3'-pyridyl chalcone (3S,3N'-ch), 3-thienyl-phenyl chalcone (3S,Ph'-ch), 3-thienyl-2'-thienyl chalcone (3S,2S'-ch), and 3-thienyl-3'-thienyl chalcone (3S,3S'-ch), [11] phenyl-3-thienyl chalcone (Ph,3S'-ch), [12] 3-hydroxyphenyl-2'-pyridyl chalcone (3OH,2N'-ch), [13] 3-hydroxyphenyl-4'-pyridyl chalcone (3OH,4N'-ch), [14] phenylbiphenyl chalcone (Ph,BiPh'-ch), [15] biphenyl-phenyl chalcone (BiPh,Ph'-ch), (BiPh,BiPh'-ch), [16] phenyl-styryl chalcone (Ph,Sty'-ch), [17] 2-pyridyl-styryl chalcone (2N,Sty'-ch), [18] 3-pyridyl-styryl chalcone (3N,Sty'-ch), [19] phenyl-4'-bromophenyl chalcone (Ph,4Br'-ch), (Ph,4F'-ch), [20] phenyl-4'-fluorophenyl chalcone (2N,4F'-ch), [21] pyridazyl-3'-pyridyl (2,5,3'-ch), [22] phenylpyridine bispyridinium salt (PhSpPy-salt), [5d] pyridine bispyridinium salt (SpPy-salt), phenylene bispyridinium salt (Ph-BBC-salt), [4] phenylpyrimidine bispyridinium salt (BTP-salt).…”

Towards Libraries of Luminescent Lanthanide Complexes and Labels from Generic Synthons

“…[37] Interestingly, the absorption bands at ca. 278 nm, generally associated to a second component between 265 and 269 nm, are present in all complexes of L 1 to L 8 and are little perturbed by the functionalization in the para position of the central pyridyl ring.…”