abstract
Two discrete mononuclear complexes, [Tb(bbpen)(NO3)] (I) and [Tb(bbppn)(NO3)] (II), for which H(2)bbp en = N,N'-bis(2-hydroxybenzyl)-N,N'-bis(pyridin-2-ylmethyl)ethylenediamine and H(2)bbppn = N,N'-bis(2-hydroxylbenzyl)-N,N'-bis (pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H(2)bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (phi) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, I and II exhibit remarkably different phi values of 21 +/- 2% and 67 +/- 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for H(2)bbpen and H(2)bbppn confirmed that both ligands are suitable to work as antennas for Tb-III. Considering the D-5(4) lifetime profiles and the significantly higher absolute quantum yield of II, it appears that thermally active nonradiative pathways present in I are minimized in II due to differences in the conformation of the ethylenediamine bridge.
keywords
PROTON-ELECTRON TRANSFER; ENERGY-TRANSFER RATES; CRYSTAL-STRUCTURES; SPECTROSCOPIC PROPERTIES; LANTHANIDE COMPLEXES; HEXADENTATE LIGANDS; IRON(III) COMPLEX; LUMINESCENCE; MODEL; EFFICIENT
subject category
Chemistry
authors
Gregorio, T; Leao, JD; Barbosa, GA; Ramos, JD; Giese, SOK; Briganti, M; Rodrigues, PC; de Sa, EL; Viana, ER; Hughes, DL; Carlos, LD; Ferreira, RAS; Macedo, AG; Nunes, GG; Soares, JF
our authors
Luís Carlos
Full professor
Maria Rute de Amorim e Sá Ferreira André
Full professoracknowledgements
This work was financially supported by Fundacao Araucaria (grants 20171010 and 283/2014, protocol 37509), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, grant 308426/2016-9), Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES, PVE A099/2013 and Finance Code 001), and Universidade Federal do Parana (UFPR). T.G., J.d.M.L., S.O.K.G., D.L.H., A.G.M., and J.F.S. also thank the CNPq, CAPES, and Fundacao Araucaria for fellowships. A.G.M. acknowledges financial support from Serrapilheira Institute (grant number Serra-1709-17054).