New Insights on Near-Infrared Emitters Based on Er-quinolinolate Complexes: Synthesis, Characterization, Structural, and Photophysical Properties

Authors


  • The “Fondazione Banco di Sardegna” and the MIUR through the PRIN project 2005033820_002 “Molecular materials with magnetic, optical and electrical properties ...”, and FIRB projects (Synergy-FIRBRBNE03S7XZ and FIRB-RBAU01N449) are gratefully acknowledged for supporting this research. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 615603, CCDC 615604, CCDC 615603. Copies of the data can be obtained free of charge from www.ccdc.cam.ac.uk/conts/retrieving.html or on application to The Director: Cambridge Crystallographic Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK. Supporting Information is available online from Wiley InterScience or from the authors.

Abstract

Erbium quinolinolates, commonly assumed to be mononuclear species with octahedral co-ordination geometry, have been proposed as promising materials for photonic devices but difficulties in obtaining well defined products have so far limited their use. We report here the conditions to obtain in high yields three different kinds of pure neutral erbium quinolinolates by mixing an erbium salt with 8-quinolinol (HQ) and 5,7-dihalo-8-quinolinol (H5,7XQ: X = Cl and Br): i) the trinuclear complex Er3Q9 (1) which is obtained with HQ deprotonated by NH3 in water or ethanol/water mixtures; ii) the already known dimeric complexes based on the unit [Er(5,7XQ)3(H2O)2] [X = Cl (2) and Br (3)]; iii) the mononuclear [Er(5,7XQ)2(H5,7XQ)2Cl] [X = Cl (4) and Br (5)] complexes, obtained in organic solvents without base addition, where the ion results coordinated to four ligands, two deprotonated chelating, and two as zwitterionic monodentate oxygen donors. These results represent a further progress with respect to a recent reinvestigation on this reaction, which has shown that obtaining pure and anhydrous octahedral ErQ3, the expected reaction product, is virtually impossible, but failed in the isolation of 1 and of the neutral tetrakis species based on H5,7XQ ligands. Structural data provide a detailed description of the molecules and of their packing which involves short contacts between quinoxaline ligands, due to π–π interactions. Electronic and vibrational studies allow to select the fingerprints to distinguish the different products and to identify the presence of water. The structure/property relationship furnishes a satisfactory interpretation of the photo-physical properties. Experimental evidence confirms that the most important quenchers for the erbium emission are the coordinated water molecules and shows that the ligand emission is significantly affected by the π–π interactions.

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