Triarylboron-Functionalized 8-Hydroxyquinoline and Their Respective Aluminum (III) and Diboron Compounds
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The purpose of this thesis was to develop the first examples of multifunctional triarylboron-functionalized 8-hydroxyquinoline, their respective aluminum (III) complexes, Al(1)3 and Al(2)3, and diboron analogues, B1 and B2. There was particular focus in investigating the electron accepting characteristics of these systems for potential use as electron transport materials (ETMs) in organic light emitting diodes (OLEDs). The first part of the thesis will discuss the aluminum complexes. Through the introduction of the triarylboron moiety these derivatives of the well-known ETM tris(8-hydroxyquinoline)aluminum (Alq3) exhibited better electron accepting properties than the parent compound. Furthermore, the complexes were able to act as sensors and indicators towards soft Lewis acids such as CN- and hard Lewis acids such as F-, respectively. First the structures of the compounds were investigated using COSY NMR, leading to the discovery that similar to Alq3 the new aluminum complexes possessed the commonly observed mer-isomeric form. Furthermore, their photophysical characteristics were investigated using UV-Vis and fluorescence spectroscopic measurements. The solid state fluorescence quantum yield of Al(1)3 (Φ=0.06) and Al(2)3 (Φ=0.02) were measured and compared to Alq3 (Φ=0.14). In order to better understand these results and gain insight into the electronic transitions of the aluminum complexes, DFT calculations were employed using the B3LYP/6-31G* level of theory. The second part of the thesis will discuss the only examples of diboron-functionalized 8-hydroxyquinoline complexes to date, with one three-coordinate and one four-coordinate boron moiety. Based on CV measurements and DFT calculations, it was discovered that the LUMO of the diboron compounds were lowered substantially compared to their aluminum analogues discussed earlier. More interestingly, it was found that only B1 has any contributions to its LUMO from the triarylboron moiety, leading to the slightly stronger electron accepting ability of B1 compared to B2. Furthermore, these compounds were both able to act as sensors towards small anions such as F-.