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Combined Effects of One 8-Hydroxyquinoline/Picolinate and “CH”/N Substitutions on the Geometry, Electronic Structure and Optical Properties of mer-Alq3

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journal contribution
posted on 2010-01-14, 00:00 authored by Godefroid Gahungu, Jingping Zhang, Vestine Ntakarutimana, Nestor Gahungu
With the aim of evaluating the combined effect of one 8-hydroxyquinoline (q)/picolinate (p) and “CH”/N substitutions on the molecular geometry, electronic structure, and optical properties of tris-(8-hydroxyquinoline)aluminum [Alq3], the density functional theory (B3LYP) and time-dependent density functional theory (TD-B3LYP), using the 6-31G(d) and 3-21+G(d,p) basis sets were applied on Alq3, Alq2p, and its “CH”/N-substitution derivatives. A comparison of the optimized ground-state (S0) geometries has shown that the molecular shape is conserved upon such a substitution. On the basis of the frontier molecular orbital and gap energy (Eg) calculations, it was shown that, comparatively to the pristine Alq2p (and to the original parent Alq3), the HOMO and LUMO are stabilized, the net effect being an increasing or a decreasing Eg, depending on the position of the substituted group. The substitution of qB by p (from Alq3 to Alq2p) was also found to induce the same feature. Starting from the S0 and S1 (first excited state) geometries, the effect of the substitution on the absorption (and emission) spectra was evaluated. It was found that the “CH”/N substitution in different positions on the two 8-hydroxyquinoline ligands may also constitute an efficient approach of tuning the Alq2p emitting color. In comparison with both Alq3 and Alq2p, an important blue shift was predicted for the 5-substituted derivative, an important red shift being observed for the 4-substituted one. Also, relatively significant blue and red shifts were predicted for the 7- and 2-substituted derivatives. Finally, revisiting the correlation between the spectrum shifts and the metal−ligand bonding, our recent findings were confirmed.

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