Density functional study on electronic structures and reactivity in methyl-substituted chelates used in organic light-emitting diodes

The electronic structure and reactivity trends of a set of tris-(n-methyl-8-quinolinolato) metal (III) (n = 0, 3, 4, 5; metal = Al +3, Ga+3) used as electrontransport layer in organic light-emitting diodes were studied and compared. All geometries were optimized at B3LYP/6-31G(d,p) level of theory. The geometries of the ground state (S 0) of unsubstituted molecules AlQ3 and GaQ3 were found to be slightly affected by the methyl group, which is in agreement with previous works. Methylderivatives conserve largely the electronic structures of AlQ3 and GaQ3. The energies of the frontier orbitals highest occupied and lowest unoccupied molecular orbital are raised by the electron-releasing effect of methyl group. Molecular orbital contribution analysis reveals that the orbital population is essentially the same for both MQ3 and their derivatives. Analyses of the ionization potential and electron affinity showed that MQ3 tend to be better hole-blockers than methylated analogues and 5Me-MQ3 have higher hole-injection capability than the other methyl-substituted derivatives. The global reactivity analysis showed that the electrophilicity index can be an indicator of electroninjection capability in these complexes. Local reactivity analysis showed that atomic sites that are prone to nucleophilic/electrophilic attack are atoms C-4 in L3/C-5 in L1. © 2009 Wiley Periodicals, Inc.