Abstract
Different disubstituted derivatives of tris(8-hydroxyquinolinato) aluminium (mer-Alq3) have been designed. An electron donating group (-CH3) has been substituted at position 4; along with electron withdrawing groups (-Cl, -CN, and -F) at position 5 (i.e. tris(4-X-5-Y-8-hydroxyquinolinato)aluminium), as well as the molecules arising from reversion of these substitutions. The designed systems have been optimized at the B3LYP/6-31G* and TD-B3LYP/6-31G* level of theories, in the ground and excited states, respectively. The absorption and emission spectra have been calculated at the TD-B3LYP/6-31G* level. A significant blue shift has been observed for tris(4-methyl-5-cyano-8-hydroxyquinolinato)aluminium (2), and red shifts for each of tris(4-methyl-5-fluoro-8-hydroxyquinolinato)aluminium (3), tris(4-chloro-5-methyl-8-hydroxyquinolinato)aluminium (4), and tris(4-cyano-5-methyl-8-hydroxyquinolinato)aluminium (5). The reorganization energy in solvent best elucidates the charge transport behaviour (p- or n-type), rather than the equivalent gas phase for mer-Alq3 and its derivatives. The reorganization energies indicate that these new derivatives have better or comparable mobility when compared to the parent molecule. The electrostatic surface potential study suggested that photostability would be enhanced. On the basis of energy decomposition analysis, we have explained the distribution pattern of frontier molecular orbitals.