Push-pull effect on the charge transfer, and tuning of emitting color for disubstituted derivatives of mer-Alq3

To design innovative and novel optical materials with high mobility, two kinds of disubstituted derivatives for meridianal isomer of tris(8-hydroxyquinolinato)aluminum (mer-Alq3) with push-pull (X-Y) substituents have been designed. The structures of tris(4-X-6-Y-8-hydroxyquinolinato)aluminum (type 1) and tris(4-Y-6-X-8-hydroxyquinolinato)aluminum (type 2) (where X = -CH3/-NH2 and Y = -CN/-Cl) in the ground (S0) and first excited (S1) states have been optimized at the B3LYP/6-31G∗ and CIS/6-31G∗ level of theory, respectively. All the designed derivatives of type 1 show blue shift while most of the type 2 derivatives show red shift as compared to the mer-Alq3. The emitting color could be tuned from blue to red. We have explained the distribution of HOMOs and LUMOs on different individual ligands. The reorganization energies of tris(4-methyl-6-chloro-8-hydroxyquinolinato)aluminum (1), tris(4-methyl-6-cyano-8-hydroxyquinolinato) aluminum (2), tris(4-chloro-6-methyl-8-hydroxyquinolinato)aluminum (5) and tris(4-cyano-6-methyl-8-hydroxyquinolinato)aluminum (6) are comparable with mer-Alq3. Thus these derivatives might be good candidates for emitting materials possessing comparable charge carrier mobility as mer-Alq3.