Quantum chemical analysis of Salen-based aluminum complexes for the blue luminescent materials

Abstract

Salen-based aluminum complexes have been synthesized recently and proposed as new blue luminescent materials. The first singlet excited-states $S_1$ have been studied by configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) using a hybrid functional. The electronic excitation and the structural relaxation in the excited-state for salen-based aluminum complexes have been interpreted in terms of the nodal characteristics of the HOMO, $HOMO_{-1}$, LUMO and $LUMO_{+1}$. The structural shift is predominantly localized on the β ring. Because of bulky t-Bu groups, the S1 geometries of Salen(3,5-t-Bu)AlX [X=OPhPh, OPh and OPh(p-OMe)], A complexes, and Salen(5-t-Bu)AlX [X = OPhPh], B complex, were derived from the $S_1$ geometries of SalenAlX [X=OPhPh, OPh and OPh(p-OMe)], C complexes. At the time-dependent density functional theory using a hybrid functional B3LYP (TD-B3LYP) level of theory, the calculated Stokes shifts are in good agreement with the experimental values. The tendencies of the absorption and emission wavelenths have been interpreted in terms of the molecular orbital shapes and energies. For more reliable interpretations, the $S_1$ geometries of A and B complexes by CIS method is needed. The reason for blue-shift in salen-based aluminum complexes were interpreted from theoretical results.