Modulation of the luminescence quantum efficiency for blue luminophor {Al(salophen)}+ by ester-substituents

Abstract

A series of Al^III complexes of a salophen (N,N′-bis(salicylidene)-o-phenylenediamine) derivative with an ester substituent at the C5 position of the salicylidene rings have been prepared and their luminescence properties investigated. All exhibit a bright blue emission (λ_em = 478 nm) that is observed neither for other metal ions nor with the non-functionalized ligand. Moreover, the ester-R group (Me, ^tBu, Ph) was found to significantly affect the quantum yields (ϕ = 12 to 20%) of the luminophor. DFT calculations have been undertaken to reveal the influence of the ester and its R-group on the frontier molecular orbitals. Preparation and photoluminescence properties in solution and solid state are reported. The crystal structure of a pyridine oxide adduct [L^tBuAl(PyO)₂]·NO₃, where L^tBu stands for the tButyl-ester functionalized Schiff base, has been solved.