Systematic design of indium-based luminophores with color-tunable emission via combined manipulation of HOMO and LUMO levels

摘要

A series of indium complexes with salen ligands bridged by aryl groups such as [Ar-{N=CH(C6H2-3-Bu-t-5-R)}21 In-Me (Ar = 4,5-dimethyl-1,2-phenylene, 1,2-phenylene, and 3,4-naphthylene; R = H, Br, Bu, Me, OMe, NMe2, and NMe3+) were prepared and fully identified by NMR spectroscopy and elemental analysis. All indium complexes are highly stable in air and aqueous solutions. Among these complexes, the structurally characterized complexes [(4,5-dimethylphenylene)bis(3-tert-butyl-5-methylsalicylideneiminato)-kappa N,N',O,O']methylindium (III) and [(2,3-naphthanlene)bis(3-tert-butyl-5-methylsalicylideneiminato)-kappa N,N',O,O']methylindium(III) have slightly distorted square-pyramidal geometries around the central indium atoms. The UV/Vis absorption and emission spectra of all indium complexes exhibited significant intramolecular charge transfer (ICT) transitions assigned to the aryl salen-centered pi-pi* transitions, which displayed a gradual bathochromic shift, resulting from the electronic alteration of the substituent at the C5 position of phenoxy ring. Furthermore, the emission bands also gradually red-shifted as the electron-donating effect of bridging aryl groups decreased. In particular, the emission spectra of the indium complexes were observed in the visible region ranging from green (ca. 500 nm) to deep red (ca. 700 nm). The colors were obtained by manipulating the HOMO and LUMO energy levels, which was further supported by both electrochemical data and theoretical calculations.