Unraveling the Remarkable Influence of Substituents on the Emission Variation and Circularly Polarized Luminescence of Dinuclear Aluminum Triple-Stranded Helicates

Abstract

This study explored the development of functional dyes using aluminum, focusing on aluminum-based dinuclear triplestranded helicates, and examined the effects of substituent variations on their structural and optical properties. Key findings revealed that the modification of methyl groups to the pyrrole positions significantly extended the conjugation system, resulting in a red shift in the absorption and emission spectra. Conversely, the modification of methyl groups at the methine positions due to steric hindrances increased the torsion angle of the ligands, leading to a blue shift in the absorption and emission spectra. A common feature across all complexes was that in the excited state, one of the three ligands underwent significant structural relaxation. This led to a pronounced Stokes shift and minimal spectra overlap with high photoluminescence behaviors. Moreover, our research extended to the optical resolution of the newly synthesized complexes by analyzing the chiroptical properties of the resulting enantiomers, including their circular dichroism and circularly polarized luminescence. These insights offer valuable contributions to the design and application of novel aluminum-based functional dyes, potentially influencing a range of fields, from materials science to optoelectronics.

Optical Property Control by the Interligand Charge Transfer Excited State in Brominated Homoleptic and Heteroleptic Aluminum Dinuclear Triple-Stranded Helicates

“…We have recently reported on dinuclear triple-stranded helicates comprising three Schiff base ligands and two aluminum ions, which exhibit circular dichroism (CD) and CPL due to the helical chirality (Figure ). , These complexes exhibit CPL properties associated with their right ( P )- and left ( M )-handed helical structures, a characteristic seldom reported in aluminum complexes. ,, Moreover, the complexes exhibit multicolor emission influenced by the type of substituents, showcasing their potential as next-generation luminescent materials. By intentionally reducing the symmetry of these molecules, we anticipate further control over their excited-state properties, including nonradiative deactivation or intersystem crossing.…”

“…Among the developments in luminescent materials, mononuclear and multinuclear complexes composed of group 13 elements such as boron, aluminum, gallium, and indium have attracted much interest. − In particular, aluminum-based complexes are promising due to the element’s abundance and low cost, which have led to extensive research efforts. − Tris­(8-quinolinolato)aluminum (AlQ 3 ) derivatives are noteworthy examples in this context. − However, the imperative for further advancements in enhancing the photofunctionality and controlling excited-state properties remains.…”