What makes efficient circularly polarised luminescence in the condensed phase: aggregation-induced circular dichroism and light emission

Abstract

In this contribution, we conceptually present a new avenue to construction of molecular functional materials with high performance of circularly polarised luminescence (CPL) in the condensed phase. A molecule (1) containing luminogenic silole and chiral sugar moieties was synthesized and thoroughly characterized. In a solution of 1, no circular dichroism (CD) and fluorescence emission are observed, but upon molecular aggregation, both the CD and fluorescence are simultaneously turned on, showing aggregation-induced CD (AICD) and emission (AIE) effects. The AICD effect is supported by the fact that the molecules readily assemble into right-handed helical nanoribbons and superhelical ropes when aggregated. The AIE effect boosts the fluorescence quantum efficiency (F F) by 136 fold (F F , $0.6% in the solution versus $81.3% in the solid state), which surmounts the serious limitations of aggregationcaused quenching effect encountered by conventional luminescent materials. Time-resolved fluorescence study and theoretical calculation from first principles conclude that restriction of the lowfrequency intramolecular motions is responsible for the AIE effect. The helical assemblies of 1 prefer to emit right-handed circularly polarised light and display large CPL dissymmetry factors (g em), whose absolute values are in the range of 0.08-0.32 and are two orders of magnitude higher than those of commonly reported organic materials. We demonstrate for the first time the use of a Teflon-based microfluidic technique for fabrication of the fluorescent pattern. This shows the highest g em of À0.32 possibly due to the enhanced assembling order in the confined microchannel environment. The CPL performance was preserved after more than half year storage under ambient conditions, revealing the excellent spectral stability. Computational simulation was performed to interpret how the molecules in the aggregates interact with each other at the molecular level. Our designed molecule represents the desired molecular functional material for generating efficient CPL in the solid state, and the current study shows the best results among the reported organic conjugated molecular systems in terms of emission efficiency, dissymmetry factor, and spectral stability.

Recent progress in research on stimuli-responsive circularly polarized luminescence based on π-conjugated molecules

“…The correlation between solid-state CPL properties and aggregation-induced emission (AIE) was reported by Wong and Tang et al [12]. Although silole derivative 8 possessing chiral sugar moieties (Fig.…”

Nanoparticles of Conjugated Molecules and Polymers for Biomedical Applications

“…Thus, they can maintain bright fluorescence in concentrated or aggregated states without typical aggregation-induced fluorescence quenching. A variety of SSF molecules, such as siloles [43][44][45][46], cyanostilbene [47,48], tetraphenylethene [49,50], distyrylanthracene derivatives [51,52], and others [53,54], have been reported (Fig. 2c) and their biomedical applications are being developed by many research groups [55][56][57][58].…”

Synthesis of polysaccharide derivatives bearing bromobenzoate pendants for use as chiral auxiliaries

“…Therefore, the acquisition of single enantiomers has become increasingly important in the pharmaceutical, agrochemical, food, and fragrance industries. Optically active compounds have also become relevant to the development of functional chiral materials, such as ferroelectric liquid crystals, nonlinear optical materials, and circularly polarized luminescent materials [6][7][8][9][10][11][12]. Asymmetric synthesis using chiral auxiliaries is a potential method for obtaining optically active compounds [13][14][15][16][17].…”