Fluorescent Properties of Morin in Aqueous Solution: A Conversion from Aggregation Causing Quenching (ACQ) to Aggregation Induced Emission Enhancement (AIEE) by Polyethyleneimine Assembly.

Unlike normal conversion from aggregation caused quenching (ACQ) to aggregation induced emission enhancement (AIEE) by introducing aromatic rotors tuning aggregation modes, in this study, it is achieved through a supramolecular assembly with polymer. Thus, it provides an easy approach for the inhibition of unwanted H-aggregation between luminogens. As a kind of flavonoid, morin has shown great potential in therapeutics. However, its poor solubility and weak emission in aqueous solution greatly limit its bioapplications. When morin is dissolved in aqueous solution, the presence of 30 × 10-6 m polyethyleneimine (PEI) induces significant emission enhancement and bathochromic shift. Consequently, the quantum yield (QY) of 24.5% is either achieved by assembling with PEI, versus 0.76% of its ACQ state composed of H-aggregation in aqueous solution. Particularly, the in-depth mechanism studies reveal that it is the assembly with PEI that disassociates the H-aggregation in aqueous solution and further restricts the stretching and/or rotation of morin, which eventually reduce the nonradiative decays and enhance the emission. Therefore, the present study reports a unique phenomenon of AIEE effects on morin. Particularly the in-depth investigation on intrinsic mechanisms will highlight and greatly expand the development of more luminogens from traditional Chinese herbals.