Research On High Efficiency Carbonyl Radical Luminescence Induced By Electrostatic Interaction

Due to its special double state and long-wavelength emission characteristics,organic luminescent radicals have a wide range of applications in organic light-emitting diodes,nearinfrared biological imaging,etc.,and have become a hot topic in the research field.However,due to the single-electron structure of organic free radicals,they have high reactive activity and are easily quenched in the air.Therefore,it is still challenging to achieve stable free radical emission and improve its emission efficiency under environmental conditions.For most free radical systems,a complex structure to shield possible negative interferences between mutual molecules leads to a more cumbersome molecular design and synthesis,often to the detriment of practical applications.Later on,with the rapid development of supramolecular chemistry,some polymer-based co-assembly strategies were gradually applied to stabilize the radical emission.However,the weak non-covalent interactions in these co-assembled systems,while enabling radical emission in a somewhat facile manner,still suffer from the defect of too low emission efficiency.Here,we propose a rational design strategy that utilizes the electrostatic interaction of ions to protect carbonyl radical excitons and significantly improve their emission efficiency.(1)We use tricarbonyl-substituted benzene molecules as the guest,and a series of imidazolium ionic liquids as the host,which are co-assembled to form host-guest systems.Among them,the tricarbonyl-substituted benzene molecules are irradiated by UV light to generate carbonyl radical anions,which can be stabilized by the electrostatic interaction of the imidazolium cations.More importantly,under environmental conditions,the free radical emission intensity is significantly improved compared with the neutral polymer matrix studied in the past.Further studies revealed that the anion species and the length of the alkyl chain significantly affected the system’s luminescence efficiency.The theory calculation suggests that together with strong electrostatic interactions,the spin delocalization effect between radical anion and imidazolium cation is observed that significantly stabilizes and protects thus radical emission.The suitable length of alkyl chains in it can avoid the short-chain system’s lower interaction energy and the long-chain system’s unfavorable molecular vibration.And the larger anionic group can produce a higher interaction energy and spin density contribution,further enhancing the system’s emission efficiency.(2)In addition,such a radical emission system also could be integrated with the fluorescence dyes to induce multi-color and even white light emission at a suitable doping ratio.And it showed the reversible temperature-responsive property because heat can quench the free radical emission.Lastly,the solution of free radical emission systems based on electrostatic interaction can be used to discern the amine compounds.In summary,this research has constructed a luminescent free radical system based on electrostatic interaction,with rich luminescence properties and high-intensity emission,which provides a new strategy for the development of high-efficiency free radical luminescence systems with multiple uses.