Preparation And Properties Of Color-tunable Organic Molecular/Clay Composite Afterglow Materials

Afterglow luminescent materials with rich excited states and long lifetime show broad application prospects in the fields of encryption and anti-counterfeiting,biomedicine,optical devices and information sensing due to their excellent photophysical luminescence properties.At present,afterglow luminescent materials with both high quantum yield and long lifetime can be effectively constructed by the strategy of host-guest self-assembly to suppress the nonradiative transition of excited triplet states.However,most of the reported afterglow materials exhibit a single emission color due to the lack of multiple interaction forces between the host and guest molecules,which will largely limit their practical application.Aiming at the above problems,this paper adopts two different self-assembly preparation methods,namely solvent-free grinding method and solvent method,to successfully develop two color-tunable organic/inorganic hybrid composite afterglow luminescent material through assembly of guest organic phosphorescent molecules and layered nanoclay layers.The specific research contents are as follows:We provide a simple and efficient approach to develop color-tunable afterglow supramolecular assembly A_xB_y@Lap in response to excitation wavelength and time simultaneously through the co-assembly of non-emissive nanoclay（Lap）and two different kinds of guests（A:Terephthalic acid（TPA）,B:Terpyridine-derivatives）using a simple solventless grinding method.By changing the excitation wavelength of the UV lamp and prolonging the decay time,the variation of the afterglow color from blue to green was achieved.In addition,A_xB_y@Lap can still maintain excellent color-tunable afterglow behavior with excitation wavelength-and time-dependent feature in an aqueous solution with water content of 99%because Laponite（Lap）exhibits good dispersibility and oxygen resistance in aqueous media.Benefiting from this excellent characteristics,the application pattern of multi-level anti-counterfeiting and encryption is exhibited.It is found that the different decay lifetimes and origin for multiple afterglow emission centers bring about the aforementioned distinctive excitation wavelength-and time-dependent feature.A new type of organic/inorganic hybrid afterglow luminescent material(AC@L-Lys_（x）)were prepared throughout the co-assembly of layered structure of aminoclay and small molecule of L-lysine（L-Lys）using a solvent method.And AC@L-Lys_（x）exhibit excitation-dependent afterglow properties.Then,AC@L-Lys_（x）was mixed with a certain amount of polyvinyl alcohol（PVA≥99.9%）for their potential application in the field of multicolor anti-counterfeiting.It is found that the luminescence intensity（fluorescence and afterglow）of AC@L-Lys_（x）is related to the loading of L-lysine in aminoclay,and this unique luminescence phenomenon can be reasonably explained by the concept of aggregation-induced emission（AIE）.In addition,the excitation wavelength-dependent afterglow properties are mainly attributed to the formation of aggregated co-assembled structures with different degrees of conjugation during the aggregation of AC@L-Lys_（x）,resulting in two different emission types of afterglow emission centers,delayed fluorescence and room-temperature phosphorescence,which can be effectively adjusted by changing the excitation wavelength,resulting in color-tunable afterglow luminescence.