Highly two-photon and X-ray excited long-persistent luminescence in a crystalline host-guest aggregate

As a unique type of supramolecular self-assemblies,crystalline host-guest aggregates have attracted extensive interests in multiple application fields.Herein,a crystalline host-guest aggregate LIFM-HG1 was obtained with curcubit[8]uril as the host and carboxypyridinium salt as the guest.Single-crystal structural analysis indicates that the presence of abundant weak interactions in LIFM-HG1 provides a rigid environment for the guest molecule and effectively blocks the external quenchers.Spectral analysis and theoretical calculations confirm the presence of robust triplet energy levels in LIFM-HG1.Even more impressively,the intersystem crossing channels of the guest molecules are greatly opened up after the formation of the crystalline host-guest aggregate,resulting in a large k_(isc)of 6.70×10^(7)s^(−1)at room temperature for LIFM-HG1(which is∼0 for pure guest),leading to fascinatingmultichannel(including one-photon,two-photon,and X-ray)excited LPL properties.In addition,the crystalline LIFM-HG1 has a much higher triplet state luminescence efficiency under X-ray and two-photon excitation than that under single-photon excitation(A_(P)/A_(F)=86.8,44.8,10.7 under the three circumstances,respectively).And the phosphorescent emission intensity of LIFM-HG1 is 27.6 times higher than that of the crystalline guest under X-ray excitation.As a result,LIFM-HG1 shows a long afterglow retention time under both single-and two-photon excitation,and an impressive afterglow retention time of 1 s under X-ray excitation.Furthermore,the excellent lysosomal targeting and low cytotoxicity by the formation of host-guest aggregate makes LIFM-HG1 promising to be used as a novel lysosomal-targeted two-photon excited phosphorescent tracer.