Dynamically responsive photonic metal–organic frameworks

Different from single and static photonic materials,dynamically responsive materials possess numerous advantages,such as being multifunctional,dynamically responsive,and able to provide multiple channels within spatially limited platforms,thus exhibiting great potential for application in the color-on-demand areas,including imaging,optical displays,anticounterfeiting,and encoding.Photonic functional metal–organic frameworks(MOFs),with highly designable framework structures and varieties of optical functional building units,possess broad research and application prospects in the field of photonics,which make it possible to design a promising platform with multifunctional and integrated photonic performance.In this review,beyond the preparation strategies of stimuli-responsive photonic MOFs,we also summarize the stimuli-responsive photonic MOFs regarding several most representative types of external stimuli(such as light,gas,pressure,and polarization).As shown,external stimulation endows the stimuli-responsive photonic MOFs with intriguing regulatable photonic properties:intensive and tunable emission,multiphoton-excitable luminescence,nonlinear optical,circularly polarized luminescence,lasing,etc.Furthermore,their advanced representative applications,such as information encryption and anticounterfeiting display,biological imaging,chemosensing,and others,are also reviewed.The challenges are proposed and the prospects are addressed.

Precise Design and Deliberate Tuning of Turn-On Fluorescence in Tetraphenylpyrazine-Based Metal-Organic Frameworks

The manipulation on turn-on fluorescence in solid state materials attracts increasing interests owing to their widespread applications.Herein we report how the nonradiative pathways of tetraphenylpyrazine(TPP)units in metal-organic frameworks(MOFs)systems could be hindered through a topological design approach.Two MOFs single crystals of different topology were constructed via the solvothermal reaction of a TPP-based 4,4',4",4"-(pyrazine-2,3,5,6-tetrayl)tetrabenzoic acid(H,TCPP)ligand and metal cations,and their mechanisms of formation have been explored.Compared with the innate lowfrequency vibrational modes of flu net Tb-TCPP-1,such as phenyl ring torsions and pyrazine twists,Tb-TCPP-2 adopts a shp net,so the dihedral angle of pyrazine ring and phenyl arms is larger,and the center pyrazine ring in TPP unit is coplanar,which hinders the radiationless decay of TPP moieties in Tb-TCPP-2.Thereby Tb-TCPP-2 exhibits a larger blue-shifted fluorescence and a higher fluorescence quantum yield than Tb-TCPP-1,which is consistent with the reduced nonradiative pathways.Furthermore,Density functional theory(DFT)studies also confirmed aforementioned tunable turn-on fluorescence mechanism.Our work constructed TPP-type MOFs based on a deliberately topological design approach,and the precise design of turn-on fluorescence holds promise as a strategy for controlling nonradiative pathways.