Viologen-based host–guest supramolecule with tunable intramolecular/intermolecular electron transfer chromism and dynamic fluorescence

Viologen,as a type of strong electron acceptor,is prone to undergo electron transfer(ET)and change color under external stimuli.However,due to the easy aggrega-tion of viologen molecules,they usually suffer from poorfluorescence emission in the condensed phase.Herein,a new viologen derivative of VioCl_(2)⋅2Cl(1^(2+)⋅2Cl)was designed and synthesized,in which thefluorescence was enhanced by intro-ducing Me-β-CD to weaken the interactions between viologen molecules.Then a viologen-based host-guest supramolecule of 1^(2+)@Me-β-CD was obtained by elec-trostatic interactions.Photo-/chemo-responded guest 1^(2+)supplies 1^(2+)@Me-β-CD,a green and dark purple caused by intramolecular and intermolecular ET.Further-more,1^(2+)@Me-β-CD displays an additional thermal responsive purple color.The triple chromic behaviors all exhibit excellent reversibility and cycling stability.As expected,1^(2+)@Me-β-CD exhibits strong photoluminescence(PL)in solid-liquid dual states,presenting an improved quantum yield(Φ)from 1^(2+)(Φ_(s)=0.37%,Φ_(1)= 16.74%)to=1^(2+)@Me-β-CD(Φ_(s)= 10.45%,Φ_(1)= 25.86%),and thefluores-=cence intensity can be dynamically modulated by light,heat,and acid/base vapors.The multi-responsive chromism and tunablefluorescence of 1^(2+)@Me-β-CD allow for potential applications in information security and smart windows.

A conductive anionic Co-MOF cage with zeolite framework for supercapacitors

Conductive MOFs could exhibit full potential as integrated electrode materials for supercapacitors without interference from additional conductive additives.Here we report an anionic Co-MOF cage with zeolite framework,which was balanced by the redox-active guest [Co(H2O)6]2+ and protonated[(CH3)2NH2]2+ ions.Benefit from the unique ion skeleton structure,Co-MOF exhibits a conductivity higher than most of reported MOFs with the value of 1.42 × 10^-3 S/cm,which can be directly fabricated as electrode for supercapacitors.A maximum specific capacitance of 236.2 F/g can be achieved at a current density of 1 A/g of Co-MOF.Additionally,the electric performance and morphology of this Co-MOF can be modified by cetyltrimethylammonium bromide(CTAB) and the maximum specific capacitance could increase up to 334 F/g at 1 A/g when the ratio of ligand and CTAB is 1:6(Co-MOF-6).Furthermore,the specific capacitance can retain at 64.04% and 77.92% of the initial value after 3000 cycles of Co-MOF and Co-CTAB-6,respectively.Obviously,the addition of CTAB further improves both capacitance and cycle stability.