We design and synthesize five novel diazocine derivatives,using diazocine as the core,amide or imine bonds as the connecting units attached with different peripheral substituents.The photoisomerization yield and thermal stability of these derivatives are tested by^(1)H NMR and UV-Vis absorption spectroscopy.Among them,the imine-linked derivative exhibits the lowest photoisomerization efficiency,while the amide-linked ones show an elevated switching efficiency in transitioning from the cis to the trans configuration,compared to the unmodified 3,3′-diamino-diazocine.Furthermore,based on experiments together with density functional theory(DFT)calculations,we find that the thermal stability of these derivatives is associated with the electron cloud density and steric hindrance of their substituents.Owing to these unique photophysical properties,diazocine derivatives provide a foundation for the development and application of molecular optical switches.
Salicylaldehyde Schiff base is a kind of important photochromism system,whose photochromism process is widely acknowledged to be co-determined by the electronic structure and molecular conformation.Normally,salicylaldehyde Schiff base derivatives withα-type structures tend to exhibit photochromism while those withβ-type structures tend to be photostable.However,more and more counterexamples are found,and the root cause of photochromism property of salicylaldehyde Schiff base is still unclear.In this work,a series of chiral salicylaldehyde Schiff bases and their racemates were prepared.The formers are photochromic while the latters are photostable.Influenced by Wallach's rule,the homochiral counterparts have looser packing modes than that of the racemic counterparts.Mechanism study revealed that the pressure should be the root cause of photochromism property.Close molecule packing can restrict the photochromism property effectively after being pressed,which also explains why the photochromism of salicylaldehyde Schiff base is usually observed in solid state.This work not only reports the unique photo-responsive difference between the chiral salicylaldehyde Schiff bases and their racemates,more importantly,provides a new perspective to understand the influence of molecule pressure on their photophysical properties.
Smart multi-stimuli responsive organic materials have become increasingly favored due to their advantages of high stability and easy regulation.In this study,a cyanostilbene derivative((αZ)-2-chloro-α-[(4-methoxyphenyl)methylene]-5-pyridinehyde,TAR)was successfully synthesized,and its polymorphs(TAR-1 and TAR-2)exhibited multiple responsive behaviors under different stimulus conditions.TAR-1 is supposed to have excellent mechanical properties,while TAR-2 shows fascinating heterotropic photochromism(green-cyan-yellow)under different intensities of ultraviolet(UV)irradiation,which has never been reported in previous studies.Further investigation revealed that this was attributed to different degrees of[2+2]cycloaddition induced by UV light.In addition,both polymorphs could be protonated during Trifluoroacetic acid fuming and deprotonate automatically after fuming,accompanied by the significant variation in fluorescence.Finally,two scenarios were designed based on their unique stimuli-responsive properties,which proved their promising potential in fields of information security and anti-counterfeiting encryption.
Four rare earth inorganic-organic hybrid compounds based on Keggin-type polyoxometalate {SiW_(12)}with general formula [{RE(DMF)_(4)(H_(2)O)_4RE(DMF)_(6)}_(2){SiW_(12)O_(40)}_(3)](RE = La(1),Pr(2),Sm(3),Eu(4),DMF=N,N-dimethylformamide) were synthesized by the conventional solution method.Structure analyses indicate that four compounds are isostructural and are all built from three [SiW_(12)O_(40)]^(4-) polyoxoanions and DMF ligands linked by RE^(3+).Compounds 1-4 are extremely sensitive to UV light and present excellent photochromic properties,in which the coloring and fading time of samples are both no more than 2 min,and the reversible coloring-fading process can be repeated for at least 10 cycles with little fatigue,suggesting that compounds 1-4 can be a series of fast-responsive and durable photochromic materials.Moreover,the solid-state photoluminescence spectra of compounds 3(Sm) and 4(Eu)display strong characteristic emissions of rare earth ions based on f-f transitions.Meanwhile,compound4(Eu) has a longer fluorescence lifetime up to 566.74 μs.Notably,co mpounds 3(Sm) and 4(Eu) exhibit the switchable luminescence behavior induced by photochromism,which allows them to be used as potential molecular switches.
Hong CuiYanli YangXue BaiXu HanWensha ZhangYing LuShuxia Liu
It remains a big challenge to develop solid-state stimuli-responsive materials for time-dependent information encryption and inkless erasable printing with long retention times.Herein,a 2D Cu_(2)I_(2)-based MOF with photoresponsive spiropyran(SP)groups orderly installed on its skeleton is developed.The structural isomerization from SP to colored merocyanine(MC)form can be triggered by removing the CH_(3)CN guests.Besides,the degree of structural isomerization and the retention time can be adjusted by controlling the amount of CH_(3)CN guests,exhibiting dynamic photochromic behavior with multicolor states and tunable retention time.Based on these advantages,time-dependent information encryption is successfully achieved.Furthermore,the long retention time(>72 h)of the MC form under daylight conditions in the CH_(3)CN-removed Cu_(2)I_(2)-based MOF and good repeatability make it promising in various applications,such as temporary calendars,price-cards,billboards,and reusable identity cards.This work provides a novel design strategy to fabricate multi-functional MOF-based smart materials for challenging applications of time-dependent information encryption and inkless erasable printing.
