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Luminescent materials responding to mechanical stimulation can visualize the strain and mechanical damage applied to objects. Mechanofluorochromism is a well‐known phenomenon induced by the mechanical force on fluorescent crystalline materials. However, simple application of the mechanofluorochromism is unsuitable for temporally and spatially detecting stress in detail because the fluorescent state is kept for rather long period. Here, the dynamic stress‐sensing luminescent solid material of a photochromic diarylethene with a fluorescent moiety is reported. Under the stress applied to the crystalline state, this material emitted cyan‐colored transient fluorescence that is rapidly diminished within a few second. This dynamic fluorescence phenomenon is well controlled by the combination of light irradiation and other external stimuli (organic solvent vapor and/or heat). In addition, the luminescence period is regulated by the excitation wavelength and magnitude of applied force. By utilizing these responses, the rewritable dynamic information encryption is successfully demonstrated. This material with transient fluorescence overcomes the persistence of fluorescence color of mechanochromism and present results provide a new principle for multifunctional light‐emitting materials responding to mechanical stimulation. [ABSTRACT FROM AUTHOR]

Using conjugate electrospinning technology to prepare Janus-structure nanofiber array and endow it with multifunctional characteristics is a very meaningful research topic. Here, photochromic adjustable magnetic bifunctional {[Eu(BA)3phen (EBP) + Tb(BA)3phen (TBP)]/polyvinylpyrrolidone (PVP)}//[Fe3O4/PVP] Janus-structure nanofiber array (defined as PM-JNA) is constructed by conjugate electrospinning. Janus-structure nanofibers are arranged in a micro-orientation, and most nanofibers have a special Janus structure. This structure confines the magnetic material and fluorescent material in two nanofibers, respectively, reduces the influence of magnetic material on fluorescence intensity, and significantly improves the fluorescence performance of the specimen. The using of conjugate electrospinning solves the problem of mutual diffusion of spinning liquid in the spinneret in parallel electrospinning and improves the separation efficiency of fluorescent substances and magnetic substances. Adjustable magnetic and luminous colors can be obtained by changing the contents of Fe3O4, EBP and TBP. Janus-structure nanofibers have been widely used in biological monitoring, medical imaging, nanodevices and multifunctional materials. [ABSTRACT FROM AUTHOR]

Because of the rich fluorescent color and unique photochromic properties, hackmanite has attracted many mineralogists. In this paper, the basic gemmological characteristics and photochromic and fluorescence mechanisms of four different colors of hackmanite are further investigated through the study of their structural, compositional, and spectroscopic features. The results show the change in the color of hackmanite in photochromism is caused by the joint action of the F-center and the oxygen hole centers. The change in the UV-Vis spectra may be caused by the superposition of two peaks. Under 365 nm UV excitation, the peak of fluorescence spectra of 662 nm is related to the 2∏g→2∏u transition of S2−, the blue emission at 441 nm is caused by the 3P0.1→1S0 transition of s2 ions (Pb2+, Tl+, Sn2+ Sb2+), and at 541 nm is caused by the Mn2+ center. The results are helpful in deepening the understanding of photochromism, fluorescence mechanism, and its structure, expanding the application of hackmanite. [ABSTRACT FROM AUTHOR]

Photochromic materials are widely used to achieve fluorescence photoswitching. Understanding the energy transfer processes occurring in these systems would be an advantage for their use and better optimization of their properties. In this scope, we studied a diarylethene-perylenebisimide (DAE-PBI) dyad that presents a bright red emission and a large ON–OFF contrast, both in solution and in an aqueous suspension of nanoparticles (NPs). Using ultrafast transient absorption spectroscopy, the excited state dynamics was characterized for this dyad in THF solution and compared to its behavior in NPs state. An efficient energy transfer process between the PBI fluorophore and the DAE photochromic unit in its closed form was demonstrated, occurring in a few hundreds of femtoseconds. [ABSTRACT FROM AUTHOR]

In recent years, some sapphires were found to fade in sunlight and to increase their color after UV irradiation. This unstable color phenomenon is attributed to the photochromism of corundum. The photochromic effect seriously affects the grading and evaluation of sapphires, although its mechanism is still uncertain. Here, we performed a set of photochromic experiments on sapphire specimens using a 254 nm shortwave UV light source and a D65 light source (which simulates sunlight) to generate different color states exhibiting characteristic absorption, emission, and excitation spectra. We observed that, for different color states, variation in the intensity of the absorption band at ~460 nm was consistent with that of orange fluorescence at 500–800 nm. This observation indicates a relationship between color instability and orange fluorescence. Peaks in excitation spectra at 320, 420, 490, 560, and 637 nm provide insight into the source(s) of excited orange fluorescence, which are related to different types of F-centers and Mg-trapped holes. We propose an explanation for the photochromic phenomenon: the color of photochromic yellow sapphire is the result of a variety of defects that release orange fluorescence simultaneously. Further, we hypothesize that the mechanism of photochromism in yellow sapphires is linked to electron transfer between F-centers and Mg-trapped holes. [ABSTRACT FROM AUTHOR]

In this work, four POM‐based compounds containing viologen ligands were synthesized, namely {CuII(tybipy)2(DMF)2[H2(β‐Mo8O26)]2} ⋅ 4 C2H7N (1), (Htybipy)2 ⋅ (β‐Mo8O26) (2) (tybipy⋅Br=1‐Thiophen‐3‐ylmethyl‐[4,4']bipyridinyl‐1‐ium bromide), [CuII(nibipy)2(4,4'‐bipy)] ⋅ (SiW12O40) (3), (Hnibipy)2 ⋅ (δ‐Mo8O26) (4) (nibipy⋅Cl=1‐(4‐Nitro‐benzyl)‐[4,4']bipyridinyl‐1‐ium chloride, 4,4'‐bipy=4,4'‐bipyridine). In compounds 1 and 3, Cu2+ and mixed organic ligands modify POM anions. On the other hand, 2 and 4 are supramolecular structures only containing ligands and anions. Under Xe lamp with filter (300‐400 nm) irradiation, these four compounds showed good photoresponse and photochromic ability, which can be used in mixed matrix films for visible UV detectors. Compounds 1–4 also have photoluminescence property and show good fluorescence quenching effect. A suspension of four compounds can be evenly spread on filter paper as inkless and erasable printing materials. Compounds 1 and 2 were also used as Hg2+ fluorescence detectors. The fluorescence intensity of 1 decreased by ca. 90 % when the concentration of Hg2+ increased to 40 mM. Moreover, we also prepared composites 1/2@Hg2+,1@Cu2+, 1@Co2+ by introducing 1/2 and Hg2+, Cu2+ and Co2+ to detection paper respectively, which can act as photochromic materials with features of fast color recovery. [ABSTRACT FROM AUTHOR]

In this work, four POM‐based compounds containing viologen ligands were synthesized, namely {CuII(tybipy)2(DMF)2[H2(β‐Mo8O26)]2} ⋅ 4 C2H7N (1), (Htybipy)2 ⋅ (β‐Mo8O26) (2) (tybipy⋅Br=1‐Thiophen‐3‐ylmethyl‐[4,4']bipyridinyl‐1‐ium bromide), [CuII(nibipy)2(4,4'‐bipy)] ⋅ (SiW12O40) (3), (Hnibipy)2 ⋅ (δ‐Mo8O26) (4) (nibipy⋅Cl=1‐(4‐Nitro‐benzyl)‐[4,4']bipyridinyl‐1‐ium chloride, 4,4'‐bipy=4,4'‐bipyridine). In compounds 1 and 3, Cu2+ and mixed organic ligands modify POM anions. On the other hand, 2 and 4 are supramolecular structures only containing ligands and anions. Under Xe lamp with filter (300‐400 nm) irradiation, these four compounds showed good photoresponse and photochromic ability, which can be used in mixed matrix films for visible UV detectors. Compounds 1–4 also have photoluminescence property and show good fluorescence quenching effect. A suspension of four compounds can be evenly spread on filter paper as inkless and erasable printing materials. Compounds 1 and 2 were also used as Hg2+ fluorescence detectors. The fluorescence intensity of 1 decreased by ca. 90 % when the concentration of Hg2+ increased to 40 mM. Moreover, we also prepared composites 1/2@Hg2+,1@Cu2+, 1@Co2+ by introducing 1/2 and Hg2+, Cu2+ and Co2+ to detection paper respectively, which can act as photochromic materials with features of fast color recovery. [ABSTRACT FROM AUTHOR]

Ultralong afterglow emissions due to room‐temperature phosphorescence (RTP) are of paramount importance in the advancement of smart sensors, bioimaging and light‐emitting devices. We herein present an efficient approach to achieve rarely accessible phosphorescence of heavy atom‐free organoboranes via photochemical switching of sterically tunable fluorescent Lewis pairs (LPs). LPs are widely applied in and well‐known for their outstanding performance in catalysis and supramolecular soft materials but have not thus far been exploited to develop photo‐responsive RTP materials. The intramolecular LP M1BNM not only shows a dynamic response to thermal treatment due to reversible N→B coordination but crystals of M1BNM also undergo rapid photochromic switching. As a result, unusual emission switching from short‐lived fluorescence to long‐lived phosphorescence (rad‐M1BNM, τRTP=232 ms) is observed. The reported discoveries in the field of Lewis pairs chemistry offer important insights into their structural dynamics, while also pointing to new opportunities for photoactive materials with implications for fast responsive detectors. [ABSTRACT FROM AUTHOR]

In this study, a microscopy apparatus that can switch between the fluorescence microscopy and ultralow-frequency Raman microscopy modes was developed. The apparatus can be easily constructed by equipping a standard epi-illumination microscope with an additional port featuring a removable half mirror. Owing to the switchability, fluorescence imaging, and spectroscopy, Raman spectroscopy in the frequency range down to ∼10 cm−1 can be performed using the apparatus. To demonstrate the advantageous features of this apparatus, micron-sized crystals of perylene, which have two polymorphic forms, were analyzed. The two polymorphs were clearly identified based on their shapes, fluorescence spectra, and ultralow-frequency Raman spectra, all of which can be observed with our apparatus alone. These results indicate that the apparatus is a powerful tool for the analysis and characterization of various nano-/micron-sized crystals. [ABSTRACT FROM AUTHOR]

Results of fundamental and applied research in the field of creating photochromic core-shell type nanoparticles in which semiconductor nanocrystals – quantum dots (QDs) – were used as a core, and the shell included physically or chemically sorbed molecules of photochromic thermally relaxing (spiropyrans, spirooxazines, chromenes, and azo compounds) or thermally irreversible compounds (diarylethenes and fulgimides) have been analyzed. It has been shown that such nanoparticles provide a reversible modulation of the QD radiation intensity, which can be used in information and biomedical technologies. [ABSTRACT FROM AUTHOR]

At present, for inorganic photochromic materials, the single function limits their application level in the field of optical storage and anti-counterfeiting. Generally, the reversible modulation of photoluminescence is achieved through a photochromic process, thereby improving the ability of the photochromic material to store information. Here, we designed a Sm3+ doped perovskite oxide (SrZrO 3 :Sm3+) inorganic photochromic material. Combined with its red photoluminescence and photochromic properties, it can realize dual information storage and recognition functions. The fluorescence regulation function is realized by the doping of Sm3+, which is conducive to the application in the direction of optical switch. The mechanism of photoluminescence and photochromism was studied. Finally, a flexible film with SrZrO 3 :Sm3+ material was fabricated to demonstrate rewritable optical recording and storage and reading of dual optical information. [ABSTRACT FROM AUTHOR]

Functional dye is a new term in the field of dye chemistry which has been specifically designed for hightechnology applications such as solar cells, photochromic dyes, liquid crystal, electrophotography, fluorescent sensors and photodynamic therapy. BODIPY and its derivatives as organic fluorophores have optical properties and can be used as potential sensors in various applications for biotechnological, industrial and medical purposes. In this research, a group of a new fluorescent indicators based on BODIPY structure were designed which have been composed from two seven-membered rings including Al or B atoms that has been connected with methine bridge complexed with NH2 or PH2 center. The geometries, optical properties and electronic structures of various designed molecules were studied using time-dependent density functional theory (TDDFT). The results of the calculations showed that the new designed structures are stable and highly optically active with considerable quantum yield (Φ) absorption and emission as if is promising candidates for hi-tech different applications. [ABSTRACT FROM AUTHOR]

Photochromism, fluorescence, and ultra‐long room temperature phosphorescence (URTP) are attractive phenomena in photonics. However, achieving multiple optical properties such as photochromism, fluorescence, and URTP on one material still remains a challenge. Here, the authors report a multifunctional optical polymeric film with photochromic, fluorescent, and URTP properties, fabricated by simply doping the naphthopyran molecule into epoxy polymer with 3D network. When the polymer network is loose, the naphthopyran‐doped film exhibits photochromic property but no fluorescence and phosphorescence. When the polymer network becomes dense, the film shows fluorescent and URTP behaviors but no photochromic property. It is noted that the room temperature phosphorescence lifetime is as high as 604 ms. Based on the excellent optical properties of reversible photochromism, fluorescence, and URTP, an advanced sixfold encryption application has been successfully established. This work not only opens up a new direction in design and fabrication of multifunctional optical materials but also offers principles for developing organic optical materials toward multilevel information encryption and data storage. [ABSTRACT FROM AUTHOR]

A series of tetraphenylethene (TPE) derivatives functionalized with highly potent electron‐deficient perfluoroaryl iodo‐triazole halogen bond (XB) donors for anion recognition are reported. 1H NMR titration experiments, fluorescence spectroscopy, dynamic light scattering measurements, TEM imaging and X‐ray crystal structure analysis reveal that the tetra‐substituted halogen bonding receptor forms luminescent nanoscale aggregates, the formation of which is driven by XB‐mediated anion coordination. This anion‐coordination‐induced aggregation effect serves as a powerful sensory mechanism, capable of luminescence chloride sensing at parts per billion concentration. Furthermore, the doubly substituted geometric isomers act as unprecedented photoswitchable XB donor anion receptors, where the composition of the photostationary state can be modulated by the presence of a coordinating halide anion. [ABSTRACT FROM AUTHOR]

While photothermal therapy is widely applied in phototherapy, there are still challenges in developing new generation phototherapy materials with precise diagnostic functions. Here we report the construction of a pH responsive upconversion fluorescence imaging precisely guided photothermal therapy system, namely NaYF4:Yb3+/Er3+@NaYF4@MnO2@Au nanocomposites, which can effectively avoid light damage to non-target tissues. Owing to the fluorescence resonance energy transfer between the upconversion nanocrystal donor and MnO2 and Au acceptor, the upconversion fluorescence is completely quenched. However, in pH 5.3 PBS buffer, MnO2 is gradually broken down, and the upconversion fluorescence is partially recovered, which could be used for upconversion fluorescence imaging to precisely guide photothermal therapy under 980 nm excitation. Simultaneously, due to the absorption of 980 nm excitation light and the emission bands of Er3+ (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transition), temperature increment of core@shell@MnO2@Au could reach 35.5 °C under 980 nm excitation at 0.8 W cm−2. The core@shell@MnO2@Au nanocomposites are supposed to contribute significantly in the biological applications of photoluminescence imaging and photothermal therapy. [ABSTRACT FROM AUTHOR]

The borondipyrromethene (BODIPY) chromophore is a versatile platform for the construction of photoresponsive dyes with unique properties. Specifically, its covalent connection to a photocleavable group can be exploited to engineer compounds with photoswitchable fluorescence. The resulting photoactivatable fluorophores can increase their emission intensity or shift their emission wavelengths in response to switching. Such changes permit the spatiotemporal control of fluorescence with optical stimulations and the implementation of imaging strategies that would be impossible to replicate with conventional fluorophores. Indeed, BODIPYs with photoactivatable fluorescence enable the selective highlighting of intracellular targets, the nanoscaled visualization of sub‐cellular components, the real‐time monitoring of dynamic events and the photochemical writing of optical barcodes. [ABSTRACT FROM AUTHOR]

Stimuli-responsive organic solid state fluorescent materials are considered as potential candidates for optoelectronic application as well as in the biomedical field. Molecular design and supramolecular interaction controlled organization in the solid state played an important role in producing switchable and tunable fluorescent materials. Excited state intramolecular proton transfer (ESIPT) mechanism-based solid state fluorescent materials showed unique photophysical properties such as a large Stokes shift and local environment (pH, polarity, ions and viscosity) responsive fluorescence modulation. The unique photophysical properties of ESIPT molecules made them interesting for various fields including laser dyes, molecular probes, optoelectronics, white emissive materials and optical information storage materials. Systematic fluorophore structural engineering has been performed over the years to gain insight on the ESIPT mechanism in order to improve the quantum efficiency and introduce desirable material attributes for functional applications. The substitutional unit, molecular conformation and supramolecular interactions played a significant role in transforming planar ESIPT fluorophores to stimuli-induced fluorescence switching materials either between two states or off–on states. In this review article, we have presented the recent developments in ESIPT-based solid state fluorescent materials and external stimuli-induced fluorescence switching. [ABSTRACT FROM AUTHOR]

A photoswitchable near-infrared (NIR) fluorescent nanoparticle (NP) was designed and prepared. The NP showed a characteristic AIE property and high-contrast NIR fluorescence photoswitching with full reversibility. Such efficient NIR fluorescence photoswitching originated from the amplified fluorescence quenching mechanism based on intermolecular energy transfer in a densely packed NP state. [ABSTRACT FROM AUTHOR]

Three kinds of thermochromic materials (DC8, DC12, DC16) were synthesized by linking the rigid 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (bpeb) with different lengths of alkyl chains. They exhibit remarkable fluorescent color changes under the irradiation of 365 nm light with elevating temperature, which is supposed to be caused by the transition between the crystal state and the amorphous state. Interestingly, the DC16 solid also has a photochromic character. It should be noticed that the phase transition temperatures of three materials measured by differential scanning calorimetry are higher than those of the fluorescence color changes during the heating process. Thus, the allochroic effect is attributed to the synergistic effect of both heating and photo-inducement (365 nm). Ethanol can turn the heated powder into the initial crystal again which indicates that their thermochromic behavior is reversible and makes the fluorescence recover. [ABSTRACT FROM AUTHOR]

As promising photoresponsive materials and potential smart materials, hybrid photochromic materials (HPMs), especially for crystalline HPMs (CHPMs), have been broadly explored for their potential in inheriting the merits of each constituents, and intriguing photomodulated functionality. Hitherto, the photoresponsive functionality in explored CHPMs mainly concentrate on dyad combination. By contrast, triple or quadruple photoresponsive properties are very rare because of the limited compatibility of multiple photoresponsive functionality in a single system. In this work, the electron‐transfer (ET) and crystal engineering strategies were utilized to predesign CHPMs with multiple photoresponsive properties via the collaboration of paramagnetic metal ion (Dy3+), electron‐donor (ED) ligand (benzene‐1,2,3‐tricarboxylic acid, H3BTA) and electron‐acceptor (EA) ligand (1,10‐phenanthroline, phen). The resulting complex [Dy(BTA)(phen)2]⋅2H2O (1) shows hybrid chain with the intrachain Dy3+ ions bridged and chelated by tricarboxylate and phen ligands, respectively. After photostimuli, the ET between tricarboxylate and phen results in photogenerated radicals and the resultant quadruple photoresponsive properties. Considering the abundant resources of paramagnetic metal ions, ED‐ and EA‐ligands, this work provides a general method to construct CHPMs with multiple photoresponsive performances via the collaboration of each unit under the guidance of ET and crystal engineering strategies. [ABSTRACT FROM AUTHOR]

In this study, photoswitchable fluorescent supramolecular metallacycles with high fatigue‐resistance have been constructed by coordination‐driven self‐assembly by using bithienylethene with dipyridyl units (BTE) as a coordination donor and a fluorescent di‐platinum(II) (Pt‐F) as a coordination acceptor. The photo‐triggered reversible transformation between the ring‐open and ring‐closed form of the metallacycles was confirmed by 1H NMR, 31P NMR, and UV/Vis spectroscopy. This unique property enabled a reversible noninvasive "off–on" switching of fluorescence through efficient Förster resonance energy transfer (FRET). Importantly, the metallacycles remained structurally intact after up to 10 photoswitching cycles. The photoresponsive property and exceptional photostability of the metallacycles posit their potential promising application in optical switching, image storage, and super‐resolution microscopy. [ABSTRACT FROM AUTHOR]

The review is devoted to mechanically sensitive indoline spiropyrans and their structural features. Recent advances in the study of their isomerization processes are considered, special attention is paid to the effect of pressure on the behavior of spiropyrans in the composition of various photochromic materials and dyes, as well as in the process of the formation of J-aggregates in Langmuir–Blodgett films. [ABSTRACT FROM AUTHOR]

A series of hydrogen‐bonded liquid crystals showing switchable fluorescence is reported. The fluorescence behavior results from the unique combination of hydrogen bonding, liquid crystallinity, and photobasicity. Thus, the molecular mobility in the mesophase is essential for the reversible photo‐initiated proton transfer switching on the fluorescence of the assemblies. The application potential of the materials for photo‐patterning was demonstrated. [ABSTRACT FROM AUTHOR]

A fluorophore encapsulated in a metal–organic framework showed photochromic multicolour fluorescence. Irradiation with an ultraviolet laser induced the relocation of the fluorophore from a polar to a nonpolar environment, altering the emission from red to blue. This change in emission color can be repeatably recovered by heating the fluorophore–MOF composite. [ABSTRACT FROM AUTHOR]

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Steady-state absorption and fluorescence spectra, fluorescence decay kinetics of CdSe/ZnS quantum dots (QD) with photochromic diarylethenes (DAE) in toluene have been studied. Two kinds of QDs emitting at 525 and 600 nm were investigated and DAE were selected to ensure good overlap of their photoinduced absorption band with QDs emission spectra. It has been found that photochromic molecules form complexes with QD which results in partial fluorescence quenching. A reversible modulation of QDs emission intensity which correlates with magnitude of transient photoinduced absorption band of the diarylethenes during photochromic transformations has been demonstrated. [ABSTRACT FROM AUTHOR]

We herein report a new coordination network that deforms in a smooth and reversible manner under either thermal or pressure stimulation. Concomitantly, the organic fluorophores coordinatively bound to the channel in a face‐to‐face arrangement respond to this structural deformation by finely adapting their conformation and arrangement. As a result, the material exhibits a remarkable dual‐stimuli‐responsive luminescence shift across almost the entire visible region: The emission color of the crystal gradually changes from cyan to green upon heating and then to red upon pressure compression. Furthermore, each stage exhibits a linear dependence of both the emission maximum and intensity on the stimulus and is fully reversible. Coping with pressure and heat: In response to changes in temperature and pressure, the flexible scaffold of a luminescent coordination network underwent smooth and reversible structural deformation that regulated the conformation and arrangement of the emissive organic molecules coordinatively bound to the channel in the structure. As a result, a reversible fluorescence shift across almost the entire visible region was observed (see picture). [ABSTRACT FROM AUTHOR]

Abstract Luminescent material Ca 2 Ba 3 (PO 4) 3 F:Eu2+ displays green emitting in the range of 400–700 nm, which is ascribed to the 4f65d1 →4f7 transition of Eu2+ ions. Amazingly, the body color of the samples can be changed between colorless and green upon alternative UV and visible light irradiation/heating treatment with robust fatigue resistance due to photochromism. The photochromic effect strongly depends on the Eu2+ doping concentration. After remote-controlled short-UV irradiation, the overall Eu2+ emission intensity presents a significant decrease, and inversely, exhibits an increase to the initial level after illuminated by longer wavelength light or heat treatment. Moreover, the fluorescence lifetime also can be regulated reversibly, of which the regulation degree depends on the short-UV irradiation and longer wavelength illumination time/heating temperature. A schematic diagram based on energy levels is proposed to illustrate the photochromism mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • AuNC-based dynamic multicolor luminescent nanoparticles were prepared. • FRET between AuNCs and spiropyran enables dynamic fluorescence response. • AuNC-based photoswitches exhibit reversible and dynamic fluorescence change. • Dynamic multicolor luminescent film shows great potential for anti-counterfeiting. Multicolor luminescent materials with time-dependent optical responses are attractive for developing advanced anti-counterfeiting techniques, but it still remains challenging to rationally design and fabricate these emerging materials. Herein, we report the design of novel dynamic luminescent materials based on spiropyran-engineered gold nanoclusters (AuNCs) for anti-counterfeiting applications. Encapsulating fluorescent AuNCs with spiropyran-labeled bovine serum albumin enables the construction of dynamic multicolor luminescent nanoparticles (DML NPs) based on fluorescence resonance energy transfer. These AuNCs-based DML NPs exhibit photochromism and dynamic fluorescence color change from green to yellow to orange-red with the extension of UV irradiation time. Moreover, the photochromism and dynamic fluorescent behavior is highly reversible when exposed to the irradiation of visible light. By taking advantage of photochromic and time-dependent dynamic fluorescence, potential application in optical information storage, dynamic anti-counterfeiting authentication and multi-mode anti-counterfeiting are successfully demonstrated based on DML NPs-deposited polyvinyl alcohol film. This study provides a new strategy of designing novel dynamic multicolor luminescent materials with promising optical properties, which can further advance the practical application of AuNCs-based luminescent materials in the field of information encryption and anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Cotton-based photochromic materials receive lots of attention due to their distinctive photoresponsivity and novel applications. Although many contributions have been devoted to this field, the color-changing effect and diversity still need to be improved. Herein, synchronous positive and negative photochromic and fluorescent color-changing smart textiles have been developed by applying spiropyran (SPOH) with a hydroxyl linking group to cotton fabrics through one-bath and coating methods, respectively. The negative photochromic cotton fabrics (NPCF) can promptly reach color saturation within 12 s and the photochromic property retention is 80 % after 15 color-changing cycles; the positive photochromic cotton fabrics (PPCF) will return to original color after 11 h under darkness and quickly fade under heating or green light. On this basis, we precisely designed positive and negative photochromic cotton fabrics (PNPCF) that can respond to both visible and ultraviolet (UV) light, and they also have fluorescent color-changing properties. In addition, photochromic cotton fabrics have potential applications in UV protection, pattern switching, information encryption and decryption. This research not only raises the value of cotton but also greatly enriches and expands the diversity of color-changing effects of photochromic cotton fabrics. [Display omitted] • This paper applies a spiropyran photochromic dye to cotton fabrics. • Synchronous positive and negative photochromic cotton fabrics have been developed. • Rapid color-changing ability and excellent color retention. • Explored applications in UV protection, information switching and encryption. [ABSTRACT FROM AUTHOR]

With the aim to explore the effect of luminol as a multifunctional dopant for conjugated polymers, the present study reports the ultrasound-assisted doping of polycarbazole (PCz) and poly( o -anisidine) (PAnis) with luminol in basic, acidic and neutral media. The synthesized homopolymers and luminol doped polymers were characterized using FT-IR, UV–visible and XRD studies while the photo-physical properties were investigated via fluorescence spectroscopy. Density functional theory (DFT) calculations were performed to get insights into the structural, optical, and electronic properties of homopolymers of polycarbazole (PCz) and poly( o -anisidine) (PAnis). Vibrational bands B3LYP/6-311G (d,p) level, UV–vis spectral bands and electronic properties such as ionization potentials (IP), electron affinities (EA) and HOMO−LUMO band gap energies of the homopolymers and doped polymers were calculated and compared. Results revealed that luminol doped polymers showed different photo-physical characteristics in acidic, basic and neutral media which could be tuned to obtain near infrared (NIR) emitting polymers. [ABSTRACT FROM AUTHOR]

A novel hybrid compound whose molecule includes the photochromic spiropyran fragment and two fluorophores – coumarin and salicylideneimine – was synthesized by the reaction of two equivalents of 8-formyl-7-hydroxy-4-methylcoumarin with 5-amino-1,3,3-trimethyl-2-methyleneindoline. Its spectral-kinetic and fluorescence properties were studied in comparison with model compounds – 7-hydroxy-4-methyl-coumarin, spiropyran of the coumarin type, and azomethinocoumarin in toluene and ethanol. It was shown that the hybrid compound exhibited photochromic transformations in both solvents. Different fluorescence emissions of the initial spirocycle and UV irradiation-induced merocyanine forms were observed. One green fluorescence emission with a maximum at 545 nm was observed for the initial closed form in toluene, and several emissions with maxima at 390 nm, 440 nm, 450 nm (violet), and 530 nm (green) appeared in ethanol. An additional red emission of the open merocyanine form in the region of 665 nm appeared after UV irradiation in both solvents. Reversible modulation of fluorescence in both the initial and photoinduced merocyanine forms in the process of photochromic transformations was discovered. It was shown that the fluorescence modulation of the hybrid compound in weakly polar toluene was caused by resonance energy transfer from the fluorescent fragment of the photochromic compound to the photoinduced merocyanine form, leading to the process of photochromic transformations. Reversible modulation of fluorescence in ethanol solutions was achieved through a photoinduced change in the ratio of the concentrations of conformers. [ABSTRACT FROM AUTHOR]

Two novel isomeric naphthopyrans substituted with phenyl (13-butyl-6,7-dimethoxy-3,3-bis(6-methoxybiphenyl-3-yl)-3,13-dihydrobenzo[h]indeno[2,1-f]chromen-13-ol) and 4-(naphthalen-1-yl)phenyl (13-butyl-6,7-dimethoxy-3,3-bis[6-methoxy-4'-(naphthalenyl)-biphenyl-3-yl]-3,13-dihydrobenzo[h]indeno[2,1-f]chromen-13-ol) moieties were synthesized. Their photochromism, electrochemical and fluorescent properties were investigated. They displayed faster color fading rate and larger fluorescence quantum yield than 13-butyl-6,7-dimethoxy-3,3-bis(4-methoxyphenyl)-3,13-dihydrobenzo[h]indeno[2,1-f]chromen-13-ol. Moreover, they showed excellent photochromic and fluorescent properties both in solution and in polymethylmethacrylate film. In addition, cyclic voltammetry tests showed that the aromatic substituents had a significant effect on the electrochemical behavior of the naphthopyran derivatives. [ABSTRACT FROM AUTHOR]

Smart clothing can be defined as textiles that respond to a certain stimulus accompanied by a change in their properties. A specific class herein is the photochromic and fluorescent textiles that change color with light. A photochromic and fluorescent cotton fabric based on pigment printing is obtained. Such fabric is prepared by aqueous-based pigment-binder printing formulation containing inorganic pigment phosphor characterized by good photo- and thermal stability. It exhibits optimal excitation wavelength (365 nm) results in color and fluorescence change of the fabric surface. To prepare the transparent pigment-binder composite film, the phosphor pigment must be well-dispersed via physical immobilization without their aggregation. The pigment-binder paste is applied successfully onto cotton fabric using screen printing technique followed by thermal fixation. After screen-printing, a homogenous photochromic film is assembled on a cotton substrate surface, which represents substantial greenish-yellow color development as indicated by CIE Lab color space measurements under ultraviolet light, even at a pigment concentration of 0.08 wt% of the printing paste. The photochromic cotton fabric exhibit three excitation peaks at 272, 325 and 365 nm and three emission peaks at 418, 495 and 520 nm. The fluorescent optical microscope, scanning electron microscope, elemental mapping, energy dispersive X-ray spectroscopy, fluorescence emission and UV/Vis absorption spectroscopic data of the printed cotton fabric are described. The printed fabric showed a reversible and rapid photochromic response during ultra-violet excitation without fatigue. The fastness properties including washing, crocking, perspiration, sublimation/heat, and light are described. [ABSTRACT FROM AUTHOR]

A new diarylethene compound with a triazole-linked rhodamine 6G unit attached to the imino group ( 1O ) was designed and synthesized. According to the test results, the solution color and fluorescence color of diarylethene can be modulated by lights and metal ions. The solution color could change from colorless to light purple when irradiated with UV light. When Cu 2+ was added to the diarylethene solution, the color of diarylethene solution became blue, the fluorescence color turned from dark to bright yellow. Although the solution color did not change by adding Fe 3+ , its fluorescence color varied from dark to yellow. Moreover, it was found that the complex ratio of the diarylethene to Cu 2+ was 1:1 and the binding stoichiometry of the diarylethene to Fe 3+ was also 1:1 based on the data of NMR, MS, and other experiments. Based on these findings, photochromic figure of the diarylethene with UV/Vis light, Cu 2+ and Fe 3+ was constructed. Furthermore, the logic circuit was designed by input signals (ultraviolet stimulus, visible light stimulus, Cu 2+ (or Fe 3+ ) and EDTA) and an output signal (fluorescent intensity at 566 nm (or 575 nm)). [ABSTRACT FROM AUTHOR]

A new category of photochromic dihydroindolizines (DHIs) incorporating substituted 2,7- and 4-substituted tetrazole and oxadiazole moieties in the fluorene skeleton (region A) were efficiently prepared utilizing “Click” chemistry approaches. The structure elucidation for all synthesized precursors as well as the target photochromic DHIs was carried out using some analytical and spectroscopic techniques. A highly tunable photochromic behaviors of the parent dihydroindolizine are possible by the introduction of substituents in different positions of the DHI framework. For example, the substituents in 2,7 and 4-positions of fluorene part showed the ability for extending photochromism. The photochromic behaviors of photochromic DHIs substituted in fluorene part (region A) such as the reaction kinetics and fluorescence properties and their photo-fatigue resistance were studied. It has been disclosed that the replacement of the tetrazole moieties in 2,7-position in (region A) by oxadiazole moieties has strong effect on both the spectral, kinetic characteristics, fluorescence emission and photostability. The observations of this work imply that the substituent groups in the fluorene part influenced the thermal back-reaction rates and played an imperative role in controlling all photochromic properties of the open form. The new synthesized substituted (DHIs) in the fluorene by both tetrazole moieties in 2,7-position and by oxadiazole moieties in 2,7 and 4 positions in fluorene part made these materials act as fluorophores and postulate new opportunities for the design of the next generation of photochromic materials which will make it talented materials in many applications such as electronic smart materials, photochromic glasses, photonic devices and fluorescent fabrics. Because of their noticeable fluorescence emission high photostability, these materials can be used as fluorophores, recording or storage information for numerous periods without color fading. [ABSTRACT FROM AUTHOR]

A novel photochromic diarylethene with a triazole-containing 2-(2′-phenoxymethyl)-benzothiazole group has been synthesized via “click” reaction. The diarylethene exhibited good photochromism and photoswitchable fluorescence. Its fluorescence emission intensity was enhanced 7-fold by acids, accompanied by the red-shift of emission peak from 526 nm to 566 nm and the concomitant color change from dark to bright flavogreen. The diarylethene selectively formed a 1:1 metal complex with Al 3+ , resulting in a “turn-on” fluorescence signal. The complexation - reaction between Al 3+ and the diarylethene is reversible with the binding constant of 2.73 × 10 3 L mol −1 . The limit of detection (LOD) of Al 3+ was determined to be 5.94 × 10 −8 mol L −1 . Based on this unimolecular platform, a logic circuit was fabricated using the fluorescence emission intensity at 572 nm as the output and the combined stimuli of Al 3+ /EDTA and UV/Vis as the inputs. [ABSTRACT FROM AUTHOR]

An NDI-based compound (2-NDI) with 2-butyric acid attached at imide N atoms was intelligently constructed. 2-NDI exhibits 2-NDI − monomer (low concentration) and 2-NDI − excimer (high concentration) emission state in different solvents after 365 nm illumination, forming multi-color radical fluorescence. It shows dynamic free radical emission in DMF solvent with rare white light emission. Theoretical calculations show that the fluorescence is derived from the D n -D 0 vertical emission of 2-NDI − monomer and 2-NDI − excimer. Finally, 2-NDI is made into PMMA film, which is successfully applied to information anti-counterfeiting and dynamic information encryption systems. [Display omitted] • 2-NDI was synthesized and showed different free radical emission colors in different solvents. • The dynamic fluorescence of 2-NDI in DMF solution changed with the irradiation time. • 2-NDI shows different free radical fluorescence emission types at different concentrations. • DFT shows that the free radical fluorescence is the vertical emission of D n -D 0. • 2-NDI PMMA film can be used for dynamic information encryption and anti-counterfeiting. Developing innovative materials with environmentally stable 1,4,5,8-Naphthalene diimide radicals (NDI −) emissions is significant. In this work, we have successfully constructed an NDI-based material 2-NDI (N, N′-bis(2-butyric acid)-1,4,5,8-naphthalene diimide) that emits strong fluorescence in solvents and polymethyl methacrylate (PMMA) upon irradiation. The radical 2-NDI − exhibits multi-color emission in different solvent systems, and the fluorescence emission is concentration-dependent. It is worth noting that it exhibits a rare dynamic fluorescence in DMF solvent, with the fluorescence color changing from yellow-green to orange and finally to white. Theoretical calculations show that the fluorescence is derived from the D n -D 0 vertical emission of 2-NDI − monomer and excimer. Owing to the outstanding free radical fluorescence emission properties, various films (PMMA systems) based on 2-NDI in different solvents have been successfully made to be applied in multiple dynamic information anti-counterfeiting and encryption. This work achieved simple and stable fluorescence emission based on NDI −, making it a potential candidate for practical applications and providing a new platform for the future design of NDI-based photochromic materials. [ABSTRACT FROM AUTHOR]

Abstract: Four tetradithienylethene (DTE) substituted porphyrins, the free base 1H2, and three metal derivatives (1Zn, 1Co, 1Ni), were synthesized and studied. These dyads, for which the DTE units are connected to the porphyrin's meso positions via a meta‐phenyl spacer, exhibit reversible photochromic properties in all cases, with conversion to the photostationary state (PSS) up to 88 %, as confirmed by absorption and NMR spectroscopies. Compounds 1H2 and 1Zn are fluorescent in solution and display a red emission. Upon irradiation with UV light to trigger the closing of the DTEs, the fluorescence of both the free base and zinc porphyrin was very efficiently quenched in solution. The reversible, photo‐switching of luminescence was retained in a tetra‐DTE free‐base porphyrin‐doped polystyrene film, for which photo‐patterning was demonstrated by confocal scanning microscopy. The tunable fluorescent properties of this multi‐DTE framework render this compound of interest as a photo‐rewritable fluorescent ink. [ABSTRACT FROM AUTHOR]

Abstract: Multicolor tunable and multistate switchable organogel is reported, which consists of a cyanostilbene organogelator showing aggregation‐induced enhanced emission and a turn‐on type photochromic diarylethene dye. The mixed organogel can be reversibly switched among four different states (blue‐emitting gel, nonemissive sol, green‐emitting gel, and green‐emitting sol) modulated by a combination of orthogonal stimuli of heat and light. It is interestingly noted that this four‐state switching constitutes a combinational logic circuit consisting of two stimuli inputs and three outputs. Reversible fluorescence writing, switching, erasing, and image patterning processes on this mixture gel system are demonstrated. [ABSTRACT FROM AUTHOR]

Most aggregation-induced emission (AIE) luminogens possess propeller-like aromatic stator-rotor structures, such as silole, tetraphenylethylene (TPE) and triphenylamine (TPA), to restrict intra-molecular motions (RIM) and avoid aggregation-caused quenching (ACQ) effects. In our work, two simple N -substituted naphthalimides were designed and synthesized by the amide condensation to create novel AIE systems. Except for the same aromatic stator (naphthalimide), N -phenyl-1,8-naphthalimide ( PhNI ) contained an aromatic rotor (phenyl group) while N -cyclohexyl-1,8-naphthalimide ( CyNI ) contained an aliphatic rotor (cyclohexyl group). The PhNI samples obtained from different preparation processes showed multiple chromisms (MC) effects and varied levels of luminescence. Despite of the same intra-molecular structure, the crystal of PhNI had staggered parallel inter-molecular conformation with weak emission but the precipitation of PhNI had cross one with strong emission. Although without MC effects, CyNI gave an excellent fluorescence quantum yield (Φ f = 0.55). The experimental results and theoretical analyses suggested that the AIE effects were decided by intra- and inter-molecular structure simultaneously and the construction and destruction of inter-molecular π-π stacking between aromatic rotors in PhNI resulted in the MC effects. [ABSTRACT FROM AUTHOR]

A novel photochromic fluorescent DASA (donor-acceptor Stenhouse adduct) switch controlled by visible light was successfully designed and synthesized. Using 1,8-naphthalimide fluorophore in combination with indoline-based “donor” and barbituric acid “acceptor”, the DASA molecule exhibits two independent absorption bands at 440 nm and 616 nm. The physical and thermodynamic properties of fluorescent donor-acceptor Stenhouse adduct (DASA-NDI ) have been investigated in different solvents. In accordance with the unique fluorescent properties under visible light/heat and H + /Cu 2+ , using fluorescence intensity at 604 nm (I 604 ) as an output and visible light, H + and Cu 2+ as inputs, a combinatorial logic gate consisting of NOR and AND logics can be described and operated. [ABSTRACT FROM AUTHOR]

A novel fluorescent organogelator NSS comprised of C N and NNH units was designed and characterized. By light irradiation, NSS could undergo trans to cis transformation both in solution and gel state, which was accompanied by dramatic color, fluorescence intensity, and emission color changes, indicating the photochromic property of NSS . Both of the gels in E-isomeric and Z-isomeric forms could selectively response to fluoride anion among tested anions. Further study presented that the two isomers displayed different signal outputs and binding mechanisms toward fluoride anion. Especially, the organogel of NSS in the E-isomeric form showed selective, visual, and reversible sensing for fluoride anion. Beside the above functions, the organogel could also response to ultrasound and heating stimuli, thus endowing the organogel with multi-stimuli responsive properties. [ABSTRACT FROM AUTHOR]

Development of powerful fluorescence imaging probes and techniques sets the basis for the spatiotemporal tracking of cells at different physiological and pathological stages. While current imaging approaches rely on passive probe-analyte interactions, here we develop photochromic fluorescent glycoprobes capable of remote light-controlled intracellular target recognition. Conjugation between a fluorophore and spiropyran produces the photochromic probe, which is subsequently equipped with a glycoligand "antenna" to actively localize a target cell expressing a selective receptor. We demonstrate that the amphiphilic glycoprobes that form micelles in water can selectively enter the target cell to operate photochromic cycling as controlled by alternate UV/Vis irradiations. We further show that remote light conversion of the photochromic probe from one isomeric state to the other activates its reactivity toward a target intracellular analyte, producing locked fluorescence that is no longer photoisomerizable. We envision that this research may spur the use of photo-chromism for the development of bioimaging probes.e [ABSTRACT FROM AUTHOR]

Herein, we report on wavelength-selective and high-contrast multicolour fluorescence photoswitching between white-, orange-, cyan-, and dark-colours in a mixture of two distinguishable emission-coloured photochromic nanoparticles composed of different pairs of a photoswitching unit and a fluorescence unit. [ABSTRACT FROM AUTHOR]

Dithienylethenes 1 and 2 , consisting of three photochromic units linked by imidazole bridges, together with its N-methylated derivatives 3 and 4 , have been synthesized. Their photochromic properties and fluorescence behaviors have also been investigated in solution by irradiation with various wavelengths of UV light. It was found that the dithienylethene 1 showed selective photochromism, indicated by the fluorescence change upon irradiation with 365 nm and 302 nm light. However, dithienylethenes 2 , 3 and 4 only underwent a photocyclization reaction in the middle switchable unit under the same conditions. Moreover, for dithienylethenes 2 and 4 , introduction of fluorine atoms on the cyclopentene evidently enhanced the photochromic properties compared with perhydro-substituted dithienylethenes 1 and 3 . And dithienylethene 3 could act as one potential fluorescent molecular switch. [ABSTRACT FROM AUTHOR]

We have synthesized and fully characterized a photochromic zinc complex with a terphenylthiazole-based ligand with a salen-like cavity. The solution stability of the complex was found to be greatly dependent on the state of the photochromic ligand and an interesting photo-triggered release and uptake of zinc ions was found as well as monitored by its fluorescence. The contrasting stability difference of the zinc complex between its two isomeric states was rationalized by DFT calculations. [ABSTRACT FROM AUTHOR]

A new fluorescent turn-on chemosensor for Al 3+ based on a diarylethene unit was designed and synthesized. Photochromism, fluorescence switch, and metal ion recognition behaviors of this diarylethene derivative were investigated by absorption and fluorescence emission spectra. It shows an outstanding fluorometric sensing ability toward Al 3+ ion, and the detection limit was measured to be 9.3 × 10 −8 mol L −1 via fluorescence methods. Based on these interesting properties, a combinational logic circuit was constructed successfully. [ABSTRACT FROM AUTHOR]

Spiropyran derivatized vinylic monomer (MSP) was prepared by coupling a typical spiropyran dye, 1′-(2-hydroxyethyl)-3′,3′-dimethyl-6-nitrospiro(2H-1-benzo-pyran-2,2′-indoline), to methacryloyl chloride. Poly(styrene-butylmethacrylate-divinylbenzene-MSP), P(S-BMA-DVB-MSP), photochromic fluorescent nanoparticles (NPs) of narrow size distribution were prepared by emulsion polymerization of the vinylic monomers: S, BMA, DVB and MSP. The influence of various polymerization parameters (e.g., concentration of the monomers, initiator and surfactant and pH) on the diameter, diameter distribution and photochromic fluorescence properties of the particles was elucidated. Spiropyran type molecules as well as MSP are colorless and non-fluorescent at the Spiro conformation. These compounds at the Merocyanine conformation are non-fluorescent in water or in non-polar organic solvents. However, when the Merocyanine conformation is entrapped within hydrophobic polymer particles, the particles exhibit blue color and strong red fluorescence. Absorbance and fluorescence measurements reveal that increasing the MSP or BMA relative concentration leads to a higher absorbance and fluorescence intensity of the formed P(S-BMA-DVB-MSP) NPs. Photoisomerization switching of the P(S-BMA-DVB-MSP) NPs was studied by exposing the NPs aqueous dispersion to alternating UV and visible light cycles. This study indicates 100% reversibility after five cycles of photoswitching. [ABSTRACT FROM AUTHOR]

A novel photochromic diarylethene with a salicylidene Schiff base group was synthesized and its multi-controllable fluorescence switching properties induced by light, base, and metal ions were investigated. The diarylethene displayed sequence-dependent responses through efficient interaction of the salicylidene Schiff base group with base and metal ions, and it could serve as a naked-eye chemosensor for highly selective detection of different metal ions in different solvents. When triggered by Zn 2+ in acetonitrile, its fluorescence was enhanced by 400 fold with a concomitant color change from dark to bright yellow. In contrast, when it bound to Al 3+ in methanol, its fluorescence was enhanced by 110-fold accompanied with a color change from dark to bright cyan. On the basis of its light-, base-, and metal-responsive fluorescence behaviors, two complicated logic gates were constructed using the fluorescence intensity as output and combinational stimuli of light and chemical species as inputs. [ABSTRACT FROM AUTHOR]