Intramolecular Rotation Research Articles

Designing of naphthalene based acylhydrazone derivative as a selective fluorogenic sensor for strong volatile acids based on aggregation-induced emission

In the present study, a cognitive self-assembled fluorescent chemosensor, (2-hydroxy-naphthalene-1-ylmethylene)-hydrazide (NIZ) was presented which disclosed sensitive and selective trace quantity detection of strong volatile acids both in binary solvent mixture [2:8 (v/v) THF/water] and solid state (thin film) based on aggregation-induced emission (AIE) characteristics. In molecularly dissolved state, NIZ participated in the excited-state intramolecular proton transfer (ESIPT), where the dynamic flexibility during a fast photoinduced process debilitated the consumed excited energy nonradiatively and enabled NIZ to be completely nonluminescent in THF (φf = 0.39%). However, vigorous rigidification of molecular framework upon exercising different noncovalent forces obstructed all possible intramolecular motions via restricted intramolecular rotation (RIR), where delimited ESIPT upon prompting the molecules into self-assembly resulted dramatically augmented emission intensity (φf = 29.8%) impregnated with AIE behavior in THF/water. Subsequently, spontaneously evolved green emissive fluorescent nanoaggregates were primarily employed as a fluorescent chemosensor for aqueous phase recognition of strong acids where protonation-induced destruction of aggregated morphology due to reasonable interaction between NIZ and analytes led to a selective fluorescence quenching towards trifluoroacetic acid [(HTFA); detection limit (DL) = 41.74 nM], hydrochloric acid [(HCl); DL = 47.47 nM] and nitric acid [(HNO3); DL = 50.17 nM). Importantly, the ready-made cost-effective test kits of NIZ exhibited a selective fluorogenic response towards vapors from HNO3, HTFA and HCl in the rapid fashion where DLs were as low as 0.88, 1.39 and 4.57 ppm respectively to demonstrate the “in-the field” monitoring of air quality. Finally, the reversible “ON-OFF” fluorogenic response from NIZ inspired us to device a “use” and “throw” security marker upon alternative presence of HTFA and triethylamine (TEA) to augment the day-to-day practical applications.

Influence of microcrystal formation on the aggregated state emission behaviour of pyrene substituted phthalonitrile positional isomers

• The present work depicts the effect of substitution position on the aggregated state emission properties of organic fluorophores. • Two D-A type organic fluorophores from pyrene and phthalonitrile counterparts were synthesized. • 3-PyPN exhibited AIE property in contrary to ACQ property with 4-PyPN . • The OMC (organic microcrystal) formation due to molecular packing with 3-PyPN may be the plausible factor for AIE behaviour. • Steric repulsion in 3-PyPN makes semi propeller geometry and restriction of intra-molecular rotation favouring OMC formation. Pyrene, due to its peculiar electronic properties is ideal for D-A type charge transfer fluorophores. Herein we synthesized pyrene and phthalonitrile incorporated D-A architectures 3-PyPN and 4-PyPN with large stoke’s shift of 184 nm and 168 nm respectively (methanolic solution). 3-PyPN exhibited weak emission compared to 4-PyPN in solution and PMMA film with quantum yields of Φ F = 0.15 (solution), 0.22 (film) for 3-PyPN and Φ F = 0.59 (solution) and 0.54 (film) for 4-PyPN . 4-PyPN suffered solid state emission decrement compared to 3-PyPN with the corresponding quantum yields being 0.12 and 0.24 respectively. Further, 3-PyPN showed AIE behaviour in contrary to the ACQ observed with 4-PyPN . Morphological and size analysis of aggregates displayed formation of ordered microcrystals of 510 nm average particle size with 3-PyPN and irregular fibrous particles of 805 nm with 4-PyPN . Plausible explanation towards this behaviour may be that 3-PyPN experiences incremental restriction of intra-molecular rotation (RIR) owing to steric hindrance and attains semi-propeller geometry. This allows staggered J- type aggregation of pyrene leading to microcrystalline morphology. Quantum chemical calculations demonstrates changes in aggregated state emission as the outcome of dihedral angle changes between 3-PyPN (θ1 = 67.44°, θ2 = 110.76°) and 4-PyPN (θ1 = 56.92°, θ2 = 125.80°) due to steric hindrance exerted by 3-PyPN due to pyrene and nitrile group proximity.

Fluorescent Covalent Organic Frameworks: A Promising Material Platform for Explosive Sensing.

Covalent organic frameworks (COFs) are a novel class of porous crystalline organic materials with organic small molecule units connected by strong covalent bonds and extending in two- or three-dimension in an ordered mode. The tunability, porosity, and crystallinity have endowed covalent organic frameworks the capability of multi-faceted functionality. Introduction of fluorophores into their backbones or side-chains creates emissive covalent organic frameworks. Compared with common fluorescent organic solid materials, COFs possess several intrinsic advantages being as a type of irreplaceable fluorescence materials mainly because its highly developed pore structures can accommodate various types of guest analytes by specific or non-specific chemical bonding and non-bonding interaction. Developments in fluorescent COFs have provided opportunities to enhance sensing performance. Moreover, due to its inherent rigidified structures and fixed conformations, the intramolecular rotation, vibration, and motion occurred in common organic small molecules, and organic solid systems can be greatly inhibited. This inhibition decreases the decay of excited-state energy as heat and blocks the non-radiative quenching channel. Thus, fluorescent COFs can be designed, synthesized, and precisely tuned to exhibit optimal luminescence properties in comparison with common homogeneous dissolved organic small molecule dyes and can even compete with the currently mainstream organic solid semiconductor-based luminescence materials. This mini-review discusses the major design principle and the state-of-the-art paragon examples of fluorescent COFs and their typical applications in the detection and monitoring of some key explosive chemicals by fluorescence analysis. The challenges and the future direction of fluorescent COFs are also covered in detail in the concluding section.

Phototoxicity of BODIPY in long-term imaging can be reduced by intramolecular motion

For long-term live-cell fluorescence imaging and biosensing, it is crucial to work with a dye that has high fluorescence quantum yield and photostability without being detrimental to the cells. In this paper, we demonstrate that neutral boron-dipyrromethene (BODIPY)-based molecular rotors have great properties for high-light-dosage demanding live-cell fluorescence imaging applications that require repetitive illuminations. In molecular rotors, an intramolecular rotation (IMR) allows an alternative route for the decay of the singlet excited state (S1) via the formation of an intramolecular charge transfer state (CT). The occurrence of IMR reduces the probability of the formation of a triplet state (T1) which could further react with molecular oxygen (3O2) to form cytotoxic reactive oxygen species, e.g., singlet oxygen (1O2). We demonstrate that the oxygen-related nature of the phototoxicity for BODIPY derivatives can be significantly reduced if a neutral molecular rotor is used as a probe. The studied neutral molecular rotor probe shows remarkably lower phototoxicity when compared with both the non-rotating BODIPY derivative and the cationic BODIPY-based molecular rotor in different light dosages and dye concentrations. It is also evident that the charge and localization of the fluorescent probe are as significant as the IMR in terms of the phototoxicity in a long-term live-cell imaging.Graphical abstract

Photo-thermo-induced room-temperature phosphorescence through solid-state molecular motion

The development of smart-responsive materials, in particular those with non-invasive, rapid responsive phosphorescence, is highly desirable but has rarely been described. Herein, we designed and prepared a series of molecular rotors containing a triazine core and three bromobiphenyl units: o-Br-TRZ, m-Br-TRZ, and p-Br-TRZ. The bromine and triazine moieties serve as room temperature phosphorescence-active units, and the bromobiphenyl units serve as rotors to drive intramolecular rotation. When irradiated with strong ultraviolet photoirradiation, intramolecular rotations of o-Br-TRZ, m-Br-TRZ, and p-Br-TRZ increase, successively resulting in a photothermal effect via molecular motions. Impressively, the photothermal temperature attained by p-Br-TRZ is as high as 102 °C, and synchronously triggers its phosphorescence due to the ordered molecular arrangement after molecular motion. The thermal effect is expected to be important for triggering efficient phosphorescence, and the photon input for providing a precise and non-invasive stimulus. Such sequential photo-thermo-phosphorescence conversion is anticipated to unlock a new stimulus-responsive phosphorescence material without chemicals invasion.

Dehydrative Substitution Reaction in Water for the Preparation of Unsymmetrically Substituted Triarylmethanes: Synthesis, Aggregation-Enhanced Emission, and Mechanofluorochromism.

Water as a reaction media in chemical transformations has several advantages in terms of safety and non-toxicity. However, dehydrative substitution reaction in water is a highly challenging operation. In this paper, we have reported a sulfamic acid-mediated dehydrative substitution reaction of benzofuryl alcohols with several nucleophiles in water towards the scalable, easily isolable, synthesis of unsymmetrically substituted triarylmethanes (TRAMs) in good to excellent yields (up to 92 %). Moreover, we have demonstrated that rationally designed propellor-shaped triarylmethanes promote aggregation-induced emission (AIE) through restricted intramolecular rotation with irreversible mechanoflurochromic property.

Aggregation-Induced Emission in Phenothiazine-Based Fluorophores: An Insight into the Excited State and Aggregate Formation Mechanism

In this study, we report evidence for emissive aggregates of push–pull phenothiazine and phenothiazine dioxide derivatives produced both in water dispersions and in the solid state, highly promising for applications in both biology and material science. An insightful investigation of the aggregation-induced emission (AIE) mechanism was carried out via time-resolved spectroscopies, with nanosecond and femtosecond temporal resolution, coupled with advanced data analysis. Our steady-state and time-resolved spectroscopic results unambiguously show that a significant AIE behavior is activated by the restriction of intramolecular rotations for the phenothiazine derivatives. Investigation of the nonlinear optical properties also revealed that aggregates exhibit notable emission upon two-photon excitation. In particular, the phenothiazine dioxide-based aggregates exhibit remarkable fluorescence efficiencies and large two-photon absorption cross sections, as well as the capability to be internalized in HeLa cells exerting no cytotoxic effect. These aggregate species thus prove to be promising as novel fluorophores for bioimaging.

Competitive ICT in asymmetric D−A Scaffolds showing visible solvatochromism, temperature-induced emission enhancement and AIE based acidochromism

Meticulous attention to details of intramolecular charge transfer (ICT) has proved to be an effective strategy to design donor-acceptor fluorophores equipped with multichromic behaviour. Herein, we report three asymmetric donor-acceptor fluorophores bearing A′−D−A−D−A′ and D′−D−A−D−D′ scaffolds. The D−A−D core has been modified by appending pyridine/pyrimidine as additional acceptor and phenyl as additional donor and piperazine as flexible spacers. The asymmetric scaffold has equipped them with naked-eye solvatochromism even under daylight which further authenticated the effective charge separation in ground as well as excited state. The comparative account of photophysical behaviour displays the varying extent of twisted intramolecular charge transfer (TICT) owing to asymmetry. The interplay of restricted intramolecular rotation (RIR) and TICT leads to AIE induced H+ sensing and reversible acidochromism in PC1 which can be visualized by a comparatively uncommon acid induced emission enhancement. The activation of vibrational bands at higher temperature leads to a rare temperature induced emission enhancement in PC1−PC3. PC1 has been developed as the very first ‘turn-on’ thermochromic sensor based on β-diketone-boron difluoride (BF2bdk) complexes.

Synthesis, photophysical behavior in solution, aggregates, solid state and computational study of new derivatives of 2,2′-bis(indolyl)methane-triphenylamine

A series of new 2,2′-bis(indolyl)methane-triphenylamine (2,2′-BIM-TPA) derivatives were synthesized and characterized. TPA units were inserted in the indole fragment, as well as in the methylene position of the BIM to obtain systems with a high degree of torsion and intramolecular rotation. Phenyl and phenylethynyl linkers between TPA and BIM units were included in the BIM-Ph-TPA and BIM-Ph-E-TPA derivatives to extend the conjugation of the methylene substituted BIMs. The absorption and emission behavior in solution, aggregates and solid state of five 2,2′-BIM-TPA derivatives was studied. Only BIM-Ph-TPA and BIM-Ph-E-TPA showed a slight solvatochromic behavior. In THF-water mixtures, non-emissive aggregates were produced, but the concentrated solutions (1000 µM) of each compound favored the formation of emissive aggregates. It was found that water acts as a fluorescence quencher of the aggregates. Additionally, the 2,2′-BIM-TPA derivatives showed fluorescence in the solid state. The DFT computational studies allowed to confirm the highly twisted molecular geometries, to elucidate the distribution and energy of the frontier molecular orbitals (HOMO-LUMO), as well as the nature of the main electronic transitions (UV–Vis).

ESIPT-Active 8-Hydroxyquinoline-Based Fluorescence Sensor for Zn(II) Detection and Aggregation-Induced Emission of the Zn(II) Complex.

A D−π–A type quinoline derivative, 2-(((4-(1, 2, 2-triphenylvinyl)phenyl)imino)methyl)quinolin-8-ol (HL), was synthesized and structurally characterized. The five-membered ring formed by the O–H···N hydrogen bond in HL contributed to the excited-state intramolecular proton transfer (ESIPT) behavior of HL, which was further verified by theoretical computations. Upon coordination with Zn2+, the hydroxyl proton in HL was removed, resulting in the inhibition of ESIPT. In the meanwhile, the formed Zn2L4 complex displayed aggregation-induced emission (AIE) character in THF/H2O mixtures, which is conducive to the fluorescence enhancement in aqueous media. Structure analysis suggested that the origin of the AIE characteristic was attributed to restriction of intramolecular rotations along with the formation of J-aggregates. Based on ESIPT coupled with AIE, HL could recognize Zn(II) in aqueous media via an orange fluorescence turn-on mode. Benefitting from the AIE property, chemosensor HL was successfully applied to fabricate test strips for rapid sensing of Zn(II) ions.

AIE mechanism of 2-(2-hydroxyphenyl) benzothiazole derivatives: CASPT2 and spin-flip study

Wang et al. synthesized phenylacetylene modified HBT derivative (HBT-s-Ph) and diphenylacetylene modified HBT derivative (HBT-d-Ph) with aggregation-induced emission (AIE) phenomenon. In this work, we have theoretically compared the photochemical and photophysical processes of HBT-s-Ph and HBT-d-Ph in the gas phase, toluene and solid phase using several theoretical methods. The ground-state, excited-state equilibrium structures, the potential energy curves and the excited-state properties were comparatively calculated for a better understanding of the AIE mechanism. The excited-state intramolecular proton transfer (ESIPT) process within HBT derivatives is very fast in both gas phase, toluene, and solid phase due to the small energy barrier, inducing the formation of Keto tautomer which is responsible for emission peaks observed in experiment in both gas phase, toluene and solid phase. But, the reaction paths are very different from there. In toluene, the non-radiative path via HBT intramolecular rotation along the C–C bond is favorable to occur, leading to low Φf of HBT-s-Ph and HBT-d-Ph in toluene. In contrast, the non-radiative path of HBT intramolecular rotation is strongly suppressed in solid phase due to the high energy barriers, which is responsible for high Φf of HBT-s-Ph and HBT-d-Ph in solid phase. The substitution effect on AIE and the large difference of Φf in HBT-s-Ph and HBT-d-Ph in solid phase have been revealed. The presents results contribute to a better understanding of the different photophysical properties of HBT derivatives in toluene and solid phase, and unveil the AIE mechanism in HBT derivatives, which provides deep insight into molecular design of organic photoelectric materials with high Φf.

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Visualization of Macrophase Separation and Transformation in Immiscible Polymer Blends

Aniline as a TICT rotor to derive methine fluorogens for biomolecules: A curcuminoid-BF2 compound for lighting up HSA/BSA

The unique structure of fluorescent proteins in which the fluorophore is encapsulated by the protein shell to restrict rotation and emit light inspired the screening of chromophores that selectively bind to biomolecules to generate fluorescence. In this paper, we report a curcuminoid-BF2-like fluorescent dye N-BF2 containing 4-dimethylaniline as an electron-donating group. When this dye is combined with HSA or BSA, the fluorescence is enhanced 90/112-fold, and the fluorescence quantum yield increases from <0.001 to 0.16/0.19. Such a large change in fluorescence enhancement is due to the encapsulation of N-BF2 in the protein cavity by HSA/BSA, which inhibits the intramolecular rotation of the aniline moiety caused by charge transfer after the fluorophore is excited by light. N-BF2 has fast and strong binding to HSA or BSA and was found to be reversible in solution and intracellularly. Since N-BF2 also has the ability to target lipid droplets, the complex of N-BF2/HSA realizes the regulation of reversible lipid droplet staining in cells.

Substitution dependent multi-color AIE behavior and ESIPT active A-D-A type triphenylamine supported bis unsymmetrical azine derivatives and their antibacterial activity

A facile synthetic approach afforded a new family of AIE active and ESIPT featured A-D-A (Acceptor-Donor-Acceptor) type symmetrical triphenylamine centered bis unsymmetrical azine derivatives TPSA, TPHY, TPDS and TPOV. Depending upon the substituent in the periphery, all compounds displayed frail fluorescence in the solution state and exhibited strong multi-color luminescence character in aggregated/solid state. The results achieved from UV–visible absorption, emission and theoretical studies confirmed the existence of the intramolecular proton transfer phenomenon in the excited state (ESIPT). The experimental results affirmed AIE behavior present in the compounds and it might be due to the restriction of the intramolecular rotation (RIR) mechanism. The in vitro antibacterial activity of the compounds was also scrutinized against elected bacterial strains (B. subtilis, S. aureus, E. coli, and P. aeruginosa) in different concentrations (0.5 mM, 1 mM, 1.5 mM). The results revealed that all four compounds have excellent antibacterial activity at 1.5 mM than other concentrations tested in the present study. Further, the fluorescence feature of the compounds was explored via fluorescence microscopy to probe the microbes (Pseudomonas aeruginosa).

Ferrocene appended 1,8-naphthalimide chromophores: Synthesis, theoretical, the effect of phenyl substitution on aggregation-induced enhanced emission and second-order nonlinear optical studies

A new ferrocene appended linear donor-π-acceptor (D-π-A) type 1,8-naphthalimide chromophores [FcPhNap-n-butyl (1) and Fc(Ph)2Nap-n-butyl (2)] have been synthesized and characterized using various analytical and spectroscopic techniques. The chromophores 1 and 2 show the one-electron transfer process, which was examined through cyclic voltammetric (CV) method. The solvatochromic studies show red shift by increasing the solvent polarity from non-polar to polar for both the chromophores 1 and 2, due to the better stabilization of the more polarized excited state than the ground state in the polar solvent. The fluorescence studies show low fluorescence emission, which was enhanced by aggregation in THF/water mixture when the water ratio is increased upto 60%, due to the restricted intramolecular rotation (RIR) process in the aggregated state. Also, the quantum yield increases 3.4 (1) and 6.8 (2) times in the aggregation induced enhanced emission (AIEE) state than THF solution for both the chromophores [THF/AIEE = 0.05/0.17 for 1 and 0.03/0.22 for 2]. The second-order non-linear optical properties of the chromophores 1 and 2 were studied using Kurtz and Perry powder technique, chromophore 2 shows 1.2 times higher SHG efficiency than 1, owing to the presence of additional phenyl group in 2, which further supports the effective charge transfer process from donor to acceptor. Furthermore, optical and non-linear optical properties of chromophores 1 and 2 were analyzed by DFT/TD-DFT calculations using different functionals (B3LYP, long-range corrected CAM-B3LYP and LC-BLYP) with 6–31+G** level of theory. The B3LYP functional shows higher hyperpolarizability values [β0 = 109.2 × 10-30 esu (1), 299.7 × 10-30 esu (2)], due to the overestimation of the dipole moment, polarizability and hyperpolarizabilities between the donor–π–acceptor systems in B3LYP-hybrid functional, which leads to incorrect long-range charge transfer.

Chitosan-salicylide Schiff base with aggregation-induced emission property and its multiple applications

Aggregation-induced emission (AIE) active compounds are fascinated due to their unique properties of limiting intramolecular rotation, and they have been developed in the biomedical fields. In this work, AIE material based on the Schiff base compound of chitosan (Cs) and salicylaldehyde (SA) was designed and synthesized. Cs-SA emits weak light in dilute aqueous solution, and emits bright light in concentrated solution and solid, showing obvious AIE performance. In addition, Cs-SA can also be used as a biosensor to detect Fe3+, and Cu2+, it has good bioimaging behavior. In addition, it can also be used as biosensor to quantitatively detect gram-positive bacteria and gram-negative bacteria, Moreover, Cs-SA shows excellent broad spectrum antibacterial performance in inhibiting E. coli and S. aureus.

Precise probe design based ESIPT coupled AIE mechanism toward endogenous cyanide in food detection and bioimaging

Cyanide (CN–) is one of the strongest and fastest-acting toxic substances, and its excessive presence will cause great harm to the environment, food and human health. Although several fluorescent probes that recognize CN– have been extensively reported, developing the fluorescent probe with aggregation-induced emission (AIE) and large Stokes shift is still an extremely difficult problem due to lack of effective strategies. Thus, continuing efforts to seek novel, structurally distinct and functionally specific structures with large Stokes shift and AIE features are highly anticipated. Herein, we design and synthesize a novel asymmetric bis-Schiff base block (named as HPBC) based on the excited state intramolecular proton transfer (ESIPT) and AIE mechanism. Benefiting from restriction of intramolecular rotation and –CN electron-withdraw nature promoting the ESIPT effect of HPBC in the recognition system, HPBC shows large Stokes shift (243 nm), high selectivity, rapid identification of CN– and AIE effects. Excitingly, the limit of detection (LOD) was calculated to be 1.32 × 10-7 M, which was much lower than the 1.9 × 10-6 M specified by the World Health Organization and better than other previously reported probes. More importantly, further investigations demonstrated that the molecule we designed was successfully applied to sense endogenous CN– in food samples and the low cytotoxicity of HPBC was allowed to discover CN– in C. elegans, mice and HeLa cells. Overall, this work provides a new viewpoint of the rational design and synthesis of fluorescent probe toward CN– with AIE and large Stokes shift features, and triggers the discovery of new functions and properties of biological materials, which would open a new frontier for probes.

Tetraphenylethylene-embedded pillar[5]arene-based orthogonal self-assembly for efficient photocatalysis in water.

Herein, we have designed and fabricated a simple and efficient supramolecular self-assembled nanosystem based on host–guest interactions between water-soluble tetraphenylethylene-embedded pillar[5]arene (m-TPEWP5) and ammonium benzoyl-ʟ-alaninate (G) in an aqueous medium. The obtained assembly of m-TPEWP5 and G showed aggregation-induced emission (AIE) via the blocking of intramolecular phenyl-ring rotations and functioned as an ideal donor. After the loading of eosin Y (EsY) as acceptor on the surface of the assembly of m-TPEWP5 and G, the worm-like nanostructures changed into nanorods, which facilitates a Förster resonance energy transfer (FRET) from the m-TPEWP5 and G assembled donor to the EsY acceptor present in the nanorod assembly. The system comprising m-TPEWP5, G and EsY displayed moderate FRET efficiency (31%) at a 2:1 molar ratio of donor-to-acceptor. Moreover, the obtained supramolecular nanorod assembly could act as a nanoreactor mimicking natural photosynthesis and exhibited a high catalytic efficiency for the photocatalytic dehalogenation reaction of various bromoketone derivatives with good yields in short reaction time in water.

An AIEgen/graphene oxide nanocomposite (AIEgen@GO)-based two-stage "turn-on" nucleic acid biosensor for rapid detection of SARS-CoV-2 viral sequence.

The ongoing outbreak of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS‐CoV‐2) pandemic has posed significant challenges in early viral diagnosis. Hence, it is urgently desirable to develop a rapid, inexpensive, and sensitive method to aid point‐of‐care SARS‐CoV‐2 detection. In this work, we report a highly sequence‐specific biosensor based on nanocomposites with aggregation‐induced emission luminogens (AIEgen)‐labeled oligonucleotide probes on graphene oxide nanosheets (AIEgen@GO) for one step‐detection of SARS‐CoV‐2‐specific nucleic acid sequences (Orf1ab or N genes). A dual “turn‐on” mechanism based on AIEgen@GO was established for viral nucleic acids detection. Here, the first‐stage fluorescence recovery was due to dissociation of the AIEgen from GO surface in the presence of target viral nucleic acid, and the second‐stage enhancement of AIE‐based fluorescent signal was due to the formation of a nucleic acid duplex to restrict the intramolecular rotation of the AIEgen. Furthermore, the feasibility of our platform for diagnostic application was demonstrated by detecting SARS‐CoV‐2 virus plasmids containing both Orf1ab and N genes with rapid detection around 1 h and good sensitivity at pM level without amplification. Our platform shows great promise in assisting the initial rapid detection of the SARS‐CoV‐2 nucleic acid sequence before utilizing quantitative reverse transcription‐polymerase chain reaction for second confirmation.

Fluorescent properties of a cage-shaped molecule composed of tetrakis[4-(4-pyridylphenyl)]ethylene moieties

A metallosupramolecular cage-shaped compound (TPPE-p) was synthesized by coordination of tetrakis[4-(4-pyridylphenyl)]ethylene (TPPE), obtained by the coupling reaction between tetrakis(4-bromophenyl)ethene and 4-pyridylboronic acid, with Pt(II) and terephthalate. Although TPPE showed no fluorescence in the solution, weak fluorescence was observed in the TPPE-p solution. When the volume ratio of poor solvent in the TPPE-p solution increased, the fluorescence intensity was dramatically enhanced. The difference in the fluorescence intensities was explained by the degree of intramolecular rotation of the substituents, and TPPE-p was found to show aggregation-induced emission.