Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

An unusual behavior of some organic luminophores in which intensity of emission is enhanced in aggregated condition is known as aggregation induced emission (AIE). The exposure of this concept to the scientific community significantly changes the perception towards conventionally used photophysical phenomena. Due to the high quantum yield and tunable emission properties, AIE luminogens (AIEgens) have become promising candidates for biosensors, opto-electronics and energy applications. The excellent stimuli responsiveness of AIE luminogens (AIEgens) provides them with a key edge for sensitive measurements such as intracellular temperature, pH, etc. In recent times the immense research interest in the AIE phenomenon stems from the inherent solid-state emission as well as its constructive effect on many other phenomena such as mechanochromism, thermally activated delayed fluorescence and circularly polarized luminescence. Many AIE fluorophores readily exhibit mechanochromism but still their interaction with external stimuli results in aggregation caused quenching (ACQ). However, the latest reports shed some light on designing and developing mechanochromophores with enhanced emission. With the inclusion of bright emission, photostability, great signal to noise ratio and non-invasiveness into one package of aggregation induced emission, a significant contribution for the enrichment of the field of photodynamic therapy and theranostics can be foreseen. Hence, the aim of this review is to provide a comprehensive study on recent developments in AIE materials and their mechanochromic, photodynamic therapeutic and theranostic, sensing and electroluminescence applications which offers new possibilities to utilize AIE materials. This review article is devoted to future research perspectives and challenges towards the development of AIE materials for modern technological and therapeutic applications.

Review on new horizons of aggregation induced emission: from design to development

Metal organic gels (MOGs) as a new type of porous soft-hybrid supramolecular material have attracted widespread interest in various aspects due to their unique optical properties. In this work, we report a novel electrochemiluminescence (ECL) emission (679 nm) lanthanide MOG, which has been synthesized by a simple and rapid method at room temperature. This MOG (Tb-Ru-MOG) consists of a central metal ion, terbium (III), and two different ligands, tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium (II) dichloride (Ru(dcbpy)32+) and 4'-(4-carboxyphenyl)-2,2':6',2″-terpyridine (Hcptpy). Compared with the classic system of tris(2,2'-bipyridyl) ruthenium (II) dichloride (Ru(bpy)32+)/S2O82-, Tb-Ru-MOG/S2O82- owns a narrower potential sweep range (0.00 to -0.85 V) and a more stable and stronger ECL signal. Interestingly, the ECL intensity only decreased 2.0 and 0.1% after continuous scanning for 8000 s and storing at room temperature for 3 months. The possible ECL mechanism has been discussed in detail, which is mainly attributed to the internal synergies (antenna effect and energy transfer) and external co-reactant. Inspired by the unique luminescence characteristics of Tb-Ru-MOG, the application in electroanalytical chemistry was identified by the ECL on-off response for epinephrine with a linear range from 1.0 × 10-10 to 1.0 × 10-3 mol·L-1 and a detection limit of 5.2 × 10-11 mol·L-1. The results suggest that the as-proposed Tb-Ru-MOG will provide a robust pathway for new ECL luminophores in analysis.

A Superstable Luminescent Lanthanide Metal Organic Gel Utilized in an Electrochemiluminescence Sensor for Epinephrine Detection with a Narrow Potential Sweep Range.

A new class of white luminescent materials, white-light-emitting graphene quantum dots (WGQDs), have attracted increasing attention because of their unique features and potential applications. Herein, we designed and synthesized a novel WGQDs via a solvothermal molecular fusion strategy. The modulation of chlorine doping amount and reaction temperature gives the WGQDs a single-crystalline structure and bright white fluorescence properties. In particular, the WGQDs also exhibit novel and robust white phosphorescence performance for the first time. An optimum fluorescence quantum yield of WGQDs is 34%, which exceeds the majority of reported WGQDs and other white luminescent materials. The WGQDs display broad-spectrum absorption within almost the entire visible light region, broad full width at half maximum and extend their phosphorescence emission to the entire white long-wavelength region. This unique dual-mode optical characteristic of the WGQDs originates from the synergistic effect of low-defect and high chlorine-doping in WGQDs and enlarges their applications in white light emission devices, cell nuclei imaging, and information encryption. Our finding provides us an opportunity to design and construct more advanced multifunctional white luminescent materials based on metal-free carbon nanomaterials.

White luminescent single-crystalline chlorinated graphene quantum dots

An alkoxy-substituted 1,3-indanedione-based chemodosimeter 1 with an aggregation-induced emission (AIE) characteristic was rationally designed and synthesized for the ultrasensitive and selective sensing of cyanide in a wide pH range of 3.0-12.0. The nucleophilic addition of cyanide to the β-conjugated carbon of the 1,3-indanedione group obstructs intramolecular charge transfer (ICT) and causes a significant change in the absorption and fluorescence spectra, enabling colorimetric and ratiometric fluorescent detection of cyanide in a 90% aqueous solution. The cyanide-sensing mechanism is supported by single-crystal X-ray diffraction analysis, time-dependent density functional theory (TD-DFT) calculations, and 1H NMR titration experiments. Sensor 1 exhibits strong yellow fluorescence in the solid state due to the AIE effect, and the paper probes containing 1 can be conveniently used to sense cyanide by the naked eye. Furthermore, chemodosimeter 1 was successfully used for sensing cyanide in real environmental water samples.

Rational Design of an ICT-Based Chemodosimeter with Aggregation-Induced Emission for Colorimetric and Ratiometric Fluorescent Detection of Cyanide in a Wide pH Range.

Designing fluorescent molecular probes with longer wavelength emission (above 600 nm) features towards exclusive detection of CN− ion is highly challenging and rarely found in the field of fluorescent sensors. The contribution here reports a unique chemodosimetric design approach for selective sensing of CN− ion, in both solution and solid states. Towards this, we have utilized an orange emitting fluorescent probe (R1) (λ emission > 600 nm), where the fluorophore is threaded by a fluorene derivative. The bulky fluorine unit regulate the interaction between the fluoropore units to minimize aggregation caused quenching (ACQ). Upon introducing CN− ion, even in the presence of several other ions, intramolecular charge transfer (ICT) from the donor (phenothiazine) to the acceptor (cyanovinyl unit) was completely blocked in the covalently threaded fluorescent moiety and as a result the fluorescence was completely quenched. More importantly, the present system retained its fluorescence properties in the solid state and hence was utilized to detect CN− ion in the solid state through fluorescence quenching mechanism, which enabled the fabrication of a test kit for on-site analysis of CN− ion. DFT and TD-DFT calculations towards validating the experimental results were also performed in order to study the changes caused in the electronic properties of R1 before and after complexation with CN− ion.

Orange emitting fluorescence probe for the selective detection of cyanide ion in solution and solid states

Fine tuning the optical properties of lanthanide-based gels using low molecular weight gelators has several advantages over the polymeric gelator analogues. Herein, we have prepared a lanthanide-based gel using low molecular weight citric acid as the assembler ligand and the optical properties of the gel were fine-tuned, utilizing a mixed ligand approach, enabling white light emission and environmental sensing (pH and temperature). The coligand utilized in the study was 4'-(4-bromophenyl)-2,2':6',2''-terpyridine. The resultant mixed-ligand gel exhibited green and red emissions in the presence of Tb(iii) ions and Eu(iii) ions, respectively. White light emission was achieved, with CIE coordinates (0.33, 0.32), in the bimetallic Tb/Eu metallogel formed by the precise control over Tb/Eu ratio. The correlated color temperature (CCT) for white-light-emitting gel was calculated, and the value of 5473 K suggests that the system generates cool white light. While most of the reported low molecular weight gelators exhibit on-off responses to stimulus at a particular value, the present system is capable of gradually monitoring changes for stimuli such as pH and temperature over a wide range (pH from 4-11 and temperature from 20 to 70 °C). The unique design strategy of the gel and the characteristic physicochemical properties of the lanthanide ions resulted in the unprecedented ability of the system to monitor changes in environmental stimuli over a considerable range.

A mixed ligand approach towards lanthanide-based gels using citric acid as assembler ligand: white light emission and environmental sensing

Organic materials exhibiting mechano-fluorochromic behavior in their gel state are extremely rare in the literature. Similarly, examples of mechano-fluorochromic organic materials with crystal-to-c...

Phenothiazine Based Mechano-fluorochromic Gels and Solids: Superhydrophobic Surface Formation and Crystal-to-Crystal Phase Transition

Semiconductor quantum dot (QD)–graphene composites are promising materials for photovoltaics and photocatalysis because of efficient charge extraction and transport property of graphene. Analysis o...

Enhanced Charge Transport and Excited-State Charge-Transfer Dynamics in a Colloidal Mixture of CdTe and Graphene Quantum Dots

Graphdiyne, a recent addition to the family of 2D covalent organic nanosheet structures, is known for its structural stability and potential applications in catalysis, sensors, electronics and optoelectronics. The design and synthesis of graphdiyne analogues with well-defined structures and useful applications remains a challenging task for materials chemists. Herein, we report a novel, well-defined 2D nanosheet from a coronene–pyrene hybrid 2D material (COPY), with extended π conjugation through acetylenic linkages. The bulk synthesis of the polymeric network has been realized via Sonogashira coupling of 1,4,7,10-tetrabromocoronene and 1,3,6,8-tetraethynylpyrene. The nanosheet is characterized using HR-SEM, TEM, AFM, FT-IR, Raman, XRD and XPS techniques. Electrostatic potential mapping of COPY reveals complete π electron delocalization over the 2D framework with a relatively high electro-negative potential at the acetylenic linkages. Computational study reveals the high planarity of the structure as a result of Cs point group symmetry and the material has a tunable bandgap with respect to the number of coronene and pyrene rings. Extended conjugation in the material accounts for the significant electrical conductivity (1.16 × 10−3 S m−1) that is one order of magnitude higher than that of graphdiyne and comparable to the previously reported pyrediyne (a graphdiyne analogue). The large surface area and porous nature of the material were utilized for oil–water separation by incorporating melamine sponge and cotton fabric. The COPY-incorporated cotton fabric exhibited an oil–water separation efficiency of 95.5%. More importantly, the COPY in the melamine sponge exhibited superhydrophobicity with a contact angle of 154.4°. The oil–water separation efficiency, significant electrical conductivity and superhydrophobicity of the material suggest that COPY can be a valuable candidate in the field of water repellency, anti-corrosion and biosensing.

Malay Krishna Mahato

Papers

Orange emitting fluorescence probe for the selective detection of cyanide ion in solution and solid states

A mixed ligand approach towards lanthanide-based gels using citric acid as assembler ligand: white light emission and environmental sensing

Phenothiazine Based Mechano-fluorochromic Gels and Solids: Superhydrophobic Surface Formation and Crystal-to-Crystal Phase Transition

Enhanced Charge Transport and Excited-State Charge-Transfer Dynamics in a Colloidal Mixture of CdTe and Graphene Quantum Dots

Conducting and superhydrophobic hybrid 2D material from coronene and pyrene