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Dimorphic biphenyl based Michael addition product displayed AIE in ethanol–water system and solid state owing to its highly twisted conformation. The quasi-isostructural nature of the two polymorphs resulted in identical photo-physical behaviours.

Carbon dots (CDs) are class of carbon based nanomaterials with excellent optical properties. However, in solid state the fluorescence of CDs is not observed due to aggregation-caused quenching effect. Herein, we present a facile thermal method for preparing solid state yellow emissive nitrogen doped carbon dots (N-CDs) using organic solvents, ethanolamine and acrylonitrile as the precursors without further surface passivation. In addition, N-CDs aqueous dispersion exhibits tunable blue to green emission, while acetone dispersion show yellow emission. Moreover, the aqueous dispersion of N-CDs is employed for detecting picric acid selectively by fluorescence quenching mode based on inner filter effect. A good linearity is observed in the range from 0 to 45 μM, with a detection limit of 1.17 μM. The method is successfully applied for determination of picric acid in environmental samples.

A nanoemulsion is a colloidal dispersion that contains very small particles with size in the range of 20-200 nm, which may be of the oil-in-water (O/W) or water-in-oil (W/O) types depending on whether the oil is dispersed as droplets in water or vice versa. Pesticides play a critical role in controlling agriculture and ensuring food safety. In the future, the utilization of pesticides will become even more important to solve food security problems associated with providing an adequate food supply for the growing world population. Hence, development of new techniques for nanoemulsions formulation in the field of agriculture and forestry are necessary. In this chapter, the synthesis, characterization, and application of nanoemulsion in pesticides formulation are reviewed. In addition, the effect of antifungal or insecticidal and antimicrobial enhancement activity of nanoemulsions with size, composition, and stability are also discussed.

Metal free room temperature phosphorescent materials have been the subject of considerable attention due to their potential applications in optoelectronic devices sensing, and security and safety signage. This study discusses how efficient fluorescent and phosphorescent chlorine doped carbon nitride dots (Cl-CNDs) were prepared by thermal treatment of guanidine hydrochloride. The Cl-CNDs prepared were characterized by field emission scanning electron microscope, dynamic light scattering, PXRD, EDX, Thermo gravimetric analysis, FT-IR, and UV-Visible spectroscopy. The Cl-CNDs exhibit a long phosphorescence lifetime of 657 ms and the phosphorescence quantum yield was found to be 2.32% upon being excited at 360 nm in ambient conditions. Formation of compact coreparticles via condensation along with hydrogen bonding of Cl-CNDs by its functional groups facilitate intersystem crossing and stabilizes the triplet states, favoring room temperature phosphorescence. The cost effective preparation and tunable optical properties of Cl-CNDs may find applications in security encryption and optoelectronic devices.

Materials having long afterglow are highly sought after for various applications such as light-emitting diodes, security signs and bioimaging. Herein, we report a simple, low-cost synthesis of a purely organic room-temperature phosphorescent nanomaterial with a pebble-like structure by heating urea, a biocompatible and easily available precursor, at 200 °C with a high phosphorescence lifetime of 1.0365 s and a visible afterglow for up to 10 s. This urea derived phosphorescent nanocomposite (UPNC) can be mixed with commercially available acrylic paint base and common gum, which can be readily used as a phosphorescent pigment.

Different metal ions and anions are crucial for the life of organisms, but their excessive intake or deficiency cause various physiological abnormalities or diseases. Toxic metal ions such as Hg2+, Cr6+, Cd2+, explosive nitroaromatic compounds, and volatile organic compounds are widely used in agriculture, rocket fuels, and industry, but they cause severe effects on human health and environmental change. Hence, sensing and identification of these analytes are important for life, health, and environment protection. Recently, metal-organic frameworks (MOFs) have been extensively explored as luminescent sensors due to their unique crystallinity, structural diversity, tunable porosity, and functional groups. This chapter reviewed the origin of luminescent of MOFs and its applications as luminescent sensors for detecting different environmentally toxic analytes such as metal ions, anions, nitroexplosives, and volatile organic compounds. In addition, the detection mechanism of MOFs and its structural dependent properties are also illustrated.

Carbon nitride materials have become highly explored carbon based nanomaterials since their rediscovery in the 1990s due to their semiconductor like behavior. Here, we report a facile one pot synthesis of sulfur and oxygen doped carbon nitride quantum dots (SCNQDs) from thiourea and ethylenediaminetetraacetic acid disodium salt by a thermal method. The SCNQDs prepared are characterized by UV–visible, FT-IR, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction, and transmission electron microscopy (TEM) imaging. We have demonstrated the Hg2+ sensing ability of SCNQDs in solution as well as in the solid phase, i.e. SCNQDs loaded onto filter paper. The Hg2+ sensing capability of the SCNQDs in the solution phase is the same for Hg2+ ion in double distilled water as well as in tap water, which gives the method a practical applicability in real conditions. The sensitivity of SCNQDs with Hg2+ follows a linear relationship in the range from 10 nM to 1 μM. The minimum detection limit is found to be 0.0...

A series of three biphenyl-based Knoevenagel products (denoted 1a, 1b, 1c) with active methylene groups has been synthesized. Compounds 1a and 1b show strong solid-state fluorescence, whereas 1c displays low emission. Effects of substituent groups in condensed phase packing of the molecules have been investigated and correlated with their photophysical properties. Interestingly, compound 1a exhibits mechanofluorochromism with emission color changes from yellow to green (wavelength shift of 40 nm) after mechanical grinding. Furthermore, fluorescence of 1a and 1b is turned off under alkaline conditions, making them potential candidates for aggregation-enhanced emission-based pH sensors.

Due to improper garbage disposal and rapid industrialization, concentrations of different metal ions are rising to toxic levels in natural water sources. Development of novel, selective and sensitive sensors for different metal ions is in high demand for rapid detection and remediation. Herein, we report nitrogen-doped carbon dots (NCDs) with high blue fluorescence, synthesized by a new one-step pyrolytic method using urea and ethylenediaminetetraacetic (EDTA) acid as precursors. The NCDs were used for parallel detection of Hg2+ and Cu2+ ions in aqueous medium through a fluorescence ON–OFF–ON process. The minimum detection limit for Hg2+ and Cu2+ were 6.2 nM and 2.304 nM, respectively, in aqueous medium, which is close to or below the allowed levels of Hg2+ and Cu2+ ions, i.e., 6 ppb and 2 ppm, respectively, in drinking water as per World Health Organisation (WHO). Hg2+ and Cu2+ ions were discriminated with vitamin C (ascorbic acid) and trisodium citrate by a fluorescence turn on process. A filter paper based microfluidic device loaded with NCDs, vitamin C and trisodium citrate was developed using candle wax channels on a filter paper as a proof of principle, projecting NCDs as a promising material for parallel detection of multiple metal ions. The device demonstrated herein is capable of detecting Hg2+ and Cu2+ ions up to 0.1 μM. This simple, low cost, disposable paper-based device will be very useful for rapid onsite analysis.