Monomolecular-layer assembly of oligothiophene on glass wafer surface and its fluorescence sensitization by formaldehyde vapor

Film Nanoarchitectonics of Pillar[5]arene for High-Performance Fluorescent Sensing: a Proof-of-Concept Study

Substrates play crucial roles for the sensing performances of fluorescent films owing to their effect on the formation of a fluorescent adlayer. However, no such film has been developed through synthesizing a substrate with a defined structure. We herein report a kind of self-standing, uniform, and thickness tunable pillar[5]arene-based nanofilms to serve as substrates for fabricating fluorescent sensing films. In comparison with a glass plate, the pillar[5]arene-based nanofilms can ensure spatial and electronic isolation of immobilized fluorophores and circumvent aggregation-caused quenching in a film state. For conceptual proof, a formic acid fluorescent sensing film was developed through simple loading of a fluorophore, a 4-azetidine-1,8-naphthalimide derivative of cholesterol (NA-Ch), onto the prepared nanofilm. Sensing performance studies demonstrated that the fluorescent film showed a sensitive, fast, and highly selective response to formic acid in air with a detection limit of lower than 2.8 mg m^-3 and a response time of less than 3 s. Moreover, the sensing is fully reversible and highly repeatable. Further studies showed that the film sensor can be used for fast determination of methanol acidity via vapor sampling. Clearly, innovation of substrates with defined structures can be taken as an effective and efficient way to develop new sensing films via combination with known fluorophores.

Flexible and Transparent Oligothiophene-o-Carborane-Containing Hybrid Films for Nonlinear Optical Limiting Based on Efficient Two-Photon Absorption

Structure-property relationship for fluorophores with favorable nonlinear optical (NLO) properties are promising topics in organic chemistry and material science. Herein, a series of terthiophene-o-carborane dyads and triads covalently linked with different end-capping styles were readily synthesized and comprehensively investigated. Quantitative values of the crystal and packing structures, photophysical parameters including aggregation-induced emission (AIE) and two-photon absorption (2PA) were provided. Significant impact of carborane unit for introducing the AIE characteristic has been investigated in contrast to the parent oligothiophene. All the obtained fluorophores exhibit maximum absorption around 370 nm in THF and emit bright reddish photoluminscence with absolute fluorescence quantum yields above 16% in solid states. Intramolecular charge communication between oligothiophene and carborane plays important roles in the related NLO properties. These results are supported well by the time-dependent DFT theoretical calculations. Effective 2PA cross sections (δ_2PA = 95-355 GM@650 nm) and transition dipole moments of the derivatives are variable for different end-capping styles. Their potential applications as optical limiting materials based on the 2PA mechanism in solutions and doped PDMS films were further evaluated. Taken together, this work provides an understanding of their structure-property relationship, and flexible PDMS films as outstanding candidates for practical applications in optical limiting.

Dual-Mode Photonic Sensor Array for Detecting and Discriminating Hydrazine and Aliphatic Amines

Colorimetric chemosensors have attracted tremendous interest for sensing hazardous substances in an uncomplicated and economical manner. Herein, a series of push-pull dicyanovinyl-substituted oligothiophene derivatives were designed, and the impacts of different end-cappers on their photophysical properties were comprehensively investigated. Interestingly, combined with a zinc porphyrin derivative (Zn-TPP), one dicyanovinyl-substituted oligothiophene derivative (NA-3T-CN) can be further developed into colorimetric and fluorescent sensor array for dual-mode detection of aliphatic amines and hydrazine. The obtained sensors showed satisfactory results between optical response and analyte's concentration both in selective single-sensor type and in enhanced multisensory mode. Based on the fluorescence change of the NA-3T-CN system, the detection limit for N₂H₄ was calculated to be around 1.22 × 10^-5 mol/L in THF. The stained TLC-supported sensor array offers obvious optical changes for down to 0.5 wt % hydrazine solution for naked-eye sensing. An aromatic amine like aniline has no obvious effect on the dicyanovinyl-substituted oligothiophene derivatives. We also found that a zinc porphyrin derivative has an obvious colorimetric response to the presence of hydrazine, ethanolamine, and aniline. Furthermore, smartphone-enabled readout system and data treatment based on RGB changes of the sensor array were performed, and the discrimination capability among hydrazine, aliphatic amines, and aromatic amine was satisfactory. In this regard, related push-pull oligothiophene derivatives not only can be regarded as models for a fundamental understanding of the relationship between molecular structure and photophysical properties but also present potential applications in the field of real-time and visual detection of hazardous chemicals.

A biotin-guided formaldehyde sensor selectively detecting endogenous concentrations in cancerous cells and tissues

A biotin appended formaldehyde sensor was found to specifically visualise both exogenous and endogenous levels of formaldehyde in biotin receptor positive cells over biotin negative cells by means of one- and two-photon excitation. The probe furthermore visualised endogenous levels of formaldehyde in tumour tissue slices up to 70 μm depth.

Detection of gaseous amines with a fluorescent film based on a perylene bisimide-functionalized copolymer

A fluorescent copolymer containing PBI units and hydroxyl-ethyl structures was developed for the fast and sensitive detection of gaseous amines

Fluorescent probes and materials for detecting formaldehyde: from laboratory to indoor for environmental and health monitoring

Formaldehyde (FA), as a vital industrial chemical, is widely used in building materials and numerous living products.

Terthiophene derivatives of cholesterol-based molecular gels and their sensing applications

Three novel terthiophene derivatives of cholesterol (TtGC, TtLPC, TtDPC), of which the two building blocks are linked by a structure of glycine, l-phenylalanine, or d-phenylalanine, respectively, were designed and prepared, and their gelation behaviors in 26 liquids were tested. It was demonstrated that the compounds show different gelation abilities with the variation of the linker structures even though the variation is small. FTIR, (1)H NMR, and UV-vis measurements revealed that intermolecular hydrogen bonding and van der Waals interaction are the main driving forces for the gel formation. As for TtDPC, CD and AFM measurements revealed that it aggregated into chiral structures of left-helical feature in benzene. Importantly, the morphologies of the gel networks could be subtly adjusted via alteration of the gelator concentration. Considering the brightness in fluorescence and the unique micro/nanostructures of the gel networks, a fluorescent film (film 1) was fabricated by simple dip-coating of TtDPC/benzene solution (before gelation) onto a glass plate surface. Fluorescent studies demonstrated that the film is photochemically unstable. Two hours UV irradiation of the film results in film 2, which is almost fluorescent silence. However, the presence of HAc vapor or the vapors of some other volatile organic liquids induces new fluorescence emission, laying the foundation for creating a turn-on type fluorescent sensor of the organic vapors. Furthermore, as a new type of low-molecular-mass gelators (LMMGs), of which oligothiophene was employed as a building block, the present study has provided a possibility to explore the photo-/electronic applications of oligothiophenes via a molecular gel strategy.

Synthesis, optical properties and explosive sensing performances of a series of novel π-conjugated aromatic end-capped oligothiophenes

Four novel terthiophene (3T) derivatives, have been synthesized by employing Grignard coupling reaction via end-capping of naphthyl (NA) or pyrenyl (Py) unit to the one or two ends of 3T. It has been shown that both increasing electron donating strength and extending conjugation are effective approaches to improve the photochemical stability of the oligothiophene. Fluorescence studies demonstrated that the emission of the 3T derivatives is sensitive to the presence of some important nitro-containing explosives in their ethanol solution, in particular, 2,4,6-trinitrophenol (PA) and 3,5-dinitro-2,6-bispicrylamino pyridine (PYX). As an example, the detection limits of 4 to PA and PYX were determined to be 6.21 × 10(-7)mol/L and 8.95 × 10(-7)mol/L, respectively. Based on the discovery, a colorimetric detection method has been developed. The sensitive and selective response of the modified 3T to the explosives have been tentatively attributed to the adsorptive affinity of the compounds to the explosives, and to the higher probability of the electron transfer from the electron-rich 3T derivatives to the electron-poor nitro-containing explosives. No doubt, present study broadens the family of fluorophores which may be employed for the development of fluorescent sensors.

Photochemical stabilization of terthiophene and its utilization as a new sensing element in the fabrication of monolayer-chemistry-based fluorescent sensing films

To improve the photochemical stability of α-terthiophene (3T) in air, we purposely introduced a naphthalene unit into its conjugated backbone, resulting in a fluorescent compound, 5-(1-naphthyl)-2,2':5',2''-terthiophene (NA-3T). The compound was further employed as a sensing element for the fabrication of a monolayer-chemistry based fluorescent sensing film. It was demonstrated that the fabricated film is highly sensitive and selective to the presence of picric acid (PA). The detection limit was found to be 3.2 × 10(-7) mol/L. The high sensitivity of the film to PA has been attributed to the specific binding of the film to the analyte because of proton transfer from PA to the amino group in the spacer, which is in accordance with the static nature of the quenching as revealed by fluorescence lifetime measurements. Further experiments demonstrated that the sensing process is fully reversible and free of interference from common organic solvents, acids and bases, etc. In addition, the film is stable, at least, within half a year provided it is properly preserved. More importantly, the present work makes it possible to use oligothiophenes as a new class of sensing elements, which may combine the advantages of conjugated polymers or oligomers and those of fluorescent compounds of low-molecular masses. This effort enlarges, definitely, the applications of oligothiophenes and the space for creating monolayer-chemistry based fluorescent sensing films.