Search

An organelle-selective vision provides insights into the physiological response of plants and crops to environmental stresses in sustainable agriculture ecosystems. Biological applications often require two-photon excited fluorophores with low phototoxicity, high brightness, deep penetration, and tuneable cell entry. We obtained three aniline-based squaraines (SQs) tuned from hydrophobic to hydrophilic characteristics by modifying terminal pendant groups and substituents, and investigated their steady-state absorption and far-red-emitting fluorescence properties. The SQs exhibited two-photon absorption (2PA) ranging from 750 to 870 nm within the first biological spectral window; their structure–property relationships, corresponding to the 2PA cross sections (δ2PA), and structure differences were demonstrated. The maximum δ2PA value was ∼1220 GM at 800 nm for hydrophilic SQ3. Distinct biological staining efficiency and selective SQ bioimaging were evaluated utilizing the onion epidermal cell model. Contrary to the hydrophobic SQ1 results in the onion epidermal cell wall, amphiphilic SQ2 tagged the vacuole and nucleus and SQ3 tagged the vacuole. Distinguishable staining profiles in the roots and leaves were achieved. We believe that this study is the first to demonstrate distinct visualisation efficiency induced by the structure differences of two-photon excited SQs. Our results can help establish the versatile roles of novel near-infrared-emitting SQs in biological applications. [ABSTRACT FROM AUTHOR]

Naphthalimide derivatives composed of donor–acceptor type structures hold significant promise across a wide range of applications. Here, the solvent polarity and viscosity controlled excited-state dynamics of a naphthalimide derivative with a donor–acceptor structure were studied using multiple spectroscopic techniques. From the stationary spectroscopic investigations, large Stokes shift and low fluorescence quantum yield were observed with increasing the solvent polarity, suggesting a more polar excited state relative to the ground state, which is evidenced by the Lippert–Mataga relationship. We also observe an enhanced fluorescence with a prolonged lifetime in a more viscous solution due to the restriction of excited-state molecular rearrangement. These observations result from the emerged twisted intramolecular charge transfer (TICT) state. The ultrafast spectroscopy studies further unravel a solvent polarity dependent excited state evolution from the intramolecular charge transfer state to the TICT state, revealing that the TICT state can be populated only in strong polar solvents. Control experiments by tuning the solvent viscosity in ultrafast experiments were employed to verify the excited state molecular rearrangement subsequently. These observations collectively emphasize how fine-tuning the photophysical properties of naphthalimide derivatives can be achieved through strategic manipulation of solvent polarity and viscosity. [ABSTRACT FROM AUTHOR]

Photo-involving aryl halide activation plays a pivotal role in organic synthesis and materials science. Revealing the mechanism and understanding the photophysical and photochemical processes in the activation is of great importance. Here, we found that aryl halides could be directly activated to form aryl radicals via halogen bonding under visible light irradiation without using photocatalysts or high power light. The interaction between the aryl halide and Lewis base (Et3N), as well as the triplet state formation, play crucial roles. Halogen bonding between aryl halide and Et3N facilitates intersystem crossing (ISC) and leads to an abundance of the triplet aryl halide/Et3N complex, where the carbon–halogen bond is much lengthened and prone to fracture. Therefore, visible light-driven photoredox catalyst-free C–C coupling reaction and radical-initiated polymerization were achieved. Avoiding the use of a catalyst not only brings convenience for low-cost operation, but also facilitates further purification. Meanwhile, the wide scope of aryl halide tolerance provides opportunities for chemical synthesis and polymerization. [ABSTRACT FROM AUTHOR]

Dynamic covalent ionic liquid (IL) gels have been proved to be promising materials for soft optical devices which possess the advantages of other dynamic gels but avoid shrinking. The focal length of the planoconvex lens made from the gels is tunable and the prism from them shows an excellent beam splitting property. Damaged devices could be re-covered via self-healing or re-molding. [ABSTRACT FROM AUTHOR]

Host–guest interaction and chemical modification are found to be effective in tuning the formation of reductive species of perylene-bisimide (PBI) derivatives in DMF. Moreover, some of the PBI derivatives as synthesized produce radical anions in the solvent without the need of a base. [ABSTRACT FROM AUTHOR]

A perylene bisimide (PBI) derivative (C-PBI-Py) of pyrene (Py) and cholesteryl residue (C) possessing intra-molecular energy transfer properties and three reference compounds (C-Py, C-PBI, PBI-Py) were designed and synthesized, where C was introduced in order to enhance the solubility of the relevant compounds in organic solvents. UV-vis absorption, steady-state fluorescence, cyclic voltammetric and theoretical calculation studies revealed that: (1) the PBI unit and Py moiety of C-PBI-Py could act as two individual chromophores, (2) the excited state energy of Py could transfer to PBI within a single molecule of the compound, and (3) the PBI moiety of the compound tends to form aggregates and shows PBI excimer emission. Time-resolved and temperature-dependent emission spectroscopy studies revealed the presence of both H-type excimer and J-type excimer, and formation of them via either the Birks' scheme or the pre-formed scheme due to strong π–π stacking that was elucidated by concentration-dependent 1H NMR spectroscopy measurement. In addition, the studies also indicated that the energy transfer occurs via an electron exchange mechanism (Dexter scheme). Results of this study will be useful in the development of new solvatochromic and other environment-sensitive fluorophores based on alteration of intra-molecular energy transfer efficiency. [ABSTRACT FROM AUTHOR]

A fluorescent 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD) derivative of cholesterol (CTN) was designed and synthesized. The compound forms a 1 : 1 non-fluorescent complex with Hg2+ in a solvent mixture of water and ethanol. Based on this discovery, a detection method with a detection limit (DL) of ∼0.08 μM for Hg2+ was developed. The presence of other commonly found metal ions has little effect on the detection. Though Fe2+ and Cu2+ have some interference, it could be avoided by a simple oxidation or reduction procedure. Further studies revealed that the complex can be used for the turn-on detection of some organophosphorus pesticides (OPs), such as DDVP, glyphosate, chlorpyrifos, diazinon and phoxim, either in solution or film state. The DLs for the five OPs are 0.015, 0.018, 0.087, 0.098 and 0.113 μg mL−1 in solution, respectively. In addition, the compound as developed is interesting and attractive because it can sense the heavy metal ion and the OPs in a fast and sensitive manner. It is therefore believed that the developed method possesses the potential to be used for rapid on-site detection of hazardous chemicals. [ABSTRACT FROM AUTHOR]

A heterojunction of ZnO/porous GaN (ZnO/PGAN) was fabricated and directly applied to a diode-type humidity sensor. ZnO disks were loaded onto PGAN using a spraying process. The structure and surface morphology of the ZnO/PGAN were characterized using X-ray diffraction and scanning electron microscopy. The heterojunction displayed an excellent diode nature, which was investigated using photoluminescence spectra and I - V characteristics. The excellent transport capability of ZnO/PGAN contributes to enhanced electron transfer, and hence results in high sensitivity and quick response/recovery properties under different relative humidity (RH) levels. In the range of 12-96% RH, a fast sensing response time as low as 7 s and a recovery time of 13 s can be achieved. The simple design of a ZnO/PGAN based humidity sensor highlights its potential in various applications., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)