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Engineering a compact, near-infrared plasmonic nanostructure with integrated image-enhancing agents for combined imaging and therapy is an important nanomedical challenge. Recently, we showed that Au@SiO 2 @Au nanomatryoshkas (NM) are a highly promising nanostructure for hosting either T 1 MRI or fluorescent contrast agents with a photothermal therapeutic response in a compact geometry. Here, we show that a near-infrared-resonant NM can provide simultaneous contrast enhancement for both T 1 magnetic resonance imaging (MRI) and fluorescence optical imaging (FOI) by encapsulating both types of contrast agents in the internal silica layer between the Au core and shell. We also show that this method of T 1 enhancement is even more effective for Fe(III), a potentially safer contrast agent compared to Gd(III). Fe-NM-based contrast agents are found to have relaxivities 2× greater than those found in the widely used gadolinium chelate, Gd(III) DOTA, providing a practical alternative that would eliminate Gd(III) patient exposure entirely. This dual-modality nanostructure can enable not only tissue visualization with MRI but also fluorescence-based nanoparticle tracking for quantifying nanoparticle distributions in vivo, in addition to a near-infrared photothermal therapeutic response.

Sunscreens contain molecules with the ability to absorb and/or reflect UVA (ultraviolet A) and UVB (ultraviolet B) radiation, thereby preventing this radiation from reaching the epidermis or dermis. Their photo stabilities after exposure to UV radiation are well known and described, but there is little data on the stability of these filters after fluorescent indoors light radiation, such as from light emitted by commercial lamps present in homes and offices. Those lamps can expose people to varying levels of UVB, UVA, visible light, and IR (infrared). This study assesses the photostability of four different commercial products containing chemical sun filters after artificial UV and fluorescent irradiation, correlating the UVB and UVA absorption efficiencies of each product against the different types of radiation. The tested products were applied on a plate of polymethylmethacrylate (PMMA) and irradiated by a solar simulator with specific filters for UVA and UVB and a commercial fluorescent light source. According to the results, three formulations did not show photostability, suffering significant changes in their UV absorption spectra, and one of the selected formulations can be considered photostable. This reinforces the importance of conducting stability studies for sunscreen formulations in different conditions, including under artificial (indoor) light exposure., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Organic fluorophores with dual-state emission (DSE) are rare or difficult to observe because most of them display either aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ). Amazing works have been accomplished, yet most of the DSE compounds were excited by UV light which limits their wide application in bioimaging. In this work, we achieved a visible-light excited DSE fluorophore and realized its imaging in SKOV-3 cells and zebrafish. The naphtho[2',3':4,5]imidazo[1,2-a]pyridine (NIP) core ensures its emission in dilute solution. Meanwhile, the twisted phenyl ring blocks fluorescence quenching induced by the π-π stacking and leads to the emission of the solid. The fluorescence intensity is steady even after 6 h of continuous intense sunlight. More importantly, photostability of NIP in cells is much better than commercial dye (mitochondrial green). [ABSTRACT FROM AUTHOR]

Gold nanoclusters (Au NCs) belong to a class of materials that is highly fluorescent and biocompatible. Bovine serum albumin (BSA) protected gold nanoclusters (BSA-Au NCs) have been extensively used in biological applications due to their easy synthesis and relatively high quantum yield. Therefore, understanding the behavior of BSA-Au NCs in different chemical and physical environments is essential to enhance their application in biological systems. In this study, we investigated the effect of plasmonic nanostructures with different localized surface plasmon resonance (LSPR) wavelengths on the behavior of BSA-Au NCs by recording time-dependent fluorescence spectra in the presence of silver nanoparticles (AgNPs) with various shapes. However, we did not observe any conclusive LSPR-wavelength-dependent fluorescent behavior. Additionally, the fluorescence intensity of BSA-Au NCs exhibited gradual decay under light excitation, even at several hundred μW/cm2 in a fluorescence spectrometer, indicating that they are not as photostable as previously assumed. We found further that the photostability of BSA-Au NCs is affected by the wavelength of the incident light (370, 420, 480, and 550 nm), which can be accurately described using bi-exponential decay functions. Our study provides an easy in situ method to evaluate the photostability of Au NCs under different-wavelength light irradiation using a commercial fluorescence spectrometer. [ABSTRACT FROM AUTHOR]

A series of new derivatives comprising heteropentacyclic 12H-quinoxalino[2,3-b]-phenoxazine (QOPO) system and functionalized with arylamide anchoring groups was synthesized. Their photostability as well as the spectral, luminescent, electrochemical, and optoelectronic properties were studied both in composites prepared by adsorption of QOPO onto the TiO2 surface and in solution. Attachment of the amide anchoring groups to the QOPO core provides high adsorption of the compounds and the onset of photovoltaic properties that were not observed in the unfunctionalized precursors. However, these groups do not provide efficient injection of excited electrons into the conduction band of the semiconductor. According to B3LYP/6-311++G(d,p) density functional calculations of the model nanoclusters QOPO/(TiO2)10, efficient electron injection and, as a consequence, high photovoltaic conversion efficiency of dye-sensitized solar cells require delocalization of the LUMO of the QOPO/TiO2 system over both structural fragments. Relevant anchoring groups are proposed. [ABSTRACT FROM AUTHOR]

The ability of P(V) phthalocyanines (Pcs) for efficient singlet oxygen (SO) generation was demonstrated for the first time by the example of unsubstituted and α- and β-octabutoxy-substituted P(V)Pcs with hydroxy, methoxy and phenoxy ligands in the apical positions of the octahedral P centre. Variation of substituents in Pc ring and P(V) axial ligands allows careful tuning of photophysical and photochemical properties. Indeed, a combination of BuO groups in the β-positions of the Pc ring and PhO groups as axial ligands provides significant SO generation quantum yields up to 90%; meanwhile, the values of SO generation quantum yields for others investigated compounds vary from 27 to 55%. All the complexes, except α-substituted P(V)Pc, demonstrate fluorescence with moderate quantum yields (10–16%). The introduction of electron-donating butoxy groups, especially in the α-position, increases the photostability of P(V)Pcs. Moreover, it has been shown in the example of β-BuO-substituted P(V) that the photostability depends on the nature of axial ligands and increases in the next row: OPh < OMe < OH. The presence of oxy/hydroxy axial ligands on the P(V) atom makes it possible to switch the photochemical and photophysical properties of P(V)Pcs by changing the acidity of the media. [ABSTRACT FROM AUTHOR]

• 4-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile. • Synthesis of peripherally tetra 4-((6-fluoro-2-methylquinolin-4-yl)oxy) substituted zinc(II) phthalocyanines and their water-soluble derivatives. • Investigation of photophysical and photochemical properties zinc(II) phthalocyanines and their water-soluble derivatives. The novel 4-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile (3a), 3-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile (3b), tetra 6-fluoro-2-methylquinolin-4-yl)oxy substituted zinc(II) phthalocyanines (4a and 4b) and their water soluble derivatives (5a and 5b) were prepared. The proposed structures of novel compounds were comfirmed via FT-IR, 1HNMR , UV–Vis and MALDI-TOF mass data. The aggregation tendency, fluorescence quantum yield, singlet oxygen quantum yield and photodegradation measurements were performed to examine the photodynamic therapy potential of both peripherally tetra substituted zinc(II) phthalocyanines (4a and 4b) and the water soluble quaternized tetra substituted zinc(II) phthalocyanines (5a and 5b). The result showed that both the novel tetra 6-fluoro-2-methylquinolin-4-yl)oxy substituted zinc(II) phthalocyanines (4a and 4b) and their water soluble derivatives (5a and 5b) could be used as photosensitizer agents in PDT thanks to their lack of aggregation tendency, having sufficient fluorescence emission for monitoring and produce high amount of singlet oxygen to destroy cancerous tissues and having moderate photostability. [Display omitted] [ABSTRACT FROM AUTHOR]

Chemical sensing in living systems demands optical sensors that are bright, stable, and sensitive to the rapid dynamics of chemical signaling. Lanthanide-doped upconverting nanoparticles (UCNPs) efficiently convert near infrared (NIR) light to higher energy emission and allow biological systems to be imaged with no measurable background or photobleaching, and with reduced scatter for subsurface experiments. Despite their advantages as imaging probes, UCNPs have little innate chemical sensing ability and require pairing with organic fluorophores to act as biosensors, although the design of stable UCNP-fluorophore hybrids with efficient upconverted energy transfer (UET) has remained a challenge. Here, we report Yb3+- and Er3+-doped UCNP-fluorophore conjugates with UET efficiencies up to 88%, and photostabilities 100-fold greater by UET excitation than those of the free fluorophores under direct excitation. Despite adding distance between Er3+ donors and organic acceptors, thin inert shells significantly enhance overall emission without compromising UET efficiency. This can be explained by the large increase in quantum yield of Er3+ donors at the core/shell interface and the large number of fluorophore acceptors at the surface. Sensors excited by UET show increases in photostability well beyond those reported for other methods for increasing the longevity of organic fluorophores, and those covalently attached to UCNP surface polymers show greater chemical stability than those directly coordinated to the nanocrystal surface. By conjugating other fluorescent chemosensors to UCNPs, these hybrids may be extended to a series of NIR-responsive biosensors for quantifying the dynamic chemical populations critical for cell signaling.

Exploring and investigating the strategies to improve quantum efficiency and photostability of light‐emitting polymers in polymer light‐emitting diodes is significantly an important topic of research. Thus this study endeavours towards the determination of the role of molecular orbital energy levels of metal oxide nanoparticles on the performance characteristics of hybrid nanocomposites. This work attempts to vary the proportions of zirconium dioxide (ZrO2) nanoparticles in nanocomposites of poly[2‐methoxy‐5‐(2'‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV), which leads to a six‐fold enhancement of luminescence quantum efficiency and increased radiative recombination rate due to an appropriate energy level alignment. An improvement in photostability was also reported due to a reduction in polymer chain defects, inhibition of moisture intervention and most importantly, impediment of the photo‐oxidation by controlling the triplet exciton dynamics. Thus, efforts are made to validate the role of energy levels of ZrO2 nanoparticles in improving the luminescence quantum efficiency and photostability of MEH‐PPV compared to ZnO incorporated MEH‐PPV. [ABSTRACT FROM AUTHOR]

[Display omitted] • SHE-2N provides quick and stably stable labeling of plasma membrane. • No cytotoxicity detected for SHE-2N at concentrations used for imaging. • Suitable for STED nanoscopy and two-photon excitation microscopy. • SHE-2N offers high photostability. • Lipid composition does not affect emission or fluorescence lifetime of SHE-2N. Plasma membranes are vital biological structures, serving as protective barriers and participating in various cellular processes. In the field of super-resolution optical microscopy, stimulated emission depletion (STED) nanoscopy has emerged as a powerful method for investigating plasma membrane-related phenomena. However, many applications of STED microscopy are critically restricted by the limited availability of suitable fluorescent probes. This paper reports on the development of two amphiphilic membrane probes, SHE-2H and SHE-2 N , specially designed for STED nanoscopy. SHE-2 N , in particular, demonstrates quick and stable plasma membrane labelling with negligible intracellular redistribution. Both probes exhibit outstanding photostability and resolution improvement in STED nanoscopy, and are also suited for two-photon excitation microscopy. Furthermore, microscopy experiments and cytotoxicity tests revealed no noticeable cytotoxicity of probe SHE-2 N at concentration used for fluorescence imaging. Spectral analysis and fluorescence lifetime measurements conducted on probe SHE-2 N using giant unilamellar vesicles, revealed that emission spectra and fluorescence lifetimes exhibited minimal sensitivity to lipid composition variations. These novel probes significantly augment the arsenal of tools available for high-resolution plasma membrane research, enabling a more profound exploration of cellular processes and dynamics. [ABSTRACT FROM AUTHOR]

Gold nanoclusters (Au NCs) belong to a class of materials that is highly fluorescent and biocompatible. Bovine serum albumin (BSA) protected gold nanoclusters (BSA-Au NCs) have been extensively used in biological applications due to their easy synthesis and relatively high quantum yield. Therefore, understanding the behavior of BSA-Au NCs in different chemical and physical environments is essential to enhance their application in biological systems. In this study, we investigated the effect of plasmonic nanostructures with different localized surface plasmon resonance (LSPR) wavelengths on the behavior of BSA-Au NCs by recording time-dependent fluorescence spectra in the presence of silver nanoparticles (AgNPs) with various shapes. However, we did not observe any conclusive LSPR-wavelength-dependent fluorescent behavior. Additionally, the fluorescence intensity of BSA-Au NCs exhibited gradual decay under light excitation, even at several hundred μW/cm2 in a fluorescence spectrometer, indicating that they are not as photostable as previously assumed. We found further that the photostability of BSA-Au NCs is affected by the wavelength of the incident light (370, 420, 480, and 550 nm), which can be accurately described using bi-exponential decay functions. Our study provides an easy in situ method to evaluate the photostability of Au NCs under different-wavelength light irradiation using a commercial fluorescence spectrometer.

The complexes [AgL2]PF6 (I) and [ZnLCl2] (II) (L = 2-(3,5-dimethyl-1H-pyrazol-1-yl)-4,6-diphenylpyrimidine) were prepared by the reaction of zinc(II) chloride or silver(I) hexafluorophosphate with L (M : L molar ratio of 1 : 1 or 1 : 2) in organic solvents. The structure of the complexes was determined by X-ray diffraction (CIF file CCDC no. 2118498). In both complexes, L is coordinated in the bidentate chelating manner; the coordination unit is a distorted tetrahedron. The coordination unit of II is formed by one coordinated molecule L and two chloride ions (ZnN2Cl2); in the case of silver(I), there are two molecules L (AgN4). The photoluminescent properties of compounds I and II in the solid state were studied. The compound II shows fluorescence (1.3, 11 ns) in the blue spectral range (λmax = 378 nm; quantum yield of 7.8%). The maximum at 530 nm in the photoluminescence spectrum of I is red-shifted by ~140–160 nm relative to the emission maxima of L and II. The complex I shows white light emission (1.6, 11 ns, quantum yield of 5.5%), which is due to intraligand transitions perturbed by the coordination of L to the silver atom. The photostability of I was studied at 300 and 80 K. [ABSTRACT FROM AUTHOR]

Photobleaching is the permanent loss of fluorescence after extended exposure to light and is a major limiting factor in super‐resolution microscopy (SRM) that restricts spatiotemporal resolution and observation time. Strategies for preventing or overcoming photobleaching in SRM are reviewed developing new probes and chemical environments. Photostabilization strategies are introduced first, which are borrowed from conventional fluorescence microscopy, that are employed in SRM. SRM‐specific strategies are then highlighted that exploit the on–off transitions of fluorescence, which is the key mechanism for achieving super‐resolution, which are becoming new routes to address photobleaching in SRM. Off states can serve as a shelter from excitation by light or an exit to release a damaged probe and replace it with a fresh one. Such efforts in overcoming the photobleaching limits are anticipated to enhance resolution to molecular scales and to extend the observation time to physiological lifespans. [ABSTRACT FROM AUTHOR]

The ability of P(V) phthalocyanines (Pcs) for efficient singlet oxygen (SO) generation was demonstrated for the first time by the example of unsubstituted and α- and β-octabutoxy-substituted P(V)Pcs with hydroxy, methoxy and phenoxy ligands in the apical positions of the octahedral P centre. Variation of substituents in Pc ring and P(V) axial ligands allows careful tuning of photophysical and photochemical properties. Indeed, a combination of BuO groups in the β-positions of the Pc ring and PhO groups as axial ligands provides significant SO generation quantum yields up to 90%; meanwhile, the values of SO generation quantum yields for others investigated compounds vary from 27 to 55%. All the complexes, except α-substituted P(V)Pc, demonstrate fluorescence with moderate quantum yields (10–16%). The introduction of electron-donating butoxy groups, especially in the α-position, increases the photostability of P(V)Pcs. Moreover, it has been shown in the example of β-BuO-substituted P(V) that the photostability depends on the nature of axial ligands and increases in the next row: OPh < OMe < OH. The presence of oxy/hydroxy axial ligands on the P(V) atom makes it possible to switch the photochemical and photophysical properties of P(V)Pcs by changing the acidity of the media.

Polychlorinated pyridyldiphenylmethyl radicals having substituents meta to the position bearing the carbon‐centered radical (α‐carbon) are synthesized. All of them are stable in ambient conditions in solutions and fluorescent in cyclohexane. The fluorescence of the radicals with bromo, phenyl, 4‐chlorophenyl, or 2‐pyridyl substituents are enhanced in chloroform, while the emission of the radicals with 2‐thienyl or 2‐furyl substituents are quenched in chloroform. DFT and TD‐DFT calculations indicate that the first doublet excited states of the former are locally excited, while the first doublet excited states of the latter are charge transfer states from the π‐electron‐donating substituent to the accepting radical. The latter also show much higher photostability under 370‐nm light irradiation compared with the first reported photostable fluorescent radical, (3,5‐dichloro‐4‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl radical (PyBTM), with pronounced bathochromic shifts of the fluorescence. [ABSTRACT FROM AUTHOR]

The basic photophysical characteristics and the hydrolytic stability and photostability of dibenzoylmethanatoboron complexes containing various substituents at the boron atom have been studied. It has been found that the hydrolytic stability of these complexes increases in the order DBMBO < DBMBF2 < DBMB(C6F5)2. The rate constants of the hydrolysis reaction and the energy (EA), enthalpy (ΔH≠), and entropy (ΔS≠) of activation have been calculated from the data obtained. The study of the photostability of boron complexes of dibenzoylmethane showed that the photodegradation of these compounds in acetonitrile increases in the order DBMBF2 < DBMBO < DBMB(C6F5)2 and correlates with the change in ΔH≠ of hydrolysis. [ABSTRACT FROM AUTHOR]

In this study, photoswitchable fluorescent supramolecular metallacycles with high fatigue‐resistance have been constructed by coordination‐driven self‐assembly by using bithienylethene with dipyridyl units (BTE) as a coordination donor and a fluorescent di‐platinum(II) (Pt‐F) as a coordination acceptor. The photo‐triggered reversible transformation between the ring‐open and ring‐closed form of the metallacycles was confirmed by 1H NMR, 31P NMR, and UV/Vis spectroscopy. This unique property enabled a reversible noninvasive "off–on" switching of fluorescence through efficient Förster resonance energy transfer (FRET). Importantly, the metallacycles remained structurally intact after up to 10 photoswitching cycles. The photoresponsive property and exceptional photostability of the metallacycles posit their potential promising application in optical switching, image storage, and super‐resolution microscopy. [ABSTRACT FROM AUTHOR]

In this work, photostable coassemblies from a nonphotostable fluorene oligomer (the energy donor) and a photostable oligomer (the energy acceptor) are fabricated. Long‐range exciton migration over a net distance of about 370 energy‐donor molecules to energy acceptors is demonstrated in such coassemblies. The fast and long energy migration allows harvesting of the excitation energy of energy donors by embedding a small number of energy acceptors for photostability enhancement. Importantly, embedding a small number of energy acceptors in coassemblies causes a negligible negative influence on the electron donation of energy donors that are desired in practical applications. The advantages of the coassemblies fabricated, that is, high photostability without disrupting the electron donation of energy donors, are well illustrated in fluorescence detection of trace explosives where prolonged working life and improved detection capacity are achieved. [ABSTRACT FROM AUTHOR]

CuInS2 (CIS) quantum dots (QDs) are known to be ideal fluorophores based on their low toxicity and tunable emission. However, due to low quantum yield (QY) and photostability, the surface is usually passivated by a higher bandgap shell (e.g. ZnS). This always resulted in a blue-shifted emission position which is not usually favourable for biological imaging. To address this problem, we herein report the passivation of green synthesized near infra-red emitting glutathione (GSH) capped CuInS2 QDs using different concentration of sodium alginate (SA) at different temperatures. The as-synthesized QDs are small (~ 3.2 nm), highly crystalline and emitted in the near infra-red region. The optical results showed a 36% increase in photostability and a 2-fold increase in quantum yield at ratio 1:8 (SA: CIS) which is suitable for prolonged biological imaging applications. Transmission electron microscope and X-ray diffraction (XRD) analyses showed that the materials are highly crystalline without any change in shape and size after passivation with the biopolymer. [ABSTRACT FROM AUTHOR]

The design of fluorescent proteins with increased photostability is an important practical task. One of the approaches to its solution is the search for amino acid residues, which play a key role in chromophore-mediated photochemical reactions. The effect of tyrosine-145 on the photooxidation of the chromophore in the EGFP (Enhanced Green Fluorescent Protein) has been previously demonstrated. We have designed the EGFP-Y145L mutant, which has exhibited a significantly reduced efficiency of photooxidation and associated photobleaching. In this work, we are looking for ways to increase the fluorescence brightness of this mutant. For this purpose, we have introduced the S205V and E222G substitutions and their combination to shift the pH equilibrium of the chromophore environment towards ionization of the chromophore. We have shown that both mutants that contain the S205V substitution carry mostly the neutral chromophore, have low brightness, and are capable of slow photoactivation. They may be of interest for studying light-dependent proton transfer. Probably, these proteins can function as time-resolved pH sensors. As we have expected, the chromophore resides in the EGFP-Y145L/E222G mutant is predominantly in the anionic form. The fluorescence brightness of this protein is four times higher than that of the original EGFP-Y145L, and its photostability is higher than that of EGFP by factors of 1.5–5. [ABSTRACT FROM AUTHOR]

Featured Application: Organic lasers active in the red–near-infrared spectral regions endowed with efficient and long-lasting emission. The disposal of long-wavelength-emitting sources is of paramount relevance in technology and biophotonics due to the low interference with the surroundings that these kinds of far-red and near-infrared radiations hold. As a result of the continued efforts carried out during the last few years by our research group to design new boron-dipyrromethene (BODIPY) dyes with improved photonic performance, two approaches were tested to develop a new generation of organic dyes able to display efficient and long-lasting laser emission in both target spectral regions. On the one hand, the annulation of aromatic benzofuran at the dipyrrin backbone leads to conformationally restricted dyes yielding photostable and bright laser emission beyond 600 nm at the far-red spectral region. On the other hand, a more pronounced shift to longer wavelengths reaching 725 nm at the near-infrared region is feasible, while keeping a reasonably high laser efficiency and tolerance to prolonged and intense pumping, based on aza-BODIPYs bearing peripheral aryl rings. These two complementary strategies yield a library of laser-emitting compounds comprising the 600–725 nm spectral region. Moreover, their laser performance is better than the commercially available dye lasers active in this spectral window. [ABSTRACT FROM AUTHOR]

In this contribution, polyvinyl pyrrolidone capped copper nanoclusters (PVP‐Cu NCs) were synthesised through a one‐pot route possessing the advantages of rapidness and environmental friendliness. Also, the optical characteristics of the as‐prepared Cu NCs were characterised using fluorescence spectroscopy, UV–vis absorption spectroscopy. The structure and composition were studied through Fourier transform infrared, transmission electron microscopy, X‐ray photoelectron spectroscopy. It exhibited good water solubility, excellent photo stability, and resistance to sodium chloride. The Cu NCs revealed blue fluorescence and displayed excitation‐dependent fluorescence characteristics. More importantly, the fluorescence intensity of PVP‐Cu NCs was linearly quenched in the range of 5–80 μM (concentrations of fluazinam) and the detection limit was 0.98 μM. Finally, the fluorescence sensor was successfully employed to detect fluazinam in natural water samples. [ABSTRACT FROM AUTHOR]

Aim. Synthesis and characterization of benzothiazole-based styrylcyanines functionalized by different N-alkyl tail groups as potential photostable probes for nucleic acids (NA) detection. Methods. Chemical synthesis, absorption and fluorescence spectroscopy, irradiation with a visible light source, confocal microscopy. Results. Styrylcyanines are weakly fluorescent when free, but in the presence of NA they show emission intensity increase of up to 83 times; the most pronounced emission increase was observed for the dyes Sbt1 and Sbt3 bearing positively charged N-alkyl tail group. Photostability of the dyes Sbt1 and Sbt3 when non-bound to NA is low while binding to DNA results in a strong increase in their photostability. Dyes with uncharged and negatively charged N-alkyl groups are more photostable when free, and DNA slightly affects their photostability. This is also due to low binding of dyes with negatively charged tail groups to DNA. Sbt1 brightly stains cytoplasm and nuclear components (probably nucleoli) of mesenchymal stem cells; therefore this dye may be used to visualize cytoplasmic RNA and nuclear RNA clusters. Conclusions. Variation of chemical nature of N-alkyl tail group allows to design styrylcyanines of different photostability. Functionalized styrylcyanine dyes may be used for detection of nucleic acids in solution and visualization of RNA-containing components in microscopy. [ABSTRACT FROM AUTHOR]

The highly substituted mono‐aryl/alkylthio‐(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di‐aryl/alkylthio‐substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio‐anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG‐substituted anthracenes (EDG=electron‐donating group, EWG=electron‐withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio‐Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o‐(1,3‐dithian‐2‐yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono‐aryl/alkylthio‐substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD‐DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono‐aryl/alkylthio‐substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen. [ABSTRACT FROM AUTHOR]

Abstract Despite extensive research on carbon dots (CDs), rare studies have been performed on the photostability of CDs. Here, the photostability of CDs synthesized with 3-aminobenzoic acid were systematically investigated under different pH conditions (5.0, 7.4 and 9.0). The results showed that under Xenon lamp irradiation, the fluorescence (FL) intensity of the CDs exhibited an increase first and then a decrease, with a gradual shift of the maximum emission wavelength to longer wavelength. Further investigation indicated that the irradiation induced the change of the CD surface functional groups and gave rise to aggregation, resulting in the formation of larger particles. This study provided important reference value towards research on CDs properties. Graphical abstract Unlabelled Image Highlights • CDs FL intensity increased first and then decreased under Xe lamp irradiation. • CDs FL emission gradually shifted to longer wavelength under Xe lamp irradiation. • Xe lamp irradiation induced aggregation of CDs and oxidation of functional groups. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Solvents in stock solution significantly affect fluorescence properties in films. • Fluorescence quantum yield of DXP in films can be enhanced by using mixed solvent. • Photostability of DXP in films can be enhanced by using mixed solvent. • The optimal ratio of mixed solvent is 2:1 for methanol:toluene. Abstract Photostability in solid state is one of the crucial parameters of fluorescent substances for their applications. Different factors during the fabrication processes can significantly affect their photostability. In this work, we prepared N,N′-Bis(2,6-dimethylphen-yl)-perylene-3,4,9,10-tetra-carboxy-licdiimide (DXP) films by directly spin-casting the precursor solutions of DXP in a mixed solvent (methanol and toluene). We found that the photostability and fluorescence quantum yield of DXP in the final solid films have strong correlation with the ratio between methanol and toluene in the precursor solutions. These results show the importance of the solvent used during the fabrication process and give suggestions for better routes. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) were obtained from medicinal turmeric leaves (Curcuma longa) by a facile one-step hydrothermal method and evaluated for their bactericidal activities against two gram-negative; Escherichia coli, Klebsiella pneumoniae, and two gram-positive counterparts; Staphylococcus aureus, S. epidermidis. The CDs exhibited spherical shapes with a mean size of 2.6 nm. The fluorescence spectra of CDs revealed intense fluorescence at λex/em = 362/429 nm with a bright blue color in an aqueous solution. The CDs showed strong photostability under various environmental conditions (pH, salt, and UV-radiation). The complete bactericidal potency of CDs was 0.25 mg/mL for E.coli and S. aureus after 8 h of exposure, while for K. pneumoniae, and S. epidermidis, the CDs at 0.5 mg/mL good antibacterial effect within 8 h and complete eradication after 24 h of exposure is observed. The release of reactive oxygen species played a crucial role in the death of the bacterial cell. The present study provides a strategy for the preparation of CDs from a medicinal plant and their potential antibacterial activities against four common contagious pathogens.

Lipid droplets (LDs) are extremely active organelles that play a crucial role in energy metabolism, membrane formation, and the production of lipid-derived signaling molecules by regulating lipid storage and release. Nevertheless, directly limited by the lack of superior fluorescent probes, studies of LDs dynamic motion velocity have been rarely reported, especially for nuclear LDs. Herein, a novel organic fluorescent probe Lipi-Bright has been rationally developed based on bridged cyclization of distyrylbenzene. The fully ring-fused molecule structure endows the probe with high photostability. Moreover, this new fluorescent probe displays the features of excellent LDs staining specificity as well as ultrahigh fluorescence brightness. Lipi-Bright labeled LDs was dozens of times brighter than representative probes BODIPY 493/503 or Nile Red. Consequently, by in-situ time-lapse fluorescence imaging, the dynamics of LDs have been quantitatively studied. For instance, the velocities of cytosolic LDs (37 ± 15 nm/s) are found to be obviously faster than those of nuclear LDs (24 ± 4 nm/s), and both the cytosolic LDs and the nuclear LDs would be moved faster or slower depend on the various stimulations. Overall, this work providing plentiful information on LDs dynamics will greatly facilitate the in-depth investigation of lipid metabolism. • A new organic fluorescent probe is developed for lipid droplets (LDs) imaging. • This new probe displays outstanding photostability and high LDs specificity. • Ultrabright labeled LDs are dozens of times brighter than commercial probes. • The dynamic trajectories and velocities of LDs were quantified. • Dynamic differences between cLDs and nLDs were determined. [ABSTRACT FROM AUTHOR]

The disposal of long-wavelength-emitting sources is of paramount relevance in technology and biophotonics due to the low interference with the surroundings that these kinds of far-red and near-infrared radiations hold. As a result of the continued efforts carried out during the last few years by our research group to design new boron-dipyrromethene (BODIPY) dyes with improved photonic performance, two approaches were tested to develop a new generation of organic dyes able to display efficient and long-lasting laser emission in both target spectral regions. On the one hand, the annulation of aromatic benzofuran at the dipyrrin backbone leads to conformationally restricted dyes yielding photostable and bright laser emission beyond 600 nm at the far-red spectral region. On the other hand, a more pronounced shift to longer wavelengths reaching 725 nm at the near-infrared region is feasible, while keeping a reasonably high laser efficiency and tolerance to prolonged and intense pumping, based on aza-BODIPYs bearing peripheral aryl rings. These two complementary strategies yield a library of laser-emitting compounds comprising the 600–725 nm spectral region. Moreover, their laser performance is better than the commercially available dye lasers active in this spectral window.

Lysosome fluorescent imaging has been widely used in the field of biological staining and diagnostics, which plays a key role in understanding intracellular metabolism and various physiological processes. However, for most currently used small-molecule lysotrackers, the photostability is often unsatisfactory when used for long-term and real-time visualization of lysosomal dynamics. Herein, we reported a new lysosome-targetable photostable fluorescent probe (i.e. MPL-NPA), and results showed that MPL-NAP possesses superior photostability, appreciable tolerance to pH change, low cytotoxicity and high lysosome targeting ability. These findings confirm that MPL-NAP is a well-suited imaging agent for targeting lysosome and enables long-term and real-time monitor of lysosome morphological changes under physiological processes. [ABSTRACT FROM AUTHOR]

Abstract Chemical sensing in living systems demands optical sensors that are bright, stable, and sensitive to the rapid dynamics of chemical signaling. Lanthanide-doped upconverting nanoparticles (UCNPs) efficiently convert near infrared (NIR) light to higher energy emission and allow biological systems to be imaged with no measurable background or photobleaching, and with reduced scatter for subsurface experiments. Despite their advantages as imaging probes, UCNPs have little innate chemical sensing ability and require pairing with organic fluorophores to act as biosensors, although the design of stable UCNP-fluorophore hybrids with efficient upconverted energy transfer (UET) has remained a challenge. Here, we report Yb3+- and Er3+-doped UCNP-fluorophore conjugates with UET efficiencies up to 88%, and photostabilities 100-fold greater by UET excitation than those of the free fluorophores under direct excitation. Despite adding distance between Er3+ donors and organic acceptors, thin inert shells significantly enhance overall emission without compromising UET efficiency. This can be explained by the large increase in quantum yield of Er3+ donors at the core/shell interface and the large number of fluorophore acceptors at the surface. Sensors excited by UET show increases in photostability well beyond those reported for other methods for increasing the longevity of organic fluorophores, and those covalently attached to UCNP surface polymers show greater chemical stability than those directly coordinated to the nanocrystal surface. By conjugating other fluorescent chemosensors to UCNPs, these hybrids may be extended to a series of NIR-responsive biosensors for quantifying the dynamic chemical populations critical for cell signaling. Highlights • NIR-excitable UCNPs conjugated to fluorophores have energy transfer efficiencies up to 88% under microscopic laser powers. • UCNP-fluorophore conjugates are up to 100-fold more photostable than free fluorophores. • Conjugates with fluorophores are covalently attached to surface polymers show greatly enhanced chemical stability. [ABSTRACT FROM AUTHOR]

ZnO quantum dots, QDs (5 nm diameter) by their photogenerated charge carriers clearly influence the degradation of the acrylate host matrix, under conditions simulating solar light. As a result, QDs undergo a partial quenching of their fluorescence. To rationalize this influence, the investigation requires understanding the photochemical behavior of the acrylate photopolymer (carrier of ester and ether groups) in the absence of nanofiller. The matrix undergoes simultaneously a post-polymerization and photooxidative degradation. Infrared analysis and headspace gas chromatography coupled with mass spectrometry reveal that the main volatile organic compounds result from the oxidation of the ether groups, supposed to be the primary sites of degradation. The nanofiller increases the rate of degradation. Also, the concentration of the volatile organic compounds is all the more important as the doping percentage increases. However, the photostability of ZnO/polymer material strongly depends on the size of the nanoparticles. Whereas ZnO QDs display a photocatalytic effect, nanoparticles with a bigger size (10–30 nm) exhibit an unexpected UV-screening effect. [ABSTRACT FROM AUTHOR]

Abstract: We recently reported that fluorescent dye PB430, which consisted of a 2‐phenyl‐substituted benzophosphole P‐oxide skeleton that was reinforced by a methylene bridge, showed pronounced photostability and, thus, high utility for applications in super‐resolution stimulated emission depletion (STED) microscopy. Herein, we replaced the methylene bridge with another P=O group to 1) investigate the role of the bridging moieties; and 2) further modulate the fluorescence properties of this skeleton. We synthesized a series of phospholo[3,2‐b]phosphole‐based dyes—trans‐PO‐PB430, cis‐PO‐PB430, and trans‐PO‐PB460—all of which showed sufficient water solubility. Moreover, trans‐PO‐PB430 and trans‐PO‐PB460 exhibited intense green and orange fluorescence, respectively, and a high photostability that was comparable to that of PB430. In contrast, cis‐PO‐PB430 underwent rapid photobleaching upon continuous photoirradiation, which demonstrated the importance of steric shielding of the polycyclic skeleton by the substituents on the bridging moieties. The fluorescence properties of these dyes were insensitive to concentration, pH value, and polarity changes of the environment in solution. In addition, even in the solid state, these dyes showed strong green to orange emissions. These results demonstrate the potential utility of trans‐PO‐PB430 and trans‐PO‐PB460 as highly photostable fluorescent dyes. [ABSTRACT FROM AUTHOR]

Folic acid, or pteroyl‑ l ‑glutamic acid (PteGlu) is a conjugated pterin derivative that is used in dietary supplementation as a source of folates, a group of compounds essential for a variety of physiological functions in humans. Photochemistry of PteGlu is important because folates are not synthesized by mammals, undergo photodegradation and their deficiency is related to many diseases. We have demonstrated that usual commercial PteGlu is unpurified with the unconjugated oxidized pterins 6‑formylpterin (Fop) and 6‑carboxypterin (Cap). These compounds are in such low amounts that a normal chromatographic control would not detect any pterinic contamination. However, the fluorescence of PteGlu solutions is due to the emission of Fop and Cap and the contribution of the PteGlu emission, much lower, is negligible. This is because the fluorescence quantum yield (Φ F ) of PteGlu is extremely weak compared to the Φ F of Fop and Cap. Likewise, the PteGlu photodegradation upon UV-A radiation is an oxidation photosensitized by oxidized unconjugated pterins present in the solution, and not a process initiated by the direct absorption of photons by PteGlu. In brief, the fluorescence and photochemical properties of PteGlu solutions, prepared using commercially available solids, are due to their unconjugated pterins impurities and not to PteGlu itself. This fact calls into question many reported studies on fluorescence and photooxidation of this compound. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescent probe is described that is based on a functionalized europium(III) coordination polymer (Eu/DPA-TA). It can be fabricated by using dipicolinic acid (DPA) as a bridging ligand (to sensitize the Eu3+ fluorescence) and terephthalic acid (TA) acting as a functional ligand to recognize the hydroxy radical (*OH). The quenching of Eu3+ fluorescence (measured at excitation/emission wavelengths of 288/615 nm) by water is strongly reduced in the presence of TA. This leads to a significant enhancement in the emission lifetime and intensity of Eu3+. Upon the addition of *OH, the fluorescence of Eu/DPA-TA showed ratiometric changes in that the TA sensitized fluorescence (peaking at 445 nm) is switched on, while the plain Eu3+ fluorescence (peaking at 615 nm) decreases. This finding led to a method for the ratiometric (2-wavelength) detection of OH* with a 0.5 µM detection limit. The method also allows OH+ to be detected with bare eyes at OH* concentrations as low as 10 µM. In our perception, this study paves the way towards the design of new functionalized lanthanide coordination polymers for fluorometric assays and biomedical imaging. [ABSTRACT FROM AUTHOR]

Novel heterocyclic Schiff base dyes were prepared by the reaction of salicylaldehyde/2-Hydroxy-1-naphthaldehyde with different heterocyclic amines. Results of the newly synthesized compounds established by FT-IR, 1H-NMR, 13C-NMR and GC–MS spectroscopic experiments were consistent with their chemical structures. Resulted heterocyclic Schiff base dyes were found to be pure from data obtained by the elemental analysis. In addition, spectrophotometric and spectrofluorimetric studies showed that these dyes were good absorbent and fluorescent. Fluorescence polarity study data revealed that some of these compounds were sensitive to the polarity of the microenvironment provided by different solvents. Time-based fluorescence steady-state measurements also showed that these heterocyclic Schiff base dyes have high photostability against photobleaching.

In modern biotechnological science, there is a need for visualization of objects under study at the levels of cells, organelles, and individual molecules. Prominent among imaging methods are the methods based on the detection of fluorescence from the fluorophores with which objects under study are labeled. Fluorescent proteins (FPs) are very popular as genetically encoded fluorescent labels for lifetime imaging of target structures and processes in living systems. One of the key characteristics of FPs is their photostability, i.e., their resistance to photochemical reactions that quench the fluorescence signal. This review describes the currently known molecular mechanisms underlying photobleaching and the methods used to improve the photostability of fluorescent proteins. [ABSTRACT FROM AUTHOR]

An amphiphilic fluorescent polymer ( Ply-EP3 ) combining an aggregation-induced emission monomer and ε-polylysine was prepared through epoxy ring-opening polymerization. 1 H NMR, FT-IR, and X-ray photoelectron spectra were conducted to characterize its chemical property. Such amphiphilic Ply-EP3 could assemble into nanoparticles in water and form fluorescent polymeric nanoparticles (FPNs) with high water dispersibility. Dynamic light scattering result of Ply-EP3 FPNs demonstrated the size distribution of 106 ± 8 nm with the polydispersity index of 0.268. Transmission electron microscopy image of Ply-EP3 FPNs showed spherical nanoparticle morphology with a size range of 50–100 nm. The optical property of FPNs indicated intense green fluorescence with a fluorescence quantum yield of 33%. The Ply-EP3 FPNs further proved excellent stability with low critical micelle concentration of 0.042 mg mL −1 . The prepared FPNs also revealed high photostability after UV light irradiation for 120 min. Such FPNs showed excellent biocompatibility as the cells retained high viability at the concentration range of 10–120 μg mL −1 of Ply-EP3 for an incubated period of 12 h or 24 h, and exhibited excellent performance for cell imaging. Thanks to the high-performance Ply-EP3 FPNs, including bright fluorescent emission, high water dispersibility and particle stability, and excellent photostability, this work provide an approach to prepare robust cross-linked biocompatible fluorescent polymers for cell imaging. [ABSTRACT FROM AUTHOR]

A family of anthracene carboxyimides with multi-color fluorescence have been successfully prepared, and their spectroscopic properties were investigated by UV–vis absorption spectroscopy, steady-state and time-resolved fluorescence spectroscopy. The photostability and solvatochromic fluorescence in organic solvents were also investigated. The parent anthracene carboxyimide 4a displays very strong green fluorescence (Φ F = 0.91 in EtOH), good pH stability and photostability, as well as a large Stokes shift. By attachment of different substituents at the 10-position of the anthracene carboxyimide, the fluorescence maxima could be effectively modulated from 500 nm to 615 nm. The 10-(picolylamine) substituted anthracene carboxyimides 5a and 5b exhibit large Stokes shifts (>80 nm) and significant positive solvatochromic fluorescence in organic solvents due to their intramolecular charge-transfer (ICT) character. Furthermore, cell staining experiments indicate that anthracene carboxyimides have excellent cell membrane permeability and good photo-bleaching resistance in living cells. Particularly, compound 5a is a specific mitochondria-targeting dye with red fluorescence. All these features enable anthracene carboxyimides to serve as promising candidates for bio-labeling/imaging applications. [ABSTRACT FROM AUTHOR]

The fluorescence spectra and photostability under 532 nm laser excitation of four different common photoswitches (an azobenzene, spiropyran, indolylfulgide, and a diarylperfluorocyclopentene) were investigated in a silica microstructured optical fibre. An example of each photoswitch was examined in solution and physically adsorbed to the silica fibre surface. This comparison was made to define fluorescence behaviour in these two states and to determine which photoswitch has the best performance in this light intense microenvironment. The azobenzene and the spiropyran switches demonstrated the strongest fluorescence response and the least degradation of the fluorescence signal. [ABSTRACT FROM AUTHOR]

Biologically active photosensitizers with long absorption wavelength are among the new generation drugs for potential application in photodynamic therapy (PDT). This study presents a new phthalocyanine photosensitizer functionalized with amino acid for application in PDT. This photosensitizer, tetra-(4-tyrosylamido) phenoxy substituted zinc(II) phthalocyanine ( ZnPcTyr ), was synthesized and chemically characterized. The properties of electronic absorption, fluorescence, photostability, and singlet oxygen generation were studied. The obtained photophysicochemical characteristics suggested that this newly synthesized tyrosine conjugated zinc(II) phthalocyanine has promising potential as photosensitizer for photodynamic therapy. [ABSTRACT FROM AUTHOR]

Ferroptosis, as a new form regulation of cell death discovered recently, is triggered by an iron-dependent accumulation of lipid reactive oxygen species and thus closely associated with cellular lipid droplets (LDs). However, directly limited by the un-sufficient photostability and low LDs specificity of common fluorescent probes, visualization of LDs during ferroptosis process particular in a long-term, in-situ, and real-time manner is highly preferred but extremely challenge. To this end, here a new LDs fluorescent probe Lipi-EP featuring with outstanding photostability and high LDs specificity have been rationally developed based on the four-ring-fused epindolidione. Experimentally, the photostability and LDs specificity of this new probe are much higher than the representative LDs probe BODIPY and Nile Red. Consequently, time-lapse multicolor imaging and time-lapse three-dimensional imaging employed this new probe have been successfully conducted to in-situ real-time monitor the LDs change during ferroptosis process up to 6 h. The morphology changes of cellular organelles (LDs, mitochondria and nucleus) and the variations of space distribution of LDs have been impressively visualized. Moreover, the sizes and numbers of LDs have been also determined based on the imaging. This work providing abundant information of LDs would significantly promote the in-depth study of LDs during ferroptosis. [Display omitted] • A new organic fluorescent probe is developed for lipid droplets (LDs) imaging. • This new probe displays outstanding photostability and high LDs specificity. • Time-lapse multicolor imaging, time-lapse three-dimensional imaging are realized. • The LDs change during ferroptosis process is in-situ real-time monitored up to 6 h. [ABSTRACT FROM AUTHOR]

A new Schiff base derived from the condensation of 6-formyl-7-hydroxy-5-methoxy-2-methylbenzo-pyran-4-one (benzopyran-4-one derivative) with cephradine drug (L) was prepared and characterized by elemental analyses and some spectroscopic studies. Also, Zn(II), Cu(II), Co(II) and Ni(II) complexes of that Schiff base were prepared by template reaction. Many tools of analysis such as elemental analyses, infrared, ultraviolet-visible and thermal analysis, as well as electrical conductance and magnetic susceptibility measurements were used to elucidate the structure of these complexes. The data showed that Zn(II)-L and Cu(II)-L complexes are 1:1 (M:L). The ligand was found to be monobasic bidentate. On the other hand, Ni(II)-L and Co(II)-L form binuclear complexes. All the complexes are non-electrolyte. The luminescence properties of the prepared Schiff base and its complexes were measured. The photostability of Schiff base, L, and its Zn(II)-L and Cu(II)-L complexes were also studied. The photobiological activity of cephradine, benzopyran-4-one derivative, Schiff base, L and the complexes were studied on mosquito larvae to investigate the extent of their photosensitization efficiency in controlling noxious insects using direct sunlight (larvicidal effect). In vitro cytotoxicity study of the Schiff base and its complexes against Hep G2-cell line was investigated by the MTT assay. The Schiff base, L, exhibits better activity against Hep G2 cell line than the complexes. [ABSTRACT FROM AUTHOR]

Effect of acidity of a medium on the spectroscopic characteristics of riboflavin aqueous solutions is investigated by the method of fluorescent and absorption spectroscopy. Significant deformation of the electronic spectra of riboflavin aqueous solutions irradiated with unfiltered light of a PRK-2 lamp is observed. It is established that riboflavin photostability in an acid medium is about twice as much as the photostability in a neutral medium, which is caused by the formation of a protonated species. [ABSTRACT FROM AUTHOR]

New polymeric materials containing dinuclear double-stranded zinc(II) helicate with bis(1,2,3,7,9-pentamethyldipyrrin-8-yl)methane have been prepared on the basis of poly(methyl methacrylate) and tetraethoxysilane. The zinc(II) complex [ZnL] retains its fluorescence properties in a poly(methyl methacrylate) film. The photostability of [ZnL] in poly(methyl methacrylate) is higher by a factor of ≈2.5 than in the benzene solution. Conditions have been found for the preparation of [ZnL]-doped silicate matrix based on tetraethoxysilane via the sol-gel method. The [ZnL] complex in the tetraethoxysilane solid matrix shows a weak fluorescence with its maximum at λ = 545-549 nm. [ABSTRACT FROM AUTHOR]