Emission In Solvents Research Articles

Synthesis and Optical Properties of Triphenylene-Based Donor-Donor and Donor-Acceptor Conjugated Polymers: A Comparative Study

Two new conjugated polymers (P1 and P2), containing a bithiophene donor unit coupled with either a triphenylene donor unit or an imide-functionalized triphenylene acceptor unit in the backbone, have been synthesized, structurally characterized, and comparatively studied by using 1H NMR, FT-IR, gel permeation chromatography, differential scanning calorimetry, cyclic voltammetry, ultraviolet-visible absorption, and fluorescence spectroscopy. Both polymers are amorphous in nature and thermally stable up to 450°C. The inclusion of the imide functionalization in the triphenylene unit significantly lowered the lowest unoccupied molecular orbital energy level and thus the bandgap of the donor-acceptor polymer P2 over the donor-donor polymer P1. P1 and P2 show very different optical properties in hexane and other solvents. P1 shows a broad emission in hexane but vibronically structured emissions in other solvents; in contrast, P2 exhibits a vibronically resolved emission in hexane, while exhibiting redshifted, broad, and featureless emissions in other solvents. P1 takes a random coil conformation in good solvents like p-xylene, benzene, toluene, anisole, chloroform, THF, and o-dichlorobenzene, whereas in hexane, it may adopt a helical folding conformation. In the poor solvent DMSO, interchain aggregates dominate. P2, on the other hand, adopts a random coil conformation in hexane but possibly the helical folding conformation in other good solvents. The opposite conformations of the two polymers may be responsible for their opposite solvent-dependent fluorescence properties. By virtue of the very different fluorescence properties of these two polymers in nonpolar solvents such as hexane and in polar solvents, the potential of using the polymers to detect the trace amount of ethanol content that is added to gasoline has been revealed with high sensitivity.

Characteristics of Aerosol Formation and Emissions During Corn Stalk Pyrolysis

The inevitable emission of aerosols during pyrolysis can negatively affect the downstream process and even pollute the environment. In this work, the characteristics of aerosols were investigated during corn stalk pyrolysis at 400–900 °C. The effects of other operation conditions on the aerosol emissions were also probed with online and offline instruments. Results show the yield of aerosol presents a regular change with temperature in a wide range ratio of 3.4–8.7 wt.%. The aerosol size distribution reveals a unimodal form mainly in the 1.1–2.1 μm accumulation range and the maximum emission achieved is about 35 mg/g for SR and SP at 500 °C. Nevertheless, SL gives about 34 mg/g at 600 °C. High temperature promotes the decomposition of polymers into partciles with small diameter (less than PM1.0). The microtopography of aerosol presents spherical droplets, elongated-like liquid and solid particles that form heterogenous or homogeneous aggregations, that also happen on account of collisions. Aerosols contain mostly organic matter, a small amount of salt and over 50% of volatile organic carbon molecules (VOCs) in the total organic carbon (OC). Proper gas flow, high vapor concentration and longer path way boost the yield of bio-oil and reduce the emission of aerosols. The direct contact is beneficial for adequate extraction, but also causes additional solvent emissions.

Oligo(ethylene glycol) (OEG) functionalized 2-(2′-Hydroxy benzofuranyl) benzoxazole (HBBO) derivatives: Synthesis, photophysical properties and biomolecules binding studies

Two molecular fluorophores based on a 2-(2′-Hydroxybenzofuranyl) benzoxazole (HBBO) scaffold and presenting an Excited-State Intramolecular Proton Transfer (ESIPT) process are reported herein. These dyes incorporate strongly electrodonating aromatic amino groups on the benzofuranyl side, enabling the appearance of a dual fluorescence emission corresponding to the radiative decay of the excited enol (E*) and keto (K*) tautomers at high and low energy respectively. It was previously demonstrated that dual E*/K* emission could originate from a beneficial decrease of phenolic acidity upon absorption of light leading to a thermodynamic stabilization of the first excited-state. The innovation within these dyes lies in the double functionalization of the aniline moiety with 2-(2-methoxyethoxy)ethyl units which allowed a better solubilization in protic solvents, as compared to their butyl analogs while keeping strong electrodonating capacity. Their intrinsic amphiphilic character leads to a good vectorization in a wide range of solvents from toluene to PBS buffer. The investigation of the photophysical properties of these dyes in solution showed a clear dual emission in apolar solvents with the E* band gradually red-shifting along with the dipole moment of the solvent. Dual emission is also observed in the solid-state when these dyes are doped as 1% wt in PMMA or PS films. Finally, the interactions of one dye with calf-thymus (ct)-DNA and Bovine Serum Albumin (BSA) have been explored and reveal pronounced modifications of the UV–Vis profile of the dye. Additionally, a gradual hypsofluorochromic shift and narrowing of the K* band along with the appearance of the E* fluorescence band upon addition of ct-DNA or BSA is also observed, presumably evidencing an intercalation mode of binding.

An increasing role for solvent emissions and implications for future measurements of volatile organic compounds

Volatile organic compounds (VOCs) are a broad class of air pollutants which act as precursors to tropospheric ozone and secondary organic aerosols. Total UK emissions of anthropogenic VOCs peaked in 1990 at 2,840 kt yr−1 and then declined to approximately 810 kt yr−1 in 2017 with large reductions in road transport and fugitive fuel emissions. The atmospheric concentrations of many non-methane hydrocarbons (NMHC) in the UK have been observed to fall over this period in broadly similar proportions. The relative contribution to emissions from solvents and industrial processes is estimated to have increased from approximately 35% in 1990 to approximately 63% in 2017. In 1992, UK national monitoring quantified 19 of the 20 most abundant individual anthropogenic VOCs emitted (all were NMHCs), but by 2017 monitoring captured only 13 of the top 20 emitted VOCs. Ethanol is now estimated to be the most important VOC emitted by mass (in 2017 approx. 136 kt yr−1 and approx. 16.8% of total emissions) followed by n-butane (52.4 kt yr−1) and methanol (33.2 kt yr−1). Alcohols have grown in significance representing approximately 10% of emissions in 1990 rising to approximately 30% in 2017. The increased role of solvent emissions should now be reflected in European monitoring strategies to verify total VOC emission reduction obligations in the National Emissions Ceiling Directive. Adding ethanol, methanol, formaldehyde, acetone, 2-butanone and 2-propanol to the existing NMHC measurements would provide full coverage of the 20 most significant VOCs emitted on an annual mass basis.This article is part of a discussion meeting issue ‘Air quality, past present and future’.

Stable Luminescent Radicals and Radical-Based LEDs with Doublet Emission

Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes (OLEDs), which adopt luminescent radicals as emitters, aiming at improving the external quantum efficienc...

Hydroxy-benzimidazoles as blue-green emitters: Synthesis, structural and DFT studies

The new benzimidazole ligands (3a-e) were synthesized using ethyl 4-(butylamino)-3-nitrobenzoate and substituted salicylaldehyde in the presence of sodium dithionite reagent which undergoes “one-pot’’ nitro reductive cyclization. Here benzimidazole moiety acts as an electron-acceptor (A) whereas substituted 2-hydroxyphenyl moiety acts as an electron-donor (D) unit. The molecular structures were characterised by FTIR, 1H NMR, 13C NMR, single crystal XRD and MS analysis. Optoelectronic properties were determined by UV–vis, solution and solid photoluminescence, quantum yield and lifetime. The solvent-dependent absorption and emission were studied using both polar protic and polar aprotic solvents. All the derivatives exhibited ESIPT, especially compound ethyl 1-butyl-2-(3,5-dichloro-2-hydroxyphenyl)-1H-benzo[d]imidazole-5-carboxylate (3e) displayed dual emission in both polar protic and polar aprotic solvents. The compound stability and electrochemical property were determined by thermal gravimetric analysis (TGA) and cyclic voltammetry (CV) respectively. The compounds emit intense blue-green fluorescence with high to moderate quantum yield. Also, these derivatives exhibited a high Stokes shift. The computational studies like Density-Functional Theory (DFT) and Molecular Electrostatic Potential (MEP) were conducted to provide important insights into the structure-property relationships. The crystal packing is stabilized through intermolecular hydrogen bonds (C---H…O) and intermolecular interactions (π… π). The findings of results help in developing novel ligands in the field of organic optoelectronics.

Potential sources and measured concentrations of VOCs in Balikesir ambient atmosphere

The assessment of volatile organic compounds (VOCs) has become an important field of interest in atmospheric pollution. This study quantifies and characterizes the ambient levels and spatial distribution of VOCs in urban and rural areas of Balikesir city, Turkey. For these assessments, passive sampling of VOCs performed at approximately 50 locations in and around the city of Balikesir. Twenty-five VOCs were regularly monitored and analyzed with the GC-FID system. The sampling periods were carried out for seven-day periods during March and August 2010. In the study, mean ∑VOC concentrations were found to be as high 67 and 51 µg m–3 for the winter and summer seasons, respectively. Median concentrations of benzene, toluene, ethylbenzene, m,p-xylene and o-xylene were 2.6, 11, 1.30, 1.80 and 0.73 μg m-3, respectively. Although there were some changes between concentrations of VOC groups between the summer and winter campaigns, differences were not dramatic. Winter-to-summer ratios of the target compounds ranged from 0.2 (1,2,4-trimethylbenzene) to 9 (hexane). Most of the target compounds have higher concentrations in winter. Only few VOCs, including n-propylbenzene, 1,2,4- trimethylbenzene, 1-undecene and 1,2,4- trichlorobenzene have higher concentrations in summer. Spatial distribution of VOCs demonstrated that the roads are hot spots for measured VOC concentrations. The drinking water treatment plant, industrial solvent emissions from pesticide and insecticide applications in agriculture, and emissions from traffic were the sources that contribute to total VOC load in the Balikesir atmosphere.

Synthesis, Solution and Solid‐State Fluorescence of 2‐(N‐cycloamino)cinchomeronic Dinitrile Derivatives

AbstractA facile approach to the synthesis of novel 2‐(N‐cycloamino)cinchomeronic dinitriles showing intense photoluminescence both in solution and solid state was developed. Absorption, fluorescence and solvatochromic properties were investigated. It was found that the 2‐(N‐cycloamino)cinchomeronic dinitrile derivatives containing conjugated aryl moiety show intense emission in nonpolar solvents with fluorescence quantum yield up to 0.8.

Dual‐Function Fluorescent Covalent Organic Frameworks: HCl Sensing and Photocatalytic H2 Evolution from Water

AbstractTwo ultrastable luminescent covalent organic frameworks (COFs), PyTA‐BC and PyTA‐BC‐Ph, are synthesized through polycondensations of 4,4′,4″,4′″‐pyrene‐1,3,6,8‐tetrayl)tetraaniline (PyTA‐4NH2) with two carbazole‐based derivatives having different degrees of conjugation. The PyTA‐BC and PyTA‐BC‐Ph COFs exhibit ultrahigh thermal stabilities (up to 421 °C), excellent crystallinity, and high Brunauer–Emmett–Teller surface areas (up to 1445 m2 g−1). These COFs display strong fluorescence emissions in various solvents, with their emission maxima gradually red‐shifting upon increasing the polarity of the solvent (solvatochromism). Upon exposure to HCl, they respond very rapidly and sensitively in terms of changing their colors and fluorescence emission maxima. In the presence of a sacrificial electron donor, these COFs mediate the highly efficient photocatalytic evolution of H2 from water. In the absence of a noble metal cocatalyst, the COFs and ascorbic acid provide a photocatalytic H2 production of up to 1183 µmol g−1 h−1 (λ ≥ 420 nm); this value is the highest reported to date for a COF. Such COFs appear to be potentially useful as chemosensors for the naked‐eye and sensitive spectroscopic detection of HCl and as cocatalysts for the sustainable photocatalytic production of H2 from water.

AIEE active novel red-emitting D-π-A phenothiazine chalcones displaying large Stokes shift, solvatochromism and “turn-on” reversible mechanofluorochromism

In an effort to develop red light emitting, AIEE active potential mechanofluorochromic smart materials, a series of novel D-π-A based phenothiazine chalcone derivatives was designed and synthesized. Various aryl groups were appended to the phenothiazine ring with the aim of tuning the donor ability and to regulate the molecular arrangements which could alter the photophysical and mechanofluorochromic (MFC) properties. Photophysical studies revealed an enhanced intramolecular donor-acceptor charge transfer by appending electron donating 4-methoxyphenyl ring on the phenothiazine moiety whereas a bulky 1-naphthyl ring led to reduced intramolecular charge transfer character. Experimental band gap energies of all the derivatives were found to be in range 2.58–2.68 eV. Existence of large Stokes shift (143–221 nm) and positive solvatochromism was observed in solvents of differing polarity. All the derivatives exhibited a yellow emission in non-polar solvent (toluene) and red emission in polar solvent (DMSO). Chalcone with naphthyl ring displayed maximum AIEE characteristics. Reversible “off-on-off” mechanofluorochromic behaviour was observed upon the subsequent exposure of mechanical stress and dichloromethane vapours or heat. Single crystal X-ray diffraction pattern analysis indicated the presence of twisted conformations and weak intermolecular interactions which are responsible for the mechanofluorochromic behaviour. Powder X-ray diffraction patterns revealed the transformation from crystalline to amorphous state upon mechanical grinding which were reversed upon exposure of dichloromethane vapours or heat.

Low-Bandgap, Donor-Acceptor Conjugates Based on Tetracyanobutadiene (TCBD) and Dicyanoquinodimethane (DCNQ): Synthesis, Structure and Photochemical Properties

Ground and excited state charge transfer interactions in donor-acceptor conjugates has been one of the most widely studied topics by the scientific community over the last two decades as its significance is profound in solar energy conversion, and building optoelectronic devices. Among these, p-conjugated donor-acceptor conjugates are appealing because of their applications in the field of non-linear optics and electroluminescent devices. The photonic properties of p-conjugated donor-acceptor conjugates can be tuned by altering the strength of the donor or acceptor units, and by varying the connecting p-linker. Photosensitizer, electron donors such as porphyrins, phthalocyanines and BODIPYs have been traditionally used as building blocks in the construction of such light-powered ensembles due to their easily modifiable spectral and redox properties.In the present contribution, we report development of a new class of intramolecular charge transfer complexes derived from nonplanar, push-pull substituted buta-1,3-dienes by [2+2] cycloaddition of either tetracyanoethene (TCNE) or tetracyano-p-quinodimethane (TCNQ) with a variety of photosensitizer (electron donor) functionalized alkynes. This reaction efficiently converted the TCNE and TCNQ entities to highly electron-deficient, tetracyanobutadiene (TCBD) and dicyanodiquinodimethane (DCNQ) entities at the buta-1,3-dienes site.1-3 These charge transfer complexes are engineered to have small bandgap to extend the absorption well into the near-IR region; that is, to provide a better optical window for optoelectronic applications, especially in organic photovoltaics that use the majority of available sunlight. The newly synthesized complexes have been fully characterized using spectral, electrochemical, spectroelectrochemical and computational methods, and occurrence of ground state charge transfer interactions have been established. Further, excited state charge transfer in the complexes has been confirmed by photochemical studies performed using time-resolved emission and femtosecond transient absorption studies in solvents of varying polarity. Ultrafast charge separation has been witnessed in these closely spaced, strongly interacting triads.1-3 1. Sharma, M. B. Thomas, R. Misra, F. D’Souza, ‘Strong Ground and Excited State Charge Transfer in C3‐Symmetric Truxene Derived, Low‐Band Gap, Phenothiazine‐Tetracyanobutadine (TCBD) and Expanded TCBD Conjugates’, Angew. Chem. Int. Ed. 2019, 58, 4350-4355.2. Y. Rout, Y. Jang, H. B. Gobeze, R. Misra, F. D’Souza, ‘Conversion of Large Bandgap Triphenylamine-Benzothiadiazole to Low Bandgap, Wide-Band Capturing Donor-Acceptor Systems by Tetracyanobutadiene and/or Dicyanoquinodimethane Insertion for Ultrafast Charge Separation’ J. Phys. Chem. C. 2019, 123, 13382-23389.3. P. Gautam, R. Misra, M. B. Thomas, F. D’Souza, Ultrafast Charge-Separation in Triphenylamine-BODIPY-Derived Triads Carrying Centrally Positioned, Highly Electron- Deficient, Dicyanoquinodimethane or Tetracyanobutadiene Electron-Acceptors’ Chem. Eur. J. 2017, 23, 9192-9200.

Effect of Solvent-Derived Highly Luminescent Multicolor Carbon Dots for White-Light-Emitting Diodes and Water Detection.

Recently, the multicolor fluorescent carbon dots (CDs) have drawn much attention due to their various applications. Herein, we report multicolor emissive CDs by solvent-controlled and solvent-responded approaches. The blue to red color emissive CDs are obtained by the solvothermal method by varying the solvent during the reaction. The red color emissive CDs (R-CDs) with good quantum yield is obtained in a water medium. The detailed characterization revealed that the solvent controls the particle size, band gap, and nitrogen doping concentration. Specifically, in the protic solvent, the high N content and presence of imine nitrogen are the reason for red emission. However, in an aprotic solvent, the least N doping and a lack of C-O groups are responsible for a blueshift. Interestingly, it was observed that the R-CDs provide a full range of visible color by dispersing in different immiscible solvents. The fluorescence emission in immiscible solvents is redshifted by enhancing the polarity. Moreover, the developed CDs detected the low water concentrations (≤0.2%, v/v) visually and fluorometrically in various organic solvents. Simultaneously, we have employed synthesized CDs in white-light-emitting diodes and fluorescent ink.

Aurone Derivative Revealing the Metabolism of Lipid Droplets and Monitoring Oxidative Stress in Living Cells.

Lipid droplets (LDs) are closely connected to many physiological processes and abnormal LDs are related to many diseases. Herein, a family of two-photon fluorescence compounds based on the aurone skeleton were developed as efficient LDs imaging probes. They exhibit the obvious solvatochromism effect from blue to orange emission (∼140 nm shift) in various solvents. The robust probes possess low toxicity to living cells, high photobleaching resistance, and superior photostability and can light up LDs with high specificity. Furthermore, the probe DMMB (aurone skeleton with dimethylamino) was carefully applied in real-time monitoring of the morphological changes of LDs and the interactions between LDs and mitochondria under specific physiological conditions (e.g., starvation). We have observed for the first time the dynamic change between mitochondria and LDs when mitochondrial damage is caused by a large excess of H2O2 in a short period of time.

Hybrid coumarin-difluoroboron dyes for mitochondrial staining

To develop new dyes with mitochondria staining capacity, a series of zwitterionic dyes of hybrid coumarin-difluoroboron have been synthesized. The hybrid dyes are conjugated by 7-diethylaminocoumarin, difluoroboron (BF2) β-diketone and electron-donating group. The dyes show deep-red emission (600–680 nm) and high fluorescence quantum yield in organic solvents. The nature of ICT and zwitterion has been fully researched by TD-DFT and ESP calculations. Co-staining with the Mito–Tracker Green shows staining capability to mitochondria in living cells by confocal cell imaging experiments. This work can provide a new strategy for the design of neutral cellular probes for mitochondria staining.

Dual luminescent charge transfer probe for quantitative detection of serum albumin in aqueous samples.

In diagnostic medicine serum albumin is considered as an important biomarker for assessment of cardiovascular functions and diagnosis of renal diseases. Herein, we report a novel donor-π-π-acceptor fluorophore for selective detection of serum albumin in urine samples. In our design, a phenolic donor was conjugated with a tricyanofuran (TCF) acceptor through a dimethine bridge via a simple condensation reaction. The stereoelectronic effects of the incorporated methoxy (-OCH3) groups and the TCF moiety-in conjunction with the extended π-electron conjugation-led to dual red and NIR-I absorption/emission in water. Moreover, due to superior electron transfer between a phenolate donor and the TCF acceptor and the subsequent energy decay from the charge transfer states, the fluorophore displayed negligible fluorescence emission in water and other polar solvents. Consequently, we have been able to utilize the fluorophore for quantitative estimation of serum albumin both in the red (<700nm) and NIR-I (700-900nm) regions of the electromagnetic spectrum with excellent reproducibility. The fluorophore selectively recognized human serum albumin over other proteins and enzymes with a limit of detection of 10mg/L and 20mg/L in simulated urine samples at red and NIR-I emission window of the spectrum, respectively. By molecular docking analysis and experimental displacement assays, we have shown that the selective response of the fluorophore toward human serum albumin is due to tighter supramolecular complexation between the fluorophore and the protein at subdomain IB, and the origin of the NIR-I (780nm) emission was attributed to a twisted conformer of phenolate-π-π-TCF system in aqueous solution. These findings indicate that the fluorophore could be utilized for quantitative detection of human serum albumin in urine samples for clinical diagnosis of albuminuria.

Evaluating the vapour evaporation from the surface of pure organic solvents and their mixtures

Some perfumery and cosmetic products represent mixtures and they include large parts of solvents as ethanol, water, acetone and isopropyl alcohol. Solvents as pure hexane and ethanol-water mix­tures are used in the solvent extraction of oil-bearing plant materials and herbs. The goal of this study was the emissions of volatile solvents released during above pointed productions to be evaluated. It was found that the specific evaporation rate varies from 1.2 kg/(m2.h) (for pure methoxy-propanol) to 66 kg/(m2.h) (for three-com­ponent mixture including acetone). The eva­poration rate is higher for solvents with higher vapour pressure and at a higher velocity of surrounding air. The evaporation is less intensive from pure solvents than their mixtures. The time for the eva­po­ration from a film of solvents and their mixtures was also evaluated. It varies from 10 s (for isopropyl alcohol) to 9 min (for methoxy-propanol).Practical applicationsThe evaluation of volatile solvent emissions is a mandatory step in the design of plants for manufacturing perfumery, cosmetics, deriving essential and edible oils by means of organic solvents. Most of volatile organic solvents used are highly flammable and healthy hazardous. For assuring fire safety and safety-health working conditions and environment the ventilation system must be designed on the base of this emission evaluated. The obtained results were applied for plant design of the company “Star Nails Bulgaria” Ltd. Plovdiv.

Emissions of selected monoaromatic hydrocarbons as a factor affecting the removal of single-use polymer barbecue and kitchen utensils from everyday use

The main focus of this study is the emission of monoaromatic hydrocarbons because these are the preliminary factors of potential solvent and monomer residues present in single-use plastic barbecue and kitchen utensils comprising polystyrene, polypropylene, natural cellulose, and biodegradable polymers intended for use with hot meal or beverages. Herein, the emissions of monoaromatic hydrocarbons (styrene, benzene, toluene, ethylbenzene, and xylene compounds and the total volatile organic compounds (TVOC)) from nine types of disposable plastic utensils are reported. Seventy two samples of single-use plastic utensils were conditioned at 40 and 80 °C using a stationary emission microchamber system. The average TVOC released from the studied polystyrene, polypropylene, and natural or biodegradable utensils were (2.3 ± 1.3), (1.01 ± 0.15), and (0.48 ± 0.37) μg g−1, respectively, at 40 °C and (11.1 ± 1.2), (46.1 ± 9.5), and (5.5 ± 1.1) μg g−1, respectively, at 80 °C. Significant emissions of styrene (ranged from 3.5 up to 15.3 × 103 ng∙g−1), toluene (from 2.8 up to 0.53 × 103 ng∙g−1), and ethylbenzene (from 3.7 up to 5.7 × 103 ng∙g−1) from the studied samples were observed, especially at 80 °C. Thus, elevated temperatures increase the potential emission of solvent and monomer residues from plastics and could affect the quality of consumed meals or beverages, such as taste. Additionally, to determine the possible interactions between the measured chemical compounds in the plastic utensils, the Pearson's correlation coefficients were calculated.

Solution‐blow spun PLA/SiO2 nanofiber membranes toward high efficiency oil/water separation

AbstractWith the ever frequent of industrial organic solvent emissions and oil spillages, the development of high efficiency oil/water separation materials has attracted extensive attention. Here, PLA‐based nanofiber membranes modified with metal oxides (SiO2, TiO2, Al2O3, and CeO2) are fabricated through blow spinning the mixed solution of polylactic acid (PLA) and metal oxide nanoparticles (NPs). Results shows that the addition of SiO2 NPs significantly increases the hydrophobicity of the membranes, while maintaining the excellent superoleophilicity. The PLA/SiO2 nanofiber membranes demonstrate a higher separation performance than pure PLA, PLA/TiO2, PLA/Al2O3, and PLA/CeO2 nanofiber membranes with high separation efficiency (~100%) and permeation flux (17,800 L m−2 h−1 for n‐heptane), as well as prominent oil adsorption capacity (19.9 g/g for n‐hexane). The successful fabrication of metal oxides modified PLA nanofiber membranes with high separation and adsorption ability, and excellent durability hold great application potential in the field of oily wastewater treatment.

Dual-Self-Restricted GFP Chromophore Analogues with Significantly Enhanced Emission.

The tremendous gap of fluorescence emission of synthetic green fluorescent protein (GFP) chromophore to the protein itself makes it impossible to use for applications in molecular and cellular imaging. Here, we developed an efficient methodology to enhance the photoluminescence response of synthetic GFP chromophore analogues by constructing dual-self-restricted chromophores. Single self-restricted chromophores were first generated with 2,5-dimethoxy substitution on the aromatic ring, which were further modified with phenyl or 2,5-dimethoxy phenyl to form dual-self-restricted chromophores. These two chromophores showed an obvious solvatofluorochromic color palette across blue to yellow with a maximum emission Stokes shift of 95 nm and dramatically enhanced fluorescence emission in various aprotic solvents, especially in hexane, where the QY reached around 0.6. Importantly, in acetonitrile and dimethyl sulfoxide, the fluorescence QYs of both chromophores were over 0.22, which were the highest reported so far in high polar organic solvents. Meanwhile, the fluorescence lifetimes also improved obviously with the maximum of around 4.5 ns. Theoretical calculations revealed a more favorable Mülliken atomic charge translocation over the double-bond bridge and illustrated much higher energy barriers for the Z/E photoisomerization together with larger bond orders compared with the GFP core chromophore, p-HBDI. Our work significantly improved the fluorescence emission of synthetic GFP chromophore analogues in polar solvents while reserved the multicolor emitting function, providing a solid molecular motif for engineering high-performance fluorescent probes.

Complementary Fluorescence Emission and Second Harmonic Spectra Improve Bilayer Characterization.

Complementary investigation of Laurdan fluorescence emission and second harmonic (SH) spectra in nonpolar, protic and aprotic polar solvents and phospholipid bilayers was carried out. SH of spectra computed using methods familiar in electro spin resonance spectroscopy yielded better resolution. Spectra were fit to log-normal distributions. SH spectra showed presence of two emissions in protic polar and nonpolar solvents and in both bilayer gel and liquid phases and a single line in aprotic polar solvents. Each of the half maximal positions of each line in both homogenous solvents and bilayers, expresses similar linearity with peak position. This shared feature suggests planar and nonplanar Laurdan conformation respectively in the longer (red) and shorter (blue) wavelength emitting states. The weaker 432nm blue line, not detected before in the gel phase, is distinguishable in the SH. Temperature trajectories of areas and peak positions of the individual lines bring new insight into the nature of lipid packing and evolution of domains, indicating inhomogeneous lipid packing even in the gel phase. The blue line identifies as emission from Laurdan in tighter packed regions and the dominant 445-448nm red line in the gel phase shifting to 484nm in the liquid phase as emission from Laurdan-water coupled states that are in varying stages of relaxation according to temperature and phase. Unexpected increase in the area of the blue line with temperature through the gel-liquid transition is consistent with coexisting low and high curvature domains and Laurdan's preference for less polar low curvature domains.