Emission In Solvents Research Articles

Single and two-photo excited violet-blue fluorescence from aza [6]helicenes and the plannar precursors based-on indole, carbazole, and fluorene

Organic π-conjugated materials exhibiting violet-blue emissions are of great interest for diverse applications. Helicenes and stilbenes hold great potential as compounds capable of achieving violet-blue fluorescence. In this study, aza[6]helicenes THNI and DHNC, along with their planar precursors DFVHI and HHIVC, were successfully synthesized using indole, carbazole, and fluorene units as building blocks. The molecular structures were verified through the utilization of 1H and 13C nuclear magnetic resonance (NMR), high resolution mass spectroscopies (HRMS), and the crystal structure of THNI was further elucidated via X-ray analysis. The synthesized material exhibited exceptional thermal stability with a Td value of ≥350 °C. The HOMO and LUMO energy levels were determined through cyclic voltammetry analysis, while density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations at the B3LYP/6-31G(d) level were employed to investigate ground-state geometries and vertical electronic transitions. Optical properties were characterized using UV–vis absorption spectroscopy as well as single- and two-photon excited photoluminescence. The UV–vis absorption spectra indicate that helicenes possess superior light-harvesting capabilities compared to their planar precursors, owing to the former's higher molar extinction coefficients. These compounds exhibit violet-blue emissions in various solvents and solid-state films. In addition, aza[6]helicenes exhibit higher photoluminescence quantum yields (PLQYs) and shorter maximum emission peaks compared to their planar precursors. However, the maximum two-photon absorption (TPA) cross section (δ) values of aza[6]helicenes are lower than those of their planar counterparts. Therefore, THNI and DHNC may be promising candidates for violet-blue emitters in OLEDs due to their curved confined π-electron systems, high thermal and optical stability, and high PLQYs. Meanwhile, DFVHI and HHIVC exhibit potential as two-photon fluorescent probes for bioimaging.

ESIPT mechanism of triple emission with hydroxy-oxadiazole compound in DMSO: A theoretical reconsideration

The compound in solvents with triple fluorescence feature of excited state intramolecular proton transfer (ESIPT) has a broad prospect in fluorescent probes, dye sensors and molecular synthesis of photosensitive dyes. An ESIPT molecule hydroxy-bis-2,5-disubstituted-1,3,4-oxadiazoles (compound 1a) emits two fluorescence peaks in dichloromethane (DCM) and three fluorescence peaks in dimethyl sulfoxide (DMSO). [Dyes and Pigments 197 (2022) 109927]. Two longer peaks were attributed to enol and keto emission in both solvents and the shortest third peak in DMSO was just attributed simply. However, there is a significant difference in proton affinity between DCM and DMSO solvents which has influence on the position of emission peaks. Therefore, the correctness of this conclusion needs to be further verified. In this research, density functional theory and time-dependent density functional theory method are used to explore ESIPT process. Optimized structures indicate ESIPT occurs through molecular bridge assisted by DMSO. The calculated fluorescence spectra demonstrate two peaks indeed originated from enol and keto in DCM, while interestingly three peaks are originated from enol, keto and intermediate in DMSO. Infrared spectrum, electrostatic potential and potential energy curves further prove existence of three structures. We reveal the mechanisms that compound 1a molecule occurs ESIPT in DCM solvent and undergoes an ESIPT through assisted by DMSO molecular bridge. Additionally, three fluorescence peaks in DMSO are reattributed. Our work is expected to provide an insight for understanding intra- and intermolecular interactions and synthesis of efficient organic lighting-emitting molecule.

Investigation of the Superoxide Anion-Triggered Chemiluminescence of Coelenterazine Analogs

Reactive oxygen species (ROS), including superoxide anion, are involved in regulating various signaling pathways and are also responsible for oxidative stress. Sensing superoxide anion is of particular importance due to its biological significance. One potential approach is to use Coelenterazine as a chemiluminescent probe for the dynamic sensing of this ROS. In this study, we investigated the superoxide anion-triggered chemiluminescence of native Coelenterazine and two halogenated analogs and found that they showed a ~100-fold enhancement of light emission in aqueous solution, which was significantly reduced in methanol and nonexistent in aprotic solvents. In fact, Coelenterazine showed more intense light emission in aprotic solvents and, interestingly, although the light emission of the analogs seemed relatively unaffected by the solvents, their chemiluminescence was significantly quenched in water compared to methanol and, especially, to aprotic media. This suggests that the quenching effect observed for Coelenterazine is responsible for the differences in aqueous media, rather than an intrinsic enhanced emission by the analogs. In summary, we present Coelenterazine analogs that could serve as a basis for enhanced sensing of superoxide anion, providing information that could further our understanding of this chemiluminescent system.

Impact of high capture rates and solvent and emission management strategies on the costs of full-scale post-combustion CO2 capture plants using long-term pilot plant data

Pilot plant campaigns are critical to our understanding of the performance of solvent-based post-combustion capture processes. During the ALIGN-CCUS project, long-term pilot plant runs in the Niederaussem lignite-fired power plant were conducted, that aimed to investigate solvent degradation and emissions management and capture rates beyond 90%. Based on these pilot runs, we here investigated the cost effect of amine degradation and emissions for two solvent systems, MEA and CESAR1, as well as the effect of incorporating degradation and emission mitigation strategies and the effect of higher carbon capture rates. We found that for lignite-fired power plants, CESAR1 is not per se a cheaper solvent system than MEA when actual solvent losses (or their mitigation measures) are considered, contrary to what earlier studies have suggested. It may, therefore, be just as good a benchmark as MEA would be, as long as all degradation and emission (mitigation) costs are included in their cost estimates. Second, MEA reclaiming with ion exchange resins and CESAR1 emission mitigation measures (dry-bed and/or turbulent flue gas pre-treatment) do not increase the cost of CO2 capture or electricity. If anything, our work suggests these measures reduce costs marginally, owing to lower solvent make up, offsetting the additional capital and operational costs. Finally, the cost effect of capture rates beyond 90% proves minimal (the cost of CO2 capture and the levelized cost of electricity increase by 3% and 5%, respectively, when moving from 90% to 98% CO2 capture rate), indicating solvent-based CO2 capture may also be a useful mitigation strategy in societies transitioning towards net-zero-CO2 emissions.

Targeted electrochemical reduction of carcinogenic N-nitrosamines from emission control systems within CO2 capture plants

N-Nitrosamines are one of the environmentally significant byproducts from aqueous amine-based post-combustion carbon capture systems (CCS) due to their potential risk to human health. Safely mitigating nitrosamines before they are emitted from these CO2 capture systems is therefore a key concern before widescale deployment of CCS can be used to address worldwide decarbonization goals. Electrochemical decomposition is one viable route to neutralize these harmful compounds. The circulating emission control waterwash system, commonly installed at the end of the flue gas treatment trains to minimize amine solvent emissions, plays an important role to capture N-nitrosamines and control their emission into the environment. The waterwash solution is the last point where these compounds can be properly neutralized before becoming an environmental hazard. In this study, the decomposition mechanisms of N-nitrosamines in a simulated CCS waterwash with residual alkanolamines was investigated using several laboratory-scale electrolyzers utilizing carbon xerogel (CX) electrodes. H-cell experiments revealed that N-nitrosamines were decomposed through a reduction reaction and are converted into their corresponding secondary amines thereby neutralizing their environmental impact. Batch-cell experiments statistically examined the kinetic models of N-nitrosamine removal by a combined adsorption and decomposition processes. The cathodic reduction of the N-nitrosamines statistically obeyed the first-order reaction model. Finally, a prototype flow-through reactor using an authentic waterwash was used to successfully target and decompose N-nitrosamines to below the detectable level without degrading the amine solvent compounds allowing them to be return to the CCS and lower the system operating costs. The developed electrolyzer was able to efficiently remove greater than 98% of N-nitrosamines from the waterwash solution without producing any additional environmentally harmful compounds and offers an effective and safe route to mitigate these compounds from CO2 capture systems.

Characteristics of Airborne Pollutants in the Area of an Agricultural–Industrial Complex near a Petrochemical Industry Facility

In the area of a petrochemical industrial site, ten monitoring stations are established to determine the airborne pollutants that are emitted, which include criteria air pollutants and 54 species of ozone formation precursors of volatile organic compounds (VOCs). The hourly pollutants are increased by human activities, such as traffic flow after 7:00 a.m., and ozone becomes more abundant as solar radiation increases in intensity. Monthly air pollutants are present in low concentrations during the rainy season from May to September and in high concentrations from October to April. Results show that VOC concentrations are low in the summer (average concentration 5.7–5.9 ppb) and more than double in the winter (11–12 ppb), with 52–63% alkanes, 18–24% aromatics, 11–22% alkenes and 4.7–7.1% alkynes. Ethane, toluene, propane, n-butane, ethylene and acetylene are the major VOCs, with an annual average concentration exceeding 0.50 ppb. In 2016–2020, the VOC concentration is decreased from 10.1 to 7.73 ppb, corresponding to the ozone formation potential (OFP) decrease from 84 to 61 μg-O3 m−3, with toluene, m,p-xylene, ethylene and propene being the most abundant species. The primary VOC sources are petrochemical industry sites, fuel combustion, vehicle exhaust emissions and evaporation, solvent application, industrial facilities and emission from farming vegetation.

Ultra-long room temperature phosphorescence carbon dots-based composites with high environmental stability

Room temperature phosphorescence (RTP) materials occupy an extremely important position in many applications, and how to achieve stable phosphorescent emission to the environment is still a huge challenge. In this article, citric acid (CA) derived carbon dots (CACDs) are firmly embedded in the melamine (MA)-derived crystals by covalently cross-linking way through a one-step hydrothermal method. The obtained CA-MA-3 composite has an ultra-long phosphorescence lifetime of 760 ms with an absolute quantum yield of 11.24%. The RTP should originate from the possible formation of hydrogen and covalent bonds between CACDs and MA-derived crystals. More importantly, the composite exhibits super-stable RTP emission in organic solvents and aqueous solutions with pH = 1 or 14. Because of the excellent phosphorescence capability of the CA-MA-3, it can be widely used for anti-counterfeiting security under extremely harsh conditions.

Impact of Electron-Donating Groups on Attaining Dual-Emitting Imidazole-Based Donor-Acceptor Materials.

Imidazole-based donor-acceptor materials are well known for their polarity-controlled trade-off phenomenon between the localized excitation-based short-wavelength (SW) emission in nonpolar solvents and charge transfer dominated long-wavelength (LW) emission in polar solvents. To attain concurrent SW- and LW-based dual-emission characteristics, a series of imidazole-based donor-acceptor fluorophores (CBImDCN, TPImDCN, PZImDCN) possessing different electron-donating groups such as carbazole, triphenylamine, and phenothiazine linked via the N-position of the imidazole core unit were synthesized and verified by NMR and mass spectroscopic techniques. As a result, the strong donating TPImDCN and PZImDCN exhibited dual emission in different solvents of varying polarity, covering the blue (SW) and green/orange (LW) regions. On the other hand, in contrast, only an SW emission band is observed with the weak donating CBImDCN. Moreover, PZImDCN shows panchromatic emission under 365 nm illumination, while only orange color emission is observed under visible light excitation, revealing two different origins of SW and LW emissions, as also evidenced from DFT calculations. Overall, this work reveals a new approach for attaining concurrent SW and LW emission characteristics from imidazole-based D-A materials and sheds light on the design and development of novel panchromatic emitters with intriguing properties for lighting and display applications.

Current status of CO2 capture with ionic liquids: Development and progress

Global warming triggered by greenhouse gas (GHG) emissions, particularly carbon dioxide (CO2), significantly influences climate change and has become a common environmental issue recently. The current amine-based technologies (ABTs) for CO2 capture (CAPCO2) have high energy demand, low absorption, and desorption rates, and are less environmentally sustainable due to high emissions of volatile solvents. Therefore, the development of environmentally friendly CAPCO2 materials and/or processes is a growing area of research. The utilization of ionic liquids (ILs) for CAPCO2 has recently attracted attention. The unique characteristics of ILs, such as their low vapor pressure and high affinity for CAPCO2 as well as their low volatility make them a viable substitute for the existing processes. This work provides a comprehensive overview of the accomplishments and challenges during the use of ILs for CAPCO2. The Review also outlines the mechanisms of the CAPCO2 with ILs at the molecular level, the properties of ILs, characterization of the CO2/IL systems, and the effect of operating conditions on CO2 uptake (UPCO2) capacity by ILs. It also emphasizes the impact of cations, anions, and functional groups on the solubility of CO2 ((SCO2)) in ILs as well as the biodegradability and toxicity of ILs. Additionally, recent advances in IL membrane technology for the CAPCO2 processes are considered. Lastly, the contribution of molecular simulations to create and assess ILs was reviewed. Protic and aprotic ILs properties have shown outstanding efficiency of UPCO2. The interactions between the anionic part of IL and CO2 enhance the UPCO2 and outperform the efficiency of traditional organic solvents. Functionalized ionic liquids (FUNILs) with tuned functional groups, supported ionic liquids membranes (SILMs) as well as reversible ionic liquids (RILs) have improved the efficiency of ILs as a promising CO2 capturing process from industrial streams even under low CO2 partial pressure. The relative importance of the chemical breakdown of the IL constituents (cation–anion interfacial structuring) during the CAPCO2 process at different operating temperatures is unclear, and more research in this area is required to better inform the design of new ILs. This review provides a proper/systematic guideline to help ILs manufacturers and engineers design high-capacity ILs for appropriate CAPCO2.

Investigating sensitivity of ozone to emission reductions in the New York City (NYC) metropolitan and downwind areas

Ozone sensitivity to emission changes in urban environments were examined using WRF and CAMx simulations for the New York City metropolitan area (NYC) with data from the 2018 Long Island Sound Tropospheric Ozone Study measurements. The WRF simulation showed large positive biases of windspeed over entire domain, but those were significantly reduced with observational nudging. The base CAMx simulation showed large positive bias for NO2 concentrations in NYC, which was corrected after NOx emission adjustment (22% reduction) based on previous work. The improved modeling platform demonstrated reliable performance skills for regulatory applications. Pollution transport from NYC to the downwind region were well captured by the model. Simulated ozone concentration increases in response to NOx emission reductions within NYC proximity suggested this area to be a VOC-limited ozone formation regime. Reducing anthropogenic emissions by 50% for all pollutants reduced the number of simulated ozone exceedances from 18 to 9 days for NYC. Emission reductions were even more effective for air quality improvements in the downwind region with ozone exceedances decreasing from 20 to 7 days. Source apportionment showed mobile and industrial solvent emission sectors to be contributing more to ozone exceedances than the electrical generating units (EGU) sector in both NYC and the downwind region. The largest air quality improvement appeared to be associated with VOC emission reductions from the industrial solvent sector. All source sectors yielded higher ozone production efficiency when emissions were reduced by 50%, suggesting remaining emissions can be more potent in producing ozone per molecule of NOx.

Synthesis of New 2D-π-2A Chromophores Based on Tetraphenyl Fulvene and Investigation of Their Optical Properties

Emitting organic molecules can find application in Light-Emitting Diodes and as Biosensors. The new generation of organic emitters are full conjugated molecules exhibiting conformational freedom that can gain emission intensity when accumulate. We synthesized new tetraphenyl fulvene (TPF) derivatives by connecting the phenyl rings 3 and 4 with electron donor groups and the fulvene carbon 6 with two electron-withdrawing groups. We analyzed the optical properties, UV–vis absorption, and emission in different solvents with different polarities. The compound with π-donor thiophene and π-acceptor methyl malonate, named 5mT, displays the highest emission intensity compared to unsubstituted TPF, the compounds with a weak electron π-donor group on phenyl rings 3 and 4, and the weak π-withdrawing group on carbon 6 of the fulvene core. The same compound exhibits emission frequencies in solutions that vary from 435 to 495 nm in the different solvents, while the emission frequency is 435 nm independently of the solvent for the other TPF derivatives. We demonstrated that D-π-A TPF derivatives with high dipolar moments display a fluorescence that is strongly influenced by conformational status and intermolecular interactions.

Twisted intramolecular charge transfer, nonlinear optical, antibacterial activity, and DFT analysis of ultrasound processed (E)-N′-(4-isopropylbenzylidene)nicotinohydrazide

Hydrazones have attracted considerable interest for their antimicrobial and nonlinear optical (NLO) applications. In the present work, a new hydrazone (E)-N′-(4-isopropylbenzylidene)nicotinohydrazide (INH) was synthesized by a condensation reaction of cuminaldehyde with nicotinic hydrazide via ultrasonication. The hydrazone was characterized by FT-IR spectroscopy, mass spectrometry, NMR (1H, 13C, HOMO-COSY, HSQC, and DEPT-135), elemental analysis, and FESEM analyses. Phase-pure and non-existent isomorphic phase transition in INH was demonstrated by X-ray diffraction and thermogravimetric analysis. The absorption maximum of INH in an aqueous solution was red-shifted compared to that of the reactant molecules, indicating that the CN bond formation efficiently enhances the resonance interaction towards the pyridine ring. Fluorescence emission of INH at a shorter wavelength is caused by a locally excited state. A longer wavelength band is caused by intramolecular proton transfer in nonpolar/aprotic solvents, while it is caused by TICT emission in protic solvents. The direct and indirect bandgaps of the INH crystals were assessed using Tauc plots and the Kubelka–Munk algorithm. The efficacy of INH for the inactivation of E. coli and B. subtilis were examined through a plate colony counting assay, and the inactivation was 62.7 ± 0.2 % and 98.3 ± 0.4 %, respectively. The geometrical structure, Mulliken, MEP surface, and electronic properties of INH are theoretically optimized using density functional theory (DFT) at the B3LYP/6-31G(d,p) level and showed good concurrence with the experimentally defined structure. The INH displays higher NLO properties compared to urea as a reference, as determined by molecular hyperpolarizability analysis. The frontier molecular orbitals and global reactivity descriptors showed that INH is more reactive and reasonably stable.

Selective Conversion of the CaO-Captured CO2 to CH4 by Ni- and Hydrogen-Assisted Calcium Looping Processes in a Batch Reactor

Storing and hydrogenating CO2 to CH4 is an efficient solution to alleviate the greenhouse effect and energy shortage. This work demonstrated that the CaO-captured CO2 could be selectively converted to CH4 by Ni- and hydrogen-assisted calcium looping (CaL) processes in a batch reactor. The Ni/CaO composite was first synthesized in one step at room temperature by calcium-induced hydrogenation of Ni-mixed calcium carbonate without the use of any solvent and CO2 emission. The CO2 capture properties over the Ni/CaO composite and the methanation properties of the Ni/CaCO3 composite produced after CO2 capture were then studied in a batch reactor. It was proved that the CO2 capture properties of CaO can be improved, the CaO recovering temperature can be significantly lowered, and valuable CH4 can be selectively produced by Ni- and hydrogen-assisted calcium looping processes at moderate/high temperature. The 68.58% methane yield and 100% methane selectivity were achieved under relatively mild conditions. After five Ni- and hydrogen-assisted CaL processes, the methane yield still reaches 45%. This study offers a novel energy-saving CaL process, which can be utilized for facile and selective conversion of the CaO-captured CO2 to CH4.

Facile synthesis and in-vitro cytotoxicity study of some 5-(4-substituted phenyl)-7-hydroxy-9-methyl-2-thioxo-2,3-dihydro-1H-dipyrimido[1,2-a:4′,5′-d]pyrimidin-4(5H)-one derivative and their Optoelectronic, DFT, and LFPs applications

A some new 5-(4-Substituted phenyl)-7-Hydroxy-9-methyl-2-thioxo-2,3-dihydro-1H-dipyrimido[1,2-a:4′,5′-d]pyrimidin-4(5H)-one derivative (4a-c) have been synthesized through multicomponent reaction using l-Proline as a catalyst and the structures were confirmed by analytical and spectroscopic techniques. Optical properties were studied in solvent media, absorption and emission bands appeared at ̴ 290 nm to 370 nm of longer wavelength. A cyclic voltammogram was used to study the redox behavior and estimation of experimental HOMO-LUMO of targeted compounds. DFT studies reveal compounds are better photoactivity and kinetic stability at the gaseous phase. Further, LFPs have been developed and visualized by powder dusting method on selected surfaces and clear observation of II and III of LFPs features under UV-Light. In addition, compounds are screened for cytotoxicity study against the A549 cell line, and compound 4c exhibits better selectivity against the cell line with a noticeable IC50 value of 16.74±0.23 µg/mL. As well compounds were analyzed for in-silico docking studies against the target enzyme EGFR Kinase protein and ADME toxicology studies reveal that obtained compounds are nontoxic. From these findings, we conclude that our obtained targets have better optoelectronic behavior and good anti-cancer agents.

Synthesis and characterization of blue light emitters based on dimers of fluorene: Effects of different pendant electron-withdrawing moieties

2,4,6-Triphenyl-1,3,5-triazine, diphenylmethanone and triphenylphosphine oxide were introduced into the 9-position of one fluorene moiety to produce donor-acceptor vertically structured emitters DFTRZ, DFCO and DFPO. The Tg of DFTRZ, DFCO and DFPO solid powder are 135 °C, 89 °C and 97 °C, and DFTRZ with the most rigid receptor of 2,4,6-triphenyl-1,3,5-triazine showed the highest thermal stability, whose Td reached 436 °C, far exceeding those of DFCO and DFPO. The absolute photoluminescence quantum yields of DFTRZ, DFCO and DFPO solid powders are 14.35%, 1.13% and 7.57%, and the molecular framework of DFTRZ is meaningful to enhance the absolute photoluminescence quantum yields of obtained emitters. The donor-acceptor vertical structures do not endow these emitters with expected thermally activated delayed fluorescence emission. Beside the local emission of fluorene-based dimers, DFTRZ exhibits additional intramolecular charge transfer emission in polar solvents. The unique polar-induced dual emission of DFTRZ in solvents deteriorates the emission purity of the obtained emitter, and this embarrassment can be eased by DFPO in some degree. However, the dual light emission of DFTRZ in some polar solvents is useful to be senser and produce white light emission in solution. The maximum luminance of devices with bis (2-methyldibenzo[f, h] quinoxaline) (acetylacetonate) iridium (III) doped in emitters DFTRZ, DFCO and DFPO is higher than those of 2,3,5,6-tetrakis[3,6-bis(1,1-dimethylethyl)− 9 H-carbazol-9-yl]benzonitrile doped devices, and the corresponding maximum luminance is 16050 cd·m−2 for DFTRZ, 4545 cd·m−2 for DFPO and 11025 cd·m−2 for DFCO. DFPO is the best host of blue light emitters for OLED applications in term of color purity.

Assessment of Degradation and Ammonia Emission of Entropy Solvents

Assessment of Degradation and Ammonia Emission of Entropy Solvents

NMVOC Emissions from Solvents Use in Greece: Monitoring and Assessment

The use of solvents and other volatile organic chemicals is a significant source of Non-Methane Volatile Organic Compounds (NMVOCs) emissions. Due to the wide spectrum of applications of solvents and numerous locations where these occur, the estimation of NMVOCs emissions can be challenging. The aim of this paper is to present the methodological framework used in Greece for the estimation of NMVOCs emissions. It covers processes and products that use solvents and other volatile organic chemicals in several industries, as well as in households. The framework is based both on existing methods found in the literature and on new emission factors developed in order to reflect the mitigation potential of EU Directives and national legislation aiming at the reduction of NMVOCs emissions. The developed framework was used to forecast future NMVOCs emissions and assess the implemented mitigation actions. Results were verified by comparison with solvent emission estimates from the European Solvent Industry Group.

Methylated Chromenoquinoline as a Novel Nucleus Fluorescent Probe for Nucleic Acid Imaging.

Two chromenoquinoline-based fluorescent probes 1a-b have been synthesized and investigated. Photofading behaviors of compounds 1a-b showed that at least 89% absorption remained after 6h irradiating, meanwhile, many of ions and amino acids had negligible impacts on their fluorescence intensity, which meant they had excellent photostability and selectivity. Probes 1a-b exhibited strong absorption and emission in organic solvents with large fluorescence quantum yields, even in water probe 1a still had a relatively large fluorescence quantum yield (20%). Combined with DFT calculation, the influence of alkylation on optical properties of 1b was elucidated. In addition, the fluorescence intensity of probe 1b with red emission enhanced by 5.4-fold and 5.3-fold after DNA and RNA added, and the fluorescence quantum yield increased from 3% to 17% and 14%, respectively, but the neutral molecule 1a had no response to nucleic acid. Furthermore, confocal microscopy imaging of probes 1a-b showed that 1a targeted lipid droplets while the methylated probe 1b to nucleus in living HeLa cells. The results indicated that the subcellular targeting zone could be changed by alkylation of nitrogen atom on chromenoquinoline-based conveniently, which provided a new idea for designing and synthesizing new subcellular labeled probes.

Combined Experimental and Theoretical Investigation into the Photophysical Properties of Halogenated Coelenteramide Analogs.

Marine Coelenterazine is one of the most well-known chemi-/bioluminescent systems, and in which reaction the chemi-/bioluminophore (Coelenteramide) is generated and chemiexcited to singlet excited states (leading to light emission). Recent studies have shown that the bromination of compounds associated with the marine Coelenterazine system can provide them with new properties, such as anticancer activity and enhanced emission. Given this, our objective is to characterize the photophysical properties of a previously reported brominated Coelenteramide analog, by employing a combined experimental and theoretical approach. To better analyze the potential halogen effect, we have also synthesized and characterized, for the first time, two new fluorinated and chlorinated Coelenteramide analogs. These compounds show similar emission spectra in aqueous solution, but with different fluorescence quantum yields, in a trend that can be correlated with the heavy-atom effect (F > Cl > Br). A blue shift in emission in other solvents is also verified with the F−Cl−Br trend. More relevantly, the fluorescence quantum yield of the brominated analog is particularly sensitive to changes in solvent, which indicates that this compound has potential use as a microenvironment fluorescence probe. Theoretical calculations indicate that the observed excited state transitions result from local excitations involving the pyrazine ring. The obtained information should be useful for the further exploration of halogenated Coelenteramides and their luminescent properties.

Binaphthanol-derived emitters with aggregation-induced emission, acidochromic and chiral optical properties

The development of chiral organic fluorescent molecules has attracted broad attention for their various optical applications. In this work, four pairs of chiral fluorescent molecules based on binaphthanol structure have been designed and synthesized. These molecules show blue fluorescent emission in organic solvents with good fluorescent quantum yields and large Stokes shifts. The molecules with benzoxazole moiety display aggregation-induced emission effect in methanol/water solutions, while molecules with quinazolinone moiety show aggregation-caused quenching properties. Moreover, compounds with quinazolinone moiety exhibit acidochromic properties in aqueous solution with different pH values, and their emission intensity are significantly enhanced in strongly acidic conditions. The chiral molecules generally have good circular dichroism intensity. Their R- and S- enantiomers show mirror-imaged circular dichroism curves. Further studies reveal that compound with mono quinazolinone moiety has specific aggregation-induced circular dichroism enhancement properties. This work provides a new strategy for obtaining chiral BINOL-based fluorescent molecules with unique optical properties.