Absolute Fluorescence Quantum Yield Research Articles

Biocompatible fluorescent carbon dots derived from roast duck for in vitro cellular and in vivo C. elegans bio-imaging.

Biocompatible fluorescent carbon dots (CDs) were prepared via a simple and green route using duck breasts as a natural carbon source. The CDs from duck breasts were well dispersed, and their mean particle size decreased from 2.59 to 1.95 nm when the roasting temperature increased from 200 to 300 °C. Abundant functional groups such as OH, COOH, and NH2 were observed on the surface of the CDs, providing the CDs with good water solubility. These CDs emitted strong fluorescence under ultraviolet light irradiation and exhibited superior photostability. The absolute fluorescence quantum yield of CDs rose from 10.53% to 38.05% when the relative nitrogen content of CDs increased from 7.18% to 12.73%. The CDs showed low toxicity to PC12 cells for prolonged exposure. Therefore, the duck CDs were successfully developed as fluorescent probes for in vitro PC12 cells and in vivo Caenorhabditis elegans imaging. These results indicated that the CDs derived from roast duck were biocompatible and can potentially be used as probes in bio-imaging.

Effects of different substituted positions on the photophysical properties of pyrene-based sulfides

A series of new pyrene-based sulfides were synthesized by the reaction between 4-methylbenzenethiol and R-bromopyrene (R = 1(1), 4(2), 2(3)). These compounds were structurally characterized and their properties were analyzed by spectroscopy, single crystal X-ray diffraction, electrochemistry and theoretical studies. Significant effect of substituted positions on photophysical properties were observed. The p-methylphenylthio group in 1- and 4-position significantly increases the absolute fluorescence quantum yield (ФF) in solid state, decreases the ФF in solution and almost does not change the ФF in film state compared to that of pyrene. However, this substituent in 2-position keeps the high ФF in solution, almost does not contribute to the ФF in solid state and significantly decreases the ФF in film state compared to that of pyrene. Moreover, compounds 1, 2 and 3 exhibit typical aggregation-induced emission (AIE) properties that were proved by time-resolved photoluminescence.

Rapid preparation of homogeneous carbon dots with yellow fluorescence and formation mechanistic investigation

In this study, homogeneous carbon dots with yellow fluorescence and high absolute fluorescence quantum yields (78.6%) were firstly prepared through a one-step solvothermal method without complicated process of separation, in which sodium citrate, carbamide, and anhydrous calcium chloride were adopted as precursors, while toluene was selected as solvent. The as-prepared carbon dots with an average size of 5.9 nm have a high degree of crystallinity. According to the discussion of the formation mechanism carbon dots, it is found that the toluene guarantee the formation of crystalline core and Ca2+ promotes the formation of carbonaceous core with high crystallinity, which is responsible for the ultrahigh quantum yield. Furthermore, the fluorescent properties of carbon dots are excellent in organic solvents and could be quenched by water, making them a promising material used without any modification in the detection of water in organic solvents, which has a great influence on organic chemical reaction, and may even determine the resultant, yield, and selectivity of organic reaction.

Synthesis and photophysical properties of dinaphtho[2,3-b:2′,3′-i]dihydrophenazine derivatives

A dinaphtho[2,3-b:2′,3′-i]dihydrophenazine (DNP) derivative was synthesized by Buchwald-Hartwig cross-coupling, and its electronic spectrum was compared with that of dinaphtho[b,i]dihydrophenazine-5,18-dione (DNP-dione) as an anthraquinone analog. An absorption band of DNP is attributed to extension of π-conjugation over the entire molecule via the N atom. DNP-dione showed a broad absorption band in the range 450–490 nm due to intramolecular charge-transfer interactions. Additionally, the absolute fluorescence quantum yield of DNP was larger than that of DNP-dione. DNP-dione exhibited reversible oxidation peaks and a similar oxidation potential to DNP, since there are very weak electronic interactions between the anthracene and anthraquinone units across the N atoms with the 4-octyloxyphenyl substituent.

Highly fluorescent triazolopyridine-thiophene D-A-D oligomers for efficient pH sensing both in solution and in the solid state.

Conjugated fluorophores have been extensively used for fluorescence sensing of various substances in the field of life processes and environmental science, due to their noninvasiveness, sensitivity, simplicity and rapidity. Most existing conjugated fluorophores exhibit excellent light-emitting performance in dilute solutions, but their properties substantially decrease or even completely vanish due to severe aggregation quenching in the solid state. Herein, we synthesize a series of triazolopyridine-thiophene donor-acceptor-donor (D-A-D) type conjugated molecules with high absolute fluorescence quantum yields (ΦF) ranging from 80% to 89% in solution. These molecules also show unusual light-emitting properties in the solid state with ΦF of up to 26%. We find that owing to the protonation-deprotonation process of the pyridine ring, these compounds display obvious changes in both fluorescence wavelength and intensity upon addition of acids, and these changes can be readily recovered by the successive introduction of bases. By harnessing this phenomenon, we further show that these fluorophores can be employed for efficient and reversible fluorescence sensing of hydrogen ions in a broad pH range (0.0-7.0). With the fabrication of pH testing papers and ink-printed complex patterns including butterflies and letters on substrates, we demonstrate the application of such sensors to fluorescence indication or solid state pH detection for real samples such as volatile acidic/basic gas and water-quality analysis.

Far-Red/Near-Infrared Emissive (1,3-Dimethyl)barbituric Acid-Based AIEgens for High-Contrast Detection of Metastatic Tumors in the Lung.

Despite of the enthusiastic research in aggregation-induced emission luminogens (AIEgens) in recent years, the ones that can be smoothly used for sophisticated biomedical applications such as in vivo bioimaging of pulmonary metastatic tumors during surgery are still limited. Herein, we report the design and synthesis of a new series of far-red/near-infrared (FR/NIR) fluorescent AIEgens that consist of methoxy-substituted tetraphenylethene (TPE) as the electron-donating moiety, (1,3-dimethyl)barbituric acid as the electron-withdrawing moiety, and different π-bridge units. As compared to benzene or 3,4-ethylenedioxythiophene, using thiophene as the π-conjugation unit between the donor and acceptor results in a relatively higher absolute fluorescence quantum yield (14.5 %) in water when formulating the corresponding AIEgens into nanoparticles (AIE dots) with an amphiphilic co-polymer as the doping matrix. The highly FR/NIR-emissive thiophene-based AIE dots are demonstrated to be potent for intraoperative detection of pulmonary metastatic tumors, particularly the micro-sized ones, with excellent signal-to-background ratio.

Highly Fluorescent Liquid Crystals from Excited‐State Intramolecular Proton Transfer Molecules

AbstractFluorescence via excited‐state intramolecular proton transfer (ESIPT) provides strong light emission with a large Stokes shift and environment‐sensitive unique spectral patterns. Particular systems including 2‐(2‐hydroxyphenyl)benzothiazole (HBT) serve as efficient solid‐state emitters with the ESIPT mechanism and aggregation‐induced emission enhancement (AIEE) property, but have not been used for liquid crystalline (LC) materials. Here, rod‐shaped fluorescent LCs with ESIPT characters are newly developed based on the HBT motif. The design of the targeted molecules is in line with a simple design principle: a molecule with an alkyl tail, rigid ring, and active HBT core. The LC C6Ph‐HBT is highly luminescent in the solid state with an absolute fluorescence quantum yield (ΦFL) up to 0.39 and exhibits anisotropic fluorescence in its nematic LC phase. C6Ph‐HBT is miscible up to 6 wt% with a conventional room‐temperature (r.t.) nematic LC 4‐cyano‐4′‐pentylbiphenyl (5CB), allowing homogeneous fluorescent r.t. LCs. The LC mixture 5CB/C6Ph‐HBT shows ΦFL of 0.26 even in the nonaggregated state, and responds to an electric field with dynamic modulation of not only the optical transparency but also polarized fluorescence. The interplay of highly efficient fluorescence from ESIPT cores and their visible transparency is encouraging for future optical applications of the present molecular systems.

Absolute fluorescence quantum yield determined by photothermal deflection spectroscopy

We present a spectroscopic method for measuring the fluorescence quantum efficiency of fluorophores that does not require calibration standards. Photothermal Deflection Spectroscopy (PDS) is combined with conventional absorbance spectroscopy, and is extracted from fits over the spectral range of interest. This technique obviates the need for multiple measurements—either on calibration standards or as a function of concentration—and yields results of in a single measurement consistent with previously reported values. Five different organic dyes are tested whose absorbance/fluorescence profiles span the visible spectrum and whose known quantum efficiencies range from 0 to near 1. The accuracy of the results over significant ranges of wavelength and quantum yield demonstrate the robustness and efficacy of this method.

1,8-Naphthalimide-based highly emissive luminogen with reversible mechanofluorochromism and good cell imaging characteristics

A 1,8-naphthalimide-based organic luminescent molecule has been designed and successfully synthesized via a Suzuki coupling reaction. The compound displayed a bright solid-state luminescence with the absolute fluorescence quantum yield up to 61.2%. Furthermore, the luminogen also exhibited reversible mechanofluorochromism behavior and good performance for cell imaging.

Luminescent columnar liquid crystals based on AIE tetraphenylethylene with hydrazone groups bearing multiple alkyl chains

A series of novel tetraphenylethylene aromatic acylhydrazone derivatives 11, 12 and 13 with 4, 8 or 12 alkyl chains were designed and synthesized in yields of 82–85%. Studies on the mesomorphic properties suggested the ordered hexagonal columnar mesophase for compounds 11, 12 and 13. The increase in the number of alkyl chains was favourable for decreasing the phase-transition temperatures and extending the mesophase temperature range. Further, samples 11, 12 and 13 presented an excellent AIE effect. The fluorescence intensities increased by 70, 84 and 43 times for samples 11, 12 and 13, respectively. The absolute fluorescence quantum yields were 18.7%, 27.4% and 23.8% in solid films at room temperature and 6.7%, 24.2% and 17.3% in the mesophase. These results suggested that the number of alkyl chains greatly influenced the fluorescence emission and sample 12 with 8 alkyl chains exhibited the strongest fluorescence emission. Sample 12 also displayed the electroluminescence performance on OLED device.

Synthesis of 9,10-distyrylanthracene derivative and its one- and two-photon induced emission in solid state

Solid fluorescence plays an important role in optoelectronic devices. In this paper, 9,10-bis(6-dimethylamino benzoxazole styryl)-anthracene (1) was synthesized. 1 displayed a strong emission in solid state (microcrystalline state, amorphous solid state and polymeric thin film) resulted from aggregation-induced emission mechanism, and a large absolute fluorescence quantum yield (ϕf = 0.65) was obtained. 1 also exhibited up-conversion emission in solid state and a strong yellow emission was observed upon excitation with 800–1064 nm, the quadratic dependence of the fluorescence on the excitation laser intensity confirmed that the up-conversion emission resulted from two-photon process.

Red fluorescent carbon dots with phenylboronic acid tags for quick detection of Fe(III) in PC12 cells

Carbon dots have attracted considerable attention in the field of biosensors and bioimaging because of their excellent optical performance and low toxicity. However, the cellular uptake of the reported carbon dots generally has a low efficiency, which limits their practical applications. In this study, we reported a novel red fluorescent sulfur and nitrogen co-doped carbon dots with small molecular phenylboronic acid tags (i.e. S, N-CDs-PBA). The S, N-CDs-PBA can be taken up rapidly by PC12 cells in twenty minutes and showed high sensitivity for the detection of Fe3+ ions. The maximum emission wavelength is at 593 nm under the excitation of 550 nm. The absolute fluorescence quantum yield is 23% in water. The fluorescence can be effectively and selectively quenched by Fe3+ ions and the linear response range of Fe3+ ions was obtained from 0.3 µM to 5.0 µM with a detection limit as low as 0.1 µM. It could be concluded that the rapid uptake of S, N-CDs-PBA into cells and high photoluminescence quantum yield of red emission are beneficial for quick detection of Fe3+ ions.

Tuning the light emission of novel donor-acceptor phenoxazine dye-based materials towards the red spectral range

A novel red fluorescent push-pull system able to generate an intramolecular charge-transfer (ICT) complex was synthesized. The novel dye (R-POX) combines some structural features which are rarely encountered in the design of other push-pull systems: hexyl-substituted phenoxazine as donor moiety, divinylketone as π-linker, and p-fluorobenzene as electron acceptor group. The relationship between the structural motif, photo-physical and electrochemical properties by UV–Vis absorption, photoluminescence and cyclic voltammetry was thoroughly investigated both as red dopant in poly(methylmethacrylate) (PMMA) or polyimide (PI) matrix, and non-doped host emitter. The molecular rigid cores of the synthesized dye formed supramolecular rod-like structures in condensed phase with a strong impact on the emissive centers. The aggregation was totally suppressed when the dye was used as dopant in an amorphous polymeric matrix, such as PMMA or PI. Electrochemical measurements revealed the dye ability for both hole and electron injection and transport. The fluorescence emission was found to be highly sensitive to solvent polarity, rendering blue-green, yellow, orange and red light emission in different organic solvents. The absolute fluorescence quantum yield reached 39.57% in solution, and dropped to 1.2% in solid state and to 14.01% when the dye was used as dopant in PMMA matrix. According to the available CIE 1931 standard, R-POX emitted pure and saturated red light of single wavelength with chromaticity coordinates very close to those of National Television System Committee (NTSC) standard red colour. The R-POX photo-optical features were compared to those of the commercial red emitter 6, 13-diphenylpentacene.

Nonblinking Quantum-Dot-Based Blue Light-Emitting Diodes with High Efficiency and a Balanced Charge-Injection Process

Blue nonblinking (>98% “on” time) ZnCdSe/ZnS//ZnS quantum dots (QDs) with absolute fluorescence quantum yield (QY) of 92% (λpeak = 472 nm) were synthesized via a low temperature nucleation and high temperature shell growth method. Such bright nonblinking ZnCdSe/ZnS//ZnS core/shell QDs exhibit not only good emission tunability in the blue-cyan range with corresponding wavelength from 450 to 495 nm but also high absolute photoluminescence (PL) QY and superior chemical and photochemical stability. Highly efficient blue quantum dot-based light-emitting diodes (QLEDs) have been demonstrated by using nonblinking ZnCdSe/ZnS//ZnS QDs as emissive layer, and the charge–injection balance within the QD active layer was improved by introducing a nonconductive layer of poly(methyl methacrylate) (PMMA) between the electron transport layer (ETL) and the QD layer, where the PMMA layer takes the role of coordinator to impede excessive electron flux. The best device exhibits outstanding features such as maximum luminance of...

Self-assembly facilitated and visible light-driven generation of carbon dots.

Carbon dots (CDs) with an absolute fluorescence quantum yield of 87% are facilely prepared via irradiation of self-assembled terthiophene amphiphile TTC4L in aqueous solution by mild visible light. Visible light irradiation of TTC4L triggers the production of superoxide radicals in water, which oxidize the closely packed terthiophene group into carbon dots. Our results reveal that the molecular self-assembly may act as important precursor for the generation of single molecule-like carbon dots; this method paves the way for the fabrication of CDs of high quality.

Nopinone-based aggregation-induced emission (AIE)-active difluoroboron β-diketonate complex: photophysical, electrochemical and electroluminescence properties.

Four difluoroboron (BF2) β-diketonate nopinone complexes 3a–3d that exhibited typical aggregation-induced emission (AIE) properties were synthesized using the natural renewable β-pinene derivative nopinone as the starting material. The thermal, photophysical, electrochemical and electroluminescent properties as well as the AIE properties of complexes 3a–3d were analyzed systematically. The data of photophysical and electrochemical demonstrated that compound 3b with a methoxy group exhibited the largest bathochromic shift, the highest absolute photoluminescence quantum yields and narrowest optical bandgap among 3a–3d. Using 3b as the emitter, electroluminescent (EL) device I exhibits blue-green light with CIE coordinates of (0.2774, 0.4531) and showed a better performance with a luminous efficacy (ηp) of 7.09 lm W−1 and correlated color temperature (TC) of 7028 K. The results demonstrate that new AIE compounds are promising solid-state luminescent materials with practical utility in electroluminescent materials.

Effect of the change of heteroatom on phenyl capped benzazole: Photophysical and electrochemical properties from the structural viewpoint

Donor-acceptor-donor type phenyl capped benzazoles were synthesized and their photophysical properties were studied. By changing the heteroatom (N, O, S and Se) of central acceptor benzazole unit, the emission color was varied from blue to green. Phenyl capped benzotriazole (1) and benzooxadiazole (2) were characterized by single crystal X-ray crystallography. The absolute solid state fluorescence quantum yields of these compounds were obtained in the range of 0.05–0.93 by a calibrated integrating sphere method. High solid state quantum yield can be attributed to the non-planarity and absence of strong intermolecular interactions in the solid state. Except phenyl capped benzotriazole (1), all compounds showed reversible reduction peak in cyclic voltammetry experiments which reflects the considerable n-type nature.

A new series of N-substituted tetraphenylethene-based benzimidazoles: Aggregation-induced emission, fast-reversible mechanochromism and blue electroluminescence

Four new N-substituted tetraphenylethene-based benzimidazoles N-R-2-(4-(1,2,2-triphenylvinyl)phenyl)-1H-benzo[d]imidazoles (R = phenyl (3a), R = 4-(tert-butyl)phenyl (3b), R = n-butyl (3c), R = n-hexyl (3d)) were synthesized conveniently by cyclization reaction of 4-tetraphenylenthenealdehyde with N-substituted ortho-nitroaniline. The four compounds exhibit typical aggregation-induced emission (AIE) property with relatively high solid state absolute fluorescence quantum yields (38.1–65.7%) and fast-recoverable mechanochromism property with solid-state fluorescence change between blue and yellow-green. They are thermally stable with decomposition temperatures above 319 °C. Both of multilayer electroluminescence devices fabricated with compounds 3b and 3c as emitters are blue emission. The turn-on voltage of device based on compound 3b is 3.3 V with maximum luminance and current efficiency of 2470 cd/m2 and 1.48 cd/A, respectively.

Alkyl length dependent reversible mechanofluorochromism of phenothiazine derivatives functionalized with formyl group

A series of D-A typed phenothiazine derivatives functionalized by formyl group (PCAn, n = 1, 2, 4 and 6) with different lengths of N-alkyl chains have been designed and synthesized to systematically investigate the effect of chain length on their solid-state fluorescence properties. The results showed that these compounds emitted strong fluorescence in solutions and solid states with 52%, 42%, 49% and 45% solid-state absolute fluorescence quantum yield (ΦF), respectively. Their emission wavelengths were strongly affected by solvent polarity, indicating intramolecular charge transfer (ICT) transitions. Interestingly, PCAn solids exhibit not only naked-eye visible and reversible mechanochromic behavior, but chain length-dependent emission properties. PCA1 shows smaller fluorescence spectrum shifts (22 nm) under mechanical force stimuli. Homologs with longer alkyl chains exhibit similar mechanochromic behaviors but larger fluorescence contrasts after grinding except for PCA6. Moreover, the fluorescence emission of ground solid PCA1 and PCA4 can recover at room temperature, PCA2 need high temperatures for fluorescence to be restored, and XRD and DSC revealed that the transformation between crystalline and amorphous states upon various external stimuli was responsible for the MFC behavior. This work demonstrates the feasibility of tuning the solid-state optical properties of fluorescent organic compounds by combining the simple alteration of chemical structure and the physical change of aggregate morphology under external stimuli.

Bis(1-pyrenylmethyl)-2-benzyl-2-methyl-malonate as a Cu2+ Ion-Selective Fluoroionophore.

A new malonate possessing two pyrene moieties was synthesized as a fluoroionophore, and its structure and fluorescence spectroscopic properties were investigated. When excited at 344 nm in acetonitrile/chloroform (9:1, v/v), the synthesized bispyrenyl malonate has the fluorescence of intramolecular excimer (λem = 467 nm) emissions and not a pyrene monomer emission (λem = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (ΦPL = 0.65) rather than in solution (ΦPL = 0.13). X-ray crystallography analysis clarified the molecular structure and alignment of the bispyrenyl malonate in the crystal phase, elucidating its fluorescence spectroscopic properties. Such analysis also suggests there are intramolecular C–H···π interactions and intermolecular π···π interactions between the pyrenyl rings. Interestingly, the synthesized bispyrenyl malonate exhibits excellent fluorescence sensing for the Cu2+ ion. Remarkable fluorescence intensity enhancement was only observed with the addition of the Cu2+ ion.