Absolute Fluorescence Quantum Yield Research Articles

Controlled Excited-State Dynamics and Enhanced Fluorescence Property of Tetrasulfone[9]helicene by a Simple Synthetic Process

Tetrasulfone[9]helicene (PTSH) was newly synthesized to improve and evaluate its fluorescence and excited-state dynamics through a single-step oxidation reaction of tetrathia[9]helicene (PTTH). In electrochemical measurements, the reduction potential of PTSH was shifted in a positive direction by approximately 1.0 V when compared to that of PTTH because of its electron-accepting sulfone units. The results of the electrochemical measurements agree with the energy levels calculated by density functional theory (DFT) methods and steady-state spectroscopic measurements. Furthermore, a significant enhancement of the absolute fluorescence quantum yield (ΦFL) was achieved. The absolute fluorescence quantum yield of PTSH attained 0.27, which is approximately 10 times larger than that of PTTH (ΦFL = 0.03). Such an enhancement of ΦFL can be successfully explained by the corresponding kinetic comparison. The reason is mainly the increased energy gap ΔEST between the lowest singlet (S1) and triplet (T1) excited state...

Design, syntheses and aggregation-induced emission properties of two new enlarged tetraarylethene-based luminogens

Two new enlarged tetraarylethene-based compounds in which biphenyl and 4,5,9,10-tetrahydropyrene cores connect multiple arylethene units have been synthesized through convenient synthetic procedures. The optical properties and electrochemical properties of the two compounds have been investigated. The two compounds possess high emission efficiency in solid state. Particularly, the absolute fluorescence quantum yield of 4,5,9,10-tetrahydropyrene-cored compound in a solid film is up to 44.1%. The emissions of the two compounds in solutions are very weak but they become strong emitters in solid state or in poor solvents, showing aggregation-induced emission (AIE) characteristics. The two compounds exhibit high thermal stability with Td above 427°C and show relatively high glass transition temperature with Tg above 142°C.

Characterization of a Squaraine/Chitosan System for Photodynamic Therapy of Cancer.

In this work, a squaraine dye CS5 was characterized and evaluated for its potential in photodynamic therapy. The studies were performed in ethanol and also in a powdered biopolymer, in this case chitosan. Ground state absorption, absolute fluorescence quantum yields, fluorescence lifetimes, and transient absorption were determined in order to evaluate the advantage of adsorbing the dye onto a biopolymer. Several concentrations of the dye, adsorbed onto chitosan, were prepared in order to evaluate the concentration effect on the photophysical parameters under study. A remarkable increase in the fluorescence quantum yield and lifetimes was detected when compared with the dye in solution. Also, a very clear dependence of the fluorescence quantum yield on the concentration range was found. A lifetime distribution analysis of these systems fluorescence evidenced the entrapment of the dye onto the chitosan environment with a monoexponential decay which corresponds to the monomer emission in slightly different environments. The transient absorption spectrum was obtained without sensitization indicating the existence of a triplet state which takes special importance in the generation of phototoxic species namely singlet oxygen. The subcellular localization of a photosensitizer is critical for efficient photoinduced cell death, in this way, colocalization studies were performed within HeLa cell line (human cervical carcinoma) through confocal microscopy. Toxicity in the dark and phototoxicity of CS5 were also evaluated for the same cellular model.

A pH dependence study of CdTe quantum dots fluorescence quantum yields using eclipsing thermal lens spectroscopy

In this study we evaluated the absolute fluorescence quantum yield (Φ) of hydrophilic CdTe QDs in function of different pHs, modified from the alkaline to acid, by using two different chemicals compounds, the mercaptosuccinic acid (MSA-the stabilizing agent of the QDs synthesis) or hydrochloric acid (HCl). The pH control of QDs suspensions is essential for the use of fluorescent nanoparticles in biological systems. We used the eclipsing thermal lens spectroscopy technique to determine the absolute fluorescence quantum yield values. The results showed variations on the Φ values as a function of the pH, which allowed a better understanding of QDs emission characteristics, establishing parameters for their use in biomedical applications such as optical images of biological systems, immunoassays, flow cytometry, biosensors and others.

Tetraphenylpyrazine-Based Luminogens with Aggregation-Enhanced Emission Characteristics: Preparation and Property

The research on aggregation-induced emission (AIE) has been a hot topic in the fields of photo-physics and luminescent materials. Design and synthesis of new AIE-active luminogens (AIEgens) will further promote the development of this area. Based on our developed new AIEgen of tetraphenylpyrazine (TPP), in this paper, we further enriched its family by covalently attaching thiophene unit on TPP core, and prepared three AIEgens of TPP-T, TPP-2T and T-TPP-T. Their structure-property relationship was studied in detail. The results showed that TPP-T, TPP-2T and T-TPP-T feature the aggregation-enhanced emission (AEE) characteristics. Their powders emit at 418, 437 and 436 nm with absolute fluorescence quantum yields of 26.8, 29.0 and 30.9%, respectively, which makes them promising to be used as emitting layer in fabrication of organic light-emitting diodes in combination with their excellent thermal stability.

The properties of PMMA/DCJTB thin-film luminescent solar concentrator with various thicknesses

The PMMA/DCJTB thin-film luminescent solar concentrators (LCSs) with various thicknesses have been successfully prepared with the spin coating process. The properties of PMMA/DCJTB thin-film LSCs with various thicknesses have been studied. The cross-sectional field-emission scanning electron microscopy (FESEM) micrographs show that the thin-films on the glass substrate are very smooth. The thicknesses are 1.36±0.03, 1.93±0.07, 2.80±0.05 and 4.00±0.06μm. The value of the absolute fluorescence quantum yield (Φf) of the as-prepared LSCs decreases from 59.09% to 51.91% when the PMMA/DCJTB thin-film thickness increases from 1.36 to 4.00μm. The values of open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and overall power conversion efficiency (η) are 0.51V, 29.47mA/cm2, 65.54%, and 9.85%, respectively, for the PMMA/DCJTB thin-film LSCs with a thickness of 4.00μm.

Characterization of the Aggregation-Induced Enhanced Emission of N,N'-bis(4-methoxysalicylide)benzene-1,4-diamine.

N,N'-bis(4-methoxysalicylide)benzene-1,4-diamine (S1) was synthesized from 4-methoxysalicylaldehyde and p-phenylenediamine and it was found to exhibit interesting aggregation-induced emission enhancement (AIEE) characteristics. In aprotic solvent, S1 displayed very weak fluorescence, whilst strong emission was observed when in protic solvent. The morphology characteristics and luminescent properties of S1 were determined from the fluorescence and UV absorption spectra, SEM, fluorescence microscope and grading analysis. Analysis of the single crystal diffraction data infers that the intramolecular hydrogen bonding constitutes to a coplanar structure and orderly packing in aggregated state, which in turn hinders intramolecular C-N single bond rotation. Given that the three benzene rings formed a large plane conjugated structure, the fluorescence emission was significantly enhanced. The absolute fluorescence quantum yield and fluorescence lifetime also showed that radiation transition was effectively enhanced in the aggregated state. Moreover, the AIEE behavior of S1 suggests there is a potential application in the fluorescence sensing of some volatile organic solvents.

Solvent Dependency in the Quantum Efficiency of 4-[(4-Aminophenyl)-(4-imino-1-cyclohexa-2, 5- dienylidene) methyl] Aniline Hydrochloride.

In the present work dual beam thermal lens technique is used for studying the solvent dependency on the quantum efficiency of a novel dye used for biomedical applications. The role of solvent in the absolute fluorescence quantum yield of 4-[(4-Aminophenyl)-(4-imino-1-cyclohexa-2, 5- dienylidene) methyl] aniline hydrochloride is studied using thermal lens technique. It is observed that the variation in solvents and its concentration results considerable variations in the fluorescence quantum yield. These variations are due to the non-radiative relaxation of the absorbed energy and because of the different solvent properties. The highest quantum yield of the dye is observed in the polar protic solvent-water.

1,8-Naphthalimide-based highly blue-emissive fluorophore induced by a bromine atom: reversible thermochromism and vapochromism characteristics

We report a structurally simple 1,8-naphthalimide-based fluorescent molecule. Its solid shows an intense blue emission with an absolute fluorescence quantum yield of up to 82.33%. The novel luminogen exhibits reversible thermochromism and vapochromism behaviors.

Unusually high fluorescence quantum yield of a homopolyfluorenylazomethine--towards a universal fluorophore.

The absolute fluorescence quantum yield (Φfl) of a polyfluorenyl azomethine homopolymer was measured as a function of solvent polarity. The solvent induced and temperature dependent fluorescence of the homopolymer were also investigated and they were compared to the corresponding monomer and copolymer. The Φfl of the homopolymer was consistent (45-70%), regardless of solvent polarity with Stokes shifts up to 7460 cm(-1) in ethanol. In contrast, the Φfl of its corresponding monomer decreased from 60% in ethanol to 1% in toluene, whereas a Φfl < 5% for its analogous copolymer was measured. Moderate fluorescence yields (Φfl ≈ 25%) were also possible in thin film when co-depositing the homopolymer with PMMA. Cryofluorescence was used to probe the excited state deactivation modes. Deactivation by internal conversion was found to compete with fluorescence. The fluorescence deactivation pathways of the homopolymer and its corresponding monomer could be suppressed at 77 K, resulting in fluorescence turn-on. Both fluorophores were found to detect nitroaromatics.

Formation of one-dimensional helical columns and excimerlike excited states by racemic quinoxaline-fused [7]carbohelicenes in the crystal.

A series of quinoxaline-fused [7]carbohelicenes (HeQu derivatives) was designed and synthesized to evaluate their structural and photophysical properties in the crystal state. The quinoxaline units were expected to enhance the light-emitting properties and to control the packing structures in the crystal. The electrochemical and spectroscopic properties and excited-state dynamics of these compounds were investigated in detail. The first oxidation potentials of HeQu derivatives are approximately the same as that of unsubstituted reference [7]carbohelicene (Heli), whereas their first reduction potentials are shifted to the positive by about 0.7 V. The steady-state absorption, fluorescence, and circular dichroism spectra also became redshifted compared to those of Heli. The molecular orbitals and energy levels of the HOMO and LUMO states, calculated by DFT methods, support these trends. Moreover, the absolute fluorescence quantum yields of HeQu derivatives are about four times larger than that of Heli. The structural properties of the aggregated states were analyzed by single-crystal analysis. Introduction of appropriate substituents (i.e., 4-methoxyphenyl) in the HeQu unit enabled the construction of one-dimensional helical columns of racemic HeQu derivatives in the crystal state. Helix formation is based on intracolumn π-stacking between two neighboring [7]carbohelicenes and intercolumn CH⋅⋅⋅N interaction between a nitrogen atom of a quinoxaline unit and a hydrogen atom of a helicene unit. The time-resolved fluorescence spectra of single crystals clearly showed an excimerlike delocalized excited state owing to the short distance between neighboring [7]carbohelicene units.

Measurement of Absolute Fluorescence Quantum Yield of Basic Fuchsin Solution Using a Dual-Beam Thermal Lens Technique

The dual beam thermal lens technique is an effective method for the measurement of fluorescence quantum yield of dye solutions. The concentration-dependent quantum yield of a novel dye of triaminotriphenylmethane family in ethanol is studied using this technique. The absolute fluorescence quantum yield is measured and is observed that the reduction in the quantum yield is due to the non-radiative relaxation of the absorbed energy.

Variations in fluorescence quantum yield of basic fuchsin with silver nanoparticles prepared by femtosecond laser ablation

Nano structured noble metals have very important applications in diverse fields such as photovoltaics, catalysis, electronic and magnetic devices, etc. In the present work, the application of dual beam thermal lens technique is employed for the determination of the absolute fluorescence quantum yield of the triaminotriphenylmethane dye, basic fuchsin in the presence of silver sol is studied. Silver sol is prepared by femtosecond laser ablation. It is observed that the presence of silver sol decreases the fluorescence quantum efficiency. The observed results are in line with the conclusion that the reduction in quantum yield in the quenching region is essentially due to the non-radiative relaxation of the absorbed energy. It is also observed that the presence of silver sol enhances the thermal lens signal which makes its detection easier at any concentration.

Quantum dots fluorescence quantum yield measured by Thermal Lens Spectroscopy.

An essential parameter to evaluate the light emission properties of fluorophores is the fluorescence quantum yield, which quantify the conversion efficiency of absorbed photons to emitted photons. We detail here an alternative nonfluorescent method to determine the absolute fluorescence quantum yield of quantum dots (QDs). The method is based in the so-called Thermal Lens Spectroscopy (TLS) technique, which consists on the evaluation of refractive index gradient thermally induced in the fluorescent material by the absorption of light. Aqueous dispersion carboxyl-coated cadmium telluride (CdTe) QDs samples were used to demonstrate the Thermal Lens Spectroscopy technical procedure.

Conjugated C3 symmetric aryl tripyrroles and aryl bipyrroles: synthesis, optical and electronic properties

Conjugated C3 symmetric molecules have been pursued for their fluorescent and electrochemical properties. The synthesis of conjugated C3 symmetric aryl tripyrroles has been performed by a route featuring three steps from trimethyl 1,3,5-benzene tricarboxylate 6: copper-catalyzed cascade addition of vinylmagnesium bromide to convert the carboxylates into γ,δ-unsaturated ketones, Tsuji–Wacker olefin oxidations to form tris(1,4-dione) 9, and Paal–Knorr condensation with ammonia and different amines to furnish the final tripyrroles (30–60% yields). In addition, incomplete reaction of vinylmagnesium bromide to 6 provided benzoate 8 possessing two γ,δ-unsaturated ketones, which were similarly converted to 3,5-dipyrrolylbenzoates 11. The absolute fluorescence quantum yields (Φfl) and electrochemical properties of 5a–c and 11a–c were investigated. The Φfl are the first reported for such compounds and they ranged between 2 and 40%, contingent on structure and solvent polarity. Cyclic voltammetry revealed that the compounds could be both oxidized and reduced, albeit irreversibly. The oxidation potentials (Eox) varied between 0.73 V and 1.2 V and the reduction potentials (Ered) varied from −0.83 V to −1.36 V. The lowest redox processes were measured for the NH–pyrrole 5a. Moreover, tripyrrole 5a was air stable and on oxidative doping with ferric chloride exhibited a 50 nm bathochromic shift in its absorbance spectrum.

Synthesis, characterization and solid-state emission properties of arylsilyl-substituted pyrene derivatives

Arylsilyl substituted pyrene derivatives were synthesized via Suzuki-Miyaura and Hagihara-Sonogashira cross-coupling reactions with boronic acid-terminated and ethynyl-terminated tetraphenylsilane at the 1-, 3-, 6- and 8-positions. The spectroscopic properties of the dyes were investigated in various solvents and in films to assess the suitability of these compounds for optoelectronic applications. A triphenylsilylphenyl substituted pyrene was found to exhibit intense emission in the solid state with an absolute fluorescence quantum yield (ΦF) of 0.65. In contrast, the emission properties of a triphenylsilylphenyl(ethynyl) substituted pyrene were found to be somewhat weaker in the solid state (ΦF = 0.16) and solvent polarity dependent in solution. Magnetic circular dichroism (MCD) spectroscopy, cyclic voltammetry, and theoretical calculations have been used to analyze the structure-property relationships with Michl's perimeter model used as a conceptual framework for rationalizing the key trends.

Turning‐on the Quenched Fluorescence of Azomethines through Structural Modifications

AbstractA series of fluorene azomethines were prepared to examine the effect of structural modification on the absolute fluorescence quantum yields (Φfl). The change in fluorescence occurring upon reversing the orientation of the azomethine bond, the number of fluorene units, and alkylation at the 9,9′‐positions of fluorene was examined. It was found that Φfl could be tailored with these structural modifications with 0.05 ≤ Φfl ≤ 0.45. The highest Φfl was measured for the trimer derived from 2,7‐diamino fluorene with each fluorene being alkylated at the 9,9′‐positions. The fluorescence quantum yields did not increase at 77 K, implying the absence of fluorescence quenching modes involving internal conversion. Fluorescence enhancement was also not observed upon protonating the imine with trifluoroacetic acid. This confirms that Waldon inversion and isomerization are not fluorescence deactivation modes. Additionally, no photoisomerization was observed either at room temperature or at 77 K when the fluorene derivatives were irradiated at 354 nm. In contrast, the Z photoisomer of a N‐benzylideneaniline analogue was spectroscopically detected both by absorbance and by 1H NMR spectroscopy.

Photophysical and Electrochemical Investigations of the Fluorescent Probe, 4,4′-Bis(2-benzoxazolyl)stilbene

In solution, 4,4'-bis(2-benzoxazolyl)stilbene (BBS) was found to exhibit consistently high absolute fluorescence quantum yields (Φ(fl) ≥ 0.88) and a monoexponential lifetime, both independent of BBS concentration. The BBS steady-state and time-resolved photophysics were investigated by different techniques to understand the various deactivation pathways. Nonradiative deactivation of BBS singlet excited state by intersystem crossing was found to be negligible. Other than fluorescence, the excited state of BBS was found to be deactivated by trans-cis photoisomerization. At low concentrations (≈5 μg/mL), UV spectroscopy and laser flash photolysis showed concordant results that the photoinduced cis isomer gradually replaced the original absorption spectrum of the pure trans isomer. However, at high concentrations (≈0.2 mg/mL), (1)H NMR and DOSY measurements confirmed that irradiating BBS at 350 nm induced a conversion from the trans-BBS into its cis isomer by photoisomerization. It was further found that the stilbene moiety of both isomers was photocleaved. The resulting photoproduct was an aldehyde that was oxidized under ambient conditions to its corresponding carboxylic acid, i.e., 4-(1,3-benzoxazol-2-yl)benzoic acid. The structure of the photoproduct was unequivocally confirmed by X-ray diffraction. Spectroscopic investigation of BBS showed a limited photoisomerization after irradiation at 350 nm of a trans solution. The BBS electrochemistry showed irreversible oxidation, resulting in an unstable and highly reactive radical cation. Similarly, the cathodic process was also found to be irreversible, giving rise to a radical anion and showing its n-doping character.

Palladium-catalyzed direct phenylation of perylene: structural and optical properties of 3,4,9-triphenylperylene and 3,4,9,10-tetraphenylperylene

We have developed one-step synthesis of multiphenylperylenes from perylene through palladium-catalyzed oxidative C–H/C–B coupling using phenylboroxin as a phenyl source. The combination of Pd(OAc)2 as a catalyst and o-chloranil as an oxidant is the key for direct C–H arylation of perylene. The X-ray crystallography of 3,4,9-triphenylperylene (3) and 3,4,9,10-tetraphenylperylene (4) revealed twisted structures of perylene core caused by steric repulsion of neighboring phenyl groups. Compounds 3 and 4 showed red shift in both absorption and fluorescence spectra compared to perylene whereas absolute fluorescence quantum yields are similarly high (ΦF=0.94).

Novel luminescent phenothiazine-based Schiff bases with tuned morphology. Synthesis, structure, photophysical and thermotropic characterization

New Schiff base dimers based on phenothiazine heterocycle have been obtained with high yield and purity by condensation of 3-formyl-10-methyl-phenothiazine with various amines. The structural characterization was performed by elemental analysis , FTIR, 1D and 2D NMR spectroscopy and single crystal and powder wide angle X-ray diffraction. The obtained compounds have high thermal stability and some of them self-assemble into cubic mesophase and form stable molecular glass. The thermotropic study performed by polarized optical microscopy and differential scanning calorimetry revealed the possibility to control the compound morphology by thermal annealing and blending miscible components. The photophysical characterization indicates green light emission, with good absolute fluorescence quantum yield , large Stokes shift and high purity and fully saturated color. The special thermal behavior and photophysical properties appear to be significantly dependent on the special supramolecular architecture generated by the hockey-stick shape of the imino-phenothiazine mesogenic core. Collectively, the properties of these azomethines provide a starting point for new compounds with great advantages for optoelectronic applications. ► New phenothiazine containing imine dimers were obtained with high yield and purity. ► The mesogenic core adopts a hockey-stick shape. ► Some dimers exhibit cubic mesophase or molecular glass forming. ► The films morphology has been controlled by thermal annealing and blending. ► The dimers emit green light with good quantum yield and large Stokes shift.