Fluorescence Quantum Yield Measurements Research Articles

Anthracene-Arrangement-Dependent Emissions of Crystals of 9-Anthrylpyrazole Derivatives

We have designed and synthesized a series of 9-anthrylpyrazole derivatives 1,4-bis(3-(9-anthryl)-1-pyrazolylmethyl)benzene (1), 1-(3-(9-anthryl)-1-pyrazolylmethyl)-4-(5-(9-anthryl)-1-pyrazolylmethyl)benzene (2), 1,4-bis(3-(9-anthryl)-1-pyrazolyl)benzene (3), and 1-(3-(9-anthryl)-1-pyrazolyl)-4-(5-(9-anthryl)-1-pyrazolyl)benzene (4). All compounds formed two types of crystals that exhibited anthracene-arrangement-dependent emission colors. For instance, crystal 1a with strong π-overlap between anthracene moieties exhibited an emission maximum at 515 nm, while 1b with no such interchromophore interactions displayed an emission band at 424 nm. The fluorescence quantum yield (ΦF) measurements showed that the blue-emitting crystals have high quantum yields (ΦF = 0.46 for 1b, 0.90 for 2a, 0.91 for 2b, 0.77 for 3b, and 0.51 for 4a), suggesting their potential as blue emitters in optoelectronics.

Dynamics of Photochemical Electron Injection and Efficiency of Electron Transport in DNA

The dynamics of electron injection and quantum yields for photoinduced dehalogenation have been investigated in a series of DNA hairpins possessing an aminopyrene capping group. Aminopyrene serves as an electron donor and is separated from a bromo- or iodoracil electron trap by 1 to 7 A-T base pairs. Broad band femtosecond transient absorption spectra and fluorescence quantum yield measurements are indicative of rapid and efficient charge separation. The resulting charge-separated state decays predominantly via charge recombination on the picosecond time scale. Steady-state irradiation in the presence of 0.1 M i-PrOH results in loss of halogen and conversion of the halouracil-containing conjugates to the corresponding uracil-containing conjugates in high yield. Dehalogenation occurs via a multistep mechanisms consisting of electron injection, electron transport to the halouracil, loss of halide, and trapping of the uracilyl radical. Quantum yields for product formation decrease by a factor of 2 for each a...

Effect of exciton self-trapping and molecular conformation on photophysical properties of oligofluorenes

Electronic absorption and fluorescence transitions in fluorene oligomers of differing lengths are studied experimentally and using density functional theory (DFT) and time-dependent DFT. Experimental values are determined in two ways: from the measured molar absorption coefficient and from the radiative rate deduced from a combination of fluorescence quantum yield and lifetime measurements. Good agreement between the calculated and measured transition dipoles is achieved. In both theory and experiment a gradual increase in transition dipoles with increasing oligomer length is found. In absorption the transition dipole follows an approximately n(0.5) dependence on the number of fluorene units n for the range of 2 < or = n < or = 12, whereas a clear saturation of the transition dipole with oligomer length is found in fluorescence. This behavior is attributed to structural relaxation of the molecules in the excited state leading to localization of the excitation (exciton self-trapping) in the middle of the oligomer for both twisted and planar backbone conformations. Twisted oligofluorene chains were found to adopt straight or bent geometries depending on alternation of the dihedral angle between adjacent fluorene units. These different molecular conformations show the same values for the transition energies and the magnitude of the transition dipole.

Synthesis, Structures, and Optical and Electrochemical Properties of Benzoporphycenes

The first facile syntheses of free-base di- and tetrabenzoporphycenes and their metal complexes are reported, based on retro-Diels-Alder reactions of the corresponding bicyclo[2.2.2]octadiene-fused porphycenes, prepared by McMurray coupling of alpha,alpha'-diformyldipyrrole. The photophysical and electrochemical properties are analyzed based on UV/Vis absorption, magnetic circular dichroism (MCD), and fluorescence emission, lifetime and quantum yield measurements, cyclic and differential pulse voltammetry (CV and DPV) and time-dependent DFT calculations based on B3LYP geometry optimizations. Benzoporphycenes are found to be prime candidates for future use in photodynamic therapy.

Syntheses and Photophysical Behavior of Porphyrin Isomer Sn(IV) Complexes

2,3,6,7,12,13,16,17-Octaethylhemiporphycenato Sn(IV) chloride, [Sn(IV)(OEHPc)Cl(2)], and 2,3,6,7,12,13,16,17-octaethylporphycenato Sn(IV) chloride, [Sn(IV)(OEPc)Cl(2)], were synthesized in high yields and fully characterized by various spectroscopic methods. The X-ray crystal structures of the Sn(IV) complexes with porphycene and hemiporphycene were determined for the first time. The photophysical and photochemical properties of the singlet state of the Sn(IV) porphycene and hemiporphycene complexes, structural isomers of porphyrin, have been investigated by fluorescence and phosphorescence spectroscopies. The relatively strong emission and long fluorescence lifetime of the Sn(IV) porphycene complexes indicated by the fluorescence quantum yield and lifetime measurement were observed in the case of the Sn(IV) porphycene ([Sn(IV)(OEPc)Cl(2)], Phi(F) = 0.125, tau(s) = 2681 ps; [Sn(IV)(OEP)Cl(2)], Phi(F) = 0.010, tau(s) = 438 ps; [Sn(IV)(OEHPc)Cl(2)], Phi(F) = 0.027, tau(s) = 733 ps). The triplet state of the Sn(IV) complexes was investigated by transient absorption spectroscopy. It became clear that the triplet lifetime of the Sn(IV) porphycene (tau(T) = 49.9 mus) was longer when compared to those of the Sn(IV) porphyrin (tau(T) = 32.6 mus) and hemiporphycene complexes (tau(T) = 28.3 mus). These porphyrin isomer Sn(IV) complexes showed the high singlet oxygen generating ability, and the photo-oxidation of the 1,5-hydroxynaphthalene mediated by the Sn(IV) porphycene was the most effective among the complexes. This result is due to its more effective light absorption in the visible region and indicated that the porphycene is an excellent candidate as a photosensitizer.

Excited State Absorption Study in Hematoporphyrin IX

We present the study of the excited state absorption of Hematoporphyrin IX dissolved in dimethyl sulfoxide. All measurements were carried out using open aperture Z-scan and white-light continuum pump-probe with picosecond pulses to avoid triplet excited state absorption. Without the latter contribution, the results obtained with both techniques show a transition to a high singlet excited state. The vibronic progression of the Q-band is observed due to photobleaching of the ground state. In addition, we show that the excited state presents reverse saturable absorption for most of the spectral range studied. A long relaxation component of the first singlet excited state was evidenced with the pump-probe experiment. This result is in agreement with fluorescence lifetime and fluorescence quantum yield measurements. In order to elucidate the origin of the nonlinear effects, we used a three-level energy diagram to describe the principal singlet-singlet transitions.

Water-soluble phthalocyanines mediated photodynamic effect on mesothelioma cells

The new peripherally 2-mercaptopyridine tetrasubstituted zinc phthalocyanine (2) and its quaternized derivative (3) have been synthesized and characterized by elemental analysis, IR, 1 H NMR spectroscopy, electronic spectroscopy and mass spectra. The quaternized compound (3) shows excellent solubility in water, which makes it a potential photosensitizer for use in photodynamic therapy (PDT) of cancer. Fluorescence and singlet oxygen quantum yield measurements were conducted on 2-mercaptopyridine appended zinc phthalocyanines in dimethylsulphoxide (DMSO) for both the non-ionic (2) and quaternized (3) derivatives, and in aqueous media for the water-soluble complex 3. General trends are described for fluorescence and singlet oxygen quantum yields of these compounds. In this study, the cells were incubated with a novel water-soluble zinc phthalocyanine derivative (3) and thereafter the cells were illuminated using broad-band incoherent light source of various energy levels. Cytotoxicity of PDT on two pleural malign mesothelioma cell lines was determined by colorimetric proliferation assay. In addition, after PDT treatment, determination of activity matrix metalloproteinases (MMPs) were evaluated using gelatine zymography.

Structural Modification of Silicon‐Bridged Ladder Stilbene Oligomers and Distyrylbenzenes

AbstractTwo kinds of the totally alkyl‐substituted ladder π‐conjugated compounds, the totally hexyl‐substituted silicon‐bridged stilbene trimer 1 and the totally propyl‐substituted silicon‐ and carbon‐bridged distyrylbenzene 2, were synthesized. X‐ray crystallography revealed that both compounds adopt the all‐parallel‐aligned packing structures through the interpenetration of the alkyl chains with those of the neighboring molecules. The effect of this packing structure on the photophysical properties was investigated. The fluorescence quantum yield measurements showed that both compounds maintained their high quantum yields (ΦF) even in the crystalline state (ΦF = 0.64 for 1; 0.63 for 2), suggesting the potential effect of the all‐parallel alignment for attaining the intense emission in the solid state.magnified image

Photo-stability and performance of CdSe/ZnS quantum dots in luminescent solar concentrators

The performances of luminescent solar concentrators (LSCs) made with two versions of quantum dots (QDs) with CdSe cores and ZnS shells are compared to LSCs containing the organic dye, Lumogen ® F Red 300 (LR), to assess the viability of QD LSCs. In addition to spectroscopic and light collection measurements, the photo-degradation response of the version I (vI) QD LSC is compared to the LR LSC. The measured fluorescence quantum yield of the version II (vII) QDs (57%) is about half that of LR (>90%) and twice that of the vI QDs (31%). Though the quantum yield for vII QDs is lower than LR, the vII QD LSC has nearly twice the short-circuit current of the LR LSCs or the vI QD LSCs when their respective red-peak optical densities are the same in 6.2 × 6.2 × 0.6 cm LSCs. This is a reflection of the main advantage of QDs for use in LSCs, that QDs collect considerably more sunlight than LR due to their broad absorption spectrum. Despite the fact that the QD LSCs absorbs more photons than the LR LSCs, the slow phase of the photo-degradation rate of the QD LSC is approximately five times slower than the LR LSC under nearly constant light exposure. Most surprising is the observation that the photo-degradation of the QD LSC’s absorption completely recovers during a prolonged dark cycle. In a normal day/night cycle, this will benefit the performance of the QD LSC.

Fluorescence quantum yield of carbon dioxide for quantitative UV laser-induced fluorescence in high-pressure flames

The fluorescence quantum yield for ultraviolet laser-induced fluorescence of CO2 is determined for selected excitation wavelengths in the range 215–250 nm. Wavelength-resolved laser-induced fluorescence (LIF) spectra of CO2, NO, and O2 are measured in the burned gases of a laminar CH4/air flame (φ=0.9 and 1.1) at 20 bar with additional NO seeded into the flow. The fluorescence spectra are fit to determine the relative contribution of the three species to infer an estimate of fluorescence quantum yield for CO2 that ranges from 2–8×10−6 depending on temperature and excitation wavelength with an estimated uncertainty of ±0.5×10−6. The CO2 fluorescence signal increases linearly with gas pressure for flames with constant CO2 mole fraction for the 10 to 60 bar range, indicating that collisional quenching is not an important contributor to the CO2 fluorescence quantum yield. Spectral simulation calculations are used to choose two wavelengths for excitation of CO2, 239.34 and 242.14 nm, which minimize interference from LIF of NO and O2. Quantitative LIF images of CO2 are demonstrated using these two excitation wavelengths and the measured fluorescence quantum yield.

Influence of the dendron chemical structure on the photophysical properties of bisfluorene-cored dendrimers

A detailed study of the photophysics of a family of bisfluorene-cored dendrimers is reported. Polarized time-resolved fluorescence, singlet-singlet exciton annihilation and fluorescence quantum yield measurements were performed and used to understand how the dendron structure affects the light-emitting properties of the materials. The exciton diffusion rate is similar in all films studied. An increase in the nonradiative deactivation rate by nearly one order of magnitude is observed in films of dendrimers with stilbenyl and carbazolyl based dendrons as compared to solutions, whereas the dendrimers with biphenyl and diphenylethylenyl dendrons showed highly efficient emission (photoluminescence quantum yields of 90%) in both solution and the solid state. The results of the materials that show fluorescence quenching can be explained by the presence of quenching sites at a concentration of just a fraction of a percent of all macromolecules. A possible explanation of this quenching is hole transfer from the emissive chromophore to the dendron in a face-to-face geometry. These results are important for the design of efficient blue emitters for optoelectronic applications.

Comparative Studies of Diphenyl-Diketo-Pyrrolopyrrole Derivatives for Electroluminescence Applications

Four different derivatives of diphenyl-diketo-pyrrolopyrrole (DPP) with alkyl side groups were synthesized to increase their solubility. Quantum chemical calculations revealed that the substitution influenced molecular geometry and subsequently modified absorption and photoluminescence spectra. The theoretical results were confirmed by experimental characterization. With increasing phenyl torsion the vibrational structure was less pronounced and larger Stokes shift was observed. Simultaneously, the molar absorption coefficient decreased as the deformation increased. On the other hand, the measured fluorescence quantum yields were modified only slightly. This indicates the possibility to prepare soluble derivatives without loss of quantum yields and to use these materials for construction of efficient and stable electroluminescent devices. Furthermore, the electroluminescence of the thin layer devices based on the soluble low molecular DPPs were characterized and discussed.

Fluorinated Diphenylpolyenes: Crystal Structures and Emission Properties

(E,E,E)-1,6-Diaryl(Ar)-1,3,5-hexatrienes (2, Ar = 4-fluorophenyl; 3, Ar = 2,4-difluorophenyl; 4, Ar = 2,4,6-trifluorophenyl; 5, Ar = perfluorophenyl) and (E,E,E)-1-perfluorophenyl-6-phenyl-1,3,5-hexatriene (6) were prepared. The absorption and fluorescence spectra in methylcyclohexane solution showed only a small dependence on the fluorine ring substituent, and were similar to those of the unsubstituted parent compound (1, Ar = phenyl). The solid-state absorption and fluorescence spectra shifted to red relative to those in solution and strongly depended on the substituent. The emission from crystals 1-5 originated mainly from monomeric species with the maximum wavelength (lambda f(max)) of 440-465 nm, which overlapped the emission from molecular aggregates (1-4) or excimeric species (5) in the red region. Crystal 6 exhibited red-shifted (lambda f(max) = 530 nm) and structureless emission due to excimers. The cocrystal of 1 and 5 (1/5) showed red-shifted (lambda f(max) = 558 nm) and distinctly structured emission, not from exciplexes but from the excited states of molecular aggregates in which molecules 1 and 5 strongly interact already in the ground state. These assignments were confirmed by the results of fluorescence lifetime and quantum yield measurements in the solid state. Single-crystal X-ray structure analyses showed that the molecules were basically planar in each crystal, whereas the crystal packing was strongly substituent-dependent. Weak pi-pi interactions in the herringbone (1 and 2) and in the pi-stacked but largely offset structures (3 and 4) account for their predominantly monomeric origin of emission. The observation of excimer fluorescence from 5 was rather unexpected, since the molecules in this crystal were arranged in an offset stacking fashion due to perfluorophenyl-perfluorophenyl (C6F5...C6F5) interaction. The structures of 6 and 1/5 considerably resembled each other, in which molecules were pi-stacked with more face-to-face geometries than those in 5, as a result of strongly attractive perfluorophenyl-phenyl (C6F5...C6H5) interaction. Nevertheless, the fluorescence origin was clearly different for 6 and 1/5. This can be ascribed to the difference in the strength of orbital-orbital interaction between molecular pi-planes in the ground and excited states in crystals.

Excited-State Structure and Dynamics of cis- and trans-Azobenzene from Resonance Raman Intensity Analysis

Resonance Raman intensity analysis was used to investigate the initial excited-state nuclear dynamics of cis- and trans-azobenzene following S1 (npi*) excitation, and fluorescence quantum yield measurements were used to estimate the excited-state lifetimes. trans-Azobenzene exhibits the strongest Raman intensities in its skeletal stretching and bending modes, while torsional motions dominate the nuclear relaxation of cis-azobenzene as indicated by intense Raman lines at 275, 542, 594, and 778 cm(-1). The very weak fluorescence quantum yield for cis-azobenzene is consistent with its approximately 100 fs electronic lifetime while trans-azobenzene, with a fluorescence quantum yield of 1.1 x 10(-5), has an estimated S1 lifetime of approximately 3 ps. The absorption and Raman cross-sections of both isomers were modeled to produce a harmonic displaced excited-state potential energy surface model revealing the initial nuclear motions on the reactive surface, as well as values for the homogeneous and inhomogeneous linewidths. For cis-azobenzene, this modeling predicts slopes on the S1 potential energy surface that when extrapolated to the position of the harmonic minimum give excited-state changes of approximately 6-20 degrees in the CNNC torsion angle and a < or =3 degrees change in the CNN bending angle. The relatively large excited-state displacements along these torsional degrees of freedom provide the driving force for ultrafast isomerization. In contrast, the excited-state geometry changes of trans-azobenzene are primarily focused on the CNN bend and CN and NN stretches. These results support the idea that cis-azobenzene isomerizes rapidly via rotation about the NN bond, while isomerization proceeds via inversion for trans-azobenzene.

Synthesis of ligand-selective ZnS nanocrystals exhibiting ligand-tunable fluorescence

High-quality ZnS nanocrystals (NCs) of nearly identical size are synthesized using isomeric ligands, o-, m-, p-phenylenediamines (PDAs) that bind to the NC cores. The fluorescence emission from the NC is tunable according to the structure of the isomer. The measured fluorescence quantum yields (QYs) are 2–3 times higher for NCs that are passivated with isomeric PDA ligands than the fluorescence QY of NCs prepared at the absence of PDAs. The NC morphologies were studied by low-angle and wide-angle X-ray diffraction (XRD), and by transmission electron microscopy (TEM). The average correlating sizes were found to be 3.0 ± 0.3 , 3.7 ± 0.30 , and 3.0 ± 0.5 nm for the NCs that were passivated with o-PDA, m-PDA, and p-PDA, respectively. The Fourier-transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies were carried out to investigate the shell structure and the interaction between the core and the shell. The adsorbed ligands were quantitatively analyzed by TGA. The structure, morphology, and optical properties of these PDA passivated NCs were compared with the NCs prepared in the absence of PDA.

Ultrafast Spectroscopy of the Solvent Dependence of Electron Transfer in a Perylenebisimide Dimer

We investigate the photoinduced intramolecular electron-transfer (IET) behavior of a perylenebisimide dimer in a variety of solvents using femtosecond transient absorption spectroscopy. Overlapping photoinduced absorptions and stimulated emission give rise to complicated traces, but they are well fit with a simple kinetic model. IET rates were found to depend heavily on solvent dielectric constant. Good quantitative agreement with rates derived from fluorescence quantum yield and time-resolved fluorescence measurements was found for forward electron transfer and charge recombination rates.

Sensitivity comparison of real-time PCR probe designs on a model DNA plasmid

We investigated three probe design strategies used in quantitative polymerase chain reaction (PCR) for sensitivity in detection of the PCR amplicon. A plasmid with a 120-bp insert served as the DNA template. The probes were TaqMan, conventional molecular beacon (MB), and shared-stem molecular beacon (ATssMB and GCssMB). A shared-stem beacon probe combines the properties of a TaqMan probe and a conventional molecular beacon. It was found that the overall sensitivities for the four PCR probes are in the order of MB > ATssMB > GCssMB > TaqMan. The fluorescence quantum yield measurements indicate that incomplete or partial enzymatic cleavage catalyzed by Taq polymerase is the likely cause of the low sensitivities of two shared-stem beacons when compared with the conventional beacon probe. A high-fluorescence background associated with the current TaqMan probe sequence contributes to the relatively low detection sensitivity and signal-to-background ratio. The study points out that the nucleotide environment surrounding the reporting fluorophore can strongly affect the probe performance in real-time PCR.

Rayleigh-calibrated fluorescence quantum yield measurements of acetone and 3-pentanone

We measured fluorescence quantum yields of acetone and 3-pentanone as a pure gas and with nitrogen diluent at room temperature at 20, 507, and 1013 mbar using 248, 266, and 308 nm excitation by calibrating the optical collection system with Rayleigh scattering from nitrogen. At 20 mbar with 308-nm excitation, the fluorescence quantum yields for acetone and 3-pentanone are 7 +/- 1 x 10(-4) and 1.1 +/- 0.2 x 10(-3), respectively, and each decreases with decreasing excitation wavelength. These directly measured values are significantly lower than earlier ones that were based on a chain of relative measurements. The observed pressure and excitation wavelength dependence is in qualitative agreement with a previously developed fluorescence quantum yield model, but the absolute numbers disagree. Changing acetone's fluorescence rate constant to 3 x 10(5) s(-1) from its previous value of 8 x 10(5) s(-1) resulted in good agreement between our measurements and the model.

Energy Dissipation Processes of singlet‐excited 1‐Hydroxyfluorenone and its Hydrogen‐bonded Complex with N‐methylimidazole¶

ABSTRACTEffects of solvent, pH and hydrogen bonding with N‐methylimidazole (MIm) on the photophysical properties of 1‐hydroxyfluorenone (1HOF) have been studied. Fluorescence lifetime, fluorescence quantum yield and triplet yield measurements demonstrated that intersystem crossing was the dominant process in apolar media and its rate constant significantly diminished with increasing solvent polarity. The acceleration of internal conversion in alcohols paralleled the strength of intermolecular hydrogen bonding. The faster energy dissipation from the singlet‐excited state in cyclohexane was attributed to intramolecular hydrogen bonding. The pKa of 1HOF decreased from 10.06 to 5.0 on light absorption, and H3O+ quenched the singletexcited molecules in a practically diffusion‐controlled reaction. On addition of MIm in toluene, dual fluorescence was observed, which was attributed to reversible formation of excited hydrogen‐bonded ion pair. Rate constants for the various deactivation pathways were derived from the combined analysis of the steady‐state and the time‐resolved fluorescence results.

Fluorescence emission control and switching of oxymethylcrowned spirobenzopyrans by metal ion

Oxymethylcrowned spirobenzopyran 1 and pyrenylspirobenzopyran 2 were synthesized, and fluorescence emission of their corresponding merocyanine form was examined in the presence of metal ions. For 2 , fluorescence emission derived from the pyrene moiety was completely quenched by photoinduced electron transfer (PET) of the nitrogen atom when the merocyanine form was not produced, namely, without metal ions. However, when 2 was converted to the merocyanine form by the complexation of its crown ether with a metal ion, fluorescence resonance energy transfer (FRET) from the pyrene to the merocyanine moieties took place to produce fluorescence emission. This result demonstrates that the spirobenzopyran isomerization can function as a fluorescence emission switch. Fluorescence quantum yield measurement for 1 and 2 showed that fluorescence emission depends on the binding metal ion in which the fluorescence quantum yield generally increased with the increase of metal ion radius.