Fluorescence Quantum Yield Measurements Research Articles

Synthesis of a New Thermal and Photostable Reference Probe for Qf Measurement in Aqua: Water Soluble N,N′-bis-(2-Hydroxy-4-benzoic Acid)-3,4,9,10-perylenebis(dicarboximide)

N,N′-bis(2-hydroxy-4-benzoic acid)-3,4,9,10-perylenebis(dicarboximide) is synthesized from perylene 3,4,9,10-tetracarboxylic dianhydride and 4-amino-3-hydroxy benzoic acid in 90% yield. Together with the photostability the dye is also very stable thermally. The fluorescence quantum yield is measured as one, Qf=1.The diimide dissolves in water at PH = 8 completely. The diimide is an ideal reference probe for fluorescence quantum yield measurements in 500–650 nm region and an attractive photosensitizer for the photoreactions occur in water.

Interactions between a surface-active cationic 3H-indole molecular probe and micellar environments

We report herein the interactions of a cationic surface-active molecular probe having long aliphatic chains, i.e., [2-(p-hexylamino)phenyl-3,3-dimethyl-5-ethoxycarbonyl-3H-indole]methyldioctadecylammonium iodide (1), with SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) micelles investigated by spectral and photophysical characterizations. According to the absorption and fluorescence spectral characteristics and the fluorescence quantum yield, the interaction of 1 with SDS exhibits different patterns that depend on the SDS concentration: (1) formation of ion-pairs at very low concentration of SDS; (2) complex coacervation below the critical micellar concentration (c.m.c.) of SDS; (3) solubilization of the coacervate phase into micelles above the c.m.c. The fluorescence quantum yield measurement as well as the pH effect studies reveal that the hexyl group and a part of the anilino moiety of 1 penetrate the micellar interface, while the indolic moiety of 1 resides in the bulk phase. Lifetime measurements support the existence of three interaction patterns between 1 and SDS, and further indicate that 1recognizes one location in the SDS micelle and two in the CTAB micelle.

Superradiance and Exciton Delocalization in Bacterial Photosynthetic Light-Harvesting Systems

We present temperature-dependent fluorescence quantum yield and lifetime measurements on the LH-1 and LH-2 complexes of Rhodobacter sphaeroides and on the isolated B820 subunit of Rhodospirillum rubrum. From these measurements the superradiance is calculated, which is related to the delocalization of excitations in these complexes. In the B820 preparation we find a radiative rate that is 30% higher than that of monomeric bacteriochlorophyll, in agreement with a dimer model of this subunit. At room temperature both LH-1 and LH-2 are superradiant relative to monomeric Bchl-a with enhancement factors of 3.8 and 2.8, respectively. In LH-2 the radiative rate does not change significantly upon lowering the temperature to 4 K. LH-1 however exhibits a strong temperature dependence, giving rise to a 2.4 times higher radiative rate at 4 K relative to room temperature. From modeling of the superradiance using a Hamiltonian based on the LH-2 structure and including site inhomogeneity, we conclude that the ratio of in...

Quantum Yields of Crude Oils

Fluorescence quantum yield measurements are reported for visible and UV excitation for neat and dilute crude oil solutions, extending earlier work with excitation in the long wavelength visible and the NIR. Large and monotonically increasing quantum yields are found with shorter wavelength excitation (to 325 nm), and all crude oils are shown to have nearly the same relative dependence of quantum yield on excitation wavelength. These observations are explained by the energy dependence of internal conversion. Dilute solutions of light crude oils exhibit higher quantum yields than those of heavy crude oils because of their lack of large chromophores. The fraction of fluorescence emission resulting from electronic energy transfer (with subsequent fluorescence emission) for neat crude oils was previously shown to vary from ∼100% for ultraviolet excitation to ∼0% for near-infrared excitation; this large variation correlates well with and is explained by the very large variation in quantum yields with excitation wavelength. Comparison of quantum yields from neat and dilute solutions shows that quenching is the other major process which occurs with chromophore interactions. The quantum yields of a maltene and resin are large and similar, while the asphaltene exhibits much smaller quantum yields because of its lack of small chromophores.

A Thermal and Photostable Reference Probe for QfMeasurements: Chloroform Soluble Perylene 3,4,9,10-Tetracarboxylic Acid-bis-N, N-Dodecyl Diimide

Abstract The synthesis of a chloroform soluble perylene 3, 4, 9, 10-tetracarboxylic acid-bis-N, N′-dodecyl diimide via condensation of perylene 3, 4, 9, 10-tetracarboxylic dianhydnde and 1, 12-diamino dodecane is described. The thermal analysis is shown thermal stabilities above 400°C. Thermal and photostable dye is measured to have a fluorescence quantum yield of unity, Qf = 1.00, in chloroform solutions. Perylene bis-dodecyl diimide is an ideal reference probe for fluorescence quantum yield measurements in 500–650 nm region and a reliable soluble photosensitizer for solar photochemical applications.

Measurement of the absolute fluorescence quantum yield of rhodamine B solution using a dual-beam thermal lens technique

The dual-beam thermal lens technique has been found to be very effective for the measurement of fluorescence quantum yields of dye solutions. The concentration-dependence of the quantum yield of rhodamine B in methanol is studied here using this technique. The observed results are in line with the conclusion that the reduction in the quantum yield in the quenching region is essentially due to the non-radiative relaxation of the absorbed energy. The thermal lens has been found to become abberated above 40 mW of pump laser power. This low value for the upper limit of pump power is due to the fact that the medium is a resonantly absorbing one.

Excited State Dynamics of 9,10-Diazaphenanthrene Studied by the Time-Resolved Transient Grating Method

The heat-releasing processes of the photoexcited states of 9,10-diazaphenanthrene (DAP) in ethanol have been directly detected using the picosecond time-resolved transient grating (TG) method. From the heat-releasing rates, a surprisingly short lifetime of the lowest excited triplet state (∼13 ns) and a relatively long lifetime of the lowest excited singlet state (4.3 ns) are detected. By measuring the heat energy coming from the excited state of DAP together with the fluorescence quantum yield measurement, the quantum yield of the triplet formation is found to be about unity. The unique photophysical properties of DAP are also discussed.

Temperature and viscosity sensitive S 1 emission from a highly substituted triene

Fluorescence from a highly substituted triene, called mini-3, studied at cryogenic temperatures, originates from the lowest excited state (S 1). Compared to the longer compounds homologous to all-trans-β-carotene, the emission is more Stokes-shifted. Another contrast is that the measured fluorescence quantum yield of mini-3 shows a distinct temperature/viscosity dependence: in 3-methylpentane decreasing from 0.61 at 77 K to 0.047 at 110 K. In room-temperature liquids it is virtually non-fluorescent. The discrepancies between mini-3 and the longer mini-carotenes are best explained by the involvement of out-of-plane vibrational modes in the coupling between S 1 and S 0 in mini-3, while only the CC stretching vibrations act as accepting and promoted modes in the longer ones. It is likely that the low-frequency modes in mini-3 are caused by a nonplanar equilibrium conformation, probably caused by steric hindrance. An Arrhenius plot resulted in an activation energy of 610 ± 200 cm −1, probably mainly governed by solvent viscosity. The fluorescence excitation anisotropy ( r s) is about 0.39, indicating that the absorption and emission transition dipoles are parallel.

Multidimensional photochemistry in 4-(N,N,-dimethylamino) stilbene

The absorption and fluorescence properties, quantum yields and lifetimes of fluorescence observed for several selectively bridged 4-dimethylaminostilbene (DS) derivatives are shown to reflect different pathways for singlet state relaxation. The single bond connecting the dialkylanilino group to the ethylene group (bond 2) is the site of decoupling between the donor and acceptor parts to form a TICT excited state. AM1 and CNDO/S calculations have been used to interpret the multidimensional photo-chemistry of DS. The potential energy curves, dipole moments, oscillator strengths and atomic charge densities have been calculated for different twist angles around the single bond 2 and the solvent-induced changes have been considered for the four lowest excited states. By bridging the single bond 2 chemically, dimensionality is reduced, and only one product state, the phantom singlet state P *, remains. For this channel, the measurements of fluorescence quantum yields and lifetimes versus temperature indicated a higher activation energy in ethanol than in diethylether.

ChemInform Abstract: Does Diphenylacetylene (Tolan) Fluoresce from Its Second Excited Singlet State? Semiempirical MO Calculations and Fluorescence Quantum Yield Measurements.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Production of the Near-Infrared Spectrofluorophotometer and Fluorescence Quantum Yield of the Cyanine Solution for Dye Laser

For the accurate measurement of fluorescence quantum yield of biological dyes, dye lasers, etc., a spectrofluorophotometer with a built-in quantum counter is used. Such spectro meters that are available at the market can be used for exciting wavelengths of up to 600nm for which a quantum counter functions correctly, but not for longer wavelengths. In this study, light quantum counter dyes that can be used for exciting light of up to 700nm have been examined with the use of eight types of dye solutions, and it has been discovered that methylene blue trihydrate is the most suitable. By using this quantum counter dye, an electric control circuit of quantum counters has been constructed, consisting of the negative feed back circuit and the photomultiplier, and verified to be a spectrofluorophotometer that is usable from the practical points of view. In addition, with regard to several types of cyanine dyes, a comparative study of their energy levels obtained by a molecular orbital method, measured fluorescence quantum yield, and dye laser outputs has been conducted to evaluate those cyanine dyes as laser dyes.

Does diphenylacetylene (tolan) fluoresce from its second excited singlet state? Semiempirical MO calculations and fluorescence quantum yield measurements

It is confirmed by measurements of fluorescence spectra and quantum yields that the fluorescence in tolan originates from the same state that causes the absorption band at lowest energy. The temp. dependence of the fluorescence quantum yield shows that this state is thermally deactivated with an activation energy of EA = 14.0 kJ/mol. Geometry optimizations of the states S0, S1, and T1 of tolane with the semiempirical AM1 method lead to planar structures with D2h symmetry. Potential energy curves along the triple-bond stretching coordinates have been calcd. for several low-lying excited states with a combination of the AM1 and the INDO/S methods. It is found that for large triple-bond lengths, the 1Au-state with sp* character becomes the lowest excited singlet state. It is proposed that thermal deactivation of S1(11Blu) leads to this state. Nonvertical excitation of 11Au could explain the weak lines found in supersonic jet expts. below the onset of the 11Ag -> 11Blu transition.

Concerning medium polarity effects on the photophysics and photochemistry of TICT-forming dyes

Mechanism and dynamics of the excited state relaxation in compounds able to form TICT states were investigated from a theoretical point of view with special reference to the dielectric solvent effects. The study included 4-dimethylamino-4'-cyanostilbene (DCS) and Michler's Hydrol Blue (MHB), which are thought to involve emitting and non-emitting TICT states, respectively. It was found that in DCS the formation of TICT states, by twisting either the dimethy lamino or the dimethylanilino groups, may in principle be induced by the solvent polarity but requires extreme conditions. In MHB, both calculations and new fluorescence quantum-yield measurements in a variety of solvents indicated that the TICT-state formation is essentially controlled by the solvent viscosity.

Picosecond study on excimer formation in pyrene crystals: Part III: Complete analysis of the high temperature phase between 5 and 300 K

Microcrystalline pyrene films deposited on silicon substrates are characterized by steady-state and picosecond spectroscopy in the temperature range between 5 and 300 K. The films reveal at high temperatures all the typical features of the single crystal high temperature phase. Upon cooling to low temperatures we find that the majority of the microcrystals does not show a phase transition thus making the crystalline high temperature phase accessible in the temperature range between helium and room temperature. For that whole range the measurements of fluorescence quantum yields and transients quantitatively confirm our concept of two-step excimer formation via the metastable precursor B-state. The same thermal activation barrier between B- and excimer state, (350 ± 30) cm -1, is found as in the single crystal. The intrinsic lifetime of the B-state is measured to be about (200 ± 10) ns in accordance with our previous estimates. From the detailed analysis of the B-fluorescence spectrum at low temperatures we conclude that already the B-state is subject to appreciable electron-phonon coupling.

Investigations of the excitation energy transport mechanism in donor-acceptor systems

Measurements of fluorescence quantum yield ηD/ηoD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C D=2·10(-2) M (system I), 1.5·10(-2) M (II), 10(-2) M (III), 3·10(-3) M (IV), and 5·10(-5) M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield ηD/ηoD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.

Limitation of the thermal-lens method in fluorescence quantum-yield measurements

Thermal-lens spectrophotometry has been used to determine fluorescence quantum yields. It is shown that the method is not always accurate, especially in the case of dye molecules which exhibit high triplet-state quantum yields.

Dephasing-induced damping of superradiant emission in J-aggregates

Results of temperature-dependent accumulated photon echo, fluorescence lifetime and fluorescence quantum yield measurements are reported on aggregates of the dye pseudoisocyanine bromide in an ethylene glycol/water glass. The results show that the lowest excited state of the J-aggregate can be described as a superradiative exciton, whose radiative and optical coherence lifetime are determined by dephasing processes. The results further indicate that the phonon-induced fluctuations of the site energies must be highly correlated. The observed discrepancy between the low-temperature photon echo decay time of 16 ps and fluorescence lifetime of 70 ps is ascribed to observation of dephasing of an excitonic wave packet in the echo and incoherent relaxation of the same k-states in the fluorescence.

Damping of superradiant excitons in molecular aggregates

Results of temperature dependent accumulated photon echo, fluorescence lifetime and fluorescence quantum yield measurements are reported on the zero-phonon transitions of structurally different aggregates of the dye molecule pseudoisocyanine. In each case a substantial discrepancy is found between the low temperature ps decay of the exciton's coherence and its population lifetime, with the former being much faster and non exponential. The difference is attributed to the fact that the excitonic wave packet excited in the photon echo is composed of different k-states that interfere in its decay. In the fluorescence lifetime measurements the incoherent relaxation of these levels is observed. The radiative rate constant of the aggregates at low temperature is found to be extremely large and interpreted as arising from the cooperative emission of hundreds of molecules. The temperature dependence of the radiative rate constant above 50 K may be understood as resulting from photon induced quenching of the superradiant emission of the aggregate.

Significance of the static fluorescence quenching limit in the finite sink approximation

In the finite sink approximation the time-independent quenching rate constant k Q( c) increases with quencher concentration c according to the equation ▪ where (2π Nc) − 1 3 ) = r 0, the most probable nearest-neighbor separation or sink radius. The predicted existence of a “static” quenching limit c = c ϱ, at which r 0 is equal to the encounter diameter ϱ and k Q ( = k 0) becomes independent of diffusion coefficient D or solvent viscosity, is confirmed by relative fluorescence quantum yield measurements reported here and elsewhere. The significance of this static limit is discussed with reference to both photostationary intensity measurements and the time-dependent fluorescence response function.

Torsional dynamics of molecules on barrierless potentials in liquids. III. Pressure dependent picosecond studies of triphenyl-methane dye solutions in a diamond anvil cell

Pressure dependent measurements of the nonradiative torsional dynamics of triphenyl-methane dyes are reported. The viscosity dependence of the excited state absorption and fluorescence decays of crystal violet, dissolved in methanol, ethanol, and n-propanol, are studied over a viscosity range of between 0.5 and 500 cP (pressures up to 1.5 GPa ∼15 000 atm). The overall viscosity dependence of the excited state decay time is linear. The nonlinear viscosity dependencies observed in earlier studies may have resulted from the complex nature of the solvents used and, in the case of fluorescence quantum yield measurements, from a pressure dependence of the radiative rate. Differences between the viscosity dependence observed when varying pressure, temperature, or solvent type at low viscosities are tentatively ascribed to pressure and temperature induced conformational changes.