Fluorescence Quantum Distributions Research Articles

Absorption and emission spectroscopic characterization of some azo dyes and a diamino-maleonitrile dye

A linear and nonlinear optical spectroscopic characterization is carried out on three azo dyes (Reactive orange 1, Reactive violet 8, and Acidproof purplish red), and on N-( p-hydroxybenzylidene)-diamino-maleonitrile. Fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes are measured. The saturable absorption is studied by nonlinear transmission measurements with intense picosecond laser pulses. The ground-state absorption recovery is studied by picosecond time-resolved pump and probe measurements. Absolute ground-state absorption cross-sections, excited-state absorption cross-sections, and dye concentrations are extracted from saturable absorption studies. The azo dyes have fluorescence lifetimes and ground-state absorption recovery times of around 2 ps and their excited-state absorption cross-sections are small (measured at 527 nm) making them good mode-locking dyes for picosecond and femtosecond lasers. The investigated diamino-maleonitrile dye exhibits sub-picosecond fluorescence lifetime and slow ground-state absorption recovery (>1 ns).

ABSORPTION, EMISSION AND NONLINEAR SPECTROSCOPIC CHARACTERIZATION OF REACTIVE DYE

An optical spectroscopic characterization is carried out on a reactive dye (reactive orange 1). This dye is widely applied in textile coloration. It is a potential candidate for photonics applications. Its absorption cross-section spectra are measured. A fluorescence spectroscopic characterization is undertaken by measuring the fluorescence quantum distributions and fluorescence quantum yields. The saturable absorption is studied by nonlinear transmission measurements with intense picosecond laser pulses (second harmonic pulses of a mode-locked Nd :glass laser). The nonlinear optical absorption and refraction coefficients are measured by using the top-hat Z-scan technique at a wavelength of 532 nm with 35 ps duration pulses. Reactive orange 1 has the two-photon absorption coefficient of 1.20 cm/GW and the nonlinear refraction coefficient of -7.33 × 10-6 cm2/GW, respectively. In reactive orange 1, there occurs fast ground-state recovery by internal conversion likely via conical intersections. Low excited-state absorption and fast ground-state absorption recovery make it an ideal candidate for passive mode-locking of picosecond and femtosecond lasers as well as for fast nonlinear optical gating.

Absorption and emission spectroscopic characterisation of a pyrene-flavin dyad

The pyrene-flavin (isoalloxazine) dyad, PFD {C 44H 31N 5O 5; CA Index name: 1-pyrenepropanoic acid, α-[[4,10-dihydro-2,4-dioxo-10-phenylbenzo[g]pteridin-3(2H)-yl)acetyl]amino]-, phenylmethyl ester, (αR)–(9Cl); CA Registry number: 618907-57-6}, dissolved in either dichloromethane or acetonitrile is characterized by absorption and emission spectroscopy. Absorption cross-section spectra, stimulated emission cross-section spectra, fluorescence quantum distributions, quantum yields, and degrees of fluorescence polarisation are determined. The fluorescence decay after femtosecond pulse excitation is determined by fluorescence up-conversion. The ground-state absorption recovery is determined by picosecond pump and probe transmission measurements. The dye photo-stability is investigated by observation of absorption spectral changes due to prolonged blue-light excitation. The absorption spectrum of PFD dyad resembles the superposition of the absorption of isoalloxazine (flavin) and 1-methylpyrene. Long-wavelength photo-excitation of the flavin moiety causes fluorescence quenching by ground-state electron transfer from pyrene to isoalloxazine. Short-wavelength photo-excitation of the pyrene moiety causes (i) excited-state electron transfer from pyrene to isoalloxazine, and (ii) Förster-type energy transfer from pyrene to flavin followed by ground-state electron transfer from pyrene to flavin.

Photophysical characterization of pyrromethene 597 laser dye in silicon-containing organic matrices

Samples of dipyrromethene-BF2 dye PM597 incorporated in copolymers of 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) with methyl methacrylate (MMA) and 2-hydroxyethylmethacrylate (HEMA), and in terpolymers of MMA, HEMA and TMSPMA are characterized. The absorption cross-section spectra, stimulated emission cross-section spectra, and the excited-state absorption cross-section at 527 nm are determined. The fluorescence quantum distributions and fluorescence lifetimes are measured. The photo-degradation is studied under cw laser excitation conditions and quantum yields of photo-degradation are extracted. PM597 solid state samples are compared with PM597 in liquid ethyl acetate solution. The fluorescence quantum yield of PM597 is higher in doped samples (around 70%) compared to PM597 in ethyl acetate (43%). The excited-state absorption cross-section was found to be negligibly small. The photo-stability is considerably larger in the polymeric samples compared to the liquid solutions.

Absorption and emission spectroscopic characterization of 10-phenyl-isoalloxazine derivatives

The flavoquinone dyes 10-phenyl-isoalloxazine-3-acetic acid ethyl ester ( 1) and 10-(4-bromo-phenyl)-3-methyl-isoalloxazine ( 2) in dichloromethane, acetonitrile, and methanol are characterized by absorption and emission spectroscopy. Absorption cross-section spectra, stimulated emission cross-section spectra, fluorescence quantum distributions, quantum yields, lifetimes, and degrees of fluorescence polarization are determined. The blue-light photo-degradation of the dyes is studied. Mass spectroscopic measurements reveal the formation of phenyl-benzo-pteridine (isoalloxazine) derivatives, tetraaza-benzo-aceanthrylene derivatives, dihydro-quinooxaline derivatives, and pyrazino-carbazole derivatives. An enhancement of photo-degradation is observed by the formed photo-fragments.

Photo-physical and lasing characterisation of a polyparaphenylenevinylene (PPV) neat film

The wave-guided travelling-wave laser action (amplified spontaneous emission) of a neat film of poly(p-phenylenevinylene) (PPV) on a quartz glass substrate prepared by a sulfinyl precursor technique is studied. The samples are transversally pumped with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs at 550 nm. The optical constants of the neat films are determined by transmittance measurements exploiting the multiple beam interference in the transparency region. A fluorescence spectroscopic characterisation is carried out determining the fluorescence quantum distribution, fluorescence quantum yield, degree of fluorescence polarisation, and fluorescence lifetime. The emitting chromophore size (emitting singlet exciton extension) is determined by the ratio of exciton radiative lifetime to repeat-unit based radiative lifetime. The obtained size of about two repeat units is discussed in a disordered solid-state polymer model.

Photophysical characterisation of some dipyrromethene dyes in ethyl acetate and covalently bound to poly(methyl methacrylate)

Abstract Analogues of the dipyrromethene-BF 2 dye PM567 modified at the 8-position by acetoxymethyl (P1Ac), s -acetoxypentyl (P5Ac), and p -acetoxymethylphenyl (PAr1Ac) groups are studied in ethyl acetate solution. PM567 modified at the 8-position by methacryloyloxymethyl (P1MA), s -methacryloyloxypentyl (P5MA), and p -methacryloyloxymethylphenyl (PAr1MA) groups have been copolymerized with methyl methacrylate (MMA), and these solid samples are also studied. The absorption cross-section and stimulated emission cross-section spectra are determined. The fluorescence quantum distributions and fluorescence lifetimes are measured. Saturable absorption measurements with picosecond laser excitation are carried out for excited-state absorption cross-section determination at the excitation wavelength. The photo-degradation of the dyes is studied under cw laser excitation conditions and quantum yields of photo-degradation are extracted.

Photo-physical and lasing characterisation of neat films of a thianthrene-substituted distyrylbenzene dye (Thianthrene-DSB)

Wave-guided travelling-wave laser action and distributed-feedback laser action of a thianthrene substituted distyrylbenzene (Thianthrene-DSB) in neat thin films on glass-substrates and corrugated gratings have been achieved by optical excitation with picosecond laser pulses. The Thianthrene-DSB dye is a model compound of previously studied Thianthrene-PPV polymers. It was found that the low molar-mass model and the corresponding polymers are similar in solid-state lasing behaviour. Some laser performance parameters are determined like laser threshold, and spectral narrowing. The Thianthrene-DSB travelling-wave laser emits at 544 nm and the threshold pump pulse energy density is about 9 μJ cm −2. The distributed feedback laser is wavelength tunable in the range from 520 to 580 nm by variation of the groove spacing and the film thickness. The refractive index and absorption cross-section spectra of the films are determined. The fluorescence behaviour of the films (fluorescence quantum distribution, fluorescence quantum yield, degree of fluorescence polarisation, fluorescence lifetime) is analysed. A fluorescence quantum yield of about 0.6 is found for both Thianthrene-DSB neat films and Thianthrene-DSB dissolved in dioxane.

Fluorescence quenching of flavin adenine dinucleotide in aqueous solution by pH dependent isomerisation and photo-induced electron transfer

Abstract The fluorescence behaviour of flavin adenine dinucleotide (FAD) in aqueous solution is investigated over a wide hydrogen ion range from pH=1 to pH=11.3. The accessible pH range is limited by room temperature hydrolysis of FAD to flavin-mononucleotide and adenosine-monophosphate at high and low pH. Fluorescence quantum distributions, fluorescence quantum yields, and fluorescence signal decays are measured. The results are compared with the pH dependence of riboflavin in aqueous solution. In the range from pH ≈ 4 to pH ≈ 9 the fluorescence quantum yield is approximately constant at φ F ≈0.033. Below pH=4 the fluorescence rises up to φ F ≈0.13 around pH=2.5 and then reduces similar as riboflavin. The fluorescence behaviour is discussed in terms of a two conformation system. In the range from pH ≈ 3.5 to pH ≈ 11 the stacked (closed) isoalloxazine–adenine conformation dominates over the un-stacked (open) conformation in the S 0 ground-state. At higher and lower pH the ground-state isomerisation equilibrium shifts towards un-stacked conformation dominance. S 1 state photo-isomerisation converts un-stacked molecules to stacked molecules, especially in the range from pH ≈ 3 to pH ≈ 11. The stacked molecules are practically non-fluorescent due to reductive photo-induced electron transfer from the adenine moiety to the isoalloxazine moiety.

Absorption and emission spectroscopic characterisation of F 3 - colour centers in a LiF crystal

For a LiF crystal containing F3 (R1, R2), F2, F3 +, F4 (N1, N2), F3 -, and F2 - colour centers the absorption and emission spectroscopic behaviour of the F3 - centers is studied. The absorption cross-section spectrum and the number density of F3 - centers are extracted from saturable absorption and transmission measurements. Additionally fluorescence quantum distribution measurements and fluorescence lifetime measurements are carried out to determine the stimulated emission cross-section spectrum and the fluorescence quantum yield of the F3 - centers. Fluorescence excitation spectroscopy reveals the presence of an absorption band with its absorption peak around 700 nm (called R′ 1 band) in addition to the ground-state to first excited-state F3 - center absorption band centered at 800 nm (called R′ 2).

Fluoresence quenching of riboflavin in aqueous solution by methionin and cystein

Abstract The fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes of riboflavin in methanol, DMSO, water, and aqueous solutions of the sulphur atom containing amino acids methionin and cystein have been determined. In methanol, DMSO, and water (pH=4–8) only dynamic fluorescence reduction due to intersystem crossing and internal conversion is observed. In aqueous methionin solutions of pH=5.25–9 a pH independent static and dynamic fluorescence quenching occurs probably due to riboflavin anion–methionin cation pair formation. In aqueous cystein solutions (pH range from 4.15 to 9) the fluorescence quenching increases with rising pH due to cystein thiolate formation. The cystein thiol form present at low pH does not react with neutral riboflavin. Cystein thiolate present at high pH seems to react with neutral riboflavin causing riboflavin deprotonation (anion formation) by cystein thiolate reduction to the cystein thiol form.

Photo-physical and lasing characterization of neat films of 4-methyl-TPD and of an alternating copolymer of 4-methyl-TPD with MEH–PPV

Wave-guided traveling wave lasing, i.e. amplification of spontaneous emission in a waveguide, is studied on neat films of the triphenylamine dimer 4-methyl-TPD ( N, N′-bis(4-methylphenyl)- N, N′-diphenyl-benzidine) and an alternating copolymer with MEH–PPV assigned as TPD(4M)–MEH–P–PPV. The solution processable polymer has been prepared via the polycondensation route. Laser action is achieved by transversally pumping neat films on glass substrates with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs around 422 nm for 4-methyl-TPD and around 544 nm for TPD(4M)–MEH–P–PPV. Below laser threshold leaky mode emission into the substrate along the film/surface interface is reported for 4-methyl-TPD. The optical constants (absorption spectra and refractive index spectra), the absorption cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes of the samples are determined for photo-physical characterization. The laser performance and the photo-physical parameters of 4-methyl-TPD are compared with the molecule 3-methyl-TPD and the non-conjugated polymer poly-TPD(4M)–DPX which is built up of 4-methyl-TPD and α,α′-diphenylxylylene units. The parameters of TPD(4M)–MEH–P–PPV are compared with the parameters of TPD(4M)–MEH–PPV another alternating copolymer of 4-methyl-TPD with MEH–PPV. The synthesis details for TPD(4M)–MEH–PPV and TPD(4M)–MEH–P–PPV are given.

Emission spectroscopic characterisation of F2− colour centres in a LiF crystal

Abstract The fluorescence quantum distribution, fluorescence quantum yield and degree of fluorescence polarisation of a LiF:F 2 − crystal is measured at room temperature by standard fluorimetric techniques. The fluorescence lifetime is determined by femtosecond laser pulse excitation and fast photodetector-oscilloscope detection. The stimulated emission cross-section spectrum is extracted from the radiative lifetime and the fluorescence quantum distribution. The effective stimulated emission cross-section spectrum is extracted from picosecond pump and probe experiments. The results indicate negligible excited state absorption in the fluorescence spectral region.

PH dependence of the absorption and emission behaviour of riboflavin in aqueous solution

The absorption and fluorescence behaviour of riboflavin is investigated in aqueous solution over a wide range of pH values from pH=−1.1 to pH=13.4. Absorption spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence signal decays are measured. Riboflavin exists in three different forms depending on the pH of the solutions. There is an equilibrium between the cationic form (RFl oxH 2 +) and the neutral form (RFl oxH) at low pH (p K c=0.4), and between the neutral form and the anionic form (RFl ox −) at high pH (p K a=9.75). The cationic, neutral, and anionic species have different absorption spectra. The fluorescence quantum yields and fluorescence lifetimes of the various forms are separated. The cationic form is non-fluorescent (fluorescence quantum yield φ F<5×10 −5), and the anionic form has a low fluorescence quantum yield of φ F≈1.2×10 −3. The fluorescence quantum yield of the neutral form is around φ F≈0.26 above pH=4 and decreases strongly below pH=4 because of [H +]-dependent excited-state reaction of RFl oxH * to RFl oxH 2 +*. At low pH the fluorescence signal decay is single-exponential since only the neutral form, RFl oxH, is emitting. At high pH a bi-exponential fluorescence decay occurs because RFl oxH and RFl ox − emit with different time constants.

Excitation energy density dependent fluorescence behaviour of a regioselectively functionalized tetraphenylporphyrin–cellulose conjugate

The fluorescence behaviour of tetraphenylporphyrin appended cellulose strands in chloroform is studied by weak cw excitation and intense picosecond laser pulse excitation (wavelength λ L=347.15 nm, duration Δt L=35 ps). With rising pump pulse energy density, a reduction of the fluorescence efficiency and a shortening of the fluorescence signal decay time are observed. The energy density dependent fluorescence quenching is analysed in terms of intra-strand singlet exciton–singlet exciton annihilation. The annihilation constant is determined and a critical singlet exciton number density ( N ex, ann =4.8×10 19 cm −3 ) as well as a critical fraction of excited repeat units ( f RU,ann=0.1) for annihilation are determined. Additionally the excited-state absorption cross-section, σ ex,L, at the pump laser wavelength, λ L, is determined by energy density dependent transmission measurements and is found to be approximately equal to the ground-state absorption, σ L, at λ L. The small-signal fluorescence quantum distribution, fluorescence quantum yield ( φ F=0.072), and degree of fluorescence polarisation ( P F=0.04) are determined by cw fluorimetry. The emitting exciton size is found to be equal to the repeat-unit size of the cellulose strands.

Travelling-wave lasing of triphenylamine-based poly(phenylene vinylene)

Travelling-wave lasing (amplified spontaneous emission) is reported for a series of triphenylamine-based poly(phenylene vinylene)-copolymers (TPA-PPVs) that have different substituents R at the vinylene double bond (R=H, CN, methoxyphenyl) and slight modifications in the alkoxy side chains (dioctyl, MEH). Wave-guiding neat films on glass substrates are transversally pumped with picosecond laser pulses (wavelength 347.15nm, duration 35ps). The laser emission occurs in the wavelength region between 515 and 560nm. Optical parameters (refractive index spectra and absorption coefficient spectra) and spectroscopic parameters (absorption cross-section and stimulated emission cross-section spectra, fluorescence quantum distributions, internal fluorescence quantum yields, and fluorescence lifetimes) of the polymers are determined. The lumophore size is extracted from fluorescence lifetime and fluorescence quantum yield measurement and found to be approximately one repeat-unit. The lasing is characterised by measuring the spectral narrowing, the temporal shortening, the laser output energy versus input pump pulse energy, and the effective length of amplification. The obtained lasing parameters compare favourably well with those of previously studied MEH-PPV and TPD-PPVs. The laser threshold pump pulse energies are <650nJ. The effective lengths of amplification are about 1mm. The spectral widths of emission are <9nm.

Photophysical characterization of pyrromethene dyes in solid matrices of acrylic copolymers

Some photophysical parameters of the pyrromethene laser dye PM567 and of two newly synthesized pyrromethene laser dyes, P5Ac and P10Ac, in solid matrices of different acrylic copolymers and in corresponding mimetic liquid solutions are determined. They include absorption cross-section and stimulated emission cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and fluorescence lifetimes. The saturable absorption behaviour due to picosecond laser pulse excitation is studied. The photodegradation under cw laser excitation and under pulsed picosecond pulse excitation is investigated.

Amplified spontaneous emission in neat films of arylene-vinylene polymers

Amplified spontaneous emission (travelling-wave lasing) was achieved for a set of 18 poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) related arylene-vinylene copolymers, a part of which substituted with additional phenyl groups at the vinyl double bond. Wave-guiding neat thin films on glass substrates were used. The samples were transversally pumped with single second harmonic pulses of a mode-locked ruby laser (wavelength 347.15 nm). Travelling-wave emission occurred in the wavelength region between 485 and 650 nm. Repeat unit based absorption cross-section spectra, normalized fluorescence quantum distributions, and amplified spontaneous emission spectra are presented. Ground-state absorption cross-sections at the wavelengths of peak amplified emission are extracted from effective gain length measurements. Effective stimulated emission cross-sections are derived from pump pulse energy densities necessary for optical narrowing.

Photo-physical and lasing characterization of an aromatic diamine-xylylene copolymer

A solution processable poly-condensation product of high glass transition temperature containing 50 mol% electrically active triphenylamine dimer (TPD) chromophores and 50 mol% non-conjugated α,α-diphenylxylylene (DPX) units in the main chain is studied for its photo-physical and lasing properties. This copolymer abbreviated as poly-TPD-DPX shows travelling-wave laser action (amplification of spontaneous emission) as neat film on a fused silica substrate and in liquid solution when transversally pumped with picosecond excitation pulses (wavelength 347.15 nm, duration 35 ps). Lasing occurs at 419 nm for the neat film and at 405 nm for the polymer in 1,4-dioxane solution. The optical constants (absorption spectrum and refractive index spectrum) of the neat film are determined by reflection and transmission measurement. The absorption cross-section spectra and fluorescence quantum distribution spectra of neat films and 1,4-dioxane solutions are compared. The fluorescence quantum yields of poly-TPD-DPX neat films and 1,4-dioxane solutions are 0.16 and 0.66, respectively.

Photo-physical characterization of rhodamine 6G in a 2-hydroxyethyl-methacrylate methyl-methacrylate copolymer

Some photo-physical parameters of 1×10 −4 and 5.9×10 −4 M samples of rhodamine 6G in a 2-hydroxyethyl-methacrylate methyl-methacrylate copolymer (volume mixture 1:1) are determined and compared with rhodamine 6G in methanol. They include the absorption cross-section and stimulated emission cross-section spectra, the fluorescence quantum distributions, quantum yields and lifetimes. The photo-degradation under steady-state and pulsed excitation is investigated. The saturable absorption behaviour under picosecond laser excitation is studied.