Triplet Absorption Spectra Research Articles

Protolytic reactions of acridine in the triplet state

The triplet—triplet (T—T) absorption spectrum of the acridinium ion (λ max=490 nm) was measured in acidic aqueous solution at pH 1.0 by means of the triplet energy transfer from the disodium salt of naphthalene disulphonic acid to the acridinium ion. The triplet acridinium ion decays by a first order process with a rate constant of 1.5 × 10 3 s −1 at a pH below about 3.8. The p Ka of acridine in the triplet state was determined to be 5.6 at 23°C from the measurements of T—T absorption spectra of both the acridine molecule and the acridinium ion. The rate constants for protonation and deprotonation in the triplet state were determined to be (3.4 – 3.8) × 10 10 M −1 s −1 and (8.5 – 9.5) × 10 4 s −1 respectively.

Triplet states of protoporphyrin IX and protoporphyrin IX dimethyl ester

Laser and conventional flash photolysis have been used to obtain the triplet—triplet absorption spectra, triplet lifetimes, rates of oxygen quenching and quantum efficiencies of triplet formation of protoporphyrin IX as the dication, monocation and free base in several solvent systems. The results are rationalised in terms of protoporphyrin IX existing as a monomer in organic or detergent solvents and as an aggregated species in aqueous environments.

SOME FUROCOUMARINS AND ANALOGS: COMPARISON OF TRIPLET PROPERTIES IN SOLUTION WITH PHOTOBIOLOGICAL ACTIVITIES IN YEAST

Abstract— Some photophysical and photochemical properties of two furocoumarins, three furochro‐menes and one difurobenzene have been studied in ethanol by laser flash spectroscopy. Such properties included the triplet absorption spectra. extinction coefficients, quantum yields of formation and reactivities with the nucleic acid bases thymine and uracil, and the amino acid tryptophan. The effects the same compounds have on survival of the yeast, Saccharomyces cerevisiae, after 365 nm photosensitization were also investigated. These effects on survival differed markedly for the different compounds. Possible correlations between the photophysical, photochemical and photobiological data are discussed.

TRIPLET EXCITED STATES OF PYRIMIDINE NUCLEOSIDES AND NUCLEOTIDES

Abstract— The triplet absorption spectra, lifetimes, extinction coefficients, eTT, and intersystem crossing quantum yields to the lowest triplet T1, øT1, of thymidine, thymidine monophosphate, uridine and uridine monophosphate, have been determined in various solvents at 300 K.The effect of H‐bonding on øT1, of these nucleosides and nucleotides and also of uracil has been determined and discussed. This effect allows, an ordering of l,3n, π* and 1,3π, π* states in protic and aprotic solvents.

Determination of the triplet and excited singlet absorption spectra of chlorophyll a with a tunable dye laser

A tunable dye laser has been used to obtain the optical spectra of the triplet and first excited sïnglet states of chlorophyll a in pyridine produced by irradiation with a nitrogen laser. The singlet spectrum is characterized by an absorption at 440 nm.

Triplet–triplet absorption of some aryl-substituted 1,3,4-oxadiazoles

The triplet–triplet absorption spectra of three naphthyl-1,3,4 oxadiazoles have been measured from 400 to 620 nm. The spectra are analyzed in terms of naphthalene perturbed in the α or β position using a theoretical simulation of the perturbation based on Pariser–Parr–Pople approximation. It is concluded that the lowest triplet state of these molecules must involve an important contribution of charge transfer configurations.

Kinetic spectroscopy of triplet states of benzenoid hydrocarbons using modulated Hg resonance radiation

Triplet—triplet absorption spectra in the 220–250 nm region, and rate constants for unimolecular and bimolecular decay of the lowest triplet states of simply substituted benzenes in the gas phase have been obtained using a phase modulation technique. For deuterium and methyl substitution, first order decay constants are of the same order as in benzene of 10 3 s −1, with second order decay constants of the order of 10 7 ℓ mol −1 s −1, also as in benzene. For trifluoromethyl substitution, these rate constants increase dramatically to of the order of 10 −5 s −1 and 10 8 ℓ mol −1 s −1 respectively, and fluorine substitution is even more dramatic, with values in the 10 6 s −1 and 10 9 ℓ mol −1 s −1 respectively.

Local structure and triplet energy migration inp-dichlorobenzene-p-dibromobenzene solid solutions

Studies of the first triplet absorption and emission spectra of p-dichlorobenzene-p-dibromobenzene (DCB-DBB) mixed crystals agree generally with the data, indicating that this system forms solid solutions. However, the spectral properties are found to be very different from that of isotopically mixed crystals of comparable concentrations. The singlet-triplet absorption spectra of the DCB-DBB mixtures are generally broad and not amenable to detailed analysis indicating significant site dependent perturbations of the DCB and DBB triplet energies. Energy migration enhances emission from the lower energy sites and in consequence a red shift in the position of the emission (0,0) is observed, which is a maximum at equimolar concentrations. The emission bands are generally much broader than found for isotopically mixed crystals, indicating that the many types of sites in the DCB-DBB system remained uncoupled. This is a direct consequence of exciton trapping by inhomogeneous energy broadening caused by the site e...

Temperature dependent triplet absorption spectra of anthracene crystals. Photoexcitation spectroscopy with a dye-laser

Singlet—triplet absorption spectra of anthracene single crystals have been investigated between 2 K and 300 K using high resolution photoexcitation spectroscopy with a tunable cw dye laser. Up to 100 K the 0, 0 Davydov components are broadened symmetrically to about 7 cm−1. At higher temperatures the line shape is dominated increasingly by Stokes and anti-Stokes phonon sideband contributions. Both 0, 0 components are shifted to higher energies with increasing temperature but in different amounts. This is explained as a superposition of a decrease both of the Davydov splitting and of the solvent shift.

Flash photolysis of human serum albumin: characterization of the indole triplet absorption spectrum and decay at ambient temperature.

The method of flash photolysis was used to identify the transient absorption spectrum and to characterize the decay kinetics of the indole triplet of human serum albumin. This protein was studied because it contains a single indole side chain which is deeply buried in an expandable oily region and because the phosphorescence of the homologous indole in bovine serum albumin could not be detected at ambient temperatures. The transient was identified on the following basis: (i) its triplet-triplet absorption spectrum was similar to those previously reported for indole and tryptophan; (ii) it was quenched by small quantities of oxygen; and (iii) it was photobleached by 370- to 700-nm light. In a nitrogen-saturated solution at room temperature, the indole triplet decays exponentially for more than a factor of 10 with a lifetime of 0.5 msec. These observations suggest that, because of its exponential decay and relatively long lifetime, the triplet will be more valuable than the indole singlet as an intrinsic reporter group for the study of the structure and dynamics of proteins in solution.

Laser flash photolysis studies on the triplet state of aromatic hydrocarbons in the vapour phase

Triplet—triplet (T 1 → T n ) absorption spectra under low resolution and decay times have been measured for a variety of simple fluorine-substituted benzenes in the vapour phase. Assignments for the observed transitions were made on the basis of CNDO calculations and comparison with the corresponding 3 B 1u → 3 E 2g − transition in benzene. Decay times measured were in the region 200 – 250 ns, orders of magnitude shorter than the corresponding decay time for benzene itself. Reasons for this shortening are briefly discussed.

Primary processes in the photochemistry of rhodamine dyes

Quantum yields for intersystem crossing in rhodamine 6G, N,N′-diethylrhodamine and rhodamine B as well as their triplet—triplet (T—T) absorption spectra were measured in aqueous solutions. The main pathways of rhodamine singlet excited state decay are fluorescence and internal conversion. The main pathways of rhodamine triplet state decay radiationless deactivation, quenching by impurities and by ion radicals, T—T interaction and self-quenching. The process of the electron transfer is considered to be the result of T—T interaction and self-quenching of rhodamine triplets in plain aqueous solutions. Triplet states of rhodamine dyes play a major role in redox reaction that occur in the presence of exogenic electron donors and acceptors. The kinetic decay of half-reduced and half-oxidized rhodamine species was studied. The peculiar properties of rhodamine 6G photoreactions occurring in alcohol solutions are considered. The rate constants of the rhodamine triplet and ion radical decay processes are determined.

Triplet excited states of carbonyl-containing polyenes

The techniques of pulse radiolysis, laser flash photolysis and conventional flash photolysis have been used to study several properties of the lowest triplet states of a series of related carbonyl polyenes: β-ionone, β-ionylidene acetaldehyde, β-apo-14′-carotenal, β-apo-8′-carotenal and torularhodinaldehyde. The corresponding triplet–triplet (T–T) absorption spectra, triplet lifetimes, triplet extinctions, quantum efficiencies of production of the lowest triplet for 265 nm excitation and lowest triplet energy levels have been estimated. Correlations between (i) the numbers of CC double bonds (n) and the T–T wavelength maxima, (ii) the singlet–singlet and T–T wavelength maxima, (iii) the T–T maximum extinction coefficients and n and (iv) the lowest triplet energies and n, were found. The results obtained for the different carbonyl polyenes are discussed in terms of varying relative positions of (n, π*) and (π, π*) levels in the corresponding singlet and triplet manifolds.

The study of the photophysics and primary photochemistry of rhodamine 6G aggregates

The decay processes of the excited singlet and triplet states of rhodamine 6G aggregates were investigated. It was shown that aggregation results in a substantial increase of the quantum yield of intersystem crossing. The triplettriplet (TT) absorption spectra of rhodamine 6G aggregates were measured. The decay kinetics of the triplet state of dye aggregates were studied. It was shown that the main pathways of triplet state deactivation are unimolecular decay and TT interaction. A correlation between the values of the rate constants of unimolecular triplet state decay and of some properties of the solvents is discussed. The mechanism of electron transfer in photoreactions of rhodamine 6G aggregates was considered. It was shown that electron transfer occurs via the triplet state of aggregates by TT interactions and reactions with electron donors and acceptors. The ability of the triplet state of rhodamine 6G aggregates to sensitize redox reactions was established. Spectra of ion radical species and the values of rate constants for some elementary steps were determined.

The Triplet State of 3‐Nitropyrene

Abstract3‐nitropyrene was exposed to a 347.2 nm laser flash in dilute solutions of organic solvents and in aqueous micellar solutions. It was found that the triplet state is formed with a quantum yield of 0.6. The triplet absorption spectrum shows a red shift with increasing polarity of the solvent. Triplet‐triplet energy transfer experiments with anthracene, pyrene and perylene were performed to obtain both the energy (190 ± 10kJ/mol) and the absolute extinction coefficient ((1.0 ± 0.1) 104 M−1 cm−1 at 530nm in benzene) of the 3‐nitropyrene triplet. Diffusion‐controlled triplet‐triplet annihilation occurs in ethanol, benzene and hexane solutions. In some micellar solutions and in glycerol, where the bimolecular triplet‐triplet interaction is retarded, the triplet was found to disappear in a first order process with a half lifetime of 230 μs.—The triplet state of 3‐nitropyrene abstracts a hydrogen atom from diphenylamine with k = 2.9 · 109 M−1 s−1. Electron abstraction from Fe2+ and CO32‐, which should be possible from the point of energetics, could not be observed.

POLARIZED TRIPLET–TRIPLET ABSORPTION SPECTRUM USING STRETCHED POLYMER FILM AT LIQUID NITROGEN TEMPERATURE: DIPHENYLACETYLENE

Abstract Measurements of a polarized triplet–triplet absorption spectrum using stretched polymer films have been attempted at liquid nitrogen temperature. The polarizations of the triplet–triplet transitions of diphenylacetylene were determined, and the molecular structure in the excited triplet state was discussed.

Triplet–triplet absorption spectra and the spectra of the photoreduced states of Rhodamine B and Rhodamine 110

Absorption spectra and extinction coefficients for triplet–triplet absorption in alcoholic solutions of Rhodamine B (R.B.) and Rhodamine 110 (R110) are presented, together with the quantum yields for production of the triplet states in solution and the first and second order rate constants for decay of triplet states in deaerated solutions. Absorption spectra for the semi-reduced forms of the dyes are also reported.

Singlet–triplet absorption spectra of some aromatic molecules in gas matrices at 10 K

Singlet–triplet transitions of some aromatic compounds have been investigated in oxygen matrices at 10 K. The technique developed in this study circumvents experimental difficulties of the classical high pressure technique of oxygen perturbation. It also overcomes the problem of estimating an accurate profile for the contact charge–transfer spectrum in the subtraction procedure by its actual measurement during the experiment. Vibrational progressions are not always lost for the studied aromatic compounds at the temperature employed and the data obtained for toluene at low temperatures may be used to add further support to recent interpretations of non-radiative rate constant data. Xenon matrix experiments indicated that the “heavy atom” effect of the gas is insufficient to produce perturbed singlet–triplet spectra at 10 K.

The triplet state of 1,1′-diethyl-2,2′-cyanine iodide in neat and mixed crystals

The singlet–triplet absorption spectrum of crystalline 1,1′-diethyl-2,2′-cyanine iodide has been obtained. The absorption origin consists of two lines separated by ∼4.0 cm−1. Zeeman spectra were used to assign the higher energy more intense line to the Au factor group state and the lower energy line to the Bu factor group state. Emission spectra have been obtained from both dilute and concentrated solid solutions of the dye. The results from the concentrated samples indicate that the largest excitation–transfer interaction between translationally inequivalent molecules is less than 1 cm−1.

The triplet state of 1,6-diphenyl-1,3,5-hexatriene and 1,8-diphenyl-1,3,5,7-octatetraene

The triplet—triplet absorption spectra, quantum efficiencies of intersystem crossing, triplet extinction coefficients, and triplet energy levels of 1,6-diphenyl-1,3,5-hexatriene, and 1,8-diphenyl-1,3,5,7-octatetraene, in ethanol and benzene have been obtained. The quantum efficiencies of intersystems crossing are found to be less than 0.03 for both molecules in both solvents, indicating that the excited singlet is efficiently deactivated by internal conversion and flourescence emission. The triplet—triplet absorption spectra and the triplet energy level of 1,6-diphenyl-1,3,5,hexatriene are compared with previous results in other solvent systems.