Deactivation Of Triplet State Research Articles

Deactivation of Triplet States of Metalloporphyrins by Molecular Oxygen

Deactivation of Triplet States of Metalloporphyrins by Molecular Oxygen

The Internal Heavy Atom Effect on the Deactivation of Triplet States of Porphyrins in the Presence of Molecular Oxygen

The Internal Heavy Atom Effect on the Deactivation of Triplet States of Porphyrins in the Presence of Molecular Oxygen

Влияние центрального иона металла на люминесцентные и фотофизические параметры фталоцианинов

Based on the data on the spectral and photophysical parameters of the metal complexes of tetraazaporphyrins and phthalocyanines, the effect of the central metal ion on the manifestation of spin-orbit interaction is considered. For complexes of phthalocyanines with Mg(II), Zn(II), Pd(II), and Pt(II) ions, the absorption spectra, luminescence spectra, and luminescence excitation spectra were measured, and the lifetimes and quantum yields of luminescence were determined. It was shown that metal phthalocyanines with Mg(II) and Zn(II) ions, as well as Mg-tetaraazaporphyrin, exhibit intense fluorescence with high quantum yields. For single molecules of Mg-tetaraazaporphyrin in a polymer film at T=6 K, the fluorescence excitation spectra consisting both exclusively of zero-phonon lines and containing phonon wings were measured. A wide distribution of the measured zero-phonon line widths was observed. It is demonstrated, that the introduction of Pd(II) and Pt(II) ions into the center of phthalocyanine macrocycles leads to a decrease in fluorescence and the appearance of intense phosphorescence even at room temperature. Based on measurements of quantum yields of photosensitized generation of singlet molecular oxygen, the quantum yield of interconversion into triplet states for the compounds under study was defined. Deactivation of the lower triplet state of phthalocyanines with Pd(II) and Pt(II) ions indicates the influence of the internal heavy atom effect on the rate of triplet state deactivation at room temperature and at 77 K.

Confining Carboxylized Carbon Nanotube for Phosphorescence Afterglow with Optical Memory Plasticity

AbstractAfterglow materials are of primary interest in optoelectronics and bioelectronics. Here, a long‐lived phosphorescence afterglow is reported from carboxylated carbon nanotubes (c‐CNTs) confined within boron oxynitride (BNO). The formation of covalent and hydrogen bonds in c‐CNT@BNO enhances the rigidity of the hybrid structure and alleviates the non‐radiative deactivation of excited triplet states, leading to room‐temperature phosphorescence (RTP). The afterglow material exhibits an ultra‐long RTP lifetime of up to 476.6 ms, with an afterglow time of 4.0 s, distinguishable by naked eyes. This unprecedented feature makes c‐CNT act like a light‐sensitive neuron and it is possible to achieve memorizing−forgetting behavior in the form of optical memory plasticity, owing to photons’ capture‐and‐slow‐release process. In analogy to the biological brain, both memory strength and forgetting time are proportional to learning exercise, including the intensity and time of irradiation training. The study provides an effective protocol for the synthesis of afterglow nanomaterials, extending their application to brain‐like intelligent technology.

Radiative Deactivation of Lowest Singlet and Triplet Excited States of Water-Soluble Porphyrins

Radiative deactivation of lowest excited triplet and singlet states for series of free bases and Zn2+-complexes of water-soluble 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin (H2T4SPP); 5,10,15,20-tetrakis-(4-N-alkylpyridyl) porphyrin (H2T4AlkPyP); and 5,10,15,20-tetrakis-(3-N-alkylpyridyl)porphyrin (H2T3AlkPyP) was studied in solutions at 77 and 293 K. The fluorescence and phosphorescence quantum yields were found to have small but detectable differences for derivatives of the same porphyrin ligand with different counterions for the ionized aryl substituents. It was shown that these differences were due to spin–orbit coupling effects and variation of the electron donor/acceptor properties of the peripheral substituents that changed the electronic energy levels in the porphyrin–counterion system.

The role of secondary processes in kinetics of triplet states of a hydrogen molecule in an ECR discharge

An electronic state sensitive semiempirical collision-radiative model of hydrogen plasma of ECR-discharge is used to analyze the applicability of emission of triplet states of molecular hydrogen for plasma diagnostics. It is shown that secondary processes make the greatest contribution to the kinetics of population-depopulation of triplet states , i3Πg and r3Πg. The secondary processes give the smallest contribution to the excitation and deactivation of triplet states . Thus a simplified coronal model (electron impact excitation followed by radiative decay) can be used to process the intensities of the dipole allowed and transitions. The complicated collision-radiative model should be used for other transitions.

Temperature Sensitive Singlet Oxygen Photosensitization by LOV-Derived Fluorescent Flavoproteins.

Optogenetic sensitizers that selectively produce a given reactive oxygen species (ROS) constitute a promising tool for studying cell signaling processes with high levels of spatiotemporal control. However, to harness the full potential of this tool for live cell studies, the photophysics of currently available systems need to be explored further and optimized. Of particular interest in this regard, are the flavoproteins miniSOG and SOPP, both of which (1) contain the chromophore flavin mononucleotide, FMN, in a LOV-derived protein enclosure, and (2) photosensitize the production of singlet oxygen, O2(a1Δg). Here we present an extensive experimental study of the singlet and triplet state photophysics of FMN in SOPP and miniSOG over a physiologically relevant temperature range. Although changes in temperature only affect the singlet excited state photophysics slightly, the processes that influence the deactivation of the triplet excited state are more sensitive to temperature. Most notably, for both proteins, the rate constant for quenching of 3FMN by ground state oxygen, O2(X3Σg-), increases ∼10-fold upon increasing the temperature from 10 to 43 °C, while the oxygen-independent channels of triplet state deactivation are less affected. As a consequence, this increase in temperature results in higher yields of O2(a1Δg) formation for both SOPP and miniSOG. We also show that the quantum yields of O2(a1Δg) production by both miniSOG and SOPP are mainly limited by the fraction of FMN triplet states quenched by O2(X3Σg-). The results presented herein provide a much-needed quantitative framework that will facilitate the future development of optogenetic ROS sensitizers.

Mechanism of Gadolinium Doping Induced Room-Temperature Phosphorescence from Porphyrin

The spin–orbit coupling mechanism was generally used to explain heavy atom effect induced room-temperature phosphorescence (RTP). Here, we demonstrate that the mechanism of RTP induced by Gd3+ from hematoporphyrin monomethyl ether (HMME) is due to the mixing of singlet (S) and triplet (T) states. The spin-forbidden transition between S and T states was partly allowed due to the states mixing, as indicated by the direct absorption corresponding to transition from S0 to T1, which was observed for the first time from RTP. The quantum yield of T1 was determined to be 0.80, and the percent of each energy transfer process was determined. Meanwhile there is no nonradiative relaxation from HMME to Gd3+ because of the large energy gap between the excited and ground states of Gd3+. The special energy level of Gd3+ as well as the states mixing between S and T states produced the strong phosphorescence emission. The population and deactivation of triplet states in heavy atom induced RTP can be used to analyze the mechanism of phosphorescent emission.

Photon upconversion in supramolecular gel matrixes: spontaneous accumulation of light-harvesting donor-acceptor arrays in nanofibers and acquired air stability.

Efficient triplet-triplet annihilation (TTA)-based photon upconversion (UC) is achieved in supramolecular organogel matrixes. Intense UC emission was observed from donor (sensitizer)-acceptor (emitter) pairs in organogels even under air-saturated condition, which solved a major problem: deactivation of excited triplet states and TTA-UC by molecular oxygen. These unique TTA-UC molecular systems were formed by spontaneous accumulation of donor and acceptor molecules in the gel nanofibers which are stabilized by developed hydrogen bond networks. These molecules preorganized in nanofibers showed efficient transfer and migration of triplet energy, as revealed by a series of spectroscopic, microscopic, and rheological characterizations. Surprisingly, the donor and acceptor molecules incorporated in nanofibers are significantly protected from the quenching action of dissolved molecular oxygen, indicating very low solubility of oxygen to nanofibers. In addition, efficient TTA-UC is achieved even under excitation power lower than the solar irradiance. These observations clearly unveil the adaptive feature of host gel nanofiber networks that allows efficient and cooperative inclusion of donor-acceptor molecules while maintaining their structural integrity. As evidence, thermally induced reversible assembly/disassembly of supramolecular gel networks lead to reversible modulation of the UC emission intensity. Moreover, the air-stable TTA-UC in supramolecular gel nanofibers was generally observed for a wide combination of donor-acceptor pairs which enabled near IR-to-yellow, red-to-cyan, green-to-blue, and blue-to-UV wavelength conversions. These findings provide a new perspective of air-stable TTA-UC molecular systems; spontaneous and adaptive accumulation of donor and acceptor molecules in oxygen-blocking, self-assembled nanomatrixes. The oxygen-barrier property of l-glutamate-derived organogel nanofibers has been unveiled for the first time, which could find many applications in stabilizing air-sensitive species in aerated systems.

Two-photon antenna-core oxygen probe with enhanced performance.

Recent development of two-photon phosphorescence lifetime microscopy (2PLM) of oxygen enabled first noninvasive high-resolution measurements of tissue oxygenation in vivo in 3D, providing valuable physiological information. The so far developed two-photon-enhanced phosphorescent probes comprise antenna-core constructs, in which two-photon absorbing chromophores (antenna) capture and channel excitation energy to a phosphorescent core (metalloporphyrin) via intramolecular excitation energy transfer (EET). These probes allowed demonstration of the methods’ potential; however, they suffer from a number of limitations, such as partial loss of emissivity to competing triplet state deactivation pathways (e.g., electron transfer) and suboptimal sensitivity to oxygen, thereby limiting spatial and temporal resolution of the method. Here we present a new probe, PtTCHP-C307, designed to overcome these limitations. The key improvements include significant increase in the phosphorescence quantum yield, higher efficiency of the antenna-core energy transfer, minimized quenching of the phosphorescence by electron transfer and increased signal dynamic range. For the same excitation flux, the new probe is able to produce up to 6-fold higher signal output than previously reported molecules. Performance of PtTCHP-C307 was demonstrated in vivo in pO2 measurements through the intact mouse skull into the bone marrow, where all blood cells are made from hematopoietic stem cells.

Temperature study of indole, tryptophan and N-acetyl-l-tryptophanamide (NATA) triplet-state quenching by iodide in aqueous solution

In this study, the temperature dependence of the measured phosphorescence lifetimes of aqueous indole, tryptophan and N-acetyl-l-tryptophanamide (NATA) between 6 and 55°C in the absence and in the presence of iodide, a suitable intersystem crossing enhancer, has been determined. The obtained results suggest the existence of one process for the temperature-dependent, non-radiative deactivation of triplet states of the aqueous indoles in the absence of iodide. This process may be associated with the high sensitivity of indole triplet state lifetime to the subtle changes in the local viscosity of the surrounding aqueous environment or may be attributed to diffusional quenching by solvent molecules and/or by possible impurities present in water. However, the steep decrease in the measured phosphorescence lifetimes of indole and tryptophan with temperature suggests that diffusion-mediated quenching processes are not prevailing. Upon increasing concentration of iodide (up to 0.1M), the obtained Arrhenius plots for the deactivation rate (1/τph) of the triplet states of the studied indoles were linear, which provided strong support for the hypothesis of the existence of one temperature dependent non-radiative process for the de-excitation of indoles triplet state. Our results showed that this process is attributed to the diffusion-controlled solute-quenching by iodide and, most probably, proceeds via reversibly formed exciplex. At concentration of iodide higher than 0.1M highly curved Arrhenius plots were obtained, which may indicate a change in the rate determining step with a change in temperature. This change most probably is associated with a transition from diffusion-controlled exciplex formation followed by rate-determining exciplex deactivation at high temperature.

Photostabilization of ascorbic acid with citric acid, tartaric acid and boric acid in cream formulations

This study involves the evaluation of the effect of certain stabilizers, that is, citric acid (CT), tartaric acid (TA) and boric acid (BA) on the degradation of ascorbic acid (AH(2) ) in oil-in-water cream formulations exposed to the UV light and stored in the dark. The apparent first-order rate constants (0.34-0.95 × 10(-3) min(-1) in light, 0.38-1.24 × 10(-2) day(-1) in dark) for the degradation reactions in the presence of the stabilizers have been determined. These rate constants have been used to derive the second-order rate constants (0.26-1.45 × 10(-2) M(-1) min(-1) in light, 3.75-8.50 × 10(-3) M(-1) day(-1) in dark) for the interaction of AH(2) and the individual stabilizers. These stabilizers are effective in causing the inhibition of the rate of degradation of AH(2) both in the light and in the dark. The inhibitory effect of the stabilizers is in the order of CT > TA > BA. The rate of degradation of AH(2) in the presence of these stabilizers in the light is about 120 times higher than that in the dark. This could be explained on the basis of the deactivation of AH(2) -excited triplet state by CT and TA and by the inhibition of AH(2) degradation through complex formation with BA. AH(2) leads to the formation of dehydroascorbic acid (A) by chemical and photooxidation in cream formulations.

Room temperature phosphorescence lifetime and quantum yield of erythrosine B and rose bengal in aerobic alkaline aqueous solution

The room-temperature phosphorescence behavior of erythrosine B (ER) and rose bengal (RB) in aerobic aqueous solution at pH 10 (10 −4 M NaOH) is investigated. The samples were excited with sliced second harmonic pulses of a Q-switched Nd:glass laser. A gated photomultiplier tube was used for instantaneous fluorescence signal discrimination and a digital oscilloscope was used for signal recording. For phosphorescence lifetime measurement the oscilloscope response time was adjusted to appropriate time resolution and sensitivity by the ohmic input resistance. In the case of phosphorescence quantum yield determination the gated photomultiplier – oscilloscope arrangement was operated in integration mode using 10 MΩ input resistance. Phosphorescence quantum yield calibration was achieved with erythrosine B and rose bengal doped starch films of known quantum yields. The determined phosphorescence lifetimes (quantum yields) of ER and RB in 0.1 mM NaOH are τ P =1.92±0.1 μs ( ϕ P=(1.5±0.3)×10 −5) and 2.40±0.1 μs ((5.7±0.9)×10 −5), respectively. The results are discussed in terms of triplet state deactivation by dissolved molecular oxygen.

Molecular thermometers based on phosphorescent porphin metal complexes

We study the temperature dependence of the radiative deactivation of triplet states of Pdand Pt-porphin molecules in n-alkane matrices in the temperature range 4.2–210 K. The nature of the thermally activated “hot” lines that are observed in phosphorescence spectra of Pdand Pt-porphin is discussed in detail. We show that, because of the degeneracy lifting of the triplet state T1, 2 in the crystal field of n-alkane matrices, lines of the transitions T1 → S0 and T2 → S0 are spectrally spaced and, in all cases, the T2 state is the first state that is activated with increasing temperature. We analyze the dependences of the T2-T1 splitting on the chelated metal ion and the type of the matrix. The possibility of measuring cryogenic temperatures with molecular thermometers that use the thermochromic properties of Pdand Pt-porphin in n-alkane matrices is discussed.

Intramolecular interactions and deuteration effect in nonradiative deactivation of lowest triplet state of anthracene and naphthalene

In the approximation of nonadiabatic interactions and considering all out-of-plane vibrational modes to be promoting ones, we calculate changes in the rate constants TsKdgs of the nonradiative degradation T1s ⇝ S0 of in-plane spin (s) triplet states as a result of the complete deuteration of anthracene and naphthalene molecules. We examine how the deuteration, the frequency factor, and the shape of promoting vibrational modes affect the squared matrix elements of both nonadiabatic coupling and adiabatic vibronically induced spin-orbit (VISO) coupling of electronic states. The compensation effect of spin-orbit interactions in structural elements of the carbon backbone of the anthracene molecule is ascertained.

Triplet state spectra and dynamics of peridinin analogs having different extents of π-electron conjugation

The Peridinin-Chlorophyll a-Protein (PCP) complex has both an exceptionally efficient light-harvesting ability and a highly effective protective capacity against photodynamic reactions involving singlet oxygen. These functions can be attributed to presence of a substantial amount of the highly-substituted and complex carotenoid, peridinin, in the protein and the facts that the low-lying singlet states of peridinin are higher in energy than those of chlorophyll (Chl) a, but the lowest-lying triplet state of peridinin is below that of Chl a. Thus, singlet energy can be transferred from peridinin to Chl a, but the Chl a triplet state is quenched before it can sensitize the formation of singlet oxygen. The present investigation takes advantage of Chl a as an effective triplet state donor to peridinin and explores the triplet state spectra and dynamics of a systematic series of peridinin analogs having different numbers of conjugated carbon-carbon double bonds. The carotenoids investigated are peridinin, which has a C(37) carbon skeleton and eight conjugated carbon-carbon double bonds, and three synthetic analogs: C(33)-peridinin, having two less double bonds than peridinin, C(35)-peridinin which has one less double bond than peridinin, and C(39)-peridinin which has one more double bond than peridinin. In this study, the behavior of the triplet state spectra and kinetics exhibited by these molecules has been investigated in polar and nonpolar solvents and reveals a substantial effect of both pi-electron conjugated chain length and solvent environment on the spectral lineshapes. However, only a small dependence of these factors is observed on the kinetics of triplet energy transfer from Chl a and on carotenoid triplet state deactivation to the ground state.

Modeling of the kinetics of pyrene-bromide phosphorescence in aqueous-micellar media

This work is devoted to a study of the processes of an increase in the phosphorescence intensity upon photoirradiation of pyrene bromide in aqueous-micellar solutions of surface-active substances. The method of mathematical modeling of the pyrene bromide triplet state deactivation processes is used to determine the rate constant of phosphorescence quenching of pyrene bromide solubilized in sodium dodecyl sulfate micelles by oxygen.

Temperature-dependent phosphorescence spectra of Pd- and Pt-porphins and their applications

In this paper the temperature dependence of radiative deactivation of Pd - and Pt -porphin triplet states in Shpol'skii matrices has been studied in the temperature range of 4.2-210 K. Dramatic changes in the phosphorescence spectra, with increasing temperature, were observed. It has been proposed that this is due to the inclusion of thermally activated states of the studied molecules in the processes of radiative deactivation of triplet states. For Pd -porphin the T 1 → S 0 emission is merely observed at liquid helium temperature. An increase in temperature leads to the activation of several radiative T i → S 0 transitions, so additional bands appear in the phosphorescence spectrum. In the case of Pt -porphin, temperature activation takes place as early as at liquid helium temperature. The degeneracy lifting of lowest T 1,2 states due to crystal field splitting was observed for both Pd - and Pt -porphins. The splitting value δ = ΔE( T 2 − T 1) has been measured in different matrices and the dependencies on both the metal ion in the given matrix and the matrix type for the given metal ion, have been revealed. The possibility of designing the luminescent molecular thermometers for cryogenic temperatures based on the high temperature sensitivity of the Pd - and Pt -porphin phosphorescence in n-alkane matrices, has been discussed. The workability of the dependence of Pd - and Pt -porphin phosphorescent properties on temperature in the design of the molecular thermometer family for the temperature range from a few K up to temperatures close to the melting point of n-alkane matrix (150-200 K) is demonstrated.

Time-resolved luminescence and singlet oxygen formation under illumination of hypericin in acetone

We present time- and spectral-resolved phosphorescence study of hypericin as well as evolution of singlet oxygen formation and elimination under the illumination of hypericin in acetone solution. The obtained time-resolved hypericin phosphorescence can be satisfactorily fitted by using a two-exponential decay curve. The value of shorter component is about 0.29 μs and is independent of the hypericin concentration in the studied range (2–200 μM). The rise time of singlet oxygen production matches this value perfectly. It confirms that singlet oxygen formation represents the significant channel of hypericin triplet state deactivation under aerobic conditions at room temperature. The total phosphorescence intensity of hypericin is linearly proportional to the hypericin concentration within the studied concentration range, but the singlet oxygen phosphorescence intensity exhibits saturation behavior. This observation is a result of at least two effects: quenching of singlet oxygen by hypericin, as well as quenching of singlet oxygen by singlet oxygen.

The triplet state decay kinetics and deactivation funnel geometry of a series of nonplanar saddle-shaped porphyrins

It is found that the triplet state lifetimes of the series of nonplanar saddle-shaped porphyrins are much shorter than those of their planar analogs (hundreds of nanoseconds vs. several milliseconds). As our calculations show, two low-lying conformations with strongly different triplet-ground singlet state energy gap Δ E TS exist for each molecule in its triplet state. An energy inversion of these conformations for the most distorted porphyrin molecule is found to be responsible for the observed non-monotonic dependence of the triplet state deactivation rate on the degree of nonplanar distortion.