Delayed Fluorescence Intensity Research Articles

9-Borafluoren-9-yl and diphenylboron tetracoordinate complexes of 8-quinolinolato ligands with heavy-atoms substituents: synthesis, fluorescence and application in OLED devices

This work describes the synthesis and characterisation of new tetrahedral boron complexes, incorporating bromine- or iodine-substituted 8-quinolinolato chelate chromophores connected to 9-borafluoren-9-yl or diphenylboron orthogonal fragments. The molecular features and photophysical properties of these complexes are analysed in both solution and solid state. Steady-state photophysical studies reveal photoluminescence quantum yields (Φf) ranging from 0.02 to 0.15 and prompt fluorescence (PF) lifetimes (τf) between 2 and 16 ns. Time-resolved photophysical experiments show the presence of delayed fluorescence (DF) and phosphorescence at both 77 K and room temperature. The DF intensity increases with a rise in temperature. This variation is ascribed to an enhancement in the intersystem crossing (ISC) process promoted by the bromine or iodine heavy-atom effect. Investigations into the dependence of DF intensity relative to the excitation dose indicate emissions stemming either from Triplet-Triplet Annihilation (TTA), Thermally Activated Delayed Fluorescence (TADF), or a combination of these competing mechanisms. The effect is related to the size and number of heavy-atom substituents in each boron complex. A study of the DF emission intensity as a function of the excitation dose reveals that diiodo-substituted 8-quinolinolato boron complexes, whether rigid or flexible, display TADF emission. Rigid 5,7-dibromo- and 5-chloro-7-iodo-substituted 8-quinolinolato complexes exhibit a combined TADF-TTA mechanism, whereas the other complexes predominantly demonstrate pure TTA emission. DFT and TDDFT calculations showed that the ground state structures reproduced the experimental geometries and only small increases in bond lengths were observed in the excited state geometries. The low energy absorption bands displayed mainly intra-ligand π→π* (8-quinolinato) character. The fluorescence emission energies were well reproduced, while the singlet-triplet energy gaps were relatively high. Ultimately, organic light-emitting diodes (OLEDs) are fabricated using the most luminescent boron complexes. The best OLED is obtained when using complex 3a, which displays green electroluminescence (EL) (λEL = 502 nm) with maximum external quantum efficiency (EQEmax) of 2.5% and maximum luminance (Lmax) of 2200 cd m-2.

Microalgae Production on Biogas Digestate in Sub-Alpine Region of Europe—Development of Simple Management Decision Support Tool

In a one-and-a-half-year study conducted in the ALS6 region in Europe (Ljubljana, Slovenia), the cultivation of microalgae in anaerobic digestate from food waste, mainly Scenedesmus dimorphus and Scenedesmus quadricauda, was investigated in three ponds (1260 L each) under a greenhouse. The effects of changing digestate quality and quantity as well as seasonal fluctuations on the productivity of the microalgae were investigated in three stages: Learning/Design (SI), Testing (SII), and Verification/Calibration (SIII). A decision support tool (DST) was developed using easy-to-measure parameters such as pH, temperature, electrical conductivity, mineral nitrogen forms and physical, biological parameters (OD, delayed fluorescence intensity). To control optimal pond operation, we proposed the photosynthetic culture index (PCI) as an early indicator for necessary interventions. Flocculation and nitrite levels (above 3 mg NO2-N L−1) were signals for the immediate remediation of the algae culture. Under optimal conditions in summer SIII, an average algal biomass production of 11 ± 1.5 g m−2 day−1 and a nitrogen use efficiency of 28 ± 2.6 g biomass/g N-input were achieved with the developed DST. The developed DST tool was, in this study, successfully implemented and used for the cultivation of microalgae consortia predominated by Scenedesmus dimorphus and S. quadricauda with biogas digestate. DST offers the possibility to be modified according to producers’ specific needs, facility, digestate and climate conditions, and as such, could be used for different microalgae cultivation processes with biogas digestate as a food source.

9-Borafluoren-9-yl and diphenylboron tetracoordinate complexes of F- and Cl-substituted 8-quinolinolato ligands: synthesis, molecular and electronic structures, fluorescence and application in OLED devices.

Six new four-coordinate tetrahedral boron complexes, containing 9-borafluoren-9-yl and diphenylboron cores attached to orthogonal fluorine- and chlorine-substituted 8-quinolinolato ligand chromophores, have been synthesised, characterised, and applied as emitters in organic light-emitting diodes (OLEDs). An extensive steady-state and time-resolved photophysical study, in solution and in the solid state, resulted in the first-time report of delayed fluorescence (DF) in solid films of 8-quinolinolato boron complexes. The DF intensity dependence on excitation dose suggests that this emission originates from triplet-triplet annihilation (TTA). Density functional theory (DFT) and time-dependent density functional theory (TDDFT) studies give insight into the ground and excited state geometries, electronic structures, absorption energies, and singlet-triplet gaps in these new organoboron luminophores. Finally, given their highly luminescent behaviour, organic light-emitting diode (OLED) devices were produced using the synthesised organoboron compounds as emissive fluorescent dopants. The best OLED displays green-blue (λmaxEL = 489 nm) electroluminescence with an external quantum efficiency (EQE) of 3.3% and a maximum luminance of 6300 cd m-2.

Some peculiarities of triplet excitations dynamics in organic macromolecules and crystals

Spectral properties of polymer macromolecules in the optical energy range and relation of these properties to the chemical structure and energy levels system of polymers were examined. The nature of optical centers of the macromolecules with π-electron systems localized on separate groups (so-called chromophores) was analyzed. It was stressed that such vitally important biopolymers as DNA and RNA belong to this type of polymers. It was shown that in synthetic and biological macromolecules with pendant aromatic groups, the triplet excitons meet and annihilate with the very high probability due to large lifetime and one-dimensional motion. The presented results prove that efficiency of triplet-triplet annihilation processes (at the used excitation power) is higher than efficiencies of other electronic processes. Consideration of this fact in the kinetic equation for triplet excitons in macromolecule leads to inverse square root dependence of phosphorescence intensity on the macromolecule length. At the same time, for three-dimensional molecular crystals of stilbene and para-terphenyl, the intensity of the delayed fluorescence is less dependent on the size of the granules compared to the dependence of the delayed fluorescence intensity on the length for one-dimensional macromolecules.

Identification of excimer delayed fluorescence by Protoporphyrin IX: A novel access to local chromophore concentration?

Protoporphyrin IX (PpIX) is a molecule produced in the mitochondria following the administration of its approved precursor, aminolevulinic acid (ALA). Strong light absorber at different wavelengths in the visible range, PpIX is extensively used as a photosensitizer (PS) for Photodynamic Therapy (PDT). PpIX is also an ideal molecular probe for the quantification of the tissue oxygen partial pressure (pO2), as its delayed fluorescence (DF) is quenched by oxygen, creating a direct relationship between the DF lifetime and the pO2. A limitation of both techniques is the ignorance of the PpIX concentration in tissues when the pO2 is measured or during PDT. In this study, the prompt (PF) and delayed fluorescence of PpIX dissolved in DiMethylFormamide (DMF) were acquired, in absence of oxygen, at different PpIX concentrations. Measurements of the PpIX emission for different excitation energies and temperatures, as well as spectral considerations led to the conclusion that E-type (thermal) DF was the dominant DF mechanism at low PpIX excited states concentrations (density of absorbed energy Hε[PpIX]<1 μJ. cm-3, H:excitation radiant exposure per pulse, ε: molar extinction coefficient at excitation wavelength) while P-type (Triplet Triplet Annihilation) DF took place at higher excited states concentrations (Hε[PpIX]>10 μJ. cm-3). The gradual development of a strong, red-shifted structureless DF peak at 670nm, invisible in the PF and absorption spectra, strongly points towards the first observation of PpIX excimer DF (EDF). It appears that, similarly to other aromatic molecules, PpIX excimers can be formed either by the encounter of two molecules in the first excited triplet state T1, or by the reaction of an excited singlet S1 with a triplet T1. Excimer DF could be beneficially used to determine the local concentration of PpIX, as the initial DF intensity ratio I0670/I0630 is linearly correlated with the local PpIX concentration, and thus rises up to the challenge of PpIX based pO2 measurement and PDT. This work could also pave the way for a fine comprehension of the production, diffusion and catabolization of PpIX in biological tissues.

Desiccation-induced changes of photosynthetic transport in Parmelina tiliacea (Hoffm.) Ach. analysed by simultaneous measurements of the kinetics of prompt fluorescence, delayed fluorescence and modulated 820 nm reflection

Simultaneous in vivo measurements of prompt fluorescence (PF), delayed fluorescence (DF) and modulated reflection (MR) at 820-nm were used to assess effect of short desiccation period (4.5 h) on Parmelina tiliacea lichen. The two performance indexes (PIABS and PItotal) as a measure of an overall photosynthetic thalli performance showed a negative effect of desiccation treatment on photosynthetic activity. The maximal intensity of PF and DF recorded during desiccation treatment decreased and at 4.5 h desiccation time Parmelina tiliacea thalli loss their variable fluorescence and DF amplitude. This loss of variable fluorescence was due to an increase in inactive reaction centers and a limitation of electron donation on the donor side of photosystem II (PSII) that caused a down-regulation of electron transport chain at the PSII level. However, the efficiency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors was less affect by desiccation treatment. In respect to MR change, re-reduction kinetics of the primary electron donors of photosystems I (P700) and plastocyanin (PC) in desiccated thalli seem to be faster, their amplitudes gradually decrease and a disconnection between the two photosystem (PSII and PSI) were observed. These responses allow to Parmelina tiliacea lichen a photoprotection mechanism from the excess light excitation.

Identification of Particles of Ionizing Radiation by the Analysis of Fluorescence Pulse Form of the Thin Pen Film Scintillator

Polyethylene 2.6-naphthalate (PEN) is a promising plastic scintillator material. In this paper, a thin PEN film was used for detection, identification, and energy spectrum measurements of various ionizing radiation particles. A thin PEN film was used to separate $\alpha $ (5.49 MeV) and $\beta $ (up to 2.2 MeV) particles coming from 238Pu and 90Sr + 90Y sources, respectively, as well as for the neutron (up to 14 MeV) and gamma separation from the isotopic PuBe neutron source. Acquired photomultiplier pulses were analyzed by the long tail method based on the delayed fluorescence intensity dependence on the mass and charge of particles absorbed. For determination of the separation quality, the figure of merit (FOM), based on the ratio of short and long tails, was used. It was found that depending on the FOM values of neutron/gamma and $\alpha /\beta $ separation, the thin PEN film is suitable for the ionizing radiation particle separation.

Validation of rapid algal bioassay using delayed fluorescence in an interlaboratory ring study

Algal growth inhibition tests are generally used to determine the toxic effects of chemical substances on algae growth. In this report, we describe a rapid and simple test procedure using delayed fluorescence (DF) to determine chemical toxicities more rapidly than the conventional 72h or 96h growth inhibition tests. We assess the suitability of DF to serve as an alternative endpoint for biomass production and determine the variability by an interlaboratory ring study using a typical reference toxicant 3,5-dichlorophenol (DCP). The results suggest that DF has the potential to be used as a surrogate measure of photosynthetically-active biomass in the algal growth inhibition tests. The half maximal effective concentration (EC50) values of DCP determined from the DF inhibition test in 6h and 24h (1.2±0.3mg/L and 2.7±0.5mg/L respectively) are in reasonable agreement with the EC50 value of DCP determined by the 72h conventional method (1.8mg/L). In the interlaboratory ring study, the intralaboratory and interlaboratory variabilities of the EC50 of the DF inhibition test for a 24h exposure period are 12% and 28% respectively. DF intensity can be considered as a surrogate of living biomass with active photosynthesis, and we conclude that a 24h exposure duration better estimates the toxic effects measured using conventional surrogate measures for dry weight such as cell counts, volume, optical density or fluorescence.

Solvent Radical Anions in Irradiated Aliphatic Ketones and Esters as Observed Using Time-Resolved Magnetic Field Effects in the Recombination Fluorescence

Abstract It has been found that addition of alcohols (~0.1 M) to some liquid ketones and esters results in well-pronounced oscillations in the decay of the delayed fluorescence intensity from irradiated solutions. The analysis of the time-resolved magnetic field effects (TR MFEs) in the recombination fluorescence has shown that these oscillations are a manifestation of singlet-triplet transitions in spin-correlated radical ion pairs (RIPs) created by irradiation. Comparison with literature data indicates that the transitions are due to hyperfine couplings (HFCs) in the solvent radical anion (RA), stabilized due to the presence of alcohol molecules. In acetone, this stabilization effect has been observed for methanol, ethanol, 2- propanol, and, to a smaller extent, for tert-butanol. Similar effects have also been observed in diethyl ketone, ethyl acetate, and methyl propionate but not in methyl tert-butyl ketone and ethyl trimethylacetate. The results obtained indicate that the interaction between the radical anions (RAs) of carbonyl compounds and alcohol molecules is of importance in pulse radiolysis studies of organic liquids and their mixtures.

Rapid ecotoxicological bioassay using delayed fluorescence in the marine cyanobacterium Cyanobium sp. (NIES-981).

The use of delayed fluorescence intensity as an endpoint for rapid estimation of the effective concentration (ECx) has been reported as an alternative to standard growth inhibition (at 72 h after exposure) in some algal species including Pseudokirchneriella subcapitata. In marine algae, although an approach of bioassaying using delayed fluorescence measurements has not been performed yet, its development would provide many benefits for marine environmental risk assessment. In this study, we selected marine cyanobacterium Cyanobium sp. (NIES-981) as our test algal species and demonstrated that this species is valid for the standard growth inhibition test based on criteria provide by Organization for Economic Co-operation and Development guidelines. Furthermore, standard inhibition tests and shorter period test using DF were performed in NIES-981 using five chemicals (3,5-DCP, simazine, diflufenican, K2Cr2O7, and CuSO4), and their EC50 and low-toxic-effect values (EC10, EC5, and NOEC) were determined from two dose-response curves. Based on comparisons of the two dose-response curves and the EC50 values, we conclude that DF intensity is useful as an endpoint for rapid estimation of EC50 in NIES-981.

Delayed fluorescence emission as a probe for the response of photosynthetic organisms to high temperature exposure: A comparative study

The effects of a short-term exposure (40s) to 50°C on the prompt fluorescence (PF), delayed fluorescence (DF) and 820nm reflection (MR) signals in three different photosynthetic organisms: Pisum sativum (angiosperm plant), Ginkgo biloba (gymnosperm tree) and thalli of Parmelina tiliacea (Hoffm.) Ach (lichen) were investigated. The aim of this study was to understand the relationship between prompt PF, DF and MR when the oxygen evolving complex (OEC) is destroyed. The signals of PF, DF and MR were measured simultaneously in plants in vivo to probe heat-induced damages in the photosynthetic electron transfer. PF is characterised by a polyphasic fluorescence rise OJIPSMT and DF induction curve has several maxima (In) and numbered in sequence according to their appearance during illumination. In control condition (25°C) leaves of pea plants yield a typical OJIP rise with a flat P-step (0.2–2s) and in G. biloba and P. tiliacea thalli, the P-level was split into two peaks, the first peak P (0.2s) is followed by a decrease of the fluorescence intensity to a dip (S) and a subsequent rise to a second peak (M). An antiparallel relation between J–I–P–S and DF curves was also observed. Methyl viologen (MV) reduced the amplitude of the I–P phase of the PF curve and this change was accompanied by a disappearance of the PSM transient. In the presence of MV, the DF intensity remained higher; and the I4 peak disappeared. We suggested that P-S-M rise from PF and I4 peak might be related to an acceleration of intersystem electron transport. After 50°C incubation, significant changes appeared in the PF, DF and MR transients and that were dependent on the photosynthetic sample. Heat treatment provoked a down regulation of electrons donation by the OEC in the three plant species and the re-reduction of P700+ and PC+ started earlier and began already after 10 ms of illumination. Inhibition of the donation of electrons by OEC after 50°C incubation indicates that DF induction depends on the concentrations of QA− and P680+ and the proton gradient.

Detecting the phase transition in thylakoid membranes of maize inbred lines by means of delayed fluorescence

In this paper the changes on growth, photosynthesis and water relations were tested by non-invasive fluorescence method. The applications of this method allow to determine some functional properties of prestigious maize inbred lines with erect top leaves. So the temperature dependency of delayed fluorescence intensity maximum of ZPPL 16 is observed at higher temperatures than for ZPPZ 62. This fact correlates with low values of phase transition of activation energy Ea in thylakoid membrane and accompanied by a decrease of the angle and area of the leaf, as well as with the content and the rate of water release from the seed. It seems reasonable to assume that, DF can be applied in breeding and maize hybrid seed production for the estimation of prestigious maize inbred lines and their resistance adaptability to increased and high temperatures, as well as, to drought.

СЕЛЕКЦИОННЫЕ И ФИЗИКО-ХИМИЧЕСКИЕ ХАРАКТЕРИСТИКИ У ИНБРЕДНЫХ ЛИНИЙ И ВЫСОКОПРОДУКТИВНЫХ ГИБРИДОВ КУКУРУЗЫ С ЭФФЕКТИВНЫМИ ФОТОСИНТЕТИЧЕСКИМИ ФУНКЦИЯМИ

Four maize inbred lines with erect top leaves and significant breeding traits, ZPPL 16, ZPPL 218, ZPPL 62 and ZPPL 233, were studied. These inbreds, as a female or a male component, are included into the development of more than 50 maize hybrids. However, only the following four hybrids are widely grown: ZP 341, ZP 434, ZP 578 and ZP 684 and they were also observed. This study confirms our hypothesis that there are elite maize inbred lines and hybrids with top erect leaves that have a dominant trait of an efficient photosynthetic model. The stated maize inbred lines with significant breeding traits are successfully used in contemporary breeding programmes and the production of hybrid seed of high quality. This observation is supported by results obtained on erect leaves of maize inbred lines with significant breeding traits, dynamics of grain dry down during the maturation period and photosynthetic and fluorescenece parameters: changes in the chlorophyll delayed fluorescence intensity during its course and dynamics, the Arrhenius plot for determination of critical temperatures (phase transition temperatures) and the activation energies, as a measure of conformational changes in the thylakoid membrane. Furthermore, a grain structure of observed maize hybrids, including its physical and chemical parameters, were studied. The presented results indicate that properties of maize inbreds and hybrids with significant breeding traits are based on nature of structural and functional changes that occur in their chloroplasts and thylakoid membranes, as well as, other chemical tissue structures of intact leaves and grain, but also on progressive effects in the process of breeding and the production of commercial maize.

Simultaneous Measurement Device of the Luciferase Bioluminescence and the Delayed Fluorescence in Lettuce

Abstract In this study, we developed the devise named “Kondotron-lettuce” that is possible to measure luciferase bioluminescence and delayed fluorescence intensity of plants which are in the state that nearer to plant factory than the conventional circadian rhythm measurement. The main refinements are two points: One is that the devise became able to measure bioluminescence from plants which are cultured under hydroponic culturing for a long term. The another is that the devise became able to measure the delayed fluorescence. This devise is useful for measuring of luciferase bioluminescence and delayed fluorescence intensity under the controlled light and hydroponic culturing conditions in the long term.

Triplet–Triplet Annihilation in a Series of Poly(p-phenylene) Derivatives

We have studied the temperature dependence of phosphorescence (Ph) and delayed fluorescence (DF) in two series of poly(p-phenylene) derivatives within a temperature range from 10 to 300 K under quasi-stationary conditions. One set of materials consists of the dimer, trimer, and polymer of ethylhexyl-substituted poly(fluorene) (PF2/6) and thus allows us to assess the effects of oligomer length. The second series addresses the influence of energetic disorder and conjugation length by being composed of the polymers alkoxy-substituted poly(p-phenylene) (DOO-PPP), poly(indenofluorene) (PIF), and ladder-type poly(p-phenylene) (MeLPPP). Under low light intensities, the DF features a maximum at a certain temperature T(max). For the dimer and trimer, the T(max) coincides with the temperature at which the phosphorescence has decayed to 1/2 of the value at 10 K, while T(max) shifts to lower temperature values along the series DOO-PPP, PIF, and MeLPPP and approaches T = 0 K for MeLPPP. By applying conventional kinetic equations we show that the occurrence of a maximum in the DF intensity is the consequence of generalized thermally activated triplet exciton transport toward quenching sites. We find the quenching rates at 0 K to be in the range of 1 s(-1) for the polymers, while they are more than an order of magnitude lower for the oligomers.

Role of salicylic acid in alleviating photochemical damage and autophagic cell death induction of cadmium stress in Arabidopsis thaliana

As a widespread pollutant in the environment, cadmium (Cd) would be accumulated in leaves and cause phytotoxic effect on plants. Salicylic acid (SA), a natural signal molecule, plays an important role in eliciting specific responses to biotic and abiotic stresses. In our case, the effect of SA on Cd-induced photochemical damage and cell death in Arabidopsis was studied. The results illustrated that Cd could cause a series of physiological events such as chloroplast structure change (e.g. irregular mesophyll cell as well as ultrastructure change), reactive oxygen species (ROS) production and cell death. Furthermore, chlorophyll fluorescence parameters (F(v)/F(m), qN and ETR) showed a rapid decrease in wild-type (WT) Arabidopsis after treatment with 50 μM CdCl(2), identical with the change in chlorophyll delayed fluorescence (DF) intensity. The changes of these parameters showed the damage of Cd toxicity to photosynthetic apparatus. We found that cell death might be autophagic cell death, which might be caused by Cd toxicity induced oxidative stress just like photosynthetic damage. The NahG plants with lower SA accumulation level showed more sensitivity to Cd toxicity, although they exhibited a decrease both in chlorophyll fluorescence parameters and DF intensity. Exogenously SA prevented the Cd-induced photochemical efficiency decrease and mitigated Cd toxicity. Additionally, SA pretreatment could alleviate Cd-induced ROS overproduction. In conclusion, our results suggested that SA could prevent Cd-induced photosynthetic damage and cell death, which might be due to the inhibition of ROS overproduction.

Mechanisms of delayed fluorescence in small molecular organic light-emitting diodes studied by transient electroluminescence

Two kinds of organic light-emitting diodes with structure of ITO/NPB/Alq₃/LiF/Al (Alq₃ bilayer device) and ITO/ NPB/Alq₃:DCM/Alq₃/LiF/Al (Alq₃:DCM device) were fabricated. The mechanisms of delayed fluorescence (DF) in the two devices were studied by transient electroluminescence. These results show that the DF in the Alq₃-based bilayer device decays fast after removing the pulsed bias. We suggest that the DF in bilayer device is caused by the decay of the singlet excitons which were formed by the delayed charge injection after removing the pulsed bias. In contrast, the DF in the Alq₃:DCM device is very strong. The dependences of DF in the Alq₃:DCM device on reverse bias after removing the pulsed bias and on the pulsed width were also analyzed. We found that the detrapping and then recombination of the trapped charge can only generate a small fraction of DF intensity in Alq₃:DCM device. Large fraction of the DF intensity results from triplet-triplet annihilation process.

Study on the Relationship between Delayed Fluorescence and Photosynthetic Capability at Elevated Temperature in Higher Plants

With the continuous elevation of the global temperature, high-temperature stress has been a major environmental factor that affects plant growth and productivity. Effects of short-term heat temperature stress on light-induced delayed fluorescence (DF) decay kinetic curve, intensity and emission spectrum have been investigated in C3 soybean (Jing Huang No.3) and C4 maize (Yun Xi No.5081) species. The temperature responses of DF decay kinetic curve from two different species show that decay rate characteristics are affected by high temperature. The spectroscopy measurements indicate that heat stress influence the shape of DF emission spectra of two species, especially the peak intensities at 685nm and 730nm. Moreover, our results clearly demonstrate that DF intensity of each plant positively correlated with F730/F685 of DF emission spectra at elevated temperatures. In addition, the net photosynthetic rate (Pn) of samples has the same temperature response with DF intensity and F730/F685. Based on these results, we can conclude that there is an excellent correlation between F730/F685 of DF emission spectra, DF intensity and Pn in both C3 and C4 plants. Therefore, we proposed that the F730/F685 of DF emission spectrum can be used to measure the photosynthetic capability of higher plants to heat stress.

Optical fiber-based setup for in vivo measurement of the delayed fluorescence lifetime of oxygen sensors

A new optical-fiber-based spectrofluorometer for in vivo or in vitro detection of delayed fluorescence is presented and characterized. This compact setup is designed so that it can be readily adapted for future clinical use. Optical excitation is done with a nitrogen laser-pumped, tunable dye laser, emitting in the UV-vis part of the spectrum. Excitation and luminescence signals are carried to and from the biological tissues under investigation, located out of the setup enclosure, by a single optical fiber. These measurements, as well as measurements performed without a fiber on in vitro samples in a thermostable quartz cell, in a controlled-atmosphere enclosure, are possible due to the efficient collection of the laser-induced luminescence light which is collected and focused on the detector with a high aperture parabolic mirror. The detection is based on a gated photomultiplier which allows for time-resolved measurements of the delayed fluorescence intensity. Thus, relevant luminescence lifetimes, typically in the sub-microsecond-to-millisecond range, can be measured with near total rejection of the sample's prompt fluorescence. The instrument spectral and temporal resolution, as well as its sensitivity, is characterized and measurement examples are presented. The primary application foreseen for this setup is the monitoring and adjustment of the light dose delivered during photodynamic therapy.

Delayed Fluorescent Emission from Pyrene Doped Phenanthrene Nanoparticles Based on Triplet‐triplet Energy Transfer

AbstractDoped nanoparticles were prepared from pyrene and phenanthrene using a facile reprecipitation method. The doped nanoparticles presented unique delayed fluorescent emissions of pyrene under the unprotected condition. The ratio of the intensity of delayed fluorescence (IDF) to that of phosphorescence (IP) is about 4:1, which almost keeps unchanged with the decrease of pyrene content at room temperature. The intensity of the delayed fluorescence emissions is dependent on the relative content of pyrene, as well as the aggregation degree of nanoparticles. The delayed emissions are contributed to efficient triplet‐triplet energy transfer from phenanthrene (donor) to pyrene (acceptor). Steady fluorescence measurement have proved that the singlet‐singlet energy transfer process was also existent dominated by the radiation energy transfer mechanism.