Phosphorescence Spectra Research Articles

Determination of 0–0-Transition Frequencies from Diffuse Vibronic Spectra

The equality of the probabilities of direct and inverse vibronic transitions between the initial and final elementary quantum Franck–Condon states in the adiabatic approximation is taken as the equality of the probabilities of one electronic transition in which only the initial and final elementary vibrational ensembles exchange places. The transition frequencies will have mirror symmetry with respect to the 0–0-transition frequency ν0. Accounting for this and selecting hot molecules in the anti-Stokes regions with the initial state in thermal equilibrium leads to a restoration of the known relation for the transition cross sections σ(ν) in the form [σ(ν)/ν] exp (±hν/2kT) = 𝜑[(ν – ν0)2], where ″+″ denotes emission; ″–″, absorption. Examples of using the relation to determine ν0 from absorption, fluorescence, and phosphorescence spectra are given and compared with ν0 obtained by jet-cooling.

Synthesis, photophysical, electrochemical and electroluminescence studies of red emitting phosphorescent Ir(III) heteroleptic complexes

Five heteroleptic, cyclometalated (C $$^{\wedge }$$ N) Iridium(III) complexes of acetylacetone (acac) and 1-phenyl-isoquinoline (piq) derivatives, Ir(acac)(piq) $$_{2}$$ , Ir(acac)(2,4-difluoro-piq) $$_{2}$$ , Ir(acac)(4-trifluoromethyl-piq) $$_{2}$$ , Ir(acac)(4-N,N-dimethyl-piq) $$_{2}$$ , Ir(acac)(4-acetyl-piq) $$_{2}$$ , were synthesized and characterized. The ( $$\text {C}^{{\wedge }}\text {N})_{2}$$ Ir(acac) complexes in toluene showed phosphorescence ( $$\uplambda _{\max }= 598$$ nm to 658 nm) with quantum yields (0.1 to 0.32) and microsecond lifetimes (0.43 to 1.9 $$\upmu $$ s). The complexes were non-luminescent in thin films due to self-quenching but luminescent when lightly doped (5%) in a host organic material, 4,4 $$^\prime $$ -Bis(N-carbazolyl)-1,1 $$^\prime $$ -biphenyl (CBP). The HOMO levels determined using cyclic voltammetric oxidation potentials were in the range −5.48 to −5.80 eV. Electroluminescence properties and performance of the Ir complexes doped in CBP (active layer) were studied in a multilayer (ITO/F4TCNQ/TPD/doped CBP/BCP/LiF/Al) organic light emitting device (OLED). The electroluminescense (EL) spectra of the device matched with the phosphorescent spectra of the Ir complexes. The turn-on voltage at $$\sim $$ 4.5 V, maximum brightness of 7600 cd/ $$\hbox {m}^{2}$$ and current efficiency of $$\sim $$ 7.0 cd/A at a brightness of $$\sim $$ 100 cd/ $$\hbox {m}^{2}$$ indicate that these are promising OLED materials. Synopsis. Heteroleptic, cyclometalated (C $$^{\wedge }$$ N) Iridium(III) complexes of acetylacetone (acac) and 1-phenyl-isoquinoline were synthesized and their photophysical, electrochemical and electroluminescence properties were studied. The OLED of Ir complex as emitting material showed turn-on voltage at $$\sim $$ 4.5 V, maximum brightness of 7600 cd/ $$\hbox {m}^{2}$$ and current efficiency of $$\sim $$ 7.0 cd/A at a brightness of $$\sim $$ 100 cd/ $$\hbox {m}^{2}$$ .

Comprehensive approach to simulate vibrationally resolved phosphorescence spectra of gold(III) complexes using DFT including temperature effects

The present paper reports on a full quantum investigation of the optical properties of six Au(III) luminescent complexes. Among others, the most striking result concerns the reproduction of the luminescent spectra of two key complexes. These simulations are in very good agreement with the measured data when temperature effects are included in the computations. Vibrational modes involved in the emission signature are assigned for one complex. In this comprehensive approach, the model used is very complete and takes into account solvent effects and vibrational contributions to the electronic transitions among others.

Theoretical Study and Design of Phosphorescent Cyclometalated (C∧C*)PtII(acac) Complexes: The Substituent Effect Controls the Radiative and Nonradiative Decay Processes.

Density functional theory (DFT) and time-dependent DFT calculations were performed to evaluate the influence of substituent effect of (1) R = 4-Me, (2) R = 4-OMe, and (3) R = 2,3-OC6H4 on the phenyl ring of (C∧C*)PtII(acac) (C∧C* = phenylimidazole, acac = acetylacetone), respectively, on absorption and phosphorescent spectra properties, as well as the radiative and nonradiative processes. We found that emissions of complexes 2 and 3 originate from the Kasha-like T1 state, whereas that of complex 1 originates from non-Kasha T2 state. Compared with the emission of complex 1, the emission peaks of 2 and 3 are red-shifted, which is attributed to p-π and π-π conjugation effects resulting from the electron-donating groups -OCH3 and -OC6H4 with ligand C∧C*, respectively. The radiative rate constants (κr) of 2 and 3 are larger than that of 1, namely, κr(1) < κr(2) < κr(3), indicating that κr can be efficiently increased by enlarging π-conjugation at the main ligand of (C∧C*)PtII(acac), which can cause the increase of spin-orbit coupling (SOC) matrix elements. At the same time, the activation energy barriers for the rate-limiting step can be largely raised accompanied by enlarging the ability of electron-donation of the substituent group at the main ligand of (C∧C*)PtII(acac), which can cause the decrease of the nonradiative rate constant (κnr), namely, κnr(1) > κnr(2) > κnr(3). According to ΦP = κr/(κr + κnr), the quantum yields should have the sequence ΦP(1) < ΦP(2) < ΦP(3), which is in accordance with the experiment. In addition, to guide experimental synthesis of highly efficient (C∧C*)PtII(acac), a new complex 4 through extending the π-conjugation in the C∧C* ligand of (C∧C*)PtII(acac) was theoretically designed, which has a larger quantum yield than 1-3.

“Oxygen quenching” in Eu-based thermographic phosphors: Mechanism and potential application in oxygen/pressure sensing

The effect of ambient oxygen concentration on thermographic phosphor thermometry was investigated to uncover the “oxygen quenching” mechanism of Eu-based phosphors using a lifetime-based measurement system. The phosphors being studied were the Eu doped yttria stabilized zirconias (YSZs) with Y3+ concentrations of 0, 8, 12 and 57mol%, having monoclinic, tetragonal, cubic and δ crystalline lattice, respectively. To vary the ambient oxygen concentration, three different gas phases (air, oxygen and nitrogen with methane) were used. It was found that the phosphorescent lifetimes and intensities of all four phosphors were sensitive to the ambient oxygen concentration, while the reference phosphor, Y2SiO5:Eu, was not influenced. The “oxygen quenching” phenomenon observed in Eu-doped YSZs was attributed to the oxygen vacancies in the phosphors. In addition, the four YSZ:Eu phosphors exhibited different sensitivity to ambient oxygen concentration. The oxygen sensitivity was found to be closely related to the site symmetry of Eu3+, which was previously determined by the phosphorescent spectra. The site symmetry of Eu3+ strongly affected the charge-transfer states and therefore determined the non-radiative decay rate. The current findings provided guidance for the phosphor selection and sensor design for oxygen/pressure sensing in high-temperature environment.

BiPh-m-BiDPO as a Hole-Blocking Layer for Organic Light-Emitting Diodes: Revealing Molecular Structure-Properties Relationship**Supported by the National Natural Science Foundation of China under Grant No 11690044.

We report a simple hole-blocking material (biphenyl-3,3’-diyl)bis(diphenylphosphine oxide) (BiPh-m-BiDPO) based on our recent advance. The bis(phosphine oxide) compound shows HOMO/LUMO levels of ∼−6.71/−2.51 eV. Its phosphorescent spectrum in a solid film features two major emission bands peaking at 2.69 and 2.4 eV, corresponding to 0–0 and 0–1 vibronic transitions, respectively. The measurement of the electron-only devices reveals that BiPh-m-BiDPO possesses electron mobility of – cmVs at E = 2– V/cm. The characterization of the sky blue fluorescent and red phosphorescent pin organic light-emitting diodes (OLEDs) utilizing BiPh-m-BiDPO as the hole blocker shows that its shallow LUMO level as well as the low electron mobility affects significantly the power efficiency and hence operational stability, relative to the luminous efficiency, especially at high luminance. In combination with our recent results, the present study provides an indepth insight on the molecular structure-property correlation in the organic phosphinyl-containing hole-blocking materials.

Comparative analysis of the phosphorescence characteristics of copper(II), platinum(II), and osmium(II) porphyrinates in polystyrene matrix at temperatures of 77 and 298 K

Comparative analysis of phosphorescence spectra of 15-crown-5-substituted copper(II) (Cu(II)TCP), platinum(II) (Pt(II)TCP), and osmium (II) (Os(II)TCP) posphyrinates in a polystyrene film, as well as of phosphorescence quenching curves, at the temperatures of 298 and 77 K is carried out. It is found that the halfwidth of emission bands decreases under cooling due to a decrease in the population of the vibration satellites of electron transitions and a shift of the emission band maximums into the blue spectral range is observed. The curves of phosphorescence quenching of metal porphyrinates at 298 and 77 K are analyzed. It is shown that copper(II) porphyrinate Cu(II)TCP can be of interest as a low-temperature sensor due to the considerable change in the phosphorescence lifetime at a decrease in temperature.

Efficient Upconversion by Highly Water-Soluble Cationic Sensitizer and Emitter in Aqueous Solutions with DNA.

Highly water-soluble cationic palladium porphyrin as a sensitizer and 9,10-bis(4-trimethylammoniumphenyl)anthracene as an emitter were newly synthesized. They were shown to be bound and immobilized in DNA double helix assembly from absorption, fluorescence, phosphorescence, and circular dichroism spectra. Upon excitation at 532 nm in deaerated aqueous solutions, they showed weak blue upconversion fluorescence, the efficiency of which increased dramatically in the presence of DNA. The threshold power density between the second-order and first-order power dependence of upconversion fluorescence decreased to less than a half upon addition of DNA. The emitter triplet lifetime estimated from time dependences of upconversion fluorescence at low power ns pulsed laser was found to considerably increase in the presence of DNA. From these results, DNA was concluded to work effectively in concentrating both sensitizer and emitter and in migrating excited triplet states, resulting in efficient upconversion.

Quantitative ratiometric phosphorescence hypoxia–sensing nanoprobes based on quantum dots/Ir(III) glycerol monoolein cubic-phase nanoparticles

A novel protocol is developed to prepare quantum dot (QD)/Ir(III) complex glycerol monoolein (GMO) cubic-phase nanoparticles (Qd/Ir GMCPNPs) as hypoxia nanoprobes, in which hypoxia probe Tris [1-phenylisoquinoline-C2, N] Iridium(III) [Ir(piq)3] and the reference QDs are separately loaded at hydrophilic and hydrophobic channels to avoid interference. Qd/Ir GMCPNPs were nearly spherical in shape, with an average size of 20–30nm. Their phosphorescence spectra showed that nanoprobes have a wide excited wave length range of 360–500nm, which is suitable for different types of measurement instruments. When the oxygen content decreased from 21% to 1%, the luminescent intensity ratio of Qd/Ir GMCPNPs in the solution and cells increased 4-fold and 2.8-fold, respectively, with an acceptable linear relationship. Particularly, extensive preliminary quantitative ratiometric oxygen sensing and long tumor imaging monitoring can be achieved with these nanoprobes.

Tuning the Geometrical Structures and Optical Properties of Blue-Emitting Iridium(III) Complexes through Dimethylamine Substitutions: A Theoretical Study.

The geometrical structures and photophysical properties of Ir(4,6-dFppy)2(pic) (FIrpic) and its derivative (o-FIr, m-FIr, p-FIr) with dimethylamine substituted at the picolinic acid (N∧O) ligand were fully investigated by density functional theory and time-dependent density functional theory. The simulated electronic structure, as well as absorption and emission spectra of FIrpic are in good agreement with the experimental observations. The introduction of dimethylamine at the N∧O ligand at different positions is beneficial to extend the π-electron delocalization, increase HOMO energy levels, and hence improve the hole injection and transfer ability compared with those of FIrpic. Furthermore, o-FIr, m-FIr, and p-FIr have large absorption intensity and participation of metal-to-ligand charge transfer (MLCT) contribution in the main absorption spectra, which would be useful to improve the intersystem crossing (ISC) from the singlet to triplet excited state. More importantly, the high quantum yield of o-FIr (which is explained based on the detailed analysis of triplet energy, ET1), participation of 3MLCT contribution in the phosphorescent spectra, and energy difference between 3MLCT and triplet metal centered (3MC) d-d excited state compared with m-FIr and p-FIr indicate that o-FIr is expected to be an excellent blue phosphorescence emitter with high efficiency.

Carbazolyl-substituted quinazolinones as high-triplet-energy materials for phosphorescent organic light emitting diodes

A series of carbazolyl-substituted quinazolinones were designed and synthesized by the Pd-catalyzed Buchwald-Hartwig, Suzuki and Heck cross-coupling reactions. Their optical, photophysical, thermal, electrochemical, and electroluminescent properties were investigated. The characterization of the synthesized compounds was carried out using experimental and theoretical methods. The determined geometries of the compounds lead to the HOMO distribution on the quinazolinone moiety and the different donor substituents. The synthesized compounds form glasses with the glass transition temperatures ranging from 97 to 159 °C. Their solutions in tetrahydrofuran absorb electromagnetic radiation in the range of 210–420 nm and emit in the range of 350–600 nm. The Stokes shifts recorded for the dilute solutions of compounds ranged from 48 to 134 nm, while those observed for the solid films were similarly in the range of 46–113 nm. The highest fluorescence quantum yield of 44.3% was recorded for the solution of 3-(9-ethyl-9H-carbazol-3-yl)-5-((E)-2-(9-ethyl-9H-carbazol-3-yl)ethenyl)-2-methylquinazolin-4(3H)-one. The triplet energy levels established for the dilute solutions of the compounds from their phosphorescence spectra at 77 K were found to be in the range of 2.55–2.99 eV. The ionization potentials of the synthesized compounds established by photoelectron emission technique in air ranged from 5.35 to 5.66 eV. The electrochemical properties of the derivatives were studied by cyclic voltammetry. All the studied compounds showed irreversible oxidation and no reduction waves. Their repeated cyclic voltammetry scans displayed increasing changes in the cyclic voltammetry traces, proving that a series of electro-polymerization reactions of the radical cations occurred. Time-of-flight hole drift mobility of the solid layer of 5-(bis(4-tert-butyldiphenyl)amino)-3-(9-ethyl-9H-carbazol-3-yl)-2-methylquinazolin-4(3H)-one reached 1.1 × 10−3 cm2/Vs at an electric field of 8.1 × 105 V/cm. This compound was tested as a host in the green and blue phosphorescent organic light emitting diodes achieving maximum external quantum efficiencies of ca. 7.1 and 6.9%, respectively.

New Insights To Simulate the Luminescence Properties of Pt(II) Complexes Using Quantum Calculations.

The present manuscript reports a thorough quantum investigation on the luminescence properties of three monoplatinum(II) complexes. First, the simulated bond lengths at the ground state are compared to the observed ones, and the simulated electronic transitions are compared to the reported ones in the literature in order to assess our methodology. In a second time we show that geometries from the first triplet excited state are similar to the ground state ones. Simulations of the phosphorescence spectra from the first triplet excited states have been performed taking into account the vibronic coupling effects together with mode-mixing (Dushinsky) and solvent effects. Our simulations are compared with the observed ones already reported in the literature and are in good agreement. The calculations demonstrate that the normal modes of low energy are of great importance on the phosphorescence signature. When temperature effects are taken into account, the simulated phosphorescence spectra are drastically improved. An analysis of the computational time shows that the vibronic coupling simulation is cost-effective and thus can be extended to treat large transition metal complexes. In addition to the intrinsic importance of the investigated targets, this work provides a robust method to simulate phosphorescence spectra and to increase the duality experiment-theory.

Room temperature phosphorescence lifetime and spectrum tuning of substituted thianthrenes

A group of thianthrene derivatives has been studied to investigate the effect of different substituents and substitution positions on their photophysical behavior. Strong room temperature phosphorescence (RTP) and dual fluorescence-phosphorescence at room temperature (RT-DFP) have been observed. Compounds with efficient (Φ ≈ 0.4) yellow and long-lived (τ = 88 ± 6 ms) green phosphorescence have been characterized. The involvement of nπ* and ππ* states was evaluated to explain their high triplet formation yield and phosphorescent properties. To give an insight into electron properties of studied molecules cyclic voltammetry and DFT calculations have been performed.

Syntheses, structures, and phosphorescence of complexes (A)[Gd(L)4] and [Gd(Phen)(L)3] (L = iso-Bu2PS 2 - , C4H8NCS 2 - ; A = NH 4 + , Et4N+)

Complexes (A)[Gd(L)4] and [Gd(Phen)(L)3] (L = iso-Bu2PS2-, C4H8NCS2-; A = NH4+, Et4N+) are synthesized. The crystal structure of compound [Gd(Phen)(iso-Bu2PS2)3] · MeCN is determined by X-ray diffraction analysis (CIF file CCDC no. 1455418). The structure consists of molecules of the mononuclear complex [Gd(Phen)(iso-Bu2PS2)3] and MeCN. The coordination polyhedron N2S6 of the Gd atom is a distorted antiprism. The complexes exhibit phosphorescence in a range of 400–600 nm. The energies of the triplet levels of the ligands C4H8NCS2-(23336 cm–1) and iso-Bu2PS2-(23506 cm–1) are determined from the phosphorescence spectra of complexes (A)[Gd(L)4] in frozen ethanol (77 K).

Thiocyanate mediated structural diversity in phenol based “end-off” compartmental ligand complexes of group 12 metal ions: Studies on their photophysical properties and phosphatase like activity

The reaction of a pentadentate compartmental ligand LH, namely 4-tert-Butyl-2,6-bis-[(2-pyridin-2-yl-ethylimino)-methyl]-phenol, with group 12 metal ions (ZnII, CdII, HgII) followed by addition of NaSCN afforded one discrete dinuclear complex [Zn2(L)(SCN)3](1), and two polymeric 1D species [Cd2.5(L)(SCN)3(AcO)]n (2) and [Hg2(L)(SCN)3]n (3). All the complexes have been structurally characterized by single crystal X-ray diffraction. The crystal structure of the complexes reveals different coordination modes of thiocyanate anion that affect the different topology detected in the compounds: the anions are μ1-NCS and μ1,1-NCS connected in complex 1, while μ1,3-NCS bridging mode is observed in 2, and μ1-SCN and μ1,3-NCS in 3. The polymeric Hg complex of the bicompartmental ligand system here reported is unprecedented. Detail study of their photophysical properties including the phosphorescence spectra at 77K has been done. Phosphatase like activity of all the three complexes has been performed in DMSO-H2O medium and their activity follows the order of 1>2>>3.

Characterization of YAG:Dy,Er for thermographic particle image velocimetry in a calibration cell

Phosphor thermometry is a promising approach for remote and non-intrusive two-dimensional temperature sensing. However, the characteristics of each phosphor material have to be carefully evaluated to avoid measurement inaccuracies. We characterized the luminescent properties of the thermographic phosphor particles YAG:Dy,Er seeded to the gas flow in a flow cell. The particles were excited by a laser sheet of a 355 nm Nd:YAG laser, and two intensified cameras were used for two-color detection of the phosphorescence spectrum. The calibration cell enables homogeneous and repeatable measurement conditions. A newly designed seeder allowed to adjust the number of particles in the cell, achieving sufficient seeding densities even at low flow rates in a wide temperature range. Additionally, the influence of the seeding density and the laser fluence on the intensity ratio were studied, both having negligible effects on the estimated temperature.

Spectral manifestation of distorted forms metalloporphyrins at low temperatures

Different spectral forms of a set of metalloporphyrins with Mg (II), Zn (II), Pd (II) and Pt (II) ions in solid solutions (Shpol'skii matrices, solid tetrahydrofuran and solid rare gas matrices) have been detected in the absorption and luminescence spectra at cryogenic temperatures. The spectral manifestation of a planar form, as well as two distorted forms for Mg- and Zn-porpyrins was formed in the ground electronic state at low temperatures. An existence of two spectral forms of Pd and Pt-porphyrins was observed in their phosphorescence spectra. In the case of Mg-porphyrin the spectral shift between positions of 0-0 transitions the planar and first distorted spectral forms is about 220 cm -1 .

Electronic Spectroscopy of Methylcyanodiacetylene (CH3 C5 N).

The results of a study devoted to the electronic spectroscopy of gaseous, solid, and cryogenic matrix-isolated methylcyanodiacetylene (CH3 C5 N) are reported. UV absorption and optical phosphorescence spectra of the compound are described here for the first time, and the corresponding vibronic assignments are proposed. UV absorption, studied directly or through the excitation of phosphorescence, revealed the B˜ 1 E--X˜ 1 A1 system, very weak A˜ 1 A2 -X˜ 1 A1 bands, and a strong, broad absorption feature, tentatively identified as D˜ 1 E-X˜ 1 A1 . Spectral measurements were assisted by quantum chemical calculations at the DFT and ab initio (coupled cluster) levels of theory.

The manifestation of optical centers in UV–Vis absorption and luminescence spectra of white blood human cells

A white blood human cells spectral investigation is presented. The aim of this series of experiments was to obtain and analyze the absorption and luminescence (fluorescence and phosphorescence) spectra at room temperature and at 78 K of newly isolated white blood human cells and their organelles. As a result the optical centers and possible biochemical components that form the studied spectra where identified. Also the differences between the spectra of abnormal cells (B-cell chronic lymphocytic leukemia BCLL) and normal ones were studied for the whole cells and individual organelles.

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone and its bis(aza-18-crown-6)-containing analogue in acetonitrile

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone (CH1) and its bis(aza-18-crown-6) derivative (CH2) in acetonitrile at ambient temperature and 77 K have been studied. The absorption, fluorescence, and phosphorescence spectra of CH1 and CH2 are similar. The probability of the formation of the triplet state is higher for CH2 molecules (λT-Tmax = 660 nm, lifetime τT ~ 20 μs). The lifetime of the CH1 molecule in the triplet state is estimated at τT ~ 2–3 μs. Photoisomers of CH1 and CH2 are formed along with the triplet state. According to DFT calculation results, the formation of trans–cis photoisomers of CH1 and CH2 is the most energetically favorable.