Phosphorescence Spectra Research Articles

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Phosphorescence and Photophysical Parameters of Porphycene in Cryogenic Matrices

Matrix isolation studies were carried out for porphycene, an isomer of porphyrin, embedded in solid nitrogen and xenon. The external heavy atom effect resulted in nearly a 100% population of the triplet state and in the appearance of phosphorescence, with the origin located at 10163 cm−1. This energy is much lower than that corresponding to the T1 position in porphyrin. This difference could be explained by postulating that the orbital origin corresponds in both isomers to the second excited singlet state, which lies much closer to S1 in porphycene. Most of the vibrational frequencies observed in the phosphorescence spectrum correspond to totally symmetric modes, but several ones were assigned to the out-of-plane Bg vibrations. These bands are not observed in fluorescence, which suggests their possible role in vibronic-spin-orbit coupling.

Theoretical investigation on orange-emitting cyclometalated platinum (II) complexes containing organosilyl/organocarbon-substituted 2-(2-thienyl)pyridine ligands.

This paper presents a theoretical investigation of structural, optical, and phosphorescence properties of four cyclometalated Pt(II) complexes containing substituted 2-(2-thienyl)pyridine ligands using DFT and TD-DFT methods. Geometrical parameters of ground states were calculated and compared with available experimental data. Electronic absorptions were studied and assigned in terms of natural transition orbitals. Phosphorescence spectra have been simulated with adiabatic Hessian and adiabatic shift approaches according to the Franck-Condon approximation. Theoretical and experimental results agree and show that the four complexes exhibit two intense bands in orange region. Main normal modes involved in phosphorescence bands were analyzed and assigned.

Photophysical properties of ammonium, pyrrolidinium, piperidinium, imidazolium, and pyridinium as a guide to prepare ionic-organic hybrid materials

Ionic liquid cations (ILCs) have been utilized in hybrid organic-inorganic perovskites (HOIPs) to enhance their photoluminescence performance. However, the high number of possible cations and anions needed to form ILCs makes the experimental measurement time and cost consuming. Computational methods that could assist the selection of ILCs for this task-specific application are highly desirable. Therefore, in this work, the photophysical properties of various ILCs, including linear aliphatic, five-membered, and six-membered cyclic aliphatic, and aromatic ILCs, were investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT). Fluorescence and phosphorescence were analyzed using excited state dynamics (ESD) modules on ORCA at the B3LYP/def2TZVP level theory. All the investigated cations show fluorescence spectra either the UV or visible range. The cations with long-chain branches show fluorescence spectra in the visible range. Five membered rings show the phosphorescence spectra in the visible range, while the six-membered rings show the phosphorescence spectra in the near-infrared range.

A Multicenter Metal–Organic Framework for Quantitative Detection of Multicomponent Organic Mixtures

A Multicenter Metal–Organic Framework for Quantitative Detection of Multicomponent Organic Mixtures

Bis-Heteroleptic Cationic Iridium(III) Complexes Featuring Cyclometalating 2-Phenylbenzimidazole Ligands: A Combined Experimental and Theoretical Study.

In this report, we investigate a new family of cationic iridium(III) complexes featuring the cyclometalating ligand 2-phenylbenzimidazole and ancillary ligand 4,4'-dimethyl-2,2'-bipyridine. Our benchmark complex IrL12 (L1 = 2-phenylbenzimidazole) displays emission properties similar to those of the archetypical complex 2,2'-dipyridylbis(2',4'-phenylpyridine)iridium(III) in deaerated CH3CN (Φ = 0.20, λem = 584 nm and Φ = 0.14, λem = 585 nm, respectively) but exhibits a higher photoluminescence quantum yield in deaerated CH2Cl2 (Φ = 0.32, λem = 566 nm and Φ = 0.20, λem = 595 nm, respectively) and especially a lower nonradiative constant (knr = 6.6 × 105 s-1 vs knr = 1.4 × 106 s-1, respectively). As a primary investigation, we explored the influence of the introduction of electron-donating and electron-withdrawing groups on the benzimidazole moiety and the synergetic effect of the substitution of the cyclometalating phenyl moiety at the para position with the same substituents. The emission energy displays very good correlation with the Hammett constants of the introduced substituents as well as with ΔEredox values, which allow us to ascribe the phosphorescence of these series to emanate mainly from a mixed metal/ligand to ligand charge transfer triplet excited state (3M/LLCT*). Two complexes (IrL52 and IrL82) display a switch of the lowest triplet excited state from 3M/LLCT* to ligand centered (3LC*), from the less polar CH2Cl2 to the more polar CH3CN. The observed results are supported by (TD)-DFT computations considering the vibrational contributions to the electronic transitions. Chromaticity diagrams based on the maximum emission wavelength of the recorded and simulated phosphorescence spectra demonstrate the strong promise of our complexes as emitting materials, together with the very good agreement between experimental and theoretical results.

Direct excitation of tryptophan phosphorescence. A new method for triplet states investigation

We studied room temperature phosphorescence of tryptophan (TRP) embedded in poly (vinyl alcohol) films. With UV (285 nm) excitation, the phosphorescence spectrum of tryptophan appears at about 460 nm. We also observed the TRP phosphorescence with blue light excitation at 410 nm, well outside of the S0 →S1 absorption. This excitation reaches the triplet state of tryptophan directly without the involvement of the singlet excited state. The phosphorescence lifetime of tryptophan is in the sub-millisecond range. The long-wavelength direct excitation to the triplet state results in high phosphorescence anisotropy which can be useful in macromolecule dynamics study via time-resolved phosphorescence.

Near-Infrared Emitting Ir(III) Complexes Bearing a Dipyrromethene Ligand for Oxygen Imaging of Deeper Tissues In Vivo.

Phosphorescence lifetime imaging microscopy (PLIM) using a phosphorescent oxygen probe is an innovative technique for elucidating the behavior of oxygen in living tissues. In this study, we designed and synthesized an Ir(III) complex, PPYDM-BBMD, that exhibits long-lived phosphorescence in the near-infrared region and enables in vivo oxygen imaging in deeper tissues. PPYDM-BBMD has a π-extended ligand based on a meso-mesityl dipyrromethene structure and phenylpyridine ligands with cationic dimethylamino groups to promote intracellular uptake. This complex gave a phosphorescence spectrum with a maximum at 773 nm in the wavelength range of the so-called biological window and exhibited an exceptionally long lifetime (18.5 μs in degassed acetonitrile), allowing for excellent oxygen sensitivity even in the near-infrared window. PPYDM-BBMD showed a high intracellular uptake in cultured cells and mainly accumulated in the endoplasmic reticulum. We evaluated the oxygen sensitivity of PPYDM-BBMD phosphorescence in alpha mouse liver 12 (AML12) cells based on the Stern-Volmer analysis, which gave an O2-induced quenching rate constant of 1.42 × 103 mmHg-1 s-1. PPYDM-BBMD was administered in the tail veins of anesthetized mice, and confocal one-photon PLIM images of hepatic tissues were measured at different depths from the liver surfaces. The PLIM images visualized the oxygen gradients in hepatic lobules up to a depth of about 100 μm from the liver surfaces with a cellular-level resolution, allowing for the quantification of oxygen partial pressure based on calibration results using AML12 cells.

Copper(II) Complexes of 10,20-Diaryl-5,15-diazaporphyrin: Alternative Synthesis, Excited State Dynamics, and Substituent Effect on the 1O2-Generation Efficiency

Abstract The synthesis, excited state dynamics, and substituent effect on the 1O2-generation efficiency of several copper(II) complexes of 5,15-diazaporphyrin (CuDAPs) bearing peripheral substituents are reported. 10,20-Diaryl-CuDAPs were prepared via a new method consisting of metal-templated cyclization and N-dealkylation as key steps. The effect of the β-substituents on the optical and redox properties of CuDAP was stronger than that of the meso-aryl groups, which can be explained by considering the characteristics of the HOMO and LUMO of the DAP ring. The excited state dynamics and 1O2-generation efficiency of CuDAPs were studied using time-resolved spectroscopic techniques; the electronic effect of the meso-aryl groups on the triplet lifetime and 1O2-generation quantum yield was relatively weak, whereas that of the β-(1-pyrazolyl) groups was appreciable. The analysis of the temperature dependence of phosphorescence spectra of 10,20-bis(2,4,6-trimethylphenyl)-CuDAP allowed the energy gap between the excited trip-quartet and trip-doublet states to be determined. The relatively long triplet lifetimes of CuDAPs show their potential for future application as photosensitizers.

Halogenated BODIPY photosensitizers: Photophysical processes for generation of excited triplet state, excited singlet state and singlet oxygen

We have systematically examined the formation of singlet oxygen O2(1Δg), the excited triplet state (T1), and excited singlet state (S1) for halogenated BODIPY photosensitizers (halogen = Cl, Br, and I) in eight solvents to understand how halogen atoms and solvent affect these properties. The phosphorescence spectra and lifetimes of singlet oxygen generated by these halogenated BODIPYs have been measured by steady state/time resolved NIR emission, while the formation quantum yield of singlet oxygen (ΦΔ) has been determined by chemical method using diphenylisobenzofuran (DPBF) as the trapping agent. The formation quantum yield ΦΔ of singlet oxygen can be as high as 0.96 for iodinated BODIPY and 0.71 for brominated BODIPY. The triplet state T1 absorption spectra of brominated and iodinated BODIPYs have been recorded by laser flash photolysis method, in which T1 shows high formation efficiency and long lifetime. The formation and decay of excited singlet state S1 of four BODIPYs have been measured by ground state (S0) absorption and steady state/time resolved fluorescence. The results show that larger halogen atoms on BODIPY core lead to smaller fluorescence quantum yield, shorter fluorescence lifetime and higher singlet oxygen formation quantum yield due to heavy atom effect that promotes the formation of triplet state. On the other hand, higher solvent polarity causes lower singlet oxygen formation quantum yield, smaller fluorescence quantum yield, and shorter fluorescence lifetime. This solvent effect is explained by the presence of photoinduced charge transfer (ICT) process from halogen atoms to BODIPY. The ICT efficiency has been estimated and the results are agreed with ICT theory. ICT process in halogenated BODIPYs has never been revealed in literature. HOMO/LUMO obtained from DFT calculation also supports the presence of ICT. The involvement of ICT in the photosensitizing process of halogenated BODIPYs provides new insights for designing BODIPY photosensitizers for photodynamic therapy of tumor.

Theoretical Design of Blue-Color Phosphorescent Complexes for Organic Light-Emitting Diodes: Emission Intensities and Nonradiative Transition Rate Constants in Ir(ppy)2(acac) Derivatives.

Theoretical calculations of phosphorescent spectra and nonradiative transition (NRT) rate constants for S1 ⇝ T1, T1 ⇝ S0, and S1 ⇝ S0 were carried out to determine the best candidate for a blue-color phosphorescent complex among several derivatives of bis(2-phenylpyridine)(acetylacetonate)iridium(III). The geometries of the ground state (S0), the lowest triplet state (T1), and the lowest excited singlet state (S1) were optimized at the levels of density functional theory, in which B3LYP functionals and SBKJC+p basis sets were used. The NRT rate constants were derived by using a generating function method within the displaced harmonic oscillator model. The results of the calculation for phosphorescence showed that the introduction of F and/or CN substituents at the 4'/6'-th and 5'-th sites in 2-phenylpyridinate (ppy) ligands, respectively, causes a blue shift of the emission spectra. They also suggest that Ir(5-CN,6-F-ppy)2(acac), denoted 3(56) in the text, is a good candidate for a blue-color phosphorescent complex because a blue shift of emission spectra and a moderate intensity are obtained for phosphorescence and, furthermore, this complex is calculated to have a large rate constant for S1 ⇝ T1 and relatively smaller rate constants for T1 ⇝ S0 and S1 ⇝ S0 based on the calculations of spin-orbit coupling and nonadiabatic coupling constants.

The intriguing effect of thiolates as co-ligands in platinum(II) complexes bearing a cyclometalated 1,3-di(2-pyridyl)benzene

Substitution of the chlorido ligand of the fascinating cyclometalated complex [Pt(5-mesityl-1,3-di(2-pyridyl)benzene)Cl] by thioacetate leads to the related thiolato complex [Pt(5-mesityl-1,3-di(2-pyridyl)benzene)(thioacetate)], which has been fully characterised. Its photophysical properties were determined in degassed dichloromethane solution, as blend in Poly(MethylMethAcrylate) (PMMA) thin films, and as powders, at room temperature. Both in solution and in thin films, an increase of the concentration of the complex leads to a red shift of the phosphorescence spectra and to a decrease of lifetime decays and quantum yield. It appears that tuning of emission spectra depends on the competition between monomeric and aggregate emissive states. No clear evidence of excimer formation has been detected. In powders, an aggregate emission spectrum is red-shifted at 602 nm, reaching a very low phosphorescence quantum yield of 1 %.

Novel persistent phosphors Eu2+ - doped Sr5SiO4Cl6 with codopants Cr3+ and Sc3+ in high temperature application

New cyan long persistent luminescence (LPL) phosphors Sr5SiO4Cl6:Eu2+, Cr3+/Sc3+ (SSC: Eu2+, Cr3+/Sc3+) have been prepared. The LPL behaviors of the SSC are greatly enhanced through incorporating Cr3+ and Sc3+ ions as trap centers. The fluorescence and phosphorescence spectra of SSC:Eu2+, Cr3+/Sc3+ both show an asymmetric wide emission band at 446 nm, which is attributed to the 4f65 d1→4f7 transitions of Eu2+ions in two different Sr2+ sites. The LPL of the SSC:0.03Eu2+, 0.03Cr3+ can remain 11760 s above the identifiable intensity level (0.32 mcd⋅m−2) after 10 min of excitation (for SSC:0.05Eu2+, 0.05Sc3+, 4080s). In addition, the temperature-dependent afterglow decay curves also show good afterglow initial brightness at 443 K for SSC:0.03Eu2+, 0.03Cr3+ (for SSC:0.05Eu2+, 0.05Sc3+, 343 K). This research provides new blue LPL phosphors with potential applications in high temperature environment.

Perylene Diimide-Based Multicomponent Metallacages as Photosensitizers for Visible Light-Driven Photocatalytic Oxidation Reaction

Perylene Diimide-Based Multicomponent Metallacages as Photosensitizers for Visible Light-Driven Photocatalytic Oxidation Reaction

The structure and spectroscopic properties of the metallophilic Pt/Pd complexes based on pyridine/pyrazol ligands: A computational investigation

DFT/TD-DFT, NBO and AIM methods were applied to explore the synthetic homo-metallophilic Pt⋅⋅⋅Pt (d8⋅⋅⋅d8) complex (self-assembled by [Pt(C^N^Npyr)(CNPh)]+, HC^N^Npyr = 2-phenyl-6-(1H-pyrazol-3-yl)-pyridine)]) recently reported with good photophysical properties. The calculated geometries and the spectroscopies of the complexes are consistent with the experiment. The strong phosphorescence of experimental observation for Pt-dimer was evidenced by its bigger order of μS1/ΔES1-T1 values (μS1: S0 → S1 transition dipole, ΔES1-T1: splitting energy between the lowest-lying singlet S1 and the triplet excited state T1 states). The phosphorescence spectra are predicted to be blue-shifted under polar solvent water comparing those in gas. The calculated maximal absorption is predominantly characteristic with MLCT/ILCT/LLCT whereas the photophysical spectrum was found to be responsible for the 3MLCT characters in the Pt-dimer. In addition, on the basis of complex Pt-monomer and Pt-dimer, Pd-monomer, Pd-dimer and Pt,Pd-dimer were constructed to investigate the modulation of Pd-substitued on the structure and spectroscopic properties of monomer and dimer [M(C^N^Npyr)(CNPh)]+ complex.

Effect of Heavy Atoms on the Doublet Components of the Phosphorescence Spectrum of Triphenylene in Carbon Tetrachloride

Effect of Heavy Atoms on the Doublet Components of the Phosphorescence Spectrum of Triphenylene in Carbon Tetrachloride

Reliable TDDFT Protocol Based on a Local Hybrid Functional for the Prediction of Vibronic Phosphorescence Spectra Applied to Tris(2,2'-bipyridine)-Metal Complexes.

An efficient computational protocol for the prediction of vibrationally resolved phosphorescence spectra is developed and validated for five tris(2,2'-bipyridine)-metal complexes ([M(bpy)3]n+, where M = Zn, Ru, Rh, Os, Ir). The outstanding feature of this protocol is the use of full linear-response time-dependent density functional theory (TDDFT) for the excited-state triplet calculation, i.e., the commonly seen strategies employing the Tamm-Dancoff approximation (TDA) or unrestricted density functional theory (DFT) calculations for the T1 state are not needed. This is achieved by the use of a local hybrid functional (LH12ct-SsirPW92) that features a real-space dependent admixture of exact exchange governed by a local mixing function. The excellent performance of this LH for triplet excitation energies known from previous studies transfers to a remarkable mean absolute error of 0.06 eV for the phosphorescence 0-0 energies investigated herein, while the popular B3PW91 functional gives an error of 0.27 eV in TDDFT and 0.09 eV in unrestricted DFT calculations, respectively. The advantages of the local hybrid are particularly apparent for excited states with a mixed-valence character. The influence of spin-orbit coupling was found to be significant for [Os(bpy)3]2+ red-shifting the 0-0 energy for phosphorescence by 0.17 eV, while the effect is negligible for the other complexes (<0.03 eV). The influence of the basis-set and integration-grid sizes is evaluated, and a computationally lighter protocol is validated that leads to drastic savings in computation time with negligible loss in accuracy.

Spectra and nature of the electronic states of [1]Benzothieno[3,2-b][1]benzothiophene (BTBT): Single crystal and the aggregates.

Absorption, fluorescence, and phosphorescence spectra of single crystals of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and BTBT dispersed in frozen n-nonane, n-hexadecane, and dichloromethane matrices were studied at 5K. Observation of a new absorption band and related changes in the fluorescence to phosphorescence intensity ratio, when the concentration of BTBT in the matrix increased above 10-4M, indicated the presence of BTBT aggregates. Quantum-chemistry calculations performed for the simplest aggregate, isolated dimer, showed that its structure is similar to the "herringbone" element in the BTBT crystal unit cell and the lowest electronic excited singlet state of the dimer has the intermolecular charge-transfer character. A qualitatively different nature of this state in dimers and in crystals, when compared with the situation in BTBT monomer [locally excited (LE) state], is associated with a decrease in the intersystem crossing yield. The structured vibronic structure of phosphorescence spectra in the studied systems indicated LE character of the triplet states.

Structural insights into new luminescent 2D lanthanide coordination polymers using an N, N′-disubstituted benzimidazole zwitterion. Influence of the ligand

A series of novel lanthanide coordination polymers (Ln-CPs) were herein prepared from lanthanide salts and a zwitterionic common ligand, under hydrothermal conditions. These cationic Ln homometallic frameworks with two-dimensional architectures, designated as [Ln(BCBI)(NO3)2(H2O)]n, where Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), and HBCBI = 1,3-bis(carboxymethyl)benzimidazole zwitterion, have been characterized by X-ray single-crystal diffraction, infrared spectroscopy, elemental and thermogravimetric analyses. Due to the 4fn-4fn transition, complexes 1, 2, 4 and 5 show the luminescence characteristic for trivalent lanthanides. Moreover, the fluorescence lifetime of 2 and the phosphorescence spectrum of 5 at 77 K have been investigated. The relationships between the lowest triplet state energy level of the HBCBI ligand and the lowest resonance energy levels of the Sm3+, Eu3+, Tb3+ and Dy3+ ions were examined. The results showed that the energy transfer from the HBCBI ligand is effective. The structural impact of the ligand is also highlighted.

Immobilization of silver and strontium oxide aluminate nanoparticles integrated into plasma-activated cotton fabric: luminescence, superhydrophobicity, and antimicrobial activity.

Smart textiles with a multifunctional surface, such as with photoluminescence, antimicrobial, and superhydrophobic properties, are highly desirable. Silver nanoparticles (Ag NPs) were prepared and immobilized onto a cotton surface using a facile pad-dry-curing technique to introduce long-lasting antimicrobial properties. The morphology of the silver immobilized cotton fibres was explored using scanning electron microscopic images and energy-dispersive X-ray spectra. The morphology of the formed Ag NPs was determined using a transmission electron microscope. Ag NPs exhibited uniform spreading and a high deposition density with a particle diameter in the range 25-55 nm. Both photoluminescence and superhydrophobic properties were explored by studying the cotton samples treated with hexadecyltrimethoxysilane nanocomposite containing lanthanide-doped strontium oxide aluminate NPs. Ultraviolet-visible light absorption, phosphorescence, and lifetime spectra were measured. The produced transparent superhydrophobic and photoluminescent film showed two absorbance bands at 273 and 367 nm and emission bands at 415 and 437 nm, as recognized by both absorption and emission spectra. Excellent antibacterial activities towards E. coli and S. aureus were monitored for the coated samples. Both fastness and colorimetric properties of Ag NPs-coated fabrics were explored.