Triplet State Energy Research Articles

Spectroscopic, luminescence and in vitro biological studies of solid ketoprofen of heavier trivalent lanthanides and yttrium(III)

Solid-state compounds of the general formulae [ML3] (M=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y; L=ketoprofen) were synthesized and characterized using infrared, diffuse reflectance and luminescence spectroscopies. IR data suggested that the carboxylate group in ketoprofen is coordinated to the metals as a bidentate ligand. The triplet state energy level was determined using the Gd3+ complex, which exhibited a ketoprofen blue luminescence when excited in the UV region. The compound containing Tb3+ ion was sensitized by the ligand and emitted in the green region of the visible spectrum. On the other hand, for the analogous species containing the dysprosium ion, a competition for luminescence between the Dy3+ and the ligand levels was observed. Finally, Tm3+ complex exhibits only ligand luminescence. These optical behaviors are discussed based on rare earth energy diagrams. In addition, the compounds were evaluated for their anti-inflammatory activities. All the compounds showed a higher production of H2O2 and IL-10 than the ketoprofen, suggesting that the compounds exhibited an immunomodulatory effect and this opens up new perspectives for immunotherapeutic approaches.

Triplet excited state energies and phosphorescence spectra of (bacterio)chlorophylls.

(Bacterio)Chlorophyll ((B)Chl) molecules play a major role in photosynthetic light-harvesting proteins, and the knowledge of their triplet state energies is essential to understand the mechanisms of photodamage and photoprotection, as the triplet excitation energy of (B)Chl molecules can readily generate highly reactive singlet oxygen. The triplet state energies of 10 natural chlorophyll (Chl a, b, c2, d) and bacteriochlorophyll (BChl a, b, c, d, e, g) molecules and one bacteriopheophytin (BPheo g) have been directly determined via their phosphorescence spectra. Phosphorescence of four molecules (Chl c2, BChl e and g, BPheo g) was characterized for the first time. Additionally, the relative phosphorescence to fluorescence quantum yield for each molecule was determined. The measurements were performed at 77K using solvents providing a six-coordinate environment of the Mg(2+) ion, which allows direct comparison of these (B)Chls. Density functional calculations of the triplet state energies show good correlation with the experimentally determined energies. The correlation determined computationally was used to predict the triplet energies of three additional (B)Chl molecules: Chl c1, Chl f, and BChl f.

DFT study of sulfur derivatives of cumulenes and their protonated forms of interstellar interest and calculations of dissociation energies of protonated forms (SC(CH)C(n-2)S)(+) (n = 3-8).

A theoretical study of the sulfur cumulenes SCnS (n = 3-8), CnS ( n = 1-8) and of their protonated forms (SCnS)H(+) and (CnS)H(+) that might exist in the interstellar environment, has been carried out by means of the standard B3LYP/6-311G** method. The geometries and relative energies of singlet and triplet states according to the number of carbons have been computed. Like neutral species, we have found that the ground state of the most stable protonated forms (SC(CH)Cn-2S)(+) and ((HC)Cn-1S)(+), alternates between a triplet state for the even series and a singlet state for the odd series. We provided the data needed to simulate infrared and microwave spectra (vibration frequencies, dipole moments, and rotational constants) for each protonated species (SCnS)H(+) and (CnS)H(+) and for each neutral CnS species. The computing of dissociation energies of the most stable protonated forms (SC(CH)Cn-2S)(+) (n = 3-8) has shown that the lowest values are obtained for the dissociation of compounds with an even number of carbons, in their triplet state, which produce the observed fragments CS and C3S. The dissociation of even protonated forms requires less energy than for the odd protonated forms.

Singlet–triplet interaction in Group 2 M2O hypermetallic oxides

This ab initio study of Group 2 M2O hypermetallic oxides focuses mainly on the two heaviest members, Ba2O and Ra2O. In accordance with previous studies in our group on the Be, Mg, Ca and Sr hypermetallic oxides, we find that the BaOBa and RaORa molecules have a linear X∼1Σg+ ground electronic state and a very low lying first excited ã3Σu+ triplet electronic state. Special attention is placed on calculating and understanding how the singlet–triplet splitting and singlet–triplet interaction strength vary down the series. The calculations reveal that MgOMg shows the largest singlet–triplet splitting and does not fit into the overall trend down the Group 2 series of elements. However, in all cases the extent of the singlet–triplet interaction between vibronic levels of the X∼ and ã states is very small. On the experimental side, there is literature evidence for the formation of electronically excited Ba2O in oxidation reactions of barium dimers, and our calculations of excited singlet and triplet state energies support that assignment.

Phosphorescence of BODIPY dyes

Abstract The phosphorescence of BODIPY dyes was observed directly in glassy solvent matrix at 78 K. The phosphorescence occurred when Br substituents are present on the BODIPY core and the solvent temperature is lower than the freezing point. The phosphorescence quantum yield (Φp) and lifetime (τp) were measured. The substitution effect of Br atoms on the phosphorescence properties of 8-phenyl-BODIPY dyes is also studied. Upon the increase in the number of Br atoms on the BODIPY core, the phosphorescence emission maximum is varied from 720 to 780 nm, the corresponding excited triplet state energy changes from 1.71 to 1.62 eV, the lifetime τp is shortened from 5.8 to 3.7 ms, while the quantum yield Φp is decreased from 3.0 × 10−3 to 1.4 × 10−3. The mechanism for the effect of Br substitution on the phosphorescence properties is revealed by calculating the rate constants of related photophysical processes. The Br substitution at position 1 or 7 showed a dramatic difference from that at positions 2, 6, 3, and 5. The steric hindrance to the rotation of the phenyl leads to the deformation of BODIPY π-core such that the phosphorescence properties change toward a different direction.

The influence of carboxilate, phosphinate and seleninate groups on luminescent properties of lanthanides complexes

The lanthanides(III) complexes [Ln(bza)3(H2O)n]·mH2O, [Ln(ppa)3(H2O)n]·mH2O and [Ln(abse)3(H2O)n]·mH2O where Ln=Eu3+, Gd3+ or Tb3+ were synthesized using sodium benzoate (Nabza), sodium phenylseleninate (Naabse) and sodium phenylphosphinate (Nappa) in order to verify the influence on coordination modes and the luminescence parameters when the carbon is exchanged by phosphorus or selenium in those ligands. The complexes׳ stoichiometries were determined by lanthanide(III) titration, microanalysis and TGA. The coordination modes were determined as bidentate bridging and chelate by the FT-IR. The triplet state energies of the ligands were obtained by two different approaches giving a difference of about ~2000cm−1 between them. The [Eu(abse)3(H2O)] complex shows the higher degree of covalence which was verified by the centroid of 5D0→7F0 transition (17,248cm−1). On the other hand the [Ln(abse)3(H2O)n]·mH2O complexes have an inefficient antenna effect verified by the low values of absolute emission quantum yields. The [Ln(ppa)3(H2O)n]·mH2O complexes have higher emission decay lifetime values among the complexes which is a result of the ability of this ligand to form coordination polymers avoiding water molecules in the first coordination sphere. The [Eu(ppa)3] complex has the highest point symmetry around europium(III) among the synthesized complexes, followed by the [Eu(bza)3(H2O)2]·3/2(H2O) and [Eu(abse)3(H2O)] complexes where europium(III) show similar point symmetries. As one may expect, the triplet state energy position would change the transfer and/or back energy transfer rates from ligand to metal. The calculation of these rates show that the back energy transfer rates are more affected than the transfer ones by changing the triplet state energy in the range of ~2000cm−1. The changes in the energy transfer rates from triplet state to europium(III) levels are not sufficient to significantly modify the population of the europium(III) 5D0,1 levels and therefore the emission quantum yield.

Synthesis and Characterization of Heteroatom-Bridged Bis-spirobifluorenes for the Application of Organic Light-Emitting Diodes

Pure 2-iodo-9,9'-spirobifluorene was synthesized by an efficient method without troublesome iodination of 9,9-spirobifluorene (SP) or the Sandmeyer reaction of 2-amino-9,9'-spirobifluorene. A series of main group element-bridged bis-9,9'-spirobifluorene derivatives were synthesized via coupling reactions of 2-iodo-9,9'-spirobifluorene and main group element-containing precursors. These heteroatom-bridged bis-spirobifluorenes show large triplet state energy gaps, high glass transition temperatures, and varied charge-transporting properties advantageous to the host materials for blue phosphorescence organic light-emitting diodes.

Europium and Terbium Coordination Polymers Assembled from Hexacarboxylate Ligands: Structures and Luminescent Properties

Six lanthanide coordination polymers of the formula [Ln(L1)0.5(H2O)2]·2H2O [where Ln3+: Eu3+ (1), Tb3+ (2), and Gd3+(3)] and [Me2NH2][Ln(H2L2)(H2O)4]·0.5DMF·xH2O [where Ln3+: Eu3+ (4), Tb3+ (5), and Gd3+(6)], based on p-terphenyl-2,2″,2‴,5,5″,5‴-hexacarboxylate acid (H6L1), and p-terphenyl-3,2″,3″,5,5″,5‴,-hexacarboxylate acid (H6L2), have been solvothermally synthesized and structurally characterized. Complexes 1–3 are 3D frameworks exhibiting 6-connected pcu alpha-Po primitive cubic network with topology (412.63), while complexes 4–6 show two-dimensional (2D) architectures showing simplified 3,4-connected binodal net and (4.62)(42.62.82) topology. Detailed photophysical behaviors have been explored on Eu3+, Tb3+, and Gd3+ complexes. The calculated triplet state energies of H6L1 and H6L2 lie above the emissive levels of Eu3+ or Tb3+ in an ideal range for sensitizing. Furthermore, it is demonstrated that the optimum energy gap between the triplet state of ligand H6L1 and the emissive level of Tb3+ ion makes the overall quantum yield of Tb3+ complex (2) larger than its corresponding Eu3+ complex (1). In addition, the coordinated water in the inner sphere has a significant negative influence on the overall quantum yield, especially for the Eu3+ complex (4) compared to the Tb3+ complex (5), due to the deactivation process caused by vibrational OH oscillators.

Computational Investigation on the Spectroscopic Properties of Thiophene Based Europium β-Diketonate Complexes.

The adiabatic transition energies from the lowest triplet states of four Europium tris β-diketonate/phenantroline complexes have been determined in vacuo and in dicholomethane solution by the ΔSCF approach at the density functional theory level, using the PBE1PBE and the CAM-B3LYP hybrid functionals. The calculated adiabatic transition energies have been compared with the experimental 0-0 transitions of each complex determined from phosphorescence spectra of the corresponding Gd(3+) complexes and followed by direct comparison between simulated and experimental spectra line shapes. For compound 1, the Eu(TTA)3Phen system, triplet states other than the lowest one and conformational isomers other than the one present in the crystallographic structure have been considered. In the crystallographic structure, this compound presents three quasi-degenerate low energy triplet states, differing for the TTA ligand where the two unpaired electrons are localized and showing close adiabatic transition energies. For compound 1, the lowest triplet states of the four investigated conformational isomers show similar characteristics and close adiabatic transition energies. On the basis of these results, an investigation of compounds 2-4 (Eu(Br-TTA)3Phen, Eu(DTDK)3Phen, and Eu(MeT-TTA)3) has been performed by considering only the isomer present in the crystallographic structure and only the lowest triplet state of each compound. For compounds 1-3, the energies of the lowest triplet states calculated by both functionals in solution including zero-point energy corrections well reproduce the experimental trends as well as the values of the adiabatic transition energies: CAM-B3LYP, the best performing functional, provides energies of the lowest triplet state with deviations from experiments lower than 1200 cm(-1). Also, the calculated vibrationally resolved phosphorescence spectra and UV-vis absorptions well reproduce the main features of their experimental counterparts. Significant differences between calculated and experimental results are observed for compound 4, for which difficulties in the experimental determination of the triplet state energy were encountered: our results show that the negligible photoluminescence quantum yield of this compound is due to the fact that the energy of the most stable triplet state is significantly lower than that of the resonance level of the Europium ion, and thus the energy transfer process is prevented. These results confirm the reliability of the adopted computational approach in calculating the energy of the lowest triplet state energy of these systems, a key parameter in the design of new ligands for lanthanide complexes presenting large photoluminescence quantum yields.

The Fate of the Triplet Excitations in the Fenna-Matthews-Olson Complex and Stability of the Complex

The Fenna-Matthews-Olson (FMO) protein complex contains strongly coupled bacteriochlorophyll a (BChl a) pigments and is part of a light harvesting antenna of green sulfur bacteria. This complex is very stable, in spite of the fact that it contains no carotenoids that are universally found to protect pigment-protein complexes against highly reactive singlet oxygen, which can form due to the transfer of energy from the triplet excited states of BChl molecules. In this work the dynamics of triplet excited states in FMO are investigated by means of nanosecond time resolved pump-probe spectroscopy. It is inferred, that triplet excited state is formed concurrently on three pigments within the FMO subunit, and its energy is then rapidly transferred to the lowest triplet energy pigment. Mixed singlet-triplet excitonic quantum-mechanical simulations reveal the structural positions of these pigments. It is concluded, that pigment #3 in the structure has the lowest triplet state energy, and that this energy is below that of the singlet oxygen, blocking energy transfer and preventing the formation of singlet oxygen. The latter is confirmed by direct measurements of BChl a triplet state energy via phosphorescence and independence of triplet state lifetime (55 µs) in FMO on the oxygen concentration. It is thus feasible to have natural antenna systems that are inherently stable without the need for carotenoids in the structure.The authors acknowledge the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy through Grant DE- FG02-09ER16084 for funding these studies.

Synthesis, Characterization and Fluorescence Properties of Poly(styrene-co-n-caprylamide maleic acid) and Its Europium(III) and Terbium(III) Complexes

Copolymer of poly(styrene-co-n-caprylamide maleic acid) (PSCMA, defined as HL) and its lanthanide complexes Ln(L)3·6H2O (Ln = Eu and Tb) had been synthesized and characterized by elemental analysis, X-ray diffraction, Fourier transform infrared spectra, UV-spectrophotometer and thermal analysis (TG–DTA). The fluorescence properties of the HL ligand and the Ln(L)3·6H2O complexes in the solid state were investigated. At room temperature, the HL ligand had a strong broad emission band at 410–575 nm (λmax = 458 nm) under excitation at 380 nm, while the respective characteristic emission of Eu(III) and Tb(III) ions was observed in Ln(L)3·6H2O complexes. This demonstrated that the HL ligand in the extra-framework channels succeeded in sensitizing Eu(III) and Tb(III) ions emission. Compared with the Eu(L)3·6H2O complex, the fluorescence intensity of the Tb(L)3·6H2O complex was much stronger. This indicated that the lowest excited triplet state energy level of HL matched well with the excited state energy level of Tb(III). With the increase of the Ln(III) ions content below 15 wt%, the fluorescence intensity increased monotonically. All the Ln(L)3·6H2O complexes exhibited high quantum yield, long fluorescence lifetime and good thermal stability.

Comparison of light out-coupling enhancements in single-layer blue-phosphorescent organic light emitting diodes using small-molecule or polymer hosts

Single-layer blue phosphorescence organic light emitting diodes (OLEDs) with either small-molecule or polymer hosts are fabricated using solution process and the performances of devices with different hosts are investigated. The small-molecule device exhibits luminous efficiency of 14.7 cd/A and maximum power efficiency of 8.39 lm/W, which is the highest among blue phosphorescence OLEDs with single-layer solution process and small molecular hosts. Using the same solution process for all devices, comparison of light out-coupling enhancement, with brightness enhancement film (BEF), between small-molecule and polymer based OLEDs is realized. Due to different dipole orientation and anisotropic refractive index, polymer-based OLEDs would trap less light than small molecule-based OLEDs internally, about 37% better based simulation results. In spite of better electrical and spectroscopic characteristics, including ambipolar characteristics, higher carrier mobility, higher photoluminescence quantum yield, and larger triplet state energy, the overall light out-coupling efficiency of small molecule-based devices is worse than that of polymer-based devices without BEF. However, with BEF for light out-coupling enhancement, the improved ratio in luminous flux and luminous efficiency for small molecule based device is 1.64 and 1.57, respectively, which are significantly better than those of PVK (poly-9-vinylcarbazole) devices. In addition to the theoretical optical simulation, the experimental data also confirm the origins of differential light-outcoupling enhancement. The maximum luminous efficiency and power efficiency are enhanced from 14.7 cd/A and 8.39 lm/W to 23 cd/A and 13.2 lm/W, respectively, with laminated BEF, which are both the highest so far for single-layer solution-process blue phosphorescence OLEDs with small molecule hosts.

A Highly Sensitive Mixed Lanthanide Metal–Organic Framework Self-Calibrated Luminescent Thermometer

A new mixed lanthanide metal-organic framework thermometer Tb0.9Eu0.1PIA with the significantly high sensitivity of 3.53% per K has been realized by making use of an organic ligand, 5-(pyridin-4-yl)isophthalate, with higher triplet state energy.

Energy-Transfer Mechanisms in IrIII -EuIII Bimetallic Complexes.

The bridging ligands in d-f bimetallic complexes play an important role in the excitation energy transfer (EET) process. To elaborate on the effect of the ligand on the EET process, a series of bridging ligands (μ-L), 1-(1',10'-phenanthrolin-2'-yl)-4,4,4-trifluorobutane-1,3-dione (phen3f), 1-(1',10'-phenanthrolin-2'-yl)-4,4,5,5,5-pentafluoropentane-1,3-dione (phen5f), 1-(2,2'-bipyridine-6-yl)-4,4,4-trifluorobutane-1,3-dione (bpy3f), and 1-(2,2'-bipyridine-6-yl)-4,4,5,5,5-pentafluoropentane-1,3-dione (bpy5f), and their corresponding iridium complexes, [(dfppy)2 Ir(μ-L)] (dfppy=2-(4',6'-difluorophenyl)pyridinato-N,C2'), as well as their corresponding heteroleptic IrIII -EuIII complexes [{(dfppy)2 Ir(μ-L)}3 EuCl]Cl2 were synthesized and characterized. Photophysical and kinetic results revealed that the alternation of the bridge ligand resulted in a systemic difference in the lowest triplet-state energy (T1 ) of the iridium complexes, the EET efficiency from iridium complexes to the EuIII ion, and a significant difference in the total luminescence quantum yields. Based on the nanosecond time-resolved phosphorescence spectra, a model for the energy-transfer mechanism was proposed for d-f bimetallic complexes, which indicated that the nonradiative relaxation of the excited energy of EuIII , especially energy dissipation by means of the T1 state, was the main reason for the discrepancy in the quantum yields of the four IrIII -EuIII complexes.

Two new dysprosium–organic frameworks contaning rigid dicarboxylate ligands: Synthesis and effect of solvents on the luminescent properties

Two new two–dimensional (2D) dysprosium coordination polymers [Dy(2,4′-bpdc)(DMF)2(NO3)]n (1) and {[Dy(2,4′–bpdc)(1,4-BDC)0.5(DMF)(H2O)]1.5H2O}n (2) (2,4′-H2bpdc=2,4′–biphenyldicarboxylic acid, 1,4-H2BDC=1,4–benzenedicarboxylic acid, DMF=N,N′-dimethylformamide) were synthesized under solvothermal condition and stucturally characterized by means of single-crystal X-ray diffraction, IR spectroscopy, and elemental analysis. Single-crystal X-ray analysis revealed that the two coordination polymers possess two types of 2D layered structures. From the viewpoint of network topology, the structures of 1 and 2 can be simplified as (4,4) network. We discuss the effect of solvents and temperature on luminescence properties. The fluorescence spectra of 1 at room temperature and 77K in the solid-state are almost the same, except the stronger emission intensities derived from ligand–centered at 77K. It is because the quenching by O3H oscillators was protected at low temperature. Coordination polymer 2 displays characteristic Dy3+ ion yellow–green luminescence under 290nm excitation in DMSO (dimethyl sulfoxide), CH3CN, and CH3OH solvents. The fluorescence intensities of 2 increased in the order of DMSO>CH3CN>CH3OH. We also studied the fluorescence lifetimes of 1 and 2, and the results revealed that the lifetime in DMSO solvent at room temperature reached to 9.53μs. Compared with the dysprosium coordination polymers, coordination polymer 2 presents a longer lifetime. Additionally, we calculate the triplet state T1 datum from the emission spectrum of the Gd3+ coordination polymer and discuss the energy transfer mechanisms. The energy transfer process from the lowest triplet state energy level of 2,4′-H2bpdc ligand to the 4F9/2 state energy level of Dy3+ ion is inefficient for both 1 and 2. The energy transfer process is effective after we introducing the chelating ligand 1,4-H2BDC to the construct of coordination polymer 2, which is ascribe to 1,4-H2BDC may participate in the process of energy transfer.

Dissociations of C5F8 and C5HF7 in Etching Plasma

Investigations of dissociations for c-C5F8 and c-C5HF7 molecules in the excited states were carried out using the molecular orbital method. The excitation energy to the lowest triplet state of c-C5F8 was lower the sum of the total energy of (C4F6+CF2) triplet state. Fragmentation by electron attachment to c-C5F8 did not take place, because the total energy of c-C5F8- is more stable than that of (C4F6+CF2)-. Hence, the main dissociative product of CF2 by electron excitation to π–π* state is created in the plasma of c-C5F8 and c-C5HF7, with reaction paths of C4F6+CF2 and C4HF5+CF2 compared with other dissociation paths of C3F4+C2F4 and C3HF3+C2F4. These dissociation pathways have suggested advantageous for dielectric etching with fluorine-deficient chemistry.

Synthesis, characterization and photophysical properties of new cyclometallated platinum(II) complexes with pyrazolonate ancillary ligand

New cyclometalated platinum(II) complexes with pyrazolonate ancillary ligand (ppy)Pt(pmip) (1) and (dfppy)Pt(pmip) (2) (ppy = 2-phenylpyridine, dfppy = (4,6-difluorophenyl)pyridine, Hpmip = 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) were synthesized and structurally characterized. Both compounds revealed square-planar geometry. The crystal cell of 1 was found to contain the monomer molecules of platinum compound whereas dimer molecules of 2 with short Pt⋯Pt contacts of 3.2217(3) Å were observed in the crystal cell of 2. Photophysical properties of 1 and 2 were investigated in detail. The highly resolved photoluminesence spectra of the platinum complexes in solution contain emission bands in the region of 470–550 nm attributed to monomer compounds 1 and 2. The triplet-state energies of 1 and 2 obtained from DFT calculations agree very well with the experimental data. In the crystalline state complex 2 revealed excimer emission as a structureless broad band at ca. 584 nm related to dimer molecules of platinum compound presented in the crystals.

Energy transfer and phosphorescence-quenching dynamics in a phosphorescent host–guest system

We investigated the energy transfer dynamics in a phosphorescent host–guest system. Two spirobifluorene derivatives, [2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene] (DPVSBF) and [2,7-bis(1,2,2-triphenylvinyl)-9,9′-spirobifluorene] (TPVSBF), were doped with the red phosphor complex [Os(bpftz)2(PPh2Me)2] (Os-R). The two hosts exhibit similar host-to-guest energy transfer efficiencies; however, the backward energy transfer from the Os-R complex to TPVSBF is slower than that from Os-R to DPVSBF. Quantum chemical calculations suggest that the backward energy transfer dynamics are related to the host’s triplet-state energy level. The greater energy of the TPVSBF triplet state compared to that of DPVSBF plays a crucial role in its ability to confine triplet excitons in Os-R.

Lanthanide coordination compounds with 1H-benzimidazole-2-carboxylic acid: syntheses, structures and spectroscopic properties

A flexible multidentate ligand, 1H-benzimidazole-2-carboxylic acid, was synthesized to construct a series of lanthanide coordination polymers [Ln(HBIC)3]n (Ln = Eu (1), Tb (2), Gd (3), Pr (4), Nd (5); H2BIC = 1H-benzimidazole-2-carboxylic acid) under hydrothermal conditions. All the compounds were fully characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, thermal analysis and various spectroscopic techniques. Structural analyses reveal that they are isostructural and feature a 2D wave-like layer structure with distorted grids, in which the adjacent Ln3+ centers are bridged by the HBIC− ligands with two kinds of new coordination modes and the adjacent HBIC− ligands are tightly bound by two types of distinct intra-layer hydrogen bonds. The adjacent 2D layers are further interconnected by strong inter-layer hydrogen bond ring motifs R22(10) to generate a 3D supramolecular architecture. Optical studies indicate that the compounds 1, 2, 4 and 5 exhibit characteristic luminescence emission bands of the corresponding lanthanide ions in the visible or near-infrared regions at room temperature. In particular, compound 2 displays bright green luminescence in the solid state with a satisfactory 5D4 lifetime of 1.2 ms and a high overall quantum yield of 31%, due to an ideal energy gap between the lowest triplet state energy level of H2BIC ligand and the 5D4 state energy level of Tb3+. The energy transfer mechanisms in compounds 1 and 2 were also described and discussed.

Energy Transfer Processes in Tb(III)-Dibenzoylmethanate Complexes with Phosphine Oxide Ligands

The Tb3+-β-diketonate complexes [Tb(DBM)3L], [Tb(DBM)2(NO3)L2] and [Tb(DBM)(NO3)2(HMPA)2] (DBM = dibenzoylmethanate; L: TPPO = triphenylphosphine oxide or HMPA = hexamethylphosphine oxide) were prepared and characterized by elemental analysis (CHN), complexometric titration with EDTA and Fourier transform infrared (FTIR) spectroscopy, and the photoluminescence properties evaluated. The triplet state energies of the coordinated DBM ligands were determined using time-resolved phosphorescence spectra of analogous Gd3+ complexes. The results show that the energies increase along with the number of coordinated nitrate anions replacing the DBM ligand in the complexes. The luminescence spectra and emission lifetime measurements revealed that the ligand-to-metal energy transfer efficiency follows the same tendency. Unlike the tris-DBM complexes, bis- and mono-DBM presented high luminescence, and may act as promising candidates for preparation of the emitting layer of light converting molecular devices (LCMDs).