Optical properties of Eu(III) and Tb(III) complexes with pyridine- and quinoline- based ligands under high hydrostatic pressure

The spectroscopy of nitrate complexes of Eu(III) and Tb(III) with chiral and racemic imine-based [L1 = (N,N'-bis (2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine) and L3 = N, N'-bis(2-quinolylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine] and amine-based [L2 = N,N'-bis(2-pyridylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine) and L4 = N,N'-bis(2-quinolylmethyl)-1,2-(R,R + S,S)-cyclohexanediamine] ligands has been studied under high hydrostatic pressure (above 100 kbar). With the increasing pressure, a reduction of the Tb(III) and Eu(III) luminescence intensity is detected for all the complexes, whilst a significant reduction of the Tb(III) and Eu(III) excited state lifetimes has been observed for all Tb-based complexes [L1Tb(NO3)(3) -> L4Tb(NO3)(3)] and only for the Eu(III) complexes containing the imine-based ligands [L1Eu(NO3)(3) and L3Eu(NO3)(3)]. This behavior has been rationalized taking into account two main aspects: i) the relative position of the energy levels of the ligands and the metal ions and ii) the change of these position upon compression DFT calculations have been also performed to elucidate the nature of the orbitals involved in the UV electronic absorption transitions (NTO orbitals) upstream of the energy transfer process to the metal ion

Photo-degradation Analysis of Luminescent Polymers with Lanthanide Complexes

UV durability of luminescent Eu(III) complexes for future solar cell application is estimated using Fourier transform infrared spectroscopy (FT-IR). Sandwich-typed glass cells containing Eu(III) complexes powders under UV irradiation are used for the carbonyl index analysis (calculation of decomposition percentage of organic ligands) using FT-IR measurements. The durability of Eu(hfa)3(TPPO)2 (hfa: hexafluoroacetylacetonate, TPPO: triphenylphospine oxide) is five times larger than that of Eu(tta)3(phen) (tta: trifluoromethylthienylacetylacetonate, phen: phenanthroline). Photophysical performance of Eu(III) complexes under UV irradiation is also evaluated using emission lifetimes and external quantum efficiency measurements of the solar cell module using EVA films with Eu(III) complexes. Photo-degradation analysis of luminescent polymer thin films with Eu(III) complexes are demonstrated for the first time

Synthesis and Photoluminescence Properties of Nonanuclear Tb(III) Clusters with Long Alkyl Chain Group

Series of nonanuclear Tb(III) clusters with ligands of different length of alkyl chain groups and their photophysical properties are demonstrated. The nonanuclear Tb(III) clusters (Tb9 clusters) are composed of nine oxygen-bridged Tb(III) ions and sixteen alkyl salicylate ligands, where alkyl chain are ethyl (Tb9-Et), propyl (Tb9-Pr), butyl (Tb9-Bu), and hexyl (Tb9-Hex) groups. The luminescence properties of the Tb9 clusters are characterized by absorption spectra, emission quantum yields, and emission lifetimes. The radiative (kr) and nonradiative (knr) rate constants were calculated from their photophysical properties. Tb9-Hex have shown the highest kr (859 s-1) and lowest knr (137 s-1), owing to the tight packing due to CH-π interaction by long alkyl chains

Spin-orbit coupling dependent energy transfer in luminescent nonanuclear Yb-Gd / Yb-Lu clusters

In luminescent lanthanide (Ln(III)) complexes, the yield and the lifetime of triplet excited state of organic ligands are crucial factors that affect the ligands-to-Ln(III) energy transfer efficiency. Such factors are dependent on spinorbit coupling induced by the Ln(III) ions that mixes different multiplicity states through heavy atom and paramagnetic effects. We investigated the role of these effects on the energy transfer efficiency in synthesized nonanuclear Yb-Gd / Yb-Lu clusters ([Ln(9)(mu-OH)(10)(butyl salicylate)(16)]NO3, Ln(9) = YbnGd9-n or YbnLu9-n, n = 0, 1, 3, 7, and 9). Based on the intensity of the fluorescence and phosphorescence of the ligands, the spin-orbit coupling strength was in the order of Yb(III) > Gd(III) > Lu(III). Various photophysical processes affecting the energy transfer efficiency in YbnGd9-n and YbnLu9-n clusters are discussed from the perspective of spin-orbit coupling and give insight in how to optimize energy transfer efficiencies

Critical Role of Energy Transfer Between Terbium Ions for Suppression of Back Energy Transfer in Nonanuclear Terbium Clusters

Lanthanide (Ln(III)) complexes form an important class of highly efficient luminescent materials showing characteristic line emission after efficient light absorption by the surrounding ligands. The efficiency is however lowered by back energy transfer from Ln(III) ion to the ligands, especially at higher temperatures. Here we report a new strategy to reduce back energy transfer losses. Nonanuclear lanthanide clusters containing terbium and gadolinium ions, TbnGd9-n clusters ([TbnGd9-n(mu-OH)(10)(but ylsalicylate)(16)](+) NO3-, n = 0, 1, 2, 5, 8, 9), were synthesized to investigate the effect of energy transfer between Tb(III) ions on back energy transfer. The photophysical properties of TbnGd9-n clusters were studied by steady-state and time-resolved spectroscopic techniques and revealed a longer emission lifetime with increasing number of Tb(III) ions in TbnGd9-n clusters. A kinetic analysis of temperature dependence of the emission lifetime show that the energy transfer between Tb(III) ions competes with back energy transfer. The experimental results are in agreement with a theoretical rate equation model that confirms the role of energy transfer between Tb(III) ions in reducing back energy transfer losses. The results provide a new strategy in molecular design for improving the luminescence efficiency in lanthanide complexes which is important for potential applications as luminescent materials

Spectrally Selective Leakage of Light from Self-Assembled Supramolecular Nanofiber Waveguides Induced by Surface Plasmon Polaritons

We report surface plasmon polariton (SPP)-induced spectrally selective leakage of light waveguided in supramolecular nanofibers. The nanofibers are fabricated by self-assembly of tris(phenylisoxazolyl)benzene derivative molecules, and their diameter ranges from nanometers to hundreds of nanometers. Nanofibers with heights of more than 200 nm are shown to function as waveguides for fluorescence excited in one location by a focused 360 nm laser. The fluorescence can transfer the whole length of the nanofibers of tens of micrometers and is outcoupled from the nanofiber ends. The waveguiding phenomenon dramatically changes when the nanofibers are deposited on SPP-generating substrates. The substrates in the form of nanohole arrays are fabricated on a gold film with a pitch of 500 nm, a diameter of 250 nm, and a depth of 40 nm. On the SPP substrates, the nanofiber waveguides exhibit strong leakage of the guided light. The spectrum of the leaked light is consistent with the SPP resonance wavelength, and its polarization corresponds to the TE waveguided mode. We propose mechanisms of the observed phenomena that include either excitation of the SPPs via the waveguide evanescent field or direct enhancement of the leakage by the modified density of states near the plasmonic substrate