Comparative analysis of lanthanide excited state quenching by electronic energy and electron transfer processes

Carbazole-Based Eu3+ Complexes for Two-Photon Microscopy Imaging of Live Cells

Lanthanide(III) complexes with two-photon absorbing antennas are attractive for microscopy imaging of live cells because they can be excited in the NIR. We describe the synthesis and luminescence and imaging properties of two Eu3+ complexes, mTAT[Eu·L-CC-Ar-Cz] and mTAT[Eu·L-Ar-Cz], with (N-carbazolyl)-aryl-alkynyl-picolinamide and (N-carbazolyl)-aryl-picolinamide antennas, respectively, conjugated to the TAT cell-penetrating peptides. Contrary to what was previously observed with related Eu3+ complexes with carbazole-based antennas in a mixture of water and organic solvents, these two complexes show very low emission quantum yield (ΦEu < 0.002) in purely aqueous buffers. A detailed spectroscopic study on mTAT[Eu·L-Ar-Cz] reveals that the quantum yield of emission is strongly polarity dependent─the less polar the medium, the higher the quantum yield─and that the emission quenching in water is likely due to a photoinduced electron transfer between the excited carbazole-based antenna and Eu3+ that efficiently competes with the energy transfer process. Nevertheless, mTAT[Eu·L-Ar-Cz] shows a significant two-photon cross-section of 100 GM at 750 nm, which is interesting for two-photon microscopy. The live cell imaging properties of mTAT[Eu·L-Ar-Cz] and the two other conjugates were investigated. Cytosolic delivery was clearly evidenced in the case of mTAT[Eu·L-Ar-Cz] when cells are coincubated with this compound and a nonluminescent dimeric TAT derivative, dFFLIPTAT.

Mechanistic Investigation of Sensitized Europium Luminescence: Excited State Dynamics and Luminescence Lifetime Thermometry

Fluorescent nanothermometers based on thermal-dependent lifetime have a significant advantage in biological imaging owing to their immunity toward scattering, absorption, and autofluorescence. In this study, we present the first example of a water-soluble europium complex ([L1Eu]-) that exhibits high sensitivity (1.2% K-1 at 298 K) based on a temperature-dependent lifetime in the millisecond time range. This complex and its analogues show considerable potential for organelle imaging. The mechanism behind this thermal-sensitive behavior has been extensively investigated using transient absorption spectroscopy and variable temperature time-resolved luminescence methods. A highly efficient ligand sensitization process and a thermally activated back energy transfer process have been demonstrated. This study bridges the gap in small molecule thermometers with lifetimes longer than 1 ms and provides guidance in ligand design for metal coordination complex thermometers.

Luminescence-Based Infrared Thermal Sensors: Comprehensive Insights

Recent chronological breakthroughs in materials innovation, their fabrication, and structural designs for disparate applications have paved transformational ways to subversively digitalize infrared (IR) thermal imaging sensors from traditional to smart. The noninvasive IR thermal imaging sensors are at the cutting edge of developments, exploiting the abilities of nanomaterials to acquire arbitrary, targeted, and tunable responses suitable for integration with host materials and devices, intimately disintegrate variegated signals from the target onto depiction without any discomfort, eliminating motional artifacts and collects precise physiological and physiochemical information in natural contexts. Highlighting several typical examples from recent literature, this review article summarizes an accessible, critical, and authoritative summary of an emerging class of advancement in the modalities of nano and micro-scale materials and devices, their fabrication designs and applications in infrared thermal sensors. Introduction is begun covering the importance of IR sensors, followed by a survey on sensing capabilities of various nano and micro structural materials, their design architects, and then culminating an overview of their diverse application swaths. The review concludes with a stimulating frontier debate on the opportunities, difficulties, and future approaches in the vibrant sector of infrared thermal imaging sensors.

Arel: Investigating [Eu(H2O)9]3+ Photophysics and Creating a Method to Bypass Luminescence Quantum Yield Determinations

Lanthanide luminescence has been treated separate from molecular photophysics, although the underlying phenomena are the same. As the optical transitions observed in the trivalent lanthanide ions are forbidden, they do belong to the group that molecular photophysics has yet to conquer, yet the experimental descriptors remain valid. Herein, the luminescence quantum yields (ϕ_lum), luminescence lifetimes (τ_obs), oscillator strengths (f), and the rates of nonradiative (k_nr) and radiative (k_r ≡ A) deactivation of [Eu(H₂O)₉]³⁺ were determined. Further, it was shown that instead of a full photophysical characterization, it is possible to relate changes in transition probabilities to the relative parameter A_rel, which does not require reference data. While A_rel does not afford comparisons between experiments, it resolves emission intensity changes due to emitter properties from intensity changes due to environmental effects and differences in the number of photons absorbed. When working with fluorescence this may seem trivial; when working with lanthanide luminescence it is not.