TADF Blue Emitters with Balanced π-Conjugation─Design, Synthesis, Spectral Characterization, and a Model OLED with 8-(5-(tert-Butyl)-1,3,4-oxadiazol-2-yl)-N,N-bis(4-(tert-butyl)phenyl)dibenzo[b,d]furan-2-amine.

Blue organic light-emitting diodes (OLED) suffer from relatively short lifetimes and a comparatively low lighting efficiency. One of the approaches to improving their characteristics is the development of luminophores with the potential for thermally activated delayed fluorescence (TADF). Herein, a set of donor-spacer-acceptor compounds with potential for TADF are designed, synthesized, and computationally and spectroscopically characterized. The excited state dynamics of the most prospective dye is monitored by time-resolved fluorescence and transient absorption spectroscopy. The experimental data are obtained and processed by a newly developed method and supplemented by quantum chemical calculations. The comprehensive approach allowed rationalization of the complex cascade-type photophysical behavior. The most promising emitter is included in an OLED displaying a blue color with a maximum EQE of 4.9% and negligible efficiency roll-off at higher luminance.

Single-Step Process for Titanium Surface Micro- and Nano-Structuring and In Situ Silver Nanoparticles Formation by Ultra-Short Laser Patterning.

Ultra-short laser (USL)-induced surface structuring combined with nanoparticles synthesis by multiphoton photoreduction represents a novel single-step approach for commercially pure titanium (cp-Ti) surface enhancement. Such a combination leads to the formation of distinct topographical features covered by nanoparticles. The USL processing of cp-Ti in an aqueous solution of silver nitrate (AgNO3) induces the formation of micron-sized spikes surmounted by silver nanoparticles (AgNPs). The proposed approach combines the structuring and oxidation of the Ti surface and the synthesis of AgNPs in a one-step process, without the use of additional chemicals or a complex apparatus. Such a process is easy to implement, versatile and sustainable compared to alternative methodologies capable of obtaining comparable results. Antimicrobial surfaces on medical devices (e.g., surgical tools or implants), for which titanium is widely used, can be realized due to the simultaneous presence of AgNPs and micro/nano-structured surface topography. The processed surfaces were examined by means of a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and Raman spectroscopy. The surface morphology and the oxidation, quality and quantity of AgNPs were analyzed in relation to process parameters (laser scanning speed and AgNO3 concentration), as well as the effect of AgNPs on the Raman signal of Titanium oxide.

Transient absorption, femtosecond dynamics, vibrational coherence and molecular modelling of the photoisomerization of N-salicylidene-o-aminophenol in solution.

This article presents a study of the excited state relaxation dynamics of N-salicylidene-o-aminophenol (SOAP) in ethanol solution. Femtosecond transient absorption (TA) spectroscopy and theoretical calculations are used in combination to establish the mechanism of the excited state relaxation and type of molecular species involved in the accompanying phototransformations. TA spectra show that upon photoexcitation two SOAP tautomers (E-enol and Z-keto) interconvert by ESIPT. The molecule can subsequently isomerize to the E-keto form of SOAP. An intriguing observation is that the TA spectra of this compound in ethanol show modulations of the signal at the stimulated emission spectral range. It is found that these modulations are due to the coherence of the excited ensemble of molecules whose evolution over time represents a moving wave packet. After Fourier transform of the modulations, two characteristic frequencies are identified. These frequencies refer to the corresponding vibrational modes of the excited state and their nature is elucidated by DFT quantum chemical calculations. The obtained experimental and theoretical data reveal the nature of the vibronic coupling between the ground and excited state and the type of molecular vibrations involved in the molecular dynamics along the potential surface of the first excited state at the initial moment right after excitation. These vibrations characterize the starting point in the excited state dynamics of the molecule toward Z-E isomerization of the keto form of SOAP. This study provides a comprehensive picture of the dynamic processes taking place upon photoexcitation of the compound, which might enable control over the various relaxation channels.

Discovering of the L ligand impact on luminescence enhancement of Eu(Dibenzoylmethane)3.Lx complexes employing transient absorption spectroscopy.

The effect of luminescent enhancement under exchange of the auxiliary ligand in Europium(III) tris(1,3-diphenyl-1,3-propanedionato) monohydrate was investigated by steady-state and time-resolved transient absorption spectroscopy. The excited state relaxation dynamics of this complex was analysed through a comparison of the experimental data obtained for several model compounds, namely Eu(DBM)3·NH3, Eu(DBM)3.EDA, Eu(DBM)3.Phen, Al(DBM)3 and dibenzoylmethane (DBM) in various solutions and polymer matrices. The results show there is no linear relationship between enhancement of the emission quantum yield and the luminescent lifetime, which suggests that the auxiliary ligand reduces the rate of nonradiative relaxation of the lanthanide ion, but also affects the excited state energy transfer from ligand to metal ion. Transient absorption data shows a clear correlation between the efficiency of the energy transfer and the degree of triplet state population expressed by an amplification of the signal for its excited state absorption band on going from Eu(DBM)3·H2O to the Eu(DBM) = .L complex. The results show that this auxiliary ligand exchange acts as a "switch" turning the intersystem crossing on or off as a competitive pathway for excited state relaxation of the europium(III) complexes.

The Alzheimer's disease amyloid-ß peptide affects the size-dynamics of raft-mimicking Lo domains in GM1-containing lipid bilayers.

Alzheimer's disease (AD) is characterized by the overproduction of the amyloid-ß peptide (Aß) which forms fibrils under the influence of raft microdomains containing the ganglioside GM1. Raft-mimicking artificial liquid ordered (Lo) domains containing GM1 enhance amyloid-ß polymerization. Other experiments suggest that Aß binds preferably to the non-raft liquid disordered (Ld) phase rather than to the Lo phase in the presence of GM1. Here, the interaction of Aß(1-42) with GM1-containing biphasic Lo-Ld giant vesicles was investigated. Fluorescence colocalisation experiments confirm that Aß(1-42) binds preferentially to the Ld phase. The effect of Aß(1-42) on the Lo-Ld size dynamics was studied using photoinduced spinodal decomposition which mimics the nanodomain-microdomain raft coalescence. Aß affects the kinetics of the coarsening phase and the size of the resulting microdomains. The effect depends on which phase is in a majority: when the Lo microdomains are formed inside an Ld phase, their growth rate becomes slower and their final size smaller in the presence of Aß(1-42), whereas when the Ld microdomains are formed inside an Lo phase, the growth rate becomes faster and the final size larger. Fluorimetric measurements on large vesicles using the probe Laurdan indicate that Aß(1-42) binding respectively increases or decreases the packing of the Ld phase in the presence or absence of GM1. The differential effects of Aß on spinodal decomposition are accordingly interpreted as resulting from distinct effects of the peptide on the Lo-Ld line tension modulated by GM1. Such modulating effect of Aß on domain dynamics could be important for lipid rafts in signaling disorders in AD as well as in Aß fibrillation.

Origin of the metastable stability in flavylium multistate systems.

Metastable states regarding the network of chemical reactions involving flavylium compounds were investigated as well as the role they may play in models for optical memories capable of write-read-erase. A necessary requirement to achieve metastable states in flavylium systems is the existence of a high cis-trans isomerization barrier, as in 4'-hydroxyflavylium described through this paper. In an optical memory, the metastable state could be the signal to be detected upon the write step. In that case the autoerase is prevented by the metastable state. Conversely, the metastable state may be the initial state and prevents the auto and unwanted write step. The compound 4'-hydroxyflavylium offers the possibility of achieving both of these two situations, depending on the sequence of the pH stimuli prior to light absorption. In this work the pH dependent distribution of the flavylium species of the network in the presence of ß-cyclodextrin was calculated. Improvement of the performance of the photochromic system in the presence of ß-cyclodextrin was observed.

Emptying the ß-cyclodextrin cavity by light: photochemical removal of the trans-chalcone of 4',7-dihydroxyflavylium.

The interaction between the network of chemical reactions of the compound 4',7-dihydroxyflavylium and ß-cyclodextrin was studied by means of pH jumps, followed by UV-vis absorption, flash photolysis, stopped flow, and NMR. The trans-chalcone is the network species exhibiting the strongest interaction with the host. In moderately acidic medium, 95% of the trans-chalcone, 2.5 × 10(-5) M, in the presence of ß-cyclodextrin, 9 × 10(-3) M, is expected to fill the host cavity (association constant 2.2 × 10(3) M(-1)). In contrast, flavylium cation does not interact (association constant ≈ 0). Irradiation of the trans-chalcone in the presence of ß-cyclodextrin 9 mM leads to the flavylium cation appearance. Light is thus capable of removing the trans-chalcone from the ß-cyclodextrin, leaving the cavity empty. The system is reversible and trans-chalcone goes back to the initial state upon switching off the light due to the thermodynamic favorable conversion of flavylium cation to trans-chalcone in the presence of ß-cyclodextrin.

The luminescence response of Eu(III)-thenoyltrifluoroacetonate complexes upon preresonant excitation with femtosecond laser pulses.

The luminescence of thenoyltrifluoroacetonate (TTA) coordination complexes of trivalent europium ion (Eu(III)) in aqueous solutions and in solid-state polymeric films is probed upon single- and two-photon preresonant excitation with Ti:sapphire femtosecond laser. Particularly, diamine-liganded Eu(III)(TTA)(3) and poly(oxyethylene phosphate)tris(beta-diketonate)Eu(III) complexes are examined aiming their possible applications as luminescent labels for sensing and imaging of biological molecules. Even at a pre-resonance, the excitation of these compounds with high-intensity, broadband light of frequency-doubled Ti:sapphire femtosecond laser centered around 400 nm results in a luminescence response suitable for fluorometric applications.