Interaction Of Chromophores Research Articles

Spiral-Locking Strategy for Efficient Narrowband Multiple Resonance Thermally Activated Delayed Fluorescence Emitters.

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials are applied in organic light-emitting diodes (OLEDs) due to their high efficiency and color purity. However, the inherent planar structure of MR emitters presents significant challenges, including concentration-induced emission quenching, spectral redshift and broadening. To address these issues, two orthorhombic asymmetric conformational materials, SBNO and SBNOS, have been developed. Both MR-TADF emitters incorporate a sterically hindered spiro-carbon bridge to minimize intermolecular chromophore interactions. Consequently, the spectra of the SBNOS-based devices exhibit only a 4 nm redshift and a 7nm broadening of the full-width at half maximum (FWHM) across a doping ratio range of 1-100 wt%. The steric effect produces pure green OLEDs with a CIE y of 0.69 and enhances performance, achieving a maximum external quantum efficiency (EQEmax) of up to 32.7%. The referent BNO without spiro skeleton suffers from serious spectral redshift and broadening as well as a lower device efficiency. This research demonstrates a promising approach to developing MR-TADF devices that resist redshift and broadening while maintaining high color purity and efficiency.

(Invited) Designing Photocatalytic Membrane to Direct Electron and Hole Transport

Surface interaction of chromophore or redox active molecule which dictate the efficiency of energy/electron transfer, plays an important role in realizing photocatalytic and optoelectronic applications. Metal halide perovskite nanocrystals are interesting in the sense that they can either transfer energy or selectively transfer electrons or holes to the adsorbed molecules.1,2 The presentation will focus on two specific scenarios of the flow of energy and electron processes in CsPbX3 (X= Br, I) nanocrystal-molecular hybrids. The energy transfer is probed through three moleculr acceptors – rhodamine B (RhB), rhodamine isothiocyanate (RhB-NCS), and rose Bengal (RoseB), which contain an increasing degree of heavy atom pendant groups. Electron and/or hole transfer from excited CsPbX3 nanocrystals to a molecular relay present near the interface offers another avenue to directly convert light energy into chemical energy. Such interfacial electron transfer of semiconductor nanocrystals has been widely explored in photocatalytic processes. A basic understanding of the fundamental differences between the two excited deactivation processes (energy and charge transfer) and ways to modulate them should enable design of more efficient light harvesting assemblies with semiconductor and molecular systems.

Stereo effects for efficient synthesis of orange-red multiple resonance emitters centered on a pyridine ring.

Despite theoretical difficulties, we herein demonstrate an effective strategy for the inaugural synthesis of an orange-red multiple resonance (MR) emitter centered on a pyridine ring via stereo effects. Compared to conventional benzene-centered materials, the pyridine moiety in the novel MR material acts as a co-acceptor. This results in a significant spectral redshift and a narrower spectrum, as well as an improved photoluminescence quantum yield (PLQY) due to the formation of intramolecular hydrogen bonds. As envisioned, the proof-of-concept emitter Py-Cz-BN exhibits bright orange-red emission peaking at 586 nm with a small full width at half maximum (FWHM) of 0.14 eV (40 nm), exceeding both the wavelength and FWHM achieved with benzene-centered BBCz-Y. Benefiting from high PLQYs (>92%) and suppressed chromophore interactions, the optimized organic light-emitting diodes achieved high maximum external quantum efficiencies of 25.3-29.6%, identical small FWHMs of 0.18 eV (54 nm), and long lifetimes over a wide range of dopant concentrations (1-15 wt%). The performance described above demonstrates the effectiveness of this molecular design and synthesis strategy in constructing high performance long-wavelength MR emitters.

Dimer Interface Destabilization of Photodissociative Dronpa Driven by Asymmetric Monomer Dynamics.

Photoswitchable Dronpa (psDronpa) is a unique member of the fluorescent protein family that can undergo reversible photoinduced switching between fluorescent and dark states and has recently been engineered into a dimer (pdDronpaV) that can dissociate and reassociate as part of its photoswitchable pathway. However, the specific details of the protein structure-function relationship of the dimer interface along with how the dimer proteins interact with each other upon chromophore isomerization are not yet clear. Classical molecular dynamics simulations were performed on psDronpa as monomers and dimers as well as the pdDronpaV dimer and with cis/trans chromophore structures. Analysis of the cis and trans isomers of the chromophore illustrated key differences between their interactions with residues in the protein in both the monomer and dimer forms of psDronpa. Examination of the psDronpa dimer showed nonidentical chromophore interactions between the domains, indicating domain directional favoring. Examination of the trans form of pdDronpaV illuminated the importance of hydrogen bonding between the monomeric domains in maintaining their association, as well as illustrating the motion of dissociation of the domains. This discovery offers important information for possible future mutations of pdDronpaV that might be made to accelerate dissociation.

Promoting multiexciton interactions in singlet fission and triplet fusion upconversion dendrimers

Singlet fission and triplet-triplet annihilation upconversion are two multiexciton processes intimately related to the dynamic interaction between one high-lying energy singlet and two low-lying energy triplet excitons. Here, we introduce a series of dendritic macromolecules that serve as platform to study the effect of interchromophore interactions on the dynamics of multiexciton generation and decay as a function of dendrimer generation. The dendrimers (generations 1–4) consist of trimethylolpropane core and 2,2-bis(methylol)propionic acid (bis-MPA) dendrons that provide exponential growth of the branches, leading to a corona decorated with pentacenes for SF or anthracenes for TTA-UC. The findings reveal a trend where a few highly ordered sites emerge as the dendrimer generation grows, dominating the multiexciton dynamics, as deduced from optical spectra, and transient absorption spectroscopy. While the dendritic structures enhance TTA-UC at low annihilator concentrations in the largest dendrimers, the paired chromophore interactions induce a broadened and red-shifted excimer emission. In SF dendrimers of higher generations, the triplet dynamics become increasingly dominated by pairwise sites exhibiting strong coupling (Type II), which can be readily distinguished from sites with weaker coupling (Type I) by their spectral dynamics and decay kinetics.

Effect of metal coordination in modulating the binding interaction of an arylimidazole-derived organic chromophore with lipase

The development of reliable fluorescent probes for selectively and sensitively detecting particular analytes in biological systems, which can acid in better understanding the roles in their native contexts. Metal-complex dyes represent a family of structures that have attracted extensive attention in broad applications owing to their unique advantages, such as stable photophysical and electromagnetic properties, as well as good biocompatibility. In this work, we synthesized and characterized a fluorescent probe called THS, which untilizes diphenylamine (DPA) as a metal chelator and an arylimidazole-derived organic chromophore as a fluorescence signal reporter. A comparative assessment of responsive THS and its Zn(II) complex to lipase, an enzyme that breaks down fats, has been performed. We have evidenced the complexation of Zn(II) improved the sensing stability, signal-to-noise ratio (SNR), and selectivity of THS toward lipase. Importantly, we successfully applied the THS-Zn(II) complex to detect lipase in serum samples. This work provides an approach for fabricating simple and effective metal complex-based fluorescence probes and a promising application for the detection of biological analytes.

Aggregation‐induced narrowband isomeric fluorophores for ultraviolet nondoped OLEDs by engineering multiple nonbonding interactions

AbstractTraditional donor‐acceptor type organic luminescent materials usually suffer from unfavorable spectral broadening and fluorescence quenching problems arising from strong inter/intra‐chromophore interactions in aggregation state. Here, two ultraviolet carbazole‐pyrimidine isomers (named o‐DCz‐Pm and m‐DCz‐Pm) with novel aggregation‐induced narrowband phenomenon are constructed and systematic investigated by experiments and theoretical simulations. Benefitting from strengthened steric hindrance and multiple noncovalent interactions, the nonradiative decay, vibrational motion, and structural relaxation of singlet state can be effectively suppressed in aggregation state. Consequently, the electroluminescence peak of 397 nm, full width at half maximum of 21 nm and external quantum efficiency of 3.4% are achieved simultaneously in nondoped o‐DCz‐Pm‐based device. This work paves an avenue toward the development of high‐performance narrowband nondoped ultraviolet materials and organic light‐emitting diodes.

Benchmarking Aspects of Ab Initio Fragment Models for Accurate Excimer Potential Energy Surfaces.

While Coupled-Cluster methods have been proven to provide an accurate description of excited electronic states, the scaling of the computational costs with the system size limits the degree for which these methods can be applied. In this work different aspects of fragment-based approaches are studied on noncovalently bound molecular complexes with interacting chromophores of the fragments, such as π-stacked nucleobases. The interaction of the fragments is considered at two distinct steps. First, the states localized on the fragments are described in the presence of the other fragment(s); for this we test two approaches. One method is founded on QM/MM principles, only including the electrostatic interaction between the fragments in the electronic structure calculation with Pauli repulsion and dispersion effects added separately. The other model, a Projection-based Embedding (PbE) using the Huzinaga equation, includes both electrostatic and Pauli repulsion and only needs to be augmented by dispersion interactions. In both schemes the extended Effective Fragment Potential (EFP2) method of Gordon et al. was found to provide an adequate correction for the missing terms. In the second step, the interaction of the localized chromophores is modeled for a proper description of the excitonic coupling. Here the inclusion of purely electrostatic contributions appears to be sufficient: it is found that the Coulomb part of the coupling provides accurate splitting of the energies of interacting chromophores that are separated by more than 4 Å.

Action spectrum for reorientations in bacteriorhodopsin of purple membrane in suspension

In the present study, the dependency of purple membrane (PM) dielectric responses on the wavelength of light in the range 380–750 nm has showed meaningful changes about the rotation of PM in suspension and about the rotation of bacteriorhodopsin (bR) trimer inside PM, as well. The action spectrum of PM random walk substantiates the existence of two states of bR. One of them (blue edge-state) lies at the blue edge and the other (red edge-state) at the red edge of the visible absorption of bR. The results might bear on correlation of these bands to some bR photocycle intermediates or bR photoproducts. The results implicate the protein–chromophore interactions that eventually underlie protein–lipid interactions. Disrupting the protein–lipid contact during the illumination with light of wavelength in ranges of (410–470 nm) and (610–720 nm) has resulted in emergence of distinct dielectric dispersion at 0.06–0.08 MHz which is comparable to the size of bR trimer or monomer.The work reports on the chromatic adaptation of bR in view of the dielectric spectral parameters of PM. It aimed to explore a correlation seemingly found between the light wavelength and the relaxations of bR trimer inside PM. Changes in rotational diffusion of bR trimer upon blue and red light illumination can influence the three dimensional data storage based on bR, which may implicate bR in bioelectronics.

It's a two-way street: Photoswitching and reversible changes of the protein matrix in photoswitchable fluorescent proteins and bacteriophytochromes.

Chromophore-bearing proteins that are (reversibly) altered after light illumination are major functional components of nature. They gained considerable attention in the last decades since the dynamic interactions of the chromophore and protein matrix can be used to control downstream effects altering the functionality of proteins, cells, or complete organisms with light (optogenetics). Additionally, the photophysical effects can be employed to add capabilities to optical imaging. For example, light can be used to reversibly switch the signal on or off (e.g., fluorescence). In this article, we review chromophore and protein matrix interactions, focusing on photoswitching fluorescent proteins of the GFP family (RSFPs) and natively photoswitching bacteriophytochromes (BphPs). This review aims to provide an in-depth understanding of the dynamic interplay between photoswitching photophysics and the protein matrix and a thorough discussion on how this connection has been harnessed for the development of optogenetic and imaging tools.

Metal–Organic Dimerization of Dissymmetrical Ligands toward Customized Through-Space Chromophore Interactions

The pursue of good photophysical properties for organic optoelectronic materials requires a well understanding of through-space chromophore interactions, which further requires a well control over the spatial arrangement of chromophores. However, it remains a challenge to precisely customize the positioning of chromophores in their aggregating form such as in a simplest cofacially stacked dimer. Herein, this work provides a customizable molecular design based on dissymmetrical ligands that can enable a precise control over chromophore interactions through the formation of metal–organic dimers. Anti-paralleled stacking of two dissymmetrical ligands in the metal–organic dimers results in a lateral shifting of chromophore stacking, whose spacing is determined and adjusted by the degree of ligand dissymmetry. Three metal–organic dimers with a variation in chromophore spacing exhibited unique photophysical properties in both solution and solid states and displayed high-efficient luminescence against quenching in their aggregating states. This strategy thereby offers a universally applicable way to construct chromophore dimers with fixed cofacial spacing and determinate through-space interactions.

Systematic Study on Nonlinear Optical Chromophores with Improved Electro-Optic Activity by Introducing 3,5-Bis(trifluoromethyl)benzene Derivative Isolation Groups into the Bridge

A series of novel chromophores A, B, C, and D, based on the julolidinyl donor and the tricyanofuran (TCF) and CF3-tricyanofuran (CF3-Ph-TCF) acceptors, have been synthesized and systematically investigated. The 3,5-bis(trifluoromethyl)benzene derivative isolation group was introduced into the bridge in the chromophores C and D. These nonlinear optical chromophores showed good thermal stability, and their decomposition temperatures were all above 220 °C. Density functional theory (DFT) was used to calculate the energy gaps and first-order hyperpolarizability (β). The macroscopic electro-optic (EO) activity was measured using a simple reflection method. The highest EO coefficient of poled films containing 35 wt% of chromophore D doped in amorphous polycarbonate afforded values of 54 pm/V at 1310 nm. The results indicate that the 3,5-bis(trifluoromethyl)benzene isolation group can suppress the dipole-dipole interaction of chromophores. The moderate r33 value, good thermal stability, and good yield of chromophores suggest their potential use in the nonlinear optical area.

TD‐DFT modeling of electronic spectra of biliverdins in different environments

AbstractNon covalent biliproteins are found in a growing number of living organisms and even in viruses, such as SARS‐CoV‐2. Unlike the well described covalent biliproteins, such as the phytochromes, they present a vast structural and functional diversity, and often with limited experimental information. A very important tool (and sometimes the only one available) to study these systems is the UV–Vis spectrum, which is modulated both by conformational changes of the biliverdin chromophore and specific interactions with the apoprotein. In this work we present a theoretical study of the microscopic determinants of the UV–Vis spectrum of these compounds through the use of hybrid QM(TD‐DFT)/MM techniques and molecular dynamics simulations. Comparing our results with existing experimental data, we prove that it is possible to predict spectroscopic properties, such as relative position and intensity ratio of main bands, with affordable methods, and to provide a microscopic explanation of them. This systematic information can be very useful for the study of described biliproteins or for those yet unknown.

Protein\u2013chromophore interactions controlling photoisomerization in red/green cyanobacteriochromes

Photoreceptors in the phytochrome superfamily use 15,16-photoisomerization of a linear tetrapyrrole (bilin) chromophore to photoconvert between two states with distinct spectral and biochemical properties. Canonical phytochromes include master regulators of plant growth and development in which light signals trigger interconversion between a red-absorbing 15Z dark-adapted state and a metastable, far-red-absorbing 15E photoproduct state. Distantly related cyanobacteriochromes (CBCRs) carry out a diverse range of photoregulatory functions in cyanobacteria and exhibit considerable spectral diversity. One widespread CBCR subfamily typically exhibits a red-absorbing 15Z dark-adapted state similar to that of phytochrome that gives rise to a distinct green-absorbing 15E photoproduct. This red/green CBCR subfamily also includes red-inactive examples that fail to undergo photoconversion, providing an opportunity to study protein–chromophore interactions that either promote photoisomerization or block it. In this work, we identified a conserved lineage of red-inactive CBCRs. This enabled us to identify three substitutions sufficient to block photoisomerization in photoactive red/green CBCRs. The resulting red-inactive variants faithfully replicated the fluorescence and circular dichroism properties of naturally occurring examples. Converse substitutions restored photoconversion in naturally red-inactive CBCRs. This work thus identifies protein–chromophore interactions that control the fate of the excited-state population in red/green cyanobacteriochromes.

Supramolecular self-assembled nonlinear optical molecular glasses with enhanced electro-optic activity and alignment stability

We have developed a series of self-assembled electro-optic dendrimers. Four dendrimers H1, H2, H3 and HLD 1 were synthesized by introducing aromatic dendron (HD), trifluorobenzyl dendron (TFD), pentafluorophenyl dendron (PFD) and anthracene ring (AH) into the donor and bridge parts of chromophores. In addition, three-arm trifluorobenzyl dendron containing multichromophore H4 was also synthesis and evaluated. These molecules were supramolecular self-assembled through the π-π interaction of HD-PFD/HD-AH/TFD-TFD to minimize the dipole-dipole interaction of chromophores and maximize the accentric order of chromophores under high load densities. High r33 (328, 317 and 279 p.m./V) have been achieved for neat films containing chromophores 1:1 H1: H3, 1:2 H3: HLD 1 and H4, respectively. Moreover, the long-term orientation stability of chromophores were also improved. After 1000 h at room temperature, the initial electro-optic coefficient of the electrode self-assembled film still remains above 95%.

Tunable Excimer Circularly Polarized Luminescence in Isohexide Derivatives from Renewable Resources.

Organic compounds showing circularly polarized luminescence (CPL) are at the forefront of novel applications and technologies. Here we show the synthesis and chiroptical properties of pyrene and perylene derivatives of inexpensive chiral scaffolds: isomannide and isosorbide. Low‐intensity ECD spectra were obtained, suggesting the absence of chromophore interaction in the ground state, except in the case of isomannide bis‐perylenecarboxylate, whose ECD spectrum showed a positive exciton couplet. All isomannide derivatives, with the only exception of the one containing a pyrenecarboxylate and a perylenecarboxylate, exhibited excimer CPL spectra, whereas isosorbide derivatives did not show any CPL. Isomannide derivatives bearing two pyrenecarboxylate or two pyrenylacetate groups showed positive CPL emission with dissymmetry factors up to 10−2, which depends on the conformational freedom of the appended units. The CPL sign, Stokes shift and order of magnitude of dissymmetry factor were reproduced by excited‐state calculations on a representative compound. Interestingly, the mixed derivative containing pyrenic units with different spacing from the isomannide scaffold showed an oppositely signed excimer band with respect to the homo‐substituted derivatives.

Multi-Step Synthesis, Photophysical and Physicochemical Properties of Novel Push- π -Pull AADC Chromophores

Coumarin based heterocyclic chalcone (E)-3-(3-(1-allyl-1H-indol-3-yl) acryloyl)-7-(diethylamino)-2H-chromen-2-one (AADC) was synthesized by the multi-steps synthesis. The structure of the AADC was established by the spectroscopic technics and purity of the AADC was confirmed by the elemental analysis. Physicochemical parameters of the AADC in ten different solvents such as molar absorption coefficient, transition dipole moments, stokes shift, oscillator strength and fluorescence quantum yield were calculated. Interaction of the AADC chromophore with cationic CATB and anionic SDS surfactants were determined by using the fluorescence spectroscopy techniques. It was observed that band fluorescence spectrum intensity increases with increasing the concentration of the surfactants. This suggests that strong interaction occurs between AADC with surfactants and this interaction arise from electrostatic forces. So, AADC chromophore could be used as analysis to define the CMC of the surfactants.

Crystallographic Studies of Rhodopsins: Structure and Dynamics.

Crystal structures have provided detailed insight in the architecture of rhodopsin photoreceptors. Of particular interest are the protein-chromophore interactions that govern the light-induced retinal isomerization and ultimately induce the large structural changes important for the various biological functions of the family. The reaction intermediates occurring along the rhodopsin photocycle have vastly differing lifetimes, from hundreds of femtoseconds to milliseconds. Detailed insight at high spatial and temporal resolution can be obtained by time-resolved crystallography using pump-probe approaches at X-ray free-electron lasers. Alternatively, cryotrapping approaches can be used. Both the approaches are described, including illumination and sample delivery. The importance of appropriate photoexcitation avoiding multiphoton absorption is stressed.

Multi-step Synthesis, Characterization and Photophysical Investigation of Novel Biologically Active Heterocyclic Chalcone (AECO).

Novel alkylated heterocyclic chalcone (E)-1-(2-(allyloxy)phenyl)-3-(9-ethyl-9H-carbazol-3-yl)prop-2-en-1-one (AECO) with extended π-bond was prepared by the multi-steps synthesis. The structure of the AECO was established by the spectroscopic technics and purity of the compound was confirmed by the elemental analysis. Physicochemical parameters of the AECO such as molar absorption coefficient, transition dipole moments, stokes shift, oscillator strength and fluorescence quantum yield were calculated in ten various solvents on the basis of polarity of the solvents to see the effect of the solvent with AECO. Interaction of the AECO chromophore with cationic CTAB and anionic SDS surfactants were determined by using the fluorescence spectroscopy techniques. The intensity of the florescence spectrum increase with increasing the concentrations of surfactants. This suggests that strong interaction occurs between AECO with surfactants and this interaction arise from electrostatic forces. So, AECO chromophore could be used as analysis to define the Critical Micelle Concentration (CMC) of the surfactants. In addition the in-vitro antibacterial active of novel heterocyclic chalcone agents four bacteria's strain were evaluated and result showed AECO is beater antibacterial agent against Gram-Negative Bacteria (E. coli and S. flexneri) as compare to the Gram Negative Bacteria with respected to the standard drug Tetracycline.

Atomically resolved single-molecule triplet quenching.

The nonequilibrium triplet state of molecules plays an important role in photocatalysis, organic photovoltaics, and photodynamic therapy. We report the direct measurement of the triplet lifetime of an individual pentacene molecule on an insulating surface with atomic resolution by introducing an electronic pump-probe method in atomic force microscopy. Strong quenching of the triplet lifetime is observed if oxygen molecules are coadsorbed in close proximity. By means of single-molecule manipulation techniques, different arrangements with oxygen molecules were created and characterized with atomic precision, allowing for the direct correlation of molecular arrangements with the lifetime of the quenched triplet. Such electrical addressing of long-lived triplets of single molecules, combined with atomic-scale manipulation, offers previously unexplored routes to control and study local spin-spin interactions.