Chromophoric System Research Articles

1,4-Benzodioxane Substituted Aza-BODIPY: Towards Photostable yet Efficient Triplet Photosensitizer.

We report herein the synthesis of aza-BODIPY substituted with 1,4-benzodioxane-6-yl substituents at 3,5 positions of the chromophore system. Both pyrrole rings of the aza-BODIPY in question were substituted with bromine atoms in order to induce highly desirable photophysical properties, such as highly populated excited triplet state (T1) and long excited triplet-state lifetime (τT) of 21 μs. The photosensitized oxygenation of a model compounds, viz. DPBF, points to a high singlet oxygen and/or other ROS formation quantum yield of 0.42. The photosensitizer studied exhibited an absorption band within the so-called "therapeutic window", with λabs 678 nm. As estimated by CV/DPV measurements the 1,4-benzodioxane-6-yl substituted aza-BODIPYs studied exhibited a multi-electron oxidations at a relatively low potentials (Eox), pointing to the very good electron-donating properties of these molecules. High photostability and thermal stability was observed for all compounds studied. The good singlet oxygen quantum yield measured combined with an exceptional photostability makes this aza-BODIPY a promising candidate for applications such as photocatalysis and photodynamic therapy (PDT).

Guest-Mediated Modulation of Photophysical Pathways in a Coronene Bisimide Cyclophane.

The properties and functions of chromophores utilized by nature are strongly affected by the environment formed by the protein structure in the cells surrounding them. This concept is transferred here to host-guest complexes with the encapsulated guests acting as an environmental stimulus. A new cyclophane host based on coronene bisimide is presented that can encapsulate a wide variety of planar guest molecules with binding constants up to (4.29 ± 0.32) × 1010 M-1 in chloroform. Depending on the properties of the chosen guest, the excited state deactivation of the coronene bisimide chromophore can be tuned by the formation of host-guest complexes toward fluorescence, exciplex formation, charge separation, room-temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). The photophysical processes were investigated by UV/vis absorption, emission, and femto- and nanosecond transient absorption spectroscopy. To enhance the TADF, two different strategies were used by employing suitable guests: the reduction of the singlet-triplet gap by exciplex formation and the external heavy atom effect. Altogether, by using supramolecular host-guest complexation, a versatile multimodal chromophore system is achieved with the coronene bisimide cyclophane.

Binaphthalene-Assisted Axial Chirality in Porphyrins: Toward Solid-State Circularly Polarized Luminescence from Self-Assembled Nanostructures.

Circularly polarized luminescence (CPL) is emerging as an effective tool to study the excited-state optical activity in molecules and their self-assembled nanostructures. Chiral porphyrins are a class of optically active molecules wherein the ground-state chirality has been extensively studied in recent times using circular dichroism (CD) spectroscopy. However, obtaining CPL from porphyrin nanostructures, which would have vast implications in biological applications, has remained an uphill task. In this work, we design and synthesize a pair of chiral porphyrin enantiomers functionalized by axially chiral binaphthalene units at the four meso-positions. The molecule undergoes self-assembly following an isodesmic polymerization model, leading to the formation of a spherical nanostructure possessing opposite chirality. Favorable thermodynamic parameters achieved through the controlled experimental conditions helped drive the self-assembly in the forward direction. The limitations imposed by a large nonradiative decay constant arising due to the aggregation-induced quenching could be overcome by fabricating self-standing polymeric films of the nanostructures. The films exhibited relatively high radiative decay and, more interestingly, good CPL activity with clear mirror image spectra for the nanostructures with opposite chirality. The work on CPL-active solid-state materials opens avenue for the design and synthesis of a variety of porphyrin-based chromophoric systems and their nanoaggregates that can find potential application in the field of chiral biosensing and bioimaging, security tags, and display devices.

Self-Assembly of Discrete Multi-Chromophoric Systems.

Self-assembly of chromophoric systems is a prerequisite to create well-ordered, processable nanomaterials with multiple functionalities. In the past two decades, the field of functional organic materials has primarily focused on systems featuring only one type of dye/π-conjugated unit. Consequently, many reports with mechanistic insights on the self-assembly of the dyes featuring different molecular packing have been reported. Subsequently, we have witnessed several attempts to organize the multi-chromophoric systems in solution and solid-state via different approaches using self-assembly as a tool. Incorporation of more than one dye is important in creating materials with tuneable optoelectronic properties. Consequently, self-assembly of more than one chromophoric systems have been investigated to some extent. This review aims to discuss the self-assembled materials derived from discrete π-conjugated systems comprising more than one dye units connected through covalent bonding (multi-chromophoric systems). Molecular design of various multi-chromophoric systems leading to the formation of crystals, liquid crystals and supramolecular polymers have been correlated with corresponding properties. We envisage that classification of self-assembled multi-chromophoric systems, with a note on tuneable optoelectronic properties, can provide a deeper understanding on the molecular design strategies, which is important in the fabrication of functional organic materials with optimum performances.

Synergistic Co-sensitization: Unlocking the potential of carbohydrazide chromophores and metal complexes for high-performance dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have emerged as a promising alternative to traditional silicon-based photovoltaic devices due to their low-cost fabrication and tunable optical properties. One effective strategy to improve the light-harvesting capabilities of DSSCs is co-sensitization, which involves combining multiple dyes with complementary absorption properties. In this study, we report the co-sensitization of carbohydrazide-based organic chromophores, namely MRK-1–2, with a benchmark metal-complex dye (black dye) to enhance the photovoltaic performance of DSSCs. The synthesis of MRK-1–2 sensitizers is described, and their photophysical properties are thoroughly analyzed. The absorption spectra of the co-sensitizers revealed distinct absorption bands associated with intramolecular charge transfer and localized aromatic π-π* transitions. Sensitization by MRK-1–2 resulted in photovoltaic efficiencies ranging between 5.02–5.88 %. The ternary co-sensitization system of carbohydrazide-based chromophores (MRK-1–2 + black dye) showed promising potential for enhancing the short-circuit current density (JSC) (20.32–21.45 mA/cm2), open-circuit voltage VOC (691–729 mV), and overall power conversion efficiency (PCE) (9.52–9.90 %). This significant improvement in photovoltaic performance is attributed to the complementary light-harvesting abilities of the co-sensitizers, leading to enhanced light absorption and efficient charge separation and injection processes. The superior performance, with a (PCE) of up to 9.90 %, can be attributed to complementary light absorption, efficient charge injection facilitated by the carboxylic acid moiety in MRK-2, and suppressed charge recombination within the co-sensitized system. The findings of this study will contribute to the advancement of DSSC technologies and bring us closer to sustainable and renewable energy solutions.

Controlling Chirogenic Effects in Porphyrin Based Supramolecular Systems: Theoretical Analysis Versus Experimental Observations.

Electronic circular dichroism (ECD) spectroscopy is a widely employed method for studying chiral analysis, requiring the presence of a chromophore close to a chiral centre. Porphyrinoids are found to be one of the best chromophoric systems serving for this purpose and enabling the application of ECD spectroscopy for chirality determination across diverse classes of organic compounds. Consequently, it is crucial to understand the induction mechanisms of ECD in the porphyrin-based complexes. The present study explores systematically the influence of secondary chromophores, bonded to an achiral zinc porphyrin or to chiral guest molecules, on the B-region of ECD spectra using the time-dependent density functional theory (TD-DFT) calculations. The study analyses the impact of change in both the conformation of achiral porphyrin (host) and change in position and conformation of chiral organic molecule (guest) on the B-band of ECD spectra (energy, intensity, sign of Cotton effect). Finally, conclusions made on model complexes are applied to published experimental data, contributing to a deeper understanding of various factors influencing ECD spectra in chiral systems. In addition, a computer program aimed to help rationalise ECD spectra by visualizing corresponding orbital energies, rotatory strengths, electric and magnetic transition moments, and angles between them, is presented.

Intramolecular charge transfer and the function of vibronic excitons in photosynthetic light harvesting.

A widely discussed explanation for the prevalence of pairs or clusters of closely spaced electronic chromophores in photosynthetic light-harvesting proteins is the presence of ultrafast and highly directional excitation energy transfer pathways mediated by vibronic excitons, the delocalized optical excitations derived from mixing of the electronic and vibrational states of the chromophores. We discuss herein the hypothesis that internal conversion processes between exciton states on the <100fs timescale are possible when the excitonic potential energy surfaces are controlled by the vibrational modes that induce charge transfer character in a strongly coupled system of chromophores. We discuss two examples, the peridinin-chlorophyll protein from marine dinoflagellates and the intact phycobilisome from cyanobacteria, in which the intramolecular charge-transfer (ICT) character arising from out-of-plane distortion of the conjugation of carotenoid or bilin chromophores also results in localization of the initially delocalized optical excitation on the vibrational timescale. Tuning of the ground state conformations of the chromophores to manipulate their ICT character provides a natural photoregulatory mechanism, which would control the overall quantum yield of excitation energy transfer by turning on and off the delocalized character of the optical excitations.

Ultrasensitive Solvatochirochromism of Single Benzene Chromophores.

Solvents influence the structure, aggregation and folding behaviors of solvatochromic compounds. Ultrasensitive solvent mediated chiroptical response is conducive to the fabrication of molecular platform for sensing and recognition, which however, remains great challenges in conceptual or applicable design. Here we report a cysteine-based single benzene chromophore system that shows ultrasensitivity to solvents. Compared to the ratiometrically responsive systems, the chiroptical activities could be triggered or inverted depending on the substituents of chiral entities with an ultralow solvent volume fraction (<1 vol %). One drop of dipolar solvents shall significantly induce the emergence or inversion of chiroptical signals in bulky phases. Based on the experimental and computational studies, the ultrasensitivity is contributed to the intimate interplay between solvents and chiral compounds that anchors the specific chiral conformation. It illustrates that structurally simple organic compounds without aggregation or folding behaviors possess pronounced solvatochiroptical properties, which sheds light on the next-generation of chiroptical sensors and switches.

Synthesis and spectral properties of mixed-ligand Zr and Hf phthalocyanine complexes with out-of-plane coordinated alkylamino-β-ketoenolate chromophores and decanoate

The development of novel materials based on modification of phthalocyanines is promising for various applications in science, medicine and technology. Here mixed-ligand Zr and Hf phthalocyanine complexes with out-of-plane coordinated alkylamino-β-ketoenolate chromophores and decanoate were synthesized for the first time. Complexes were obtained by one stage reaction of bis(decanoato)zirconium and hafnium phthalocyanines with alkylamino-β-ketoenols that resulted in replacement of only one decanoate ligand with the alkylamino-β-ketoenol. Therefore, mixed-ligand Zr and Hf complexes with two chromophore systems (phthalocyanine and alkylamino-β-ketoenol) were synthesized by using four different alkylamino-β-ketoenols, and their structural characterizations were carried out by using some spectroscopic methods: 1H NMR, UV–Vis, IR and MALDI TOF MS. In the UV–Vis spectra of the obtained complexes, the absorption bands characteristic for phthalocyanine system were observed along with additional absorption band of out-of-plane ligand (in the region 440–480 nm). The fluorescence spectra of investigated compounds are characterized by a maximum at about 690 nm, which corresponds to the emission of the phthalocyanine macrocycle, while the emission of alkylamino-β-ketoenol ligand is not observed.

SYNTHESIS AND PROPERTIES OF PERIPHERALLY AND NONPERIPHERALLY SUBSTITUTED ZINC AND MAGNESIUM PHTHALOCYANINES BASED ON 3/4-(4-BROMO-2-((4-METHOXYPHENYL)DIAZENYL)PHENOXY)PHTHALONITRILE

The work describes the optimization of the procedure for the synthesis of 4-bromo-2-methoxyphenyldiazenylphenol, which is used as a nucleophile in the presence of 3- and 4-nitrophthalonitriles. The resulting 3-(4-bromo-2-((4-methoxyphenyl)diazenyl)phenoxy)- and 4-(4-bromo-2-((4-methoxyphenyl)diazenyl)phenoxy)phthalonitriles were used for template condensation with magnesium or zinc acetate. Methods for isolating and purifying the synthesized compounds are described. The structure and composition were confirmed using IR, 1H NMR and electron spectroscopy. Peripheral functionalization of macrocycle by a conjugate azochromophore fragment gives molecules phthalocyanine with special optical properties. This class of phthalocyanines containing an additional chromophore system in their composition is attractive for potential use not only as pigments and dyes traditional for phthalocyanine compounds, but also as chemical sensors, dye-sensitized solar cells and photosensitizers for PDT. The resulting nitriles and phthalocyanine complexes dissolve in chloroforms, toluene, THF, and DMF. The influence of the substituent location on the spectral properties of the obtained metal complexes (Zn, Mg) in organic solvents has been studied. For non-peripherally substituted metal phthalocyanines, acid-base properties are studied. To observe and study the acid-base effect, spectrophotometric titration of the trifluoroacetic acid complex in toluene is used. It is shown that the magnesium complex is more basic than the zinc complex. In this work, the luminescent properties are also studied and the quantum yields of singlet oxygen formation for synthesized complexes in THF are determined. The influence of the substituent location on the quantum yield of fluorescence, as well as on the generation of singlet oxygen, is noted in the work.

Potential energy interpolation with target-customized weighting coordinates: application to excited-state dynamics of photoactive yellow protein chromophore in water.

Interpolation of potential energy surfaces (PESs) can provide a practical route to performing molecular dynamics simulations with a reliability matching a high-level quantum chemical calculation. An obstacle to its widespread use is perhaps the lack of general and optimal interpolation settings that can be applied in a black-box manner for any given molecular system. How to set up the weights for interpolation is one such task, and we still need to diversify the approaches in order to treat various systems. Here, we develop a new interpolation weighting scheme, which allows us to choose the weighting coordinates in a system-specific manner, by amplifying the contribution from specific internal coordinates. The new weighting scheme with an appropriate selection of coordinates is proved to be effective in reducing the interpolation error along the reaction pathway. As a demonstration, we consider the photoactive yellow protein chromophore system, as it constitutes itself as an interesting target that bears long-standing questions related to excited-state dynamics inside protein environments. We build its two-state diabatic interpolated PES with the new weighting scheme. We indeed see the utility of our scheme by conducting nonadiabatic molecular dynamics simulations with the required semi-global PES based on a limited number of data points.

Probes for noninvasive biological visualization and biosensing of cancer cells

The early detection of tumors and precancerous conditions is vital for cancer diagnosis. Advances in fluorescence microscopic techniques and materials synthesis processes have revolutionized biomarker detection and image-guided cancer surveillance. In particular, novel materials-based diagnostic tools and innovative therapies have facilitated a precise understanding of biological processes at the molecular level. This critical review presents an overview of bioimaging probes, including functionalized chromophoric systems, non-functionalized chromophoric systems, and nanoscale biosensors. Technical challenges and future directions related to these approaches are considered.

Vibronic dynamics from real-time time-dependent density-functional theory coupled to the Ehrenfest scheme: the example of p-coumaric acid

We investigate the vibronic dynamics of a modified version of the p-coumaric acid using real-time time-dependent density-functional theory coupled with the Ehrenfest scheme in the adiabatic local density approximation. Due to the issues of this functional to yield a reliable starting point for the evolution of the electron-nuclear system triggered by a pulse, we start off the simulations constraining the electronic occupation of the molecule in two excited states corresponding to a bright, delocalized transition, and a dark, charge-transfer-like excitation. By monitoring the kinetic energy spectral density, we analyze the nature of the nuclear motion over a time window of 300 fs. Anharmonic effects appear at low frequencies, below 500 cm^{-1}, and are particularly pronounced in the charge-transfer excitation. In this case, after about 200 fs, the molecular backbone becomes largely distorted and the initially constrained occupations evolve toward a different electronic configuration. On the other hand, the dynamics initialized from the delocalized bright excitation are electronically and structurally stable, and the resulting nuclear motion is markedly harmonic. Our results provide indications to decipher the vibronic dynamics of this chromophore and related systems in view of more elaborated simulations embedding the molecules in a realistic environment.

Absolute configuration reassignment of nectamazin A: Implications to related neolignans

The ability of nature to produce structurally complex molecules makes the determination of the absolute configuration of natural products a challenging task. Although extensive NMR analysis generally allows for the reliable assignment of relative configurations, the assignments of absolute stereochemistry are commonly performed by empirical comparisons of optical rotation (OR) and/or electronic circular dichroism (ECD) data obtained for related molecules. Such an approach, however, may lead to misassignments and consequent error propagations. Herein, we present the case of the bicyclo(3.2.1)octane neolignan named (+)-nectamazin A. This compound was first reported in 2009 from Nectandra amazonum Nees. (Lauraceae) and had its absolute configuration determined as 7R,8S,3′S,4′R,5′S by means of experimental ECD spectroscopy. Our chemical studies on Ocotea aciphylla (Lauraceae) led to the isolation of (+)-nectamazin A. The extensive analysis of OR, ECD, and vibrational CD data aided by quantum chemical calculations, however, indicated (+)-nectamazin A to have the 7S,8R,3′R,4′S,5′R absolute configuration, in conflict with the configuration reported in the literature. The cause of the original incorrect assignment of (+)-nectamazin A derives from the direct comparison of experimental OR and ECD data obtained for structurally related molecules with different chromophoric systems. As an alternative, VCD spectroscopy is presented as a more reliable and sensitive technique to stereochemical investigations of bicyclo(3.2.1)octane neolignans.

Pronounced Chirality Effect on the Ferroelectricity of Hydrogen-Bonded Supramolecular Assemblies of Ambipolar Chromophoric Systems

Pronounced Chirality Effect on the Ferroelectricity of Hydrogen-Bonded Supramolecular Assemblies of Ambipolar Chromophoric Systems

Protein-Mediated Carotenoid Delivery Suppresses the Photoinducible Oxidation of Lipofuscin in Retinal Pigment Epithelial Cells.

Lipofuscin of retinal pigment epithelium (RPE) cells is a complex heterogeneous system of chromophores which accumulates as granules during the cell's lifespan. Lipofuscin serves as a source of various cytotoxic effects linked with oxidative stress. Several age-related eye diseases such as macular degeneration of the retina, as well as some severe inherited eye pathologies, are accompanied by a significant increase in lipofuscin granule concentration. The accumulation of carotenoids in the RPE could provide an effective antioxidant protection against lipofuscin cytotoxic manifestations. Given the highly lipophilic nature of carotenoids, their targeted delivery to the vulnerable tissues can potentially be assisted by special proteins. In this study, we demonstrate how protein-mediated delivery of zeaxanthin using water-soluble Bombyx mori carotenoid-binding protein (BmCBP-ZEA) suppresses the photoinducible oxidative stress in RPE cells caused by irradiation of lipofuscin with intense white light. We implemented fluorescence lifetime imaging of the RPE cell culture ARPE-19 fed with lipofuscin granules and then irradiated by white light with and without the addition of BmCBP-ZEA. We demonstrate that after irradiation the mean fluorescence lifetime of lipofuscin significantly increases, while the presence of BmCBP-ZEA at 200 nM concentration suppresses the increase in the average lifetime of lipofuscin fluorescence, indicating an approx. 35% inhibition of the oxidative stress. This phenomenon serves as indirect yet important evidence of the efficiency of the protein-mediated carotenoid delivery into pigment epithelium cells.

Antibiotic-sterol interactions provide insight into the selectivity of natural aromatic analogues of amphotericin B and their photoisomers

Aromatic heptaene macrolides (AHMs) belong to the group of polyene macrolide antifungal antibiotics. Members of this group were the first to be used in the treatment of systemic fungal infections. Amphotericin B (AmB), a non-aromatic representative of heptaene macrolides, is of significant clinical importance in the treatment of internal mycoses. It includes the all-trans heptaene chromophore, whereas the native AHMs contain two cis-type (Z) double bonds within the chromophore system. Lately we have proven that it is possible to obtain AHMs’ stable derivatives in the form of all-trans (AmB-type) isomers by photochemical isomerization. Our further studies have shown that such alteration leads to the improvement of their selective toxicity in vitro. Computational experiments carried out so far were only an initial contribution in the investigation of the molecular basis of the mechanism of action of AHMs and did not provide explanation to observed differences in biological activity between the native (cis-trans) and isomeric (all-trans) AHMs. Herein, we presented the results of two-dimensional metadynamics studies upon AmB and its aromatic analogues (AHMs), regarding preferable binary antibiotic/sterol complexes orientation, as well as more detailed research on the behaviour of AHMs’ alkyl-aromatic side chain in cholesterol- or ergosterol-enriched lipid bilayers.

Quasiparticle Self-Consistent GW-Bethe-Salpeter Equation Calculations for Large Chromophoric Systems.

The GW-Bethe-Salpeter equation (BSE) method is promising for calculating the low-lying excitonic states of molecular systems. However, so far it has only been applied to rather small molecules and in the commonly implemented diagonal approximations to the electronic self-energy, it depends on a mean-field starting point. We describe here an implementation of the self-consistent and starting-point-independent quasiparticle self-consistent (qsGW)-BSE approach, which is suitable for calculations on large molecules. We herein show that eigenvalue-only self-consistency can lead to an unfaithful description of some excitonic states for chlorophyll dimers while the qsGW-BSE vertical excitation energies (VEEs) are in excellent agreement with spectroscopic experiments for chlorophyll monomers and dimers measured in the gas phase. Furthermore, VEEs from time-dependent density functional theory calculations tend to disagree with experimental values and using different range-separated hybrid (RSH) kernels does change the VEEs by up to 0.5 eV. We use the new qsGW-BSE implementation to calculate the lowest excitation energies of the six chromophores of the photosystem II (PSII) reaction center (RC) with nearly 2000 correlated electrons. Using more than 11,000 (6000) basis functions, the calculation could be completed in less than 5 (2) days on a single modern compute node. In agreement with previous TD-DFT calculations using RSH kernels on models that also do not include environmental effects, our qsGW-BSE calculations only yield states with local characters in the low-energy spectrum of the hexameric complex. Earlier works with RSH kernels have demonstrated that the protein environment facilitates the experimentally observed interchromophoric charge transfer. Therefore, future research will need to combine correlation effects beyond TD-DFT with an explicit treatment of environmental electrostatics.

Development of novel reversible thermometer from N‐isopropylacrylamide and dicyanodihydrofuran hydrazone probe

AbstractA simple‐structured polymeric colorimetric thermometer with selective colorimetric changes over a specific temperature range was developed. Thermo‐responsive poly(N‐isopropylacrylamide‐co‐Dicyanodihydrofuran hydrazone) [Poly(NIPAM‐co‐DCDHFH)] organogel imprinted with DCDHFH chromophoric probe was prepared via free radical polymerization. The DCDHFH chromophore bearing a vinyl group was prepared by azo‐coupling of DCDHF with a diazonium salt of 2‐amino‐5‐nitrophenol bearing a vinyl substituent. The poly(NIPAM‐co‐DCDHFH) consists of DCDHFH chromophore and N‐isopropylacrylamide (NIPAM) monomers. The chemical structure of DCDHFH probe was verified by 1H NMR and FT‐IR. The thermochromic property can be attributed to a heat‐stimulated polymer self‐assembly process controlling the inner hydrophobicity leading to charge delocalization on the molecular system of the DCDHFH chromophore. Poly(NIPAM‐co‐DCDHFH) functioned as a thermochromic detector displaying colorful shifts between yellow (422 nm) and blue (580 nm) with raising the temperature of the aqueous poly(NIPAM‐co‐DCDHFH). These color shifts were correlated to the temperature increment from 28 to 46°C owing to the phase changes of the poly(NIPAM‐co‐DCDHFH) copolymer in aqueous media. The morphological features of the organogel nanofibers were studied by transmission electron microscope (TEM) and scanning electron microscopy (SEM). The working mechanism accounting for the thermochromic performance of poly(NIPAM‐co‐DCDHFH) was explored. The cytotoxicity of the poly(NIPAM‐co‐DCDHFH) hydrogel was also evaluated. This is a significant study for a variety of potential applications, such as functional apparel and medicinal applications.

Synthesis and characterization of new azo saccharin derivatives dyes and their applications on different fibers

Azo is one of the most effective functional groups used to synthesis commonly colors and plays an important role in several applications of industrial dyes. More specifically, saccharin has been extensively used in the field of human food. In this paper, saccharin has been successfully implemented as a primary material for the preparation of new AZO dyes, which illustrates the novelty of this research. The chromophore system mainly consists of a group (-N = N-) associated with one or more different aromatic. The invented dyes are identified by spectroscopic that measured the stability of these dyes and evaluated the color of the polystyrene and nylon.6 on the fibers. The influence of the substitution groups on the stability of the color of newly prepared dyes is also investigated.