Efficient Chromophores Research Articles

Efficient Chromophore Design with PICT Coupled TICT: Computational Studies on Hyperpolarizabilities of Pyridinium Benzimidazolates

AbstractPreviously synthesized six selected Pyridinium‐Benzimidazolate based zwitterions were investigated in this contribution. Of the selected molecules, two are TICT, two are PICT (twisted and planar intramolecular charge transfer types respectively), and the other two are PICT+TICT types. Generally, TICT vs PICT is the most widely used strategy for chromophore design by earlier researchers. In this work, impacts of PICT+TICT effects (two effects combined in one chromophore), through p‐phenylene bridges, on various fundamental properties like, dipole moments, polarizabilities, hyperpolarizabilities, adiabatic excitations were analyzed. Nonlinear optical (NLO) responses of the six molecules indicate that PICT more efficient than TICT (6‐11‐times enhanced β), and PICT+TICT more efficient than both PICT (~4 times enhanced β) and TICT (20–40 times enhanced β). Current work also shows the role of aromatic p‐phenylene bridge as an efficient communicator between the donor and acceptor, in enhancing the NLO and other response properties. This work suggests that inducing bridge aromatic control to a TICT chromophore (making it to exhibit an amalgamation of PICT and TICT effects) is an effective and efficient strategy in the designing of molecular nonlinear optical chromophores, over either PICT or TICT only.

Defect‐Rich Graphdiyne Quantum Dots as Efficient Electron‐Donors for Hydrogen Generation

AbstractDownsizing the graphdiyne (GDY) network to shape quantum dots (QDs) will provide attractive optical and electronic properties associated with quantum confinement and edge effects. Here, it is demonstrated that quantum confinement and defect introduction allow using GDY in donor–acceptor photocatalytic systems for solar‐to‐hydrogen conversion. The defect‐rich GDY QDs (GDYO‐QDs) exhibit a blue‐to‐green excitation‐dependent photoluminescence behavior, demonstrating their ability to harvest light over a wide energy range. Quantum‐chemical calculations evidenced an increase in the electronic bandgap of GDY upon quantum confinement and defect introduction without the appearance of trap states that can hamper charge transport properties. Such a unique optical behavior of QDs is used in photocatalytic hydrogen generation through the hybridization with TiO2 as a model photocatalyst. Theoretical and experimental results demonstrate that the donor−acceptor system tremendously boosts the photocatalytic performance, reaching 5288 µmol g−1 after 4 h of illumination at a constant rate of 1322 µmol g−1 h−1, using a low volume of a sacrificial electron donor (6% v/v). The QDs act as efficient chromophores harvesting UV and visible light while injecting electrons into the TiO2. This work opens a new area of using GDYO‐QDs as an efficient chromophore in developing donor–acceptor systems for photocatalysis and future photovoltaic devices.

Not fully twisted, not fully planar, but intermediate torsions for ideal chromophore design: A computational study on p‐phenylene bridged pyridinium phenolate betaines

AbstractThis contribution reports extensive studies on structure–property correlations of two isoelectronic betaine metamers (positional isomers). These zwitterions differ from each other with respect to bonding modes of pyridinium acceptors (Reichardt's mode: through N‐atom versus Brooker's mode: through C‐atom) with the p‐phenylene bridged phenolate donors. Various quantum chemical methodologies are used in this investigation, with time‐dependent (TD) and coupled perturbed (CPHF) theories for computations of many molecular response properties. Analysis of first hyperpolarizabilities (β) indicates that Reichardt's metamer (ωB97xD: β = 349.5 × 10−30 esu) is more efficient chromophore (~5‐fold enhanced) than Brooker's metamer (ωB97xD: β = 69.4 × 10−30 esu). The gyratory abilities of the bridge junctions resulted in a cohort of metastable conformations, in the rotational potential energy surfaces (PES) of the two metamers. Moreover, rotational PES establishes that intermediary torsions are suitable for optimal chromophore design strategies (Reichardt's metamer: β = 956.5 × 10−30 esu, and Brooker's metamer: β = 1104.7 × 10−30 esu), Thus suitable conformational manipulations, can be used to obtain more efficient zwitterionic molecular chromophores. Compared unbridged prototype molecules, p‐phenylene bridged zwitterions showed ~6–9 times enhanced values of β. In addition, important aspects of suitable chromophore design strategies are suggested.

Better performances of benzene‐based over thiophene‐based aromatic anionic donors: Computational studies on metameric conformational selectivity and hyperpolarizability of organic inner salts

AbstractEarlier experimental works report the synthesis of zwitterions with anionic p‐dicyanomethanide (coupled to benzene and thiophene) donors. In this report, four such zwitterions (two metameric pairs) are investigated using HF, B3LYP, CAM‐B3LYP, HSE06, and ωB97xD methodologies. This work is focused on (1) metameric (Reichardt's and Brooker's) induced conformational selectivity (twisted vs. planar) and (2) efficiency assessments of benzene‐ versus thiophene‐based anionic donors. These effects were found to have significant influences on many tensorial and nontensorial properties. For Reichardt's type, large twisting was observed for the benzene case and lower twisting for the thiophene case. Enhanced first hyperpolarizability were observed for Reichardt's type (257.2 × 10−30 esu) than Brooker's type (67.2 × 10−30 esu), thus indicating the former type to be more efficient (approximately fourfold enhancement) chromophore (approximately seven‐time enhancement for thiophene‐based systems). Similarly, between the benzene versus thiophene cases, enhanced hyperpolarizabilities were observed for the former (257.2 × 10−30 esu) than the latter type (112.0 × 10−30 esu), indicating the benzene type as more efficient (more than twofold enhancement) donor (approximately four‐time enhancement for Brooker's types). The structure–property manipulations strategies investigated here can be used as valuable tools in the designing of efficient functional molecular materials for various fundamental applications.

Enhanced optoelectronic properties with aromatic bridges: A computational study on N‐methyl pyridinium and phenolate types of push‐pull zwitterions

AbstractA series of zwitterions with varying bridges, connecting N‐methyl pyridinium acceptor, with phenolate donor, are investigated using various methodologies like, HF, B3LYP, CAM‐B3LYP and ωB97xD. In this systematic study effects of various mono aromatic rings as bridges, on the response properties like, the dipole moments (μ), polarizabilities (α), hyperpolarizabilities (β) and adiabatic absorptions were analyzed using CPHF and TDDFT (or TDHF) theories. Compared to many traditional bridges, as well as without a bridge, enhanced nonlinear optical (2ND order NLO) responses were observed for these aromatically bridged zwitterions (with benzene ring as bridge ~5.3 times and ~7.9 times enhanced hyperpolarizabilities were observed compared to either the ethylene bridge or without any bridge cases, respectively). Also, many significant differences and large enhancements in response properties were observed compared to our earlier works on non‐zwitterionic system (~4.3 times enhanced hyperpolarizability—benzene as bridge case). For some bridge cases, 10‐ to 15‐fold enhanced hyperpolarizabilities were observed compared to without any bridge case. This work reports a class of non‐TICT chromophores, promoting bridge aromaticity control on structure–property correlation, as a suitable and efficient chromophore design strategy to create a wide range of function molecular chromophores. Also, unidirectional natures of response properties and large dipole moments can make these zwitterions suitable 1D‐molecular materials for various contemporary technological applications, as poled polymer‐based materials.

Metameric influences on conformational selectivity for zwitterionic pyridinium cyclopentadienide and its aza analogues. Quantum mechanical studies on linear and nonlinear optoelectronic properties

AbstractThis contribution reports the structure–property correlations for few already synthesized bi‐aryl types of zwitterionic molecules. Quantum mechanical methodologies like, HF, MP2, B3LYP, CAM‐B3LYP, LC‐ωPBE, M06‐2X, and ωB97xD were used to investigate the optoelectronic properties of some interesting metameric pairs, where the molecules were bonded either through Reichardt's or Brooker's modes. Different bonding modes and inter‐ring attractive forces are assigned to investigate three distinct cases (i) metameric enforcements & preferential resonance stabilizations, (ii) inter‐ring hydrogen bonded stabilizations through hetero‐atoms in the ring, and (iii) an amalgamation of these two forces. Computations indicate unusual structural preferences (planar vs. twisted) by the metameric pairs, and thus direct reflections of these behaviors on some of the important tensorial properties like, dipole moments, polarizabilities, hyperpolarizabilities, and so forth were observed. The metameric manipulation on structure–property correlations shown by these molecules can be utilized as useful strategies for efficient chromophore design, not only in the field of nonlinear optics, but also in other areas of research connecting to advanced functional materials for technological applications.

Metameric Brooker's versus Reichardt's zwitterions: Conformational metamorphosis on optoelectronic properties, using coupled‐perturbed and finite field theories

AbstractThis contribution reports influences of unusual conformational metamorphosis shown by Reichardt's and Brooker's metameric zwitterions by an earlier work, on various intrinsic electronic and optoelectronic properties. Detailed quantum mechanical investigations were carried out using HF, B3LYP, CAM‐B3LYP, and ωB97xD methodologies. Observations suggest that whereas certain properties were directly and strongly influenced by the conformation preferences (twisted vs. planar), others were not strongly inclined to such conformational transformations. Interestingly, even with inherent conformational differences, observed properties were found to have only one major contributing component in each molecule and can be beneficial in one dimensional (1D) or pseudo‐1D chromophore design strategies. Both coupled perturbed (CP) and finite field (FF) theories were used to compute dipole moments, polarizabilities, and hyperpolarizabilities, and so on, and excellent agreements (or exact matching results) were observed between the two theories. Reichardt's metamer was found to be more efficient in many aspects than Brooker's metamer. The direct and strong influences of metameric manipulations on structure–property correlations shown in this work can be adopted as a useful strategy for efficient chromophore design. Such a strategy is useful in the field of nonlinear optics, and may also find applications in various other areas of material sciences.

The binding of secondary chromophore for thermally stable rhodopsin makes more stable with temperature

AbstractMicrobial rhodopsin is a transmembrane protein that functions with a chromophore and is regulated by light. In nature, regulation through the retinal chromophore plays an important role in physiological phenomena. However, living organisms in soil, sea, and freshwater synthesize carotenoids preferentially over retinal in the biosynthetic pathway. Evolution has extended the energy conversion photosystem with additional pigments that act as antennae. Previously, Gloeobacter rhodopsin and xanthorhodopsin have been reported to form secondary chromophores with carotenoids. In this study, we report that a thermophilic rhodopsin (TR) and Tara76 rhodopsin, the latter of which is classified as a blue light‐absorbing proteorhodopsin, can form secondary chromophores with canthaxanthin (CAN). Tara76 rhodopsin and TR were found to exhibit high thermal stabilities and photophysical properties following their interaction with CAN. Isothermal titration calorimetry analysis, spectral shift measurements, and exciton analysis were used to examine the interactions of these rhodopsins with CAN. It was found that these interactions increased the stability toward temperature and pH through highly efficient chromophore formation, in addition to rapidly recruiting the retinal at a rate approximately twice as high as that obtained in the absence of CAN.

The danger of dichloromethane in the synthesis and application of imidazole-based dyes

In this paper, a lophine-based phenol compound has been prepared and identified as an efficient chromophore for the determination of hydrogen peroxide (H2O2) with enzymatic method. A dry chemistry analytic agent was also prepared involving this compound, showing good accuracy in the determination of uric acid. However, a commonly used solvent dichloromethane (DCM) could react with this imidazole derivative when the reaction mixture was irradiated under UV (365 nm). We explored the possible mechanism and identified several by-products caused by the acidity and ultraviolet oxidation of DCM. Caution should be taken in the synthesis and application of such imidazole-based dyes in DCM, especially when phenol group was introduced to the imidazole moiety.

Circularly Permuted Far-Red Fluorescent Proteins.

The color palette of genetically encoded fluorescent protein indicators (GEFPIs) has expanded rapidly in recent years. GEFPIs with excitation and emission within the “optical window” above 600 nm are expected to be superior in many aspects, such as enhanced tissue penetration, reduced autofluorescence and scattering, and lower phototoxicity. Circular permutation of fluorescent proteins (FPs) is often the first step in the process of developing single-FP-based GEFPIs. This study explored the tolerance of two far-red FPs, mMaroon1 and mCarmine, towards circular permutation. Several initial constructs were built according to previously reported circularly permuted topologies for other FP analogs. Mutagenesis was then performed on these constructs and screened for fluorescent variants. As a result, five circularly permuted far-red FPs (cpFrFPs) with excitation and emission maxima longer than 600 nm were identified. Some displayed appreciable brightness and efficient chromophore maturation. These cpFrFPs variants could be intriguing starting points to further engineer far-red GEFPIs for in vivo tissue imaging.

Promoting photocatalytic CO2 reduction with a molecular copper purpurin chromophore

CO2 reduction through artificial photosynthesis represents a prominent strategy toward the conversion of solar energy into fuels or useful chemical feedstocks. In such configuration, designing highly efficient chromophores comprising earth-abundant elements is essential for both light harvesting and electron transfer. Herein, we report that a copper purpurin complex bearing an additional redox-active center in natural organic chromophores is capable to shift the reduction potential 540 mV more negative than its organic dye component. When this copper photosensitizer is employed with an iron porphyrin as the catalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as the sacrificial reductant, the system achieves over 16100 turnover number of CO from CO2 with a 95% selectivity (CO vs H2) under visible-light irradiation, which is among the highest reported for a homogeneous noble metal-free system. This work may open up an effective approach for the rational design of highly efficient chromophores in artificial photosynthesis.

Dual-state efficient chromophore with pH-responsive and solvatofluorochromic properties based on an asymmetric single benzene framework.

We present a unique single-benzene-based chromophore with asymmetric structure that emits efficient luminescence in both solid and solution states and shows solvatofluorochromism, large Stokes shift (154-219 nm) and an extraordinary wide range of solvent compatibility. The asymmetric structural feature endows this chromophore with significant ratiometric pH-dependent fluorescence for accurate and fast pH sensing over a pH range from 4.0 to 8.2, which could be applied for visual identification of different brands of drinking water. It may find broad applications in environmental sensing and pH-associated physiological processes.

Development of a novel chromophore reaction-based fluorescent probe for biogenic amines detection.

Biogenic amines (BAs) are important biomarkers to monitor meat spoilage. However, the design of efficient BA fluorescent probes with distinct colorimetric and ratiometric fluorescent dual-channels is still a critical challenge because of similar chemical properties and basicity between BAs and other amines. Herein, pyrrolopyrrole cyanine (PPCy-1) is reported to display distinctly high reactivity toward BAs through an ultrasensitive irreversible chromophore reaction for the first time. The reaction mechanism is ascribed to synergistic aza-Michael addition and B-N detachment, followed by hydrolysis to produce low-conjugated diketopyrrolopyrrole and heteroaromatic acetonitrile compounds. As a result, colorimetric and ratiometric fluorescent dual-channel (Δλab = 188 nm and Δλem = 151 nm) signals and a limit of detection up to 62.1 nM level for BA solution are acquired. In addition, the colorimetric detection of volatile amine vapor using the PPCy-1-loaded filter paper, showing a color change from green to yellow, is feasible. A simple and cost-effective fluorescence "turn on" method using the filter paper or the CAD-40 resin loaded with PPCy-1 to detect TVB (total volatile bases) originating from shrimp spoilage is further demonstrated.

Role of Spin-Orbit Coupling in Long Range Energy Transfer in Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are emerging as a promising platform for solar energy conversion applications. Their potential utilization as efficient chromophores in artificial photosynthesis is closely related to the understanding of light-harvesting and energy transfer processes that occur within these molecular scaffolds. Herein, we present the photophysical investigation of Ru(II), Ir(III), and Os(II) polypyridyl complexes incorporated into the backbone of UiO-67. In this work, we systematically study the effect of spin-orbit coupling on dipole-dipole energy transfer in MOFs using steady-state and time-resolved spectroscopic techniques. The results of our work indicate successful triplet-to-singlet energy transfer and a sizable increase in the transfer kinetics and critical distance, as direct consequences of strong spin-orbit couplings. Remarkably, the reported R0 value for OsDCBPY (R0 = 88 ± 10 Å) represents one of the largest Förster distances observed in an MOF. Collectively, this work contributes to the general knowledge of energy transfer in materials and provides groundwork for efficient utilization in artificial photosynthetic assemblies.

A novel and efficient chromophore reaction based on a lactam-fused aza-BODIPY for polyamine detection

Polyamines (such as spermine, spermidine) play important roles in biomedical and food field. The elevated polyamines have been proposed to serve as target analytes for monitoring meat spoilage. Because of structural similarity and low concentration of polyamines in real samples, it is exceedingly challenging to design and develop sensitive probes for visual detection of polyamines. To address this issue, a highly efficient probe was reported based on a newly developed chromophore reaction between lactam-fused aza-BODIPY (abbreviation: LAB) and polyamines by virtue of unique multiple amino groups character of polyamines. This chromophore reaction includes a kinetic-controllable reaction of a B–N bond cleavage by polyamines followed by a fast hydrolysis reaction to yield much smaller conjugated molecules. With 130 nm hypsochromic shift of the absorption peak and up to 99% fluorescence quenching within 1 min, LAB can be used as a highly sensitive fluorescent probe for detection of polyamines solution and monitoring fish spoilage with synchronous colorimetric and fluorescent changes.

A mutant of the phototoxic protein KillerRed that does not form DsRed-like chromophore

Genetically encodable photosensitizers based on fluorescent proteins produce reactive oxygen species when illuminated with light. Although widely used as optogenetic tools, existing photosensitizers with green fluorescence possess suboptimal properties motivating for a search of new protein variants with efficient chromophore maturation and high phototoxicity. Here we report a mutant of the phototoxic fluorescent protein KillerRed protein with fluorescence in the green part of the spectrum. The mutant variant carries mutations I64L, D114G, and T115S and does not form a DsRed-like chromophore. The protein can be used as a template to create new genetically encodable photosensitizers that are spectrally different from KillerRed.

Benzothiadiazole with π-Spacer as Efficient Chromophore for Bulk Heterojunction Organic Solar Cells

Benzothiadiazole with π-Spacer as Efficient Chromophore for Bulk Heterojunction Organic Solar Cells

Examining the Role of Cone-expressed RPE65 in Mouse Cone Function

Efficient chromophore supply is paramount for the continuous function of vertebrate cone photoreceptors. It is well established that isomerization of all-trans- to 11-cis- retinoid in the retinal pigmented epithelium by RPE65 is a key reaction in this process. Mutations in RPE65 result in a disrupted chromophore supply, retinal degeneration, and blindness. Interestingly, RPE65 has recently been found to also be expressed in cone photoreceptors in several species, including mouse and human. However, the functional role of cone-expressed RPE65 has remained unknown. Here, we used loss and gain of function approaches to investigate this issue. First, we compared the function of cones from control and RPE65-deficient mice. Although we found that deletion of RPE65 partially suppressed cone dark adaptation, the interpretation of this result was complicated by the abnormal cone structure and function caused by the chromophore deficiency in the absence of RPE65 in the pigmented epithelium. As an alternative approach, we generated transgenic mice to express human RPE65 in the cones of mice where RPE65 expression is normally restricted to the pigmented epithelium. Comparison of control (RPE65-deficient) and transgenic (RPE65-expressing) cones revealed no morphological or functional changes, with only a slight delay in dark adaptation, possibly caused by the buffering of retinoids by RPE65. Together, our results do not provide any evidence for a functional role of RPE65 in mouse cones. Future studies will have to determine whether cone-expressed RPE65 plays a role in maintaining the long-term homeostasis of retinoids in cones and their function and survival, particularly in humans.

On stress – strain responses and photoinduced properties of some azo polymers

Mechanical properties of two amorphous azo polymers were characterized in tensile measurements and correlated with photoinduced behaviour of the materials observed upon irradiation with blue light of moderate intensity. Side-chain azobenzene poly(amide imide)s capable of forming high-quality free-standing layers of a large area and thickness of a few micrometers were chosen for the investigations. High Young's modulus of ca. 2 GPa and yield stress of the order of 30 MPa were found for the materials. Photoinduced birefringence measurements evidenced efficient chromophore orientation in both polymers, while polymer mass transport upon illumination with interference pattern was hardly observed. Nevertheless, subtle periodic changes in the surface topography of the films after irradiation with right- and left-handed circularly polarized beams suggested that opto-mechanical stress reached the value of a few tens of MPa, i.e., the minimum value needed for inducing plastic deformations in the studied azo polymers.

Photocathode Chromophore–Catalyst Assembly via Layer-By-Layer Deposition of a Low Band-Gap Isoindigo Conjugated Polyelectrolyte

Low band-gap conjugated polyelectrolytes (CPEs) can serve as efficient chromophores for use on photoelectrodes for dye-sensitized photoelectrochemical cells. Herein is reported a novel CPE based on poly(isoindigo-co-thiophene) with pendant sodium butylsulfonate groups (PiIT) and its use in construction of layer-by-layer (LbL) chromophore–catalyst assemblies with a Pt-based H+ reduction catalyst (PAA-Pt) for water reduction. A novel Stille polymerization/postpolymerization ion-exchange strategy was used to convert an organic-soluble CPE to the water-soluble poly(isoindigo-co-thiophene). The anionic PiIT polyelectrolyte- and polyacrylate-stabilized Pt-nanoparticles (PAA-Pt) were codeposited with cationic poly(diallyldimethylammonium) chloride (PDDA) onto inverse opal (IO), nanostructured indium tin oxide film (nITO) (IO nITO) atop fluorine doped tin oxide (FTO), by using LbL self-assembly. To evaluate the performance of novel conjugated PiIT//PAA-Pt chromphore–catalyst assemblies, interassembly hole transfe...