Aggregation Of Chromophores Research Articles

DNA G-Quadruplexes as a Template To Direct Cyanine Dyes To Form H-Aggregates and Application of the Self-Assembly Entity as a New G-Quadruplexes Ligands Screening Platform.

The organization of organic chromophores to form H-/J-aggregates can result in new biomaterials with unique properties and applications. DNA-template self-assembly is one of the most attractive strategies to guide the formation of chromophore aggregates. However, the DNA templates are mainly limited to canonical nucleic acids structures [single (ss)- and double (ds)-stranded DNA]. DNA G-quadruplexes (GQs), with distinct and various structural features, were rarely exploited to guide the formation of dye aggregates. In this study, we present the spontaneous assembly of cyanine dye IR786 to form H-aggregates on DNA GQs exclusively, but no IR786 aggregates formed by adjusting the experimental parameters or on ss-/ds-DNA. Furthermore, on the basis of the assembly entity (GQs-IR786), an adaptive GQs-FID (fluorescence intercalator displacement) assay for screening of GQs ligands was developed. In contrast with the existing GQs-FID screening schemes, this assay displayed attractive performance in many aspects (such as turn-on signal output, broad screening range, and time saving). All these results have undoubtedly demonstrated the great values of DNA GQs as a template to guide the formation of dye aggregates. We hope that more GQs structures would be exploited as templates to expand the variety of functional materials in the future. Moreover, the specifically formed H-aggregates of IR786 on GQs are significant for GQs' detection, and we also expect that this GQs-FID assay would be further studied and finally applied to screen GQs ligands in a high-throughput manner in the future.

Bathophenanthroline Disulfonate Ligand-Induced Self-Assembly of Ir(III) Complexes in Water: An Intriguing Class of Photoluminescent Soft Materials.

Strong evidence of concentration-induced and dissolved electrolyte-induced chromophore aggregation has been universally observed in numerous water soluble bis-cyclometalated Ir(III) photosensitizers bearing the sulfonated diimine ligands bathophenanthroline disulfonate and bathocuproine disulfonate. This new class of aqueous-based soft materials was highly photoluminescent in their aggregated state where detailed spectroscopic investigations of this phenomenon revealed significant blue shifts of their respective photoluminescence emission spectra with concomitant increases in excited-state lifetimes and quantum yields initiating even at micromolar chromophore concentrations in water or upon the addition of a strong electrolyte. A combination of nanoscale particle characterization techniques, static and dynamic photoluminescence spectroscopic studies, along with atomistic molecular dynamics (MD) simulations of these soft materials suggests the formation of small, heterogeneous nanoaggregate structures, wherein the sulfonated diimine ancillary ligand serves as a pro-aggregating subunit in all instances. Importantly, the experimental and MD findings suggest the likelihood of discovering similar aqueous aggregation phenomena occurring in all transition-metal complexes bearing these water-solubilizing diimine ligands.

Donor-Acceptor-Collector Ternary Crystalline Films for Efficient Solid-State Photon Upconversion.

It is pivotal to achieve efficient triplet-triplet annihilation based photon upconversion (TTA-UC) in the solid-state for enhancing potentials of renewable energy production devices. However, the UC efficiency of solid materials is largely limited by low fluorescence quantum yields that originate from the aggregation of TTA-UC chromophores and also by severe back energy transfer from the acceptor singlet state to the singlet state of the triplet donor in the condensed state. In this work, to overcome these issues, we introduce a highly fluorescent singlet energy collector as the third component of donor-doped acceptor crystalline films, in which dual energy migration, i.e., triplet energy migration for TTA-UC and succeeding singlet energy migration for transferring energy to a collector, takes place. To demonstrate this scheme, a highly fluorescent singlet energy collector was added as the third component of donor-doped acceptor crystalline films. An anthracene-based acceptor containing alkyl chains and a carboxylic moiety is mixed with the triplet donor Pt(II) octaethylporphyrin (PtOEP) and the energy collector 2,5,8,11-tetra- tert-butylperylene (TTBP) in solution, and simple spin-coating of the mixed solution gives acceptor films of nanofibrous crystals homogeneously doped with PtOEP and TTBP. Interestingly, delocalized singlet excitons in acceptor crystals are found to diffuse effectively over the distance of ∼37 nm. Thanks to this high diffusivity, only 0.5 mol % of doped TTBP can harvest most of the singlet excitons, which successfully doubles the solid-state fluorescent quantum yield of acceptor/TTBP blend films to 76%. Furthermore, since the donor PtOEP and the collector TTBP are separately isolated in the nanofibrous acceptor crystals, the singlet back energy transfer from the collector to the donor is effectively avoided. Such efficient singlet energy collection and inhibited back energy transfer processes result in a large increase of UC efficiency up to 9.0%, offering rational design principles toward ultimately efficient solid-state upconverters.

Utilizing formation of dye aggregates with aggregation-induced emission characteristics for enhancement of two-photon absorption

Femtosecond Z-scan measurements of aggregates of a quadrupolar D-π-D dye, provide direct evidence that aggregation of this AIE chromophore leads to a sizeable enhancement of the intrinsic two-photon absorption cross section.

Exciton localization in excited-state dynamics of a tetracene trimer: a surface hopping LC-TDDFTB study.

Excitons in the molecular aggregates of chromophores are key participants in important processes such as photosynthesis or the functioning of organic photovoltaic devices. Therefore, the exploration of exciton dynamics is crucial. Here we report on exciton localization during excited-state dynamics of the recently synthesized tetracene trimer [Liu et al., Org. Lett., 2017, 19, 580]. We employ the surface hopping approach to nonadiabatic molecular dynamics in conjunction with the long-range corrected time-dependent density functional tight binding (LC-TDDFTB) method [Humeniuk and Mitrić, Comput. Phys. Commun., 2017, 221, 174]. Utilizing a set of descriptors based on the transition density matrix, we perform comprehensive analysis of exciton dynamics. The obtained results reveal an ultrafast exciton localization to a single tetracene unit of the trimer during excited-state dynamics, along with exciton transfer between units.

Reversible mechanofluorochromism of aniline-terminated phenylene ethynylenes.

Seven three-ring phenylene-ethynylene (PE) structural analogs, differing only in the lengths of alkyl chains on terminal aniline substituents, show 50-62 nm bathochromic shifts in emission maxima in response to mechanical force (mechanofluorochromism, MC). These shifts are fully reversible with heat or solvent fuming. Shearing of these solids yields a transition from green-emitting crystalline phases to orange-emitting amorphous phases as established by differential scanning calorimetry and X-ray diffraction. Molecules with shorter alkyl chain lengths required higher temperatures to recover the hypsochromically shifted crystalline phases after grinding, while the recovery with chain lengths longer than butyl occurred at room temperature. In addition to this structure-dependent thermochromism, these compounds retain their MC properties in polymer hosts to various extents. The crystalline phases of these materials have PE chromophores that are twisted due to non-covalent perfluoroarene-arene (ArF-ArH) interactions involving perfluorophenyl pendants and the terminal rings of the PE chromophore, resulting in interrupted conjugation and an absence of chromophore aggregation. The MC behavior of an analog without the perfluoroarene rings is severely attenuated. This work demonstrates the general utility of twisted PEs as stimuli-responsive moieties and reveals clear structure-property relationships regarding the effects of alkyl chain length on these materials.

Photocurrent Enhancement in DNA‐Scaffolded Chromophore–Aggregate‐Functionalized Systems Containing Multiple Types of Chromophores

AbstractThe construction of one‐dimensional chromophore aggregates of naphthalenediimide (NDI) and bis(2‐thienyl)diketopyrrolopyrrole (TDPP) using 40‐mer oligodeoxythymidines (dT40) as a scaffold was previously reported. Furthermore, the chromophore‐aggregate (NDI‐dT40/TDPP‐dT40) co‐immobilized heterojunction gold electrode exhibited a more efficient photocurrent than the TDPP–dT40‐immobilized electrode with selective photoexcitation of TDPP‐dT40. In this work, a system comprising three components (in which the chromophore aggregates of diphenyl‐diketopyrrolopyrrole (PDPP‐dT40) are employed as a third component) was examined in order to enhance photocurrent efficiency. Selective photoexcitation of TDPP‐dT40 on the NDI‐dT40/TDPP‐dT40/PDPP‐dT40 electrode shows photocurrent responses with greater quantum yield than those of the TDPP‐dT40, NDI‐dT40/TDPP‐dT40 and TDPP‐dT40/PDPP‐dT40 electrodes. The results suggest the addition of PDPP‐dT40 can control charge separation and charge recombination between the electron and the hole (generated by an electron transfer from the photoexcited TDPP‐dT40 to NDI‐dT40).

Programmed coherent coupling in a synthetic DNA-based excitonic circuit.

Natural light-harvesting systems spatially organize densely packed chromophore aggregates using rigid protein scaffolds to achieve highly efficient, directed energy transfer. Here, we report a synthetic strategy using rigid DNA scaffolds to similarly program the spatial organization of densely packed, discrete clusters of cyanine dye aggregates with tunable absorption spectra and strongly coupled exciton dynamics present in natural light-harvesting systems. We first characterize the range of dye-aggregate sizes that can be templated spatially by A-tracts of B-form DNA while retaining coherent energy transfer. We then use structure-based modelling and quantum dynamics to guide the rational design of higher-order synthetic circuits consisting of multiple discrete dye aggregates within a DX-tile. These programmed circuits exhibit excitonic transport properties with prominent circular dichroism, superradiance, and fast delocalized exciton transfer, consistent with our quantum dynamics predictions. This bottom-up strategy offers a versatile approach to the rational design of strongly coupled excitonic circuits using spatially organized dye aggregates for use in coherent nanoscale energy transport, artificial light-harvesting, and nanophotonics.

Printable Fluorescent Hydrogels Based on Self-Assembling Peptides

Fluorescent hydrogels (FH) have a variety of potential applications in the field of soft electronics. However, fabrication of mechanically stable and printable fluorescent hydrogels remains challenging. Here, we report a kind of fluorescent hydrogel based on the co-assembly of peptide motif and transition metal ions. The metal ions are captured in the hydrogel network at specific positions through covalently linked ligands on the peptide hydrogelators. This efficiently prevents the aggregation and self-quenching of organometallic chromophores. In addition, the formation of metal-ligand complexes introduces additional interactions to stabilize the hydrogel network, making the FH even more stable after the incorporation of metal ions. The FH is optically transparent but highly fluorescent. By using three different metal ions, the white light fluorescent supramolecular hydrogel has been achieved. As a proof-of-principle, we demonstrate the printability of the hydrogels to various patterns. We anticipate that with the improved fluorescent performance and stability, this kind of FH can find broad applications in extrusion-based 3D printing for the construction of soft electronics.

Synthesis and characterization of new second-order NLO chromophores containing the isomeric indolizine moiety for electro-optical materials

To further explore the potential application of the indolizine donor group in nonlinear optical (NLO) chromophores, we have designed and synthesized new push-pull chromophores (MPI-1)-V-TCF and (MPI-3)-V-TCF, having isomeric 3(1)-methyl-2-phenylindolizin-1(3)-yl (MPI-1(3)) electron donor and TCF acceptor, and compared them with dimethyl aniline (DMA) analogues. The Uv-Vis (linear optical) properties and solvatochromic behavior were also investigated; theoretical predictions of molecular NLO characteristics were done on the basis of the DFT calculations. The indolizine-based chromophores have high thermal stability: the decomposition temperature is 348 °C for (MPI-1)-V-TCF and 343 °C for the (MPI-3)-V-TCF, which is by 10–15 °C higher than that for the chromophore DMA-V-TCF. An important role is played by the bulky phenyl group, which prevents the aggregation of chromophores in guest-host doped polymer films. In NLO activities, the doped (MPI-1)-V-TCF/PMMA and (MPI-3)-V-TCF/PMMA films display the NLO coefficient, d33, values of 40 and 42 pm/V, correspondingly, at the chromophore load of 20 wt%.

Absorption Spectra for Disordered Aggregates of Chromophores Using the Exciton Model.

Optimizing the optical properties of large chromophore aggregates and molecular solids for applications in photovoltaics and nonlinear optics is an outstanding challenge. It requires efficient and reliable computational models that must be validated against accurate theoretical methods. We show that linear absorption spectra calculated using the molecular exciton model agree well with spectra calculated using time-dependent density functional theory and configuration interaction singles for aggregates of strongly polar chromophores. Similar agreement is obtained for a hybrid functional (B3LYP), a long-range corrected hybrid functional (ωB97X), and configuration interaction singles. Accounting for the electrostatic environment of individual chromophores in the parametrization of the exciton model with the inclusion of atomic point charges significantly improves the agreement of the resulting spectra with those calculated using all-electron methods; different charge definitions (Mulliken and ChelpG) yield similar results. We find that there is a size-dependent error in the exciton model compared with all-electron methods, but for aggregates with more than six chromophores, the errors change slowly with the number of chromophores in the aggregate. Our results validate the use of the molecular exciton model for predicting the absorption spectra of bulk molecular solids; its formalism also allows straightforward extension to calculations of nonlinear optical response.

Aggregation-induced emission: Materials and biomedical applications

Abstract

Substituent Effects That Control Conjugated Oligomer Conformation through Non-covalent Interactions.

Although understanding the conformations and arrangements of conjugated materials as solids is key to their prospective applications, predictive power over these structural factors remains elusive. In this work, substituent effects tune non-covalent interactions between side-chain fluorinated benzyl esters and main-chain terminal arenes, in turn controlling the conformations and interchromophore aggregation of three-ring phenylene-ethynylenes (PEs). Cofacial fluoroarene-arene (ArF-ArH) interactions cause twisting in the PE backbone, interrupting intramolecular conjugation as well as blocking chromophore aggregation, both of which prevent the typically observed bathochromic shift observed upon transitioning PEs from solution to solid. This work highlights two structural factors that determine whether the ArF-ArH interactions, and the resulting twisted, unaggregated chromophores, occur in these solids: (i) the electron-releasing characteristic of substituents on ArH, with more electron-releasing character favoring ArF-ArH interactions, and (ii) the fluorination pattern of the ArF ring, with 2,3,4,5,6-pentafluorophenyl favoring ArF-ArH interactions over 2,4,6-trifluorophenyl. These trends indicate that considerations of electrostatic complementarity, whether through a polar-π or substituent-substituent mechanism, can serve as an effective design principle in controlling the interaction strengths, and therefore the optoelectronic properties, of these molecules as solids.

Photorefractive hyper-structured molecular glasses constructed by calix[4]resorcinarene core and carbazole-based methine nonlinear optical chromophore

Seven C-methylcalix[4]resorcinarene (CRA)-based photorefractive (PR) hyper-structured molecular glasses (HSMGs) containing carbazole-based methine nonlinear optical (NLO) chromophores were designed and synthesized via esterification between carboxyl-containing asymmetric CRA core molecule and hydroxyl-containing functional compounds. When the feed ratio of hydroxyl-containing NLO functional compounds to carboxyl groups of CRA-COOH was kept at 1.5/1 by mole, the degree of introduction of NLO chromophore to the CRA core was above 70%. All the HSMGs show low glass transition temperatures (Tg), and good solubility in common low boiling point solvents such as THF, CHCl3, etc. Powder XRD and UV–vis absorption in films of HSMGs indicate that the aggregation, packing and crystallization of the NLO chromophores in these HSMGs had been effectively reduced. Doping with N-ethyl-carbazole (ECz) as a plasticizer and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a photosensitizer, all the HSMGs composites showed good PR effects. All the coupling gain coefficients (Γ) of HSMGs-based composites are about twice to the corresponding small molecular NLO chromophores-based composites, thanks to the decreased NLO chromophores antiparallel packing caused by the asymmetric CRA core. Among them, CRA-CSN/ECz/PCBM (69:30:1, wt%) composite exhibited the best performance with the Γ value of 78.2 cm−1 at the external electric field of 12.5 V μm−1, which is one of the best performance in molecular glasses under the same test conditions. Coupled with their convenient synthesis, this work will provide a new simple design strategy for organic PR materials.

Water in Biomolecular Fluorescence Spectroscopy and Imaging: Side Effects and Remedies.

Historically, many of the classical organic fluorescent dyes were developed as laser dyes and characterized and optimized in organic solvents. Since then, fluorescence has, however, found a vast range of applications in the life sciences in which the fluorophores are usually surrounded by water and not by organic solvents. The omnipresence of water in biomolecular fluorescence spectroscopy and imaging leads to some unwanted but nonetheless unavoidable consequences on the photophysical properties of the dyes, which may impact the quality and complicate quantitative interpretation of the experiments. This paper discusses and illustrates with examples two such water-induced phenomena, namely chromophore aggregation in water and fluorescence quenching by water, as well as some ways to overcome them.

Preparation of a white-light-emitting fluorescent supramolecular polymer gel with a single chromophore and use of the gel to fabricate a protected quick response code

We report here a novel yet facile approach to prepare white fluorescent polymeric materials based on the aggregation of a single fluorescent chromophore.

Emissive Molecular Aggregates and Energy Migration in Luminescent Solar Concentrators.

Luminescent solar concentrators (LSCs) are light harvesting devices that are ideally suited to light collection in the urban environment where direct sunlight is often not available. LSCs consist of highly luminescent compounds embedded or coated on a transparent substrate that absorb diffuse or direct solar radiation over a large area. The resulting luminescence is trapped in the waveguide by total internal reflection to the thin edges of the substrate where the concentrated light can be used to improve the performance of photovoltaic devices. The concept of LSCs has been around for several decades, and yet the efficiencies of current devices are still below expectations for commercial viability. There are two primary challenges when designing new chromophores for LSC applications. Reabsorption of dye emission by chromophores within the waveguide is a significant loss mechanism attenuating the light output of LSCs. Concentration quenching, particularly in organic dye systems, restricts the quantity of chromophores that can be incorporated in the waveguide thus limiting the light absorbed by the LSC. Frequently, a compromise between increased light harvesting of the incident light and decreasing emission quantum yield is required for most organic chromophore-based systems due to concentration quenching. The low Stokes shift of common organic dyes used in current LSCs also imposes another optimization problem. Increasing light absorption of LSCs based on organic dyes to achieve efficient light harvesting also enhances reabsorption. Ideally, a design strategy to simultaneously optimize light harvesting, concentration quenching, and reabsorption of LSC chromophores is clearly needed to address the significant losses in LSCs. Over the past few years, research in our group has targeted novel dye structures that address these primary challenges. There is a common perception that dye aggregates are to be avoided in LSCs. It became apparent in our studies that aggregates of chromophores exhibiting aggregation-induced emission (AIE) behavior are attractive candidates for LSC applications. Strategic application of AIE chromophores has led to the development of the first organic-based transparent solar concentrator that harvests UV light as well as the demonstration of reabsorption reduction by taking advantage of energy migration processes between chromophores. Further developments led us to the application of perylene diimides using an energy migration/energy transfer approach. To prevent concentration quenching, a molecularly insulated perylene diimide with bulky substituents attached to the imide positions was designed and synthesized. By combining the insulated perylene diimide with a commercial perylene dye as an energy donor-acceptor emitter pair, detrimental luminescence reabsorption was reduced while achieving a high chromophore concentration for efficient light absorption. This Account reviews and reinspects some of our recent work and the improvements in the field of LSCs.

Ultra-fast computation of electronic spectra for large systems by tight-binding based simplified Tamm-Dancoff approximation (sTDA-xTB).

The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the well established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H-Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first benchmarked for vertical excitation energies of open- and closed-shell systems in comparison to other semi-empirical methods and applied to exemplary problems in electronic spectroscopy. As side products of the development, a robust and efficient valence electron TB method for the accurate determination of atomic charges as well as a more accurate calculation scheme of dipole rotatory strengths within the Tamm-Dancoff approximation is proposed.

Structural insight into DNA-assembled oligochromophores: crystallographic analysis of pyrene- and phenanthrene-modified DNA in complex with BpuJI endonuclease.

The use of the DNA duplex as a supramolecular scaffold is an established approach for the assembly of chromophore aggregates. In the absence of detailed structural insight, the characterization of thus assembled oligochromophores is, today, largely based on solution-phase spectroscopy. Here, we describe the crystal structures of three DNA-organized chromophore aggregates. DNA hybrids containing non-nucleosidic pyrene and phenanthrene building blocks were co-crystallized with the recently described binding domain of the restriction enzyme BpuJI. Crystal structures of these complexes were determined at 2.7, 1.9 and 1.6 Å resolutions. The structures reveal aromatic stacking interactions between pyrene and/or phenanthrene units within the framework of the B-DNA duplex. In hybrids containing a single modification in each DNA strand near the end of the duplex, the two polyaromatic hydrocarbons are engaged in a face-to-face stacking orientation. Due to crystal packing and steric effects, the terminal GC base pair is disrupted in all three crystal structures, which results in a non-perfect stacking arrangement of the aromatic chromophores in two of the structures. In a hybrid containing a total of three pyrenes, crystal lattice induced end-to-end stacking of individual DNA duplexes leads to the formation of an extended aromatic π-stack containing four co-axially arranged pyrenes. The aromatic planes of the stacked pyrenes are oriented in a parallel way. The study demonstrates the value of co-crystallization of chemically modified DNA with the recombinant binding domain of the restriction enzyme BpuJI for obtaining detailed structural insight into DNA-assembled oligochromophores.

Electrochemical Deposition of Azobenzene-Containing Network Films with High-Contrast and Stable Photoresponse.

To fabricate stable photoresponsive films and devices, a cross-linked network that firmly fixes the position of the chromophores is an ideal structure, because aggregation and/or phase separation effects of chromophores in matrix can be effectively restrained in such robust films. Herein, the in situ electrochemical deposition (ED) of azo-based precursors containing multielectroactive carbazole units is utilized to construct highly cross-linked photoresponsive films. 2-(4-(9,9-bis(6-(9H-carbazol-9-yl)hexyl)-9H-fluoren-2-yl)phenyl)-1-(4-(9,9-bis(6-(9H-carbazol-9-yl)hexyl)-9H-fluoren-7-yl)phenyl)diazene (BFCzAzo) with high solvability in electrolyte solution, high electroactivity, and highly efficient photoresponsive ability is synthesized by Suzuki coupling reaction as a kind of ED precursor. A highly cross-linked photoresponsive film is fabricated by ED method using BFCzAzo as ED precursor. The film can be patterned in large area by irradiation with interfering laser beam (355 nm), and the pattern possesses excellent thermal stability and insoluble ability in both organic and inorganic solvents. Excellent reversibility of the nanostructures is demonstrated by irradiation with 550 nm laser beam.