Chromophore Molecules Research Articles

(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.

Metal–organic frameworks for nonlinear optics and lasing

AbstractNonlinear optics (NLO) is a crucial branch of photonics that greatly facilitates the transmission, processing, and storage of photonic signals. It meets the needs of the rapidly growing information demands of modern society. Materials with NLO properties and laser capabilities have a wide range of applications in fields such as optical communication, optical information storage, biomedical imaging, laser technology, and quantum information technology. Metal–organic frameworks (MOFs) have emerged as particularly exciting hybrid inorganic–organic porous materials that can be easily self‐assembled from corresponding inorganic metal ions/clusters and organic linkers. The structural diversity and flexibility of MOFs offer ample opportunities for the orderly organization of highly hyperpolarizable chromophore molecules within confined spaces. This makes it ideal for NLO signal and laser emissions. In this review, we provide a comprehensive overview of strategies to construct MOFs with NLO and laser properties, as well as recent research developments for enhancing and adjusting these properties. Through analysis of chromophore arrangement and various interactions within the framework, we aim to gain insight into the correlation between MOF structures and optical properties. This will facilitate the design and synthesis of MOFs with excellent NLO and laser capabilities through the judicious selection of metal ions and organic linkers. Finally, we outline the future challenges and potential research directions for MOFs in NLO and laser fields.

Synthesis, electro‐optic properties, and performance of novel fluorinated polyurethaneimide

AbstractUrethane imide anhydride oligomers with terminal groups as anhydride groups were designed and synthesized using second‐order nonlinear optical chromophore molecule, bisphenol AF‐type diethylidene dianhydride, and toluene diisocyanate as monomers. Polyurethaneimide (PUI) second‐order nonlinear optical polymers with the structure of imide and amino ester chain segments were then synthesized by the polycondensation reaction between urethane imide anhydride oligomers and aromatic diamine monomers. The glass transition temperature (Tg) of PUI reached 186°C, and the 5% heat‐loss decomposition temperature was 320°C. The corona‐polarized PUI had an electro‐optic (EO) coefficient (γ33) of 82 pm/V tested by the reflection method. The loss of light transmission of the polymer waveguide prepared with PUI as electro‐optical material was 1.13 dB/cm at 1550 nm. Mach–Zehnder type polymer waveguide electro‐optical modulators have been prepared based on the properties of the electro‐optic material PUI. The fabricated polymer EO modulators had favorable electro‐optic modulation response performance for low‐frequency electrical signals. The good modulation characteristics of the manufactured electro‐optical modulators proved that the synthesized PUI was a waveguide polymer material with good comprehensive performance.Highlights Electro‐optic fluorinated polyurethaneimide was synthesized. Polyurethaneimide as core material, polymer waveguide EO modulators were fabricated. The prepared modulators had good electro‐optic modulation performance.

Effects of tetraphenylethylene groups on the crystallization of poly(ʟ-lactide) with different molecular weights

Degradable polymers incorporated with chromophore molecules have great potential in biomedical field. In this paper, hydroxyl functionalized tetraphenylethylene (TPE-2OH) was employed as the initiator to synthesize two-armed poly(ʟ-lactide) (PLLA) with varying molecular weights (TPE-PLLA-L, TPE-PLLA-M and TPE-PLLA-H) by ring-opening polymerization (ROP). Their crystallization behaviors were compared with those of PLLA with similar molecular weights initiated by ethylene glycol (EG-PLLA-L, EG-PLLA-M and EG-PLLA-H). A significant inhibiting effect on crystallization was found in TPE-PLLA-L with low molecular weight (Mw = 6400 g mol-1, ∼40 repeating units per chain) because of the large and rigid TPE cores, which significantly restricted the folding and transportation of the short PLLA chains and resulted the formation of smaller lamellar thickness (lc = 3.9 nm). However, when the chain length of PLLA increased, the proportion of TPE in the TPE-PLLA molecular decreased dramatically, and the nucleation of crystallization was improved because of the aggregation of TPE cores in TPE-PLLA-M (Mw = 13600 g mol-1, ∼90 repeating units per chain) and TPE-PLLA-H (Mw = 19000 g mol-1, ∼125 repeating units per chain) in the molten state. After the crystallization of TPE-PLLA, the aggregation state of TPE groupschanged. This work shed some light on the crystallization behavior of PLA with fluorescence properties.

A theoretical investigation for improving the performance of non-fullerene organic solar cells through side-chain engineering of BTR non-fused-ring electron acceptors

In the current quantum chemical study, indacenodithiophene donor core-based the end-capped alterations of the reference chromophore BTR drafted eight A2-A1-D-A1-A2 type small non-fullerene acceptors. All the computational simulations were executed under MPW1PW91/6-31G (d, p) level of DFT. The UV–Vis absorption, open circuit voltage, electron affinity, ionization potential, the density of states, reorganization energy, orbital analysis, and non-covalent interactions were studied and compared with BTR. Several molecules of our modeled series BT1-BT8 have shown distinctive features that are better than those of the BTR. The open circuit voltage (VOC) of BT5 has a favorable impact, allowing it to replace BTR in the field of organic solar cells. The charge carrier motilities for proposed molecules generated extraordinary findings when matched to the reference one (BTR). Further charge transmission was confirmed by creating the complex with a PM6 donor molecule. The remarkable dipole moment contributes to the formation of non-covalent bond interactions with chloroform, resulting in superior charge mobility. Based on these findings, it can be said that every tailored molecule has the potential to surpass chromophore molecule (BTR) in OSCs. So, all tailored molecules may enhance the efficiency of photovoltaic cells due to the involvement of potent terminal electron-capturing acceptor2 moieties. Considering these obtained results, these newly presented molecules can be regarded for developing efficient solar devices in the future.

Synthesis of Perylene Diimide Modified by POSS and its Assembly Behavior in Solution and SBS Matrix

In this work, Perylene diimide derivatives 1,7- POSS-PDI-C12 (PPC) were synthesized using 1,7-Br-PDI- C12, 18-crown-6 ether as phase transfer agent, K2CO3 as catalyst and THF as solvent in a reaction system. Subsequently, the POSS-SH group was successfully introduced into the perylene imide bay site in high yield. The chemical structure and molecular weight of the products were characterized by 1H-NMR, 13C-NMR, MALDI-TOF MS and FT-IR. The self-assembly behavior in different solvents was studied using the research solution self-assembly method. PPC remained in a single monomolecular state due to the bulky POSS group, which introduced large steric hindrance in the molecular packing, leading to the weakening of the π–π interactions. Then, the Composite thin films containing PPC in SBS was prepared. PPC do not exhibit significant force-chromic behavior owing to the dispersion of single- molecule states. This shows that in the construction of mechanochromic materials, chromophore molecules need to have a certain degree of aggregation in the matrix, but the aggregation degree should not be too high.

Synthesis and characterization of fluorinated polyurethaneimide electro-optic waveguide material with novel structure

Abstract Structurally novel fluorinated polyurethaneimide (PUI) electro-optic polymer based on chromophore molecule b, diisocyanate MDI and anhydride BPAFDA was synthesized by stepwise polymerization of oligomer PUI with fluorinated aromatic diamines BATB and BATPP. Electro-optic (EO) PUI chain structure had the structure of polyimide and polyurethane chain segments, integrating the advantages of polyimide and polyurethane. The PUI possessed good film-forming property, a high glass transition temperature (T g = 193 °C) and good thermal stability (5 % weight loss temperature T d up to 320 °C). Y-Structured inverted ridge polymer optical waveguides were designed and fabricated using the PUI as the waveguide core material. The PUI had good optical performance with an EO coefficient (γ33) of 79 pm/V and 1.1 dB/cm optical propagation loss at a wavelength of 1550 nm. The results showed that the synthesized PUI met the performance requirements for the preparation of polymer optical waveguide devices and was suitable as a polymer electro-optic waveguide material.

Modulating photophysical properties in a flexible porous host by regulating guest-assisted charge transfer interactions.

The 1D array of electron donor-acceptor chromophoric organic molecules is of paramount importance for photovoltaic, catalytic and optoelectronic applications. Herein, we report coordination driven 1D arrays of an electron-donor guest (fluorene, carbazole, dibenzofuran, and dibenzothiophene) and o-phen chelator as an acceptor in a Zn-based porous coordination polymer, {[Zn(o-phen)(ndc)]·DMF} (PCP-1). All the guest-encapsulated PCPs were characterized by performing single-crystal structure determinations and showed emission driven by charge transfer. Exciton binding energies were calculated and correlated with electron-donating capabiliities of the guest molecules.

Thioindigo photoswitches available for the modulation of hydrogels’ stiffness by visible light

Chromophore molecules that undergo reversible isomerization under excitation by two different wavelengths of light are commonly referred to as photoswitchable molecules. Through the use of light-induced reversible changes combined with precisely spatial and temporal light control, photoswitchable molecules can be applied in areas such as actuators, optics, molecular motors, and photobiology.

Tunable Tamm plasmon cavity as a scalable biosensing platform for surface enhanced resonance Raman spectroscopy

Surface enhanced Resonance Raman spectroscopy (SERRS) is a powerful technique for enhancing Raman spectra by matching the laser excitation wavelength with the plasmonic resonance and the absorption peak of biomolecules. Here, we propose a tunable Tamm plasmon polariton (TPP) cavity based on a metal on distributed Bragg reflector (DBR) as a scalable sensing platform for SERRS. We develop a gold film-coated ultralow-loss phase change material (Sb2S3) based DBR, which exhibits continuously tunable TPP resonances in the optical wavelengths. We demonstrate SERRS by matching the TPP resonance with the absorption peak of the chromophore molecule at 785 nm wavelength. We use this platform to detect cardiac Troponin I protein (cTnI), a biomarker for early diagnosis of cardiovascular disease, achieving a detection limit of 380 fM. This scalable substrate shows great promise as a next-generation tunable biosensing platform for detecting disease biomarkers in body fluids for routine real-time clinical diagnosis.

Electron‐Poor Acridones and Acridiniums as Super Photooxidants in Molecular Photoelectrochemistry by Unusual Mechanisms

AbstractElectron‐deficient acridones and in situ generated acridinium salts are reported as potent, closed‐shell photooxidants that undergo surprising mechanisms. When bridging acyclic triarylamine catalysts with a carbonyl group (acridones), this completely diverts their behavior away from open‐shell, radical cationic, ‘beyond diffusion’ photocatalysis to closed‐shell, neutral, diffusion‐controlled photocatalysis. Brønsted acid activation of acridones dramatically increases excited state oxidation power (by +0.8 V). Upon reduction of protonated acridones, they transform to electron‐deficient acridinium salts as even more potent photooxidants (*E1/2=+2.56–3.05 V vs SCE). These oxidize even electron‐deficient arenes where conventional acridinium salt photooxidants have thusfar been limited to electron‐rich arenes. Surprisingly, upon photoexcitation these electron‐deficient acridinium salts appear to undergo two electron reductive quenching to form acridinide anions, spectroscopically‐detected as their protonated forms. This new behaviour is partly enabled by a catalyst preassembly with the arene, and contrasts to conventional SET reductive quenching of acridinium salts. Critically, this study illustrates how redox active chromophoric molecules initially considered photocatalysts can transform during the reaction to catalytically active species with completely different redox and spectroscopic properties.

Electron-Poor Acridones and Acridiniums as Super Photooxidants in Molecular Photoelectrochemistry by Unusual Mechanisms.

Electron-deficient acridones and in situ generated acridinium salts are reported as potent, closed-shell photooxidants that undergo surprising mechanisms. When bridging acyclic triarylamine catalysts with a carbonyl group (acridones), this completely diverts their behavior away from open-shell, radical cationic, 'beyond diffusion' photocatalysis to closed-shell, neutral, diffusion-controlled photocatalysis. Brønsted acid activation of acridones dramatically increases excited state oxidation power (by +0.8 V). Upon reduction of protonated acridones, they transform to electron-deficient acridinium salts as even more potent photooxidants (*E1/2 =+2.56-3.05 V vs SCE). These oxidize even electron-deficient arenes where conventional acridinium salt photooxidants have thusfar been limited to electron-rich arenes. Surprisingly, upon photoexcitation these electron-deficient acridinium salts appear to undergo two electron reductive quenching to form acridinide anions, spectroscopically-detected as their protonated forms. This new behaviour is partly enabled by a catalyst preassembly with the arene, and contrasts to conventional SET reductive quenching of acridinium salts. Critically, this study illustrates how redox active chromophoric molecules initially considered photocatalysts can transform during the reaction to catalytically active species with completely different redox and spectroscopic properties.

Trap or Triplet? Excited-State Interactions in 2D Perovskite Colloids with Chromophoric Cations.

Movement of energy within light-harvesting assemblies is typically carried out with separately synthesized donor and acceptor species, which are then brought together to induce an interaction. Recently, two-dimensional (2D) lead halide perovskites have gained interest for their ability to accommodate and assemble chromophoric molecules within their lattice, creating hybrid organic-inorganic compositions. Using a combination of steady-state and time-resolved absorption and emission spectroscopy, we have now succeeded in establishing the competition between energy transfer and charge trapping in 2D halide perovskite colloids containing naphthalene-derived cations (i.e., NEA2PbX4, where NEA = naphthylethylamine). The presence of room-temperature triplet emission from the naphthalene moiety depends on the ratio of bromide to iodide in the lead halide sublattice (i.e., x in NEA2Pb(Br1-xIx)4), with only bromide-rich compositions showing sensitized emission. Photoluminescence lifetime measurements of the sensitized naphthalene reveal the formation of the naphthalene triplet excimer at room temperature. From transient absorption measurements, we find the rate constant of triplet energy transfer (kEnT) to be on the order of ∼109 s-1. At low temperatures (77 K) a new broad emission feature arising from trap states is observed in all samples ranging from pure bromide to pure iodide composition. These results reveal the interplay between sensitized triplet energy transfer and charge trapping in 2D lead halide perovskites, highlighting the need to carefully parse contributions from competing de-excitation pathways for optoelectronic applications.

Self-Assembly of Functional Organic Chromophores

Aggregate structures of organic chromophores strongly affect their properties and so has become an active area of research. Self-assembly and supramolecular methods present important means to influence aggregation processes, and these have become active areas of research. We have studied the self-assembly of differently structured chromophore molecules with emphasis on porphyrins,1 pyrazinacenes,2 hexabenzocoronenes (HBC) and oligophenylenes (such as sexiphenyl), and the various methods of doing this including molecular design, surface assembly (under ambient or UHV conditions), and using interfacial media such as in the Langmuir and Langmuir-Blodgett techniques. For the latter, we have applied principles of amphiphilicity to generate on-interface structures,3 which can be lifted as multilayered films and exploited for the preparation of electronic devices.4 In this work, we will describe the self-assembly properties based on precipitation/gelation, assembly at solid surfaces, and interactions at an air-water interface. We will emphasize the molecular structure as a key feature including the effects of π-π stacking, conformational flexibility and amphiphilicity. Self-assembly and supramolecular techniques stand out as the most effective methods for obtaining nanomaterials having the molecule-level definition of structure important for any applications of the resulting materials.

Computer aided molecular design coupled to deep learning techniques as a less-expensive approach to design organic photoredox catalysts

To date, the prediction of electronic absorption spectra of organic molecules by computational chemistry methods is still limited, with differences of even 100 nm between the theoretical and experimental values, often at relatively high computational cost. In this work, we present a computationally cheaper approach for the design of new molecules that may be candidates for organic photoredox catalysts based on the prediction of their absorbance in the visible region of the electromagnetic spectrum. This problem is important to promote the development and use of solar energy in chemical processes, as an exemplary application. The design of new chromophoric molecules is approached as a two-step procedure. In the first step, a Mixed-Integer Nonlinear Programming (MINLP) model was formulated for the In-silico design of organic chromophores. A quantitative structure–activity relationship model was developed for the prediction of the difference in energy from the HOMO to the LUMO orbitals of organic dyes. This molecular design approach produced 4 molecules, where 3 have not been previously reported. In the second step, a large chemical compound database was leveraged to develop a deep learning model aimed at forecasting the absorption of visible light by such and related compounds. We have taken advantage of the deep learning model to verify that the light absorption between this model and the results of the MINLP formulation match with reasonable accuracy. For 3 of the 4 molecules, both results appear similar, allowing to verify that the molecules could in fact offer the desired absorbance at the target wavelength.

Ultrafast energy transfer from perovskite quantum dots to chromophore

Energy transfer plays an essential role in inorganic semiconductor nanocrystal-chromophore hybrids which show potential applications in light collection and emitting. The understanding of the fundamental mechanics of energy transfer processes is vital to enhance the performance of light-harvesting optoelectronic devices. Here we report the effect of varying donor sizes on energy transfer from perovskite nanocrystals to chromophore molecules. Both single energy transfer and triplet transfer mechanisms have been identified to occur between CsPbBr3 quantum dots linked to a Rhodamine B dye. The ease of adjusting optical properties via particle-size controlling provides a particular platform to accommodate excited-state couplings in perovskite-chromophore hybrids.

Plasmon Mediated Near‐Field Energy Transfer From Solid‐State, Electrically Injected Excitons to Solution Phase Chromophores

AbstractAn organic diode is demonstrated that near‐field energy transfers to molecules in solution via surface plasmon polaritons, in contrast to typical far‐field excitation via absorption of traveling photons. Electrically generated excitons couple to surface plasmon modes in the cathode; the plasmons subsequently excite chromophore molecules on top of the cathode. External quantum efficiency and time resolved photoluminescence measurements are used to characterize the diode and the near‐field energy transfer process. In addition, it is shown that excited chromophores can charge‐transfer to quencher molecules, illustrating the potential of this device to be used for photochemical applications.

The Mechanism of the Channel Opening in Channelrhodopsin-2: A Molecular Dynamics Simulation.

Channelrhodopsin-2 (ChR2) has been one of the most important objects in the study of optogenetics. The retinal chromophore molecule absorbs photons and undergoes an isomerization reaction, which triggers the photocycle, resulting in a series of conformational changes. In this study, a series of intermediate structures (including D470, P500, P390-early, P390-late, and P520 states) of ChR2 in the photocycle were modeled, and molecular dynamics (MD) simulations were performed to elucidate the mechanism of ion channel opening of ChR2. The maximum absorption wavelength of these intermediates calculated by time-dependent density function theory (TD-DFT) is in general agreement with the experimental values, the distribution of water density gradually increases in the process of photocycle, and the radius of the ion channel is larger than 6 Å. All these results indicate that our structural models of the intermediates are reasonable. The evolution of protonation state of E90 during the photocycle is explained. E90 will deprotonate when the P390-early transforms into P390-late, in which the two conformations of P390-early and P390-late obtained from the simulations are consistent with the experimental descriptions. To validate the conductive P520 state, the potential mean force (PMF) of Na+ ions passing through the P520 intermediate was calculated by using steered molecular dynamics (SMD) simulation combined with umbrella sampling. The result shows that the Na+ ions passing through the channel with a very low energy barrier, especially in the central gate, is almost barrierless. This indicates that the channel is open in the P520 state.

Engineering excitonically coupled dimers in an artificial protein for light harvesting via computational modeling.

In photosynthesis, pigment-protein complexes achieve outstanding photoinduced charge separation efficiencies through a set of strategies in which excited states delocalization over multiple pigments ("excitons") and charge-transfer states play key roles. These concepts, and their implementation in bioinspired artificial systems, are attracting increasing attention due to the vast potential that could be tapped by realizing efficient photochemical reactions. In particular, de novo designed proteins provide a diverse structural toolbox that can be used to manipulate the geometric and electronic properties of bound chromophore molecules. However, achieving excitonic and charge-transfer states requires closely spaced chromophores, a non-trivial aspect since a strong binding with the protein matrix needs to be maintained. Here, we show how a general-purpose artificial protein can be optimized via molecular dynamics simulations to improve its binding capacity of a chlorophyll derivative, achieving complexes in which chromophores form two closely spaced and strongly interacting dimers. Based on spectroscopy results and computational modeling, we demonstrate each dimer is excitonically coupled, and propose they display signatures of charge-transfer state mixing. This work could open new avenues for the rational design of chromophore-protein complexes with advanced functionalities.

Effects of hydrogen bonds on two-photon absorption of Green fluorescent protein chromophore analogue

Effects of hydrogen bonds on two-photon absorption (TPA) of a new donor-acceptor type green fluorescent protein chromophore analogue are investigated by employing a combined molecular dynamics and quantum chemistry method. The probable configurations of the chromophore in water are extracted from molecular dynamics simulation and the TP A properties of more than twenty hydrogen bond complexes are computed by quadratic response theory. Thereby, the structure and property relations are established. Three types of hydrogen bonds including O⋯H–O, N–H⋯O and N⋯H–O can be formed between the chromophore and water molecules. The O⋯H–O induces a little decrease of TPA cross section with a red-shifted wavelength. The N–H⋯O gives rise to a great enhancement of TP A at a longer wavelength, while the N⋯H–O decreases TP A significantly and makes the wavelength blue-shifted. The reasons for these effects are rationalized well by using a two-state model analysis. The related molecular orbitals are also plotted to visualize the charge transfer characters. In addition, the averaged TP A spectrum is obtained by calculating the probabilities of various hydrogen bond complexes. Our research could provide a good insight into the design of two-photon materials by making use of hydrogen bond networks.