Intramolecular Charge Transfer Behavior Research Articles

Use of DFT Calculations as a Tool for Designing New Solvatochromic Probes for Biological Applications

The intramolecular charge transfer behavior of push–pull dyes is the origin of their sensitivity to environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Those that are solvatochromic are of particular interest in studies of lipid dynamics and heterogeneity. The development of new solvatochromic probes has been driven largely by the need to tune desirable properties such as solubility, emission wavelength, or the targeting of a particular cellular structure. DFT calculations are often used to characterize these dyes. However, if a correlation between computed (dipole moment) and experimentally measured solvatochromic behavior can be established, they can also be used as a design tool that is accessible to students. Here, we examine this correlation and include case studies of the effects of probe modifications and conformation on dipole moments within families of solvatochromic probes. Indeed, the ground state dipole moment, an easily computed parameter, is correlated with experimental solvatochromic behavior and can be used in the design of new environment-sensitive probes before committing resources to synthesis.

Highly Emissive and Robust Cd-Based MOF with an Unprecedented Topology for Tetracycline Sensing.

Herein, an unprecedented cadmium-based metal-organic framework (JNU-106) fabricated by utilizing pyrazole-functionalized tetraphenylethylene ligands (Py-TPE) and rod-shaped secondary building units is reported, possessing a new (3,3,3,6,6,8)-connected topological network. Thanks to the ingeniously designed intramolecular charge transfer behavior, which originates from the congruent coplanarity between Py and TPE, JNU-106 exhibits intense green luminescence with a quantum yield increased by 1.5 times. The phenomenon of remarkable fluorescence quenching of JNU-106 reveals that it possesses extremely high anti-interference performance, superior sensitivity, and dedicated selectivity toward tetracycline antibiotics (TCAs) in aqueous solutions, which are comparable to those of the state-of-the-art porous sensing compounds. Taking the theoretical calculations and experimental results into account, the luminescence quenching is mainly attributed to the internal filtration effect and the static quenching effect. Considering the portable and rapid performance of JNU-106-based testing strips for sensing TCAs, the fabricated JNU-106 provides an alternative for ecological monitoring and environmental governance.

Colorimetric and fluorometric bimodal amine chemosensor based on deprotonation-induced intramolecular charge transfer: Application to food spoilage detection

Amine derivatives are signature organic compounds generated from rotten protein food. Thus, sensitive detection of the presence of amines in protein foods can be a critical technique for monitoring their quality. In this study, we develop an organic chemosensor probe, 4-(2-(3-(dicyanomethylene)− 5,5-dimethylcyclohex-1-en-1-yl)vinyl)-N,N-diethylbenzenaminium chloride (DEAH), to effectively detect amines through discernible bimodal (colorimetric and fluorometric) changes. By exploiting the amine-triggered intramolecular charge transfer behavior, DEAH exhibits rapid color changes (<1 s) with an excellent detection limit (36.9 nM) and also fluorescence turn-on in response to amine gas. Moreover, it possesses detection capabilities in versatile conditions, including solutions, solids, and coated films, suggesting its practical applicability. In particular, DEAH shows dramatic color change from yellow to violet with exceptional color difference (△Eab) over 98, repeatable usability, and excellent selectivity to amines. Based on these compelling advantages, we successfully demonstrate real-time monitoring of amine gas generated from spoiled protein foods using DEAH-coated films.

Calix[4]arene-Derived 2D Covalent Organic Framework with an Electron Donor-Acceptor Structure: A Visible-Light-Driven Photocatalyst.

The calixarenes are ideal building blocks for constructing photocatalytic covalent organic frameworks (COFs), owing to their electron-rich and bowl-shaped π cavities that endow them with electron-donating and adsorption properties. However, the synthesis and structural confirmation of COFs based on calixarenes are still challenging due to their structural flexibility and conformational diversity. In this study, a calix[4]arene-derived 2D COF is synthesized using 5,11,17,23-tetrakis(p-formyl)-25,26,27,28-tetrahydroxycalix[4]arene (CHO-C4A) as the electron donor and 4,7-bis(4-aminophenyl)-2,1,3-benzothiadiazole (BTD) as the acceptor. The powder X-ray diffraction data and theoretical simulation of crystal structure indicate that COF-C4A-BTD exhibits high crystallinity and features a non-interpenetrating undulating 2D layered structure with AA-stacking. The density functional theory theoretical calculation, transient-state photocurrent tests, and electrochemical impedance spectroscopy confirm the intramolecular charge transfer behavior of COF-C4A-BTD with a donor-acceptor structure, leading to its superior visible-light-driven photocatalytic activity. COF-C4A-BTD exhibits a narrow band gap of 1.99eV and a conduction band energy of -0.37V versus normal hydrogen electrode. The appropriate energy band structure can facilitate the participation of ·O2- and h+ . COF-C4A-BTD demonstrates high efficacy in removing organic pollutants, such as bisphenol A, rhodamine B, and methylene blue, with removal rates of 66%, 85%, and 99% respectively.

Turning enol* emission of SBOH via restricting twisted intramolecular charge transfer behavior by pressure.

Stimuli-responsive luminogens with aggregation-induced emission and excited state intramolecular proton transfer (ESIPT) properties have applications in storage devices, anti-counterfeiting, imaging, and sensors. Nevertheless, group rotation appears in twisted intramolecular charge transfer (TICT) state, resulting in decreased fluorescence intensity. Inhibiting TICT remains a challenge based on their intrinsic molecular configuration. Herein, we present a simple facile pressure-induced method to restrict the TICT behavior. Steady-state spectroscopy measurement shows that fluorescence enhancement and color shifts can be achieved under high pressure. Combined with in situ high-pressure ultrafast spectroscopy and theoretical calculations, the TICT behavior was restricted in two aspects. The ESIPT process was damaged, hence more particles stored in the E* state, and transferred to the TICT state hardly. Also, the rotation of (E)-dimethyl5-((4-(diethylamino)-2-hydroxybenzylidene)amino)isophthalate (SBOH) was restricted, significantly increasing the fluorescence intensity. This approach provides a new strategy for the development of stimulus-responsive materials.

DFT calculations, spectroscopic investigations, and molecular docking study of Methylprednisolone with some selective cancer proteins

Cancer refers to a group of diseases caused by the abnormal growth and uncontrolled division of cells with the potential to spread over the surrounding tissues. Methylprednisolone is a corticosteroid that exhibits a broad spectrum of anti-inflammatory and antioxidant properties. In this study, the structural analysis (bond length, bond angle), spectroscopic (FTIR, Raman, SERS), and anticancer activity study of Methylprednisolone are carried out. The geometrical optimization and the theoretical vibrational analysis are performed at B3LYP/6–311 + G(d,p) computational level under density functional theory (DFT) and correlated with experimental data. The NBO and AIM analyses are conducted to probe the intramolecular charge transfer behavior and the strength of interactions. The MEP and HOMO-LUMO analyses are carried out to study the reactivity of the complex. The molecular docking analysis is performed against some cancer-related target proteins, which shows better inhibitory activity of Methylprednisolone against the 2VCJ (skin cancer) receptor with the binding energy of − 8.21 kcal/mol.

Solvatochromic Behavior of 2,7-Disubstituted Sila- and Germafluorenes

Push–pull dyes exhibit intramolecular charge transfer behavior, which due to changes in the dipole moment upon excitation, is the origin of their sensitivity to the environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Desirable biological probes absorb in the visible region, have high extinction coefficients, high quantum yield and excellent photostability. Fluorophores with scaffolding that can be used to tune and optimize solvatochromic behavior are of particular interest. Here, we investigate the environmental sensitivity of a small library of highly fluorescent 2,7-disubstituted sila- and germafluorenes. Density functional theory (DFT) calculations show that charge transfer occurs from the alkyne core out to the 2,7-substitutents and 3,6-methoxy substituents, the hallmark of push–pull behavior. They exhibit HOMO–LUMO energy gaps of about 3 eV with desirable dipole moments ranging from 2 to 9 D. These compounds exhibit desirable Stokes shifts in various solvents (25 to 102 nm). Interestingly, silafluorene with a benzaldehyde substituent exhibits competitive solvatochromic behavior. With the ability to tune push–pull properties via the 2,7-substituent, these disubstituted sila- and germafluorenes have excellent potential as biological probes.

Observation of protonation-induced intra-molecular metal-to-metal charge transfer in cyano-bridged [Fe-CN-Mn/Ni] dinuclear complexes.

A key challenge in the design of magnetic molecules with intramolecular charge transfer behavior is to obtain reversible magnetic bistability triggered by external stimuli. Here, we show that two dinuclear metal complexes, [(bbp)Fe(CN)3Mn(Py5Me2)]·2.5CH3OH (4) and [(bbp)Fe(CN)3Ni(Py5Me2)]·2.5CH3OH (5) (Py5Me2 = 2,6-bis(1,1-di(pyridine-2-yl)ethyl)pyridine, H2bbp = 2,6-bis(benzimidazole-2-yl)pyridine), were self-assembly synthesized by (Bu4N)2[(bbp)FeIII(CN)3] and [Mn(Py5Me2)(OH2)](ClO4)2 or [Ni(Py5Me2)(OH2)](ClO4)2, respectively. Complexes 4 and 5 exhibited intramolecular metal-to-metal charge transfer with the addition of acids or bases in solution by UV-visible spectrophotometric measurements and electrochemistry studies, and concomitant switching of the {FeIII(μ-CN)MnII/NiII} state to the {FeII(μ-CN)MnIII/NiIII} state.

Effects of Twisted Intramolecular Charge Transfer Behavior on Excited-State Intramolecular Proton Transfer Reactions of Methyl Benzoate Derivatives in Water Solution.

Many methyl benzoate derivatives were found to show intramolecular charge transfer (ICT), intramolecular proton transfer, and other properties, which have extensive applications in lasing media, metal ion sensors, active materials, and fluorescence probe fields. However, the intrinsic relationship and reaction mechanism between the excited-state intramolecular proton transfer (ESIPT) and ICT between methyl benzoate derivatives with different substituents have not been explained. In this paper, the density functional theory and time-dependent density functional theory methods were used to study the ESIPT and ICT behaviors of p-aminosalicylic acid methyl ester and p-dimethylaminosalicylic acid methyl ester in water and obtain the intrinsic interaction between the two behaviors. The bond parameters, infrared spectra, reduced density gradient scatter plots, and topological analyses of these two molecules in the ground state and excited state were analyzed to confirm the enhancement of the excited-state intramolecular hydrogen bonds (IHBs). The simulated absorption and fluorescence spectra of these molecules agreed well with the experimental values. Based on the optimized structure, we also plotted the natural transition orbitals, electron density difference maps, and frontier molecular orbitals (FMOs), which showed the changes of the charge distribution of these molecules intuitively upon photoexcitation. In addition, we also found that the degree of IHB enhancement with -N(CH3)2 substituents was less than that with -NH2, reflecting an inhibition effect of twisted intramolecular charge transfer (TICT) on ESIPT reaction. This conclusion was confirmed by our calculated potential energy curves. This work may better deepen the comprehension of the intrinsic relationship between ESIPT and TICT behavior and sequentially provide better theoretical guidance for the synthesis of fluorescent molecules related to these two behaviors.

Synthesis of isoniazid-substituted tetraphenylethylene stereoisomers with dramatic differences on aggregate morphologies, optical and mechanocharomic properties

Stereoisomers play an irreplaceable prominent role in life sciences. In molecular engineering, the isomers have been continuously designed and synthesized, and their interrelationships among structure-property-function have also been explored. However, the difficulties in purification and structural confirmation of tetraphenylethene (TPE) derivatives' stereoisomers hinder their structural diversity and scope of functions. Meanwhile, there were few researches on the macroscopic optical differences about TPE derivatives isomers. Herein, isoniazid-substituted TPE derivatives stereoisomers have been synthesized, as confirmed by single crystal data, mass spectrometry and NMR spectroscopy. The different photophysical properties were caused by the introduction of functional group isoniazid on the periphery of TPE. These isomers possessed dramatic differences in fluorescent properties, and exhibited diverse changes in response to stimuli. They also have distinct aggregated self-assembly morphologies because of different intermolecular hydrogen bonding, and they can be used as efficient fluorescent probes for detecting copper. Based on the coordination-driven sensing system, the morphologies of isomers aggregates changed significantly after interaction with copper, and the stoichiometry between them is 2:1. The theoretical calculation demonstrated that they have obvious intramolecular charge transfer behavior. Our research provided a good strategy for designing different substituted groups that can produce various functions and have more potential applications.

A novel, anthracene-based naked eye probe for detecting Hg2+ ions in aqueous as well as solid state media

A novel di-Schiff base colorimetric sensor, 2-((E)-(((E)-anthracen-9-ylmethylene)hydrazineylidene)methyl)quinolin-8-ol (coded as AQ), connecting anthracene and 8-hydroxyquinaldehyde functionalities is developed for the naked eye detection of Hg2+ ions in HEPES buffered CH3OH: H2O (7: 3) solvent system within neutral pH range. The sensor witnessed high selectivity towards Hg2+ ions in the presence of various other metal ions with naked eye colour change from yellow to pink. The quantitative detection limit of 220 nM was achieved through UV–Vis spectroscopy. The change in the intramolecular charge transfer behaviour of AQ has been proposed to be responsible for the observed absorption as well as colour change as evident from 1H NMR titration, FT-IR studies and DFT calculations. Moreover, the probe AQ has been efficiently applied for the solid state naked eye detection of Hg2+ ions in the form of filter paper strips and solid silica gel (60–120 mesh), pre-impregnated with AQ, and for the detection of Hg2+ ions in real water samples.

Revealing high hydrogen evolution activity in zinc porphyrin sensitized hierarchical porous TiO2 photocatalysts

In this work, a dye/TiO2 system for hydrogen generation via the reduction of water has been investigated. The use of simple and template free synthesis process for hierarchical porous architecture of TiO2 (HPT) with a panchromatic Zinc-porphyrin (LG5) sensitizer has been identified as the potential material in photoinduced hydrogen production. The effect of the dye absorbed by the Pt-HPT has been tested for the hydrogen production under visible light irradiation in presence of triethanolamine (TEOA) or Glycerol (Gly) as sacrificial electron donor (SED). The enhanced activity and effective charge transfer from the dye to the TiO2 molecule is significant in the PHPT-LG5 composite. The PHPT-LG5 catalyst exhibited higher photocatalytic activity of 4196 μmol g−1 h−1 with an impressive turnover numbers (TON) of 8392 and apparent quantum yield (AQY) of 7.43% of light irradiation using 450 W Xe lamp when compared to the corresponding simple semiconductor as well as the N719 dye loaded catalysts. The acrylic group present in the dye molecule helps in binding the semiconductor with the dye molecule and leads to superior photocatalytic activity. The diffuse reflectance spectroscopy (DRS), and computational studies of the dye molecule and the composite suggests the better photocatalytic performance of the composite. The Fourier Transform Infra-Red Spectroscopy (FTIR) studies reveals the strong attachment of the dye molecule with the semiconductor hierarchical porous TiO2 (HPT) results in the enhancement in hydrogen production, the stability tests of the photocatalyst shows higher reproducibility at neutral pH in TEOA. A systematic study of LG5 with sacrificial electron donors and pH were performed and are correlated with the photocatalytic activity of N719 dye. The presence of the cyanoacrylic group as an anchoring group in the LG5 leads to red shift in S and Q bands suggesting the efficient intramolecular charge transfer behavior (CT) and possess strategies for broadening the light harvesting properties. The present work opens up a new window toward solar energy conversion with extended light harvesting capacity and enhanced photocatalytic activity.

Study on TICT emission of TPE-BODIPY derivatives mediated by methyl group on BODIPY

A series of tetraphenylethene-borondipyrromethene (TPE-BODIPY) derivatives with different numbers of methyl groups on BODIPY cores were designed and synthesized. The intramolecular charge transfer behaviors from donor TPE to accepter BODIPY were investigated. Aggregation-induced emission (AIE), theoretical calculation, single crystal structure and solvent effect all proved that the introduction of methyl group to BODIPY can inhibit the intramolecular charge transfer behavior. Red organic luminescent material 8-TPEBODIPY (TPB) with no methyl groups showing twisted intramolecular charge transfer (TICT) emission peak both in solution and in film state, presents obviously AIE and solvatochromic properties and a large Stokes shifts over 100 nm, which can be employed as a fluorescent sensor for the detection of water in THF.

Donor-Acceptor Conjugated System: A Neutral Hydrophobic Fluorescence Probe

Fluorescence probe with intramolecular charge transfer behavior has received a great deal of attention in recent years Such molecule is highly sensitive to its local environment and plays critical role in many industrial and biological applications Donor acceptor conjugated systems based on diphenylpolyene are one of such example The presence of conjugated chain length and the donor acceptor substituent rsquo s at the appropriate position allows the molecule to cover a wide range of absorption and fluorescence wavelength and hence the optical property of the molecule is attenuated easily Thus diphenylpolyenes are suitable candidate for various fluorescence probe applications The above mentioned aspects have been discussed and summarized in this paper

Estimation of Ground-State and Singlet Excited-State Dipole Moments of Substituted Schiff Bases Containing Oxazolidin-2-one Moiety through Solvatochromic Methods

Absorption and fluorescence studies on novel Schiff bases (E)-4-(4-(4-nitro benzylideneamino)benzyl)oxazolidin-2-one (NBOA) and (E)-4-(4-(4-chlorobenzylidene amino)benzyl)oxazolidin-2-one (CBOA) were recorded in a series of twelve solvents upon increasing polarity at room temperature. Large Stokes shift indicates bathochromic fluorescence band for both the molecules. The photoluminescence properties of Schiff bases containing electron withdrawing and donating substituents were analyzed. Intramolecular charge transfer behavior can be studied based on the influence of different substituents in Schiff bases. Changes in position and intensity of absorption and fluorescence spectra are responsible for the stabilization of singlet excited-states of Schiff base molecules with different substituents, in polar solvents. This is attributed to the Intramolecular charge transfer (ICT) mechanism. In case of electron donating (-Cl) substituent, ICT contributes largely to positive solvatochromism when compared to electron withdrawing (-NO2) substituent. Ground-state and singlet excited-state dipole moments of NBOA and CBOA were calculated experimentally using solvent polarity function approaches given by Lippert-Mataga, Bakhshiev, Kawskii-Chamma-Viallet and Reichardt. Due to considerable π- electron density redistribution, singlet excited-state dipole moment was found to be greater than ground-state dipole moment. Ground-state dipole moment value which was determined by quantum chemical method was used to estimate excited-state dipole moment using solvatochromic correlations. Kamlet-Abboud-Taft and Catalan multiple linear regression approaches were used to study non-specific solute-solvent interaction and hydrogen bonding interactions in detail. Optimized geometry and HOMO-LUMO energies of NBOA and CBOA have been determined by DFT and TD-DFT/PCM (B3LYP/6-311G (d, p)). Mulliken charges and molecular electrostatic potential have also been evaluated from DFT calculations.

The first porphyrin-subphthalocyaninatoboron(iii)-fused hybrid with unique conformation and intramolecular charge transfer behavior.

Porphyrin and subphthalocyaninatoboron(iii) chromophores have been fused through a quinoxaline moiety, resulting in the first porphyrin-subphthalocyaninatoboron(iii)-fused hybrid with intramolecular charge transfer from tetrapyrrole/tripyrrole chromophores to the quinoxaline moiety. The unique plane-bowl molecular structure of this hybrid was revealed based on single crystal X-ray diffraction analysis for the first time.

Synthesis and solvatochromic behavior of branched oligophenylenes with hydroxy groups

Investigation of the solvatochromic behavior in branched oligophenylenes (OPs) will lead to a better understanding of intramolecular charge transfer behavior in the aromatic compounds and toward the development of new functional materials. However, there is no report on solvatochromism of branched OP. In this study, branched OPs with phenolic hydroxy groups were synthesized by using reactions with transition metal complexes. The treatment of these compounds with a base produced corresponding deprotonated species, whose absorption and photoluminescence peak positions in solution shifted towards longer wavelengths with an increase in the donor numbers of the solvents. These results will be useful in providing information for the development of new solvatochromic and energy trapping materials based on branched aromatic compounds. Copyright © 2014 John Wiley & Sons, Ltd.

Heteropolyanion-paired cross-linked ionic copolymer: An efficient heterogeneous catalyst for hydroxylation of benzene with hydrogen peroxide

A heteropolyanion-based cross-linked ionic copolymer was prepared by the anion-exchange of heteropolyacid (HPA) H5PMo10V2O40 with polymeric ionic liquid (PIL) poly(divinylbenzene-3-n-butyl-1-vinylimidazolium)Br, and characterized by FI-IR, UV–vis, XRD, TG, SEM, elemental analysis and BET surface areas. The characterization results show that the ionic copolymer is an amorphous HPA salt of PIL-cation with a considerable thermal stability, high surface area and large pore volume. Further, the ionic copolymer is revealed to be a highly efficient heterogeneous catalyst for hydroxylation of benzene with H2O2 to phenol, showing high activity, convenient recovery and steady reuse. The excellent performance of the novel porous HPA-based copolymer catalyst is discussed in relation to its textural property and intramolecular charge transfer behavior.

Synthesis and photophysics of a novel photocatalyst for hydrogen production based on a tetrapyridoacridine bridging ligand

Molecular photocatalysts allow for selectively tuning their function on a molecular level based on an in-depth understanding of their chemical and photophysical properties. This contribution reports the synthesis and photophysical characterization of the novel molecular photocatalyst [(tbbpy) 2Ru(tpac)PdCl 2] 2+ RutpacPd (with tpac = tetrapyrido[3,2- a:2′,3′- c:3″,2″- h:2‴,3‴- j]acridine) and its mononuclear building block. Furthermore, detailed photocatalytic activity measurements of RutpacPd are presented. The introduction of the tpac-ligand into the molecular framework offers a potential route to reduce the impact of water as compared to the well-studied class of RutpphzPd (with tpphz = tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine) complexes. The distinct impact of water on the electron-transfer processes in tpphz-ligands stems from the possibility of water to form hydrogen bonds to the phenazine nitrogen atoms and will potentially reduced when replacing the phenazine by the acridine unit. The effect of this structural variation on the catalytic properties and the underlying ultrafast intramolecular charge transfer behavior will be discussed in detail.

Tuning of Photocatalytic Hydrogen Production and Photoinduced Intramolecular Electron Transfer Rates by Regioselective Bridging Ligand Substitution

Artificial photosynthesis based on supramolecular photocatalysts offers the unique possibility to study the molecular processes underlying catalytic conversion of photons into chemical fuels in great detail and to tune the properties of the photocatalyst by alterations of the molecular framework. Herein we focus on both possibilities in studying the photocatalytic reduction of protons by derivatives of the well-known photocatalyst [(tbbpy)(2)Ru(tpphz)PdCl(2)](PF(6))(2) [4,4'-di-tert-butyl-2,2'-bipyridine (tbbpy), tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine (tpphz)]. We report on a modified photocatalyst where the crucial bridging ligand tpphz is substituted by bromine and investigate the effect of the structural variation on the catalytic properties of the complex and its ultrafast intramolecular charge transfer behavior. It is found that structural modification stabilizes the phenanthroline-centered metal-to-ligand charge-transfer state on the tpphz moiety, thereby reducing the electron transfer gradient across the entire electron-relaying bridging ligand and at the same time accelerating nanosecond ground-state recovery. The same structural modifications cause an overall reduction of the catalytic activity of the complex. Thus, the results highlight the potential of small structural variations in the molecular framework of supramolecular catalysts in understanding the photoinduced charge-transfer processes and optimizing their catalytic performance.