A selective colorimetric chemosensor for thiols based on intramolecular charge transfer mechanism

Compound 1 as an electron donor-acceptor compound with N,N-dimethylaniline and quinone units was designed for a highly selective colorimetric determination of thiol-containing amino acids and peptides, by making use of the unique reactivity of thiol towards quinone. Compound 1 shows a strong intramolecular charge transfer (ICT) band around 582 nm; but, it decreased after addition of either cysteine (Cys) or glutathione (GSH). Moreover, the ICT band intensity at 582 nm decreased linearly with the increasing concentrations of Cys or GSH. The interference from other amino acids can be neglected. Therefore, compound 1 can be employed as a selective colorimetric visual chemosensor for thiol-containing amino acids and peptides.     

电化学方法用于分子内电荷转移特性的研究

设计合成一系列具有不同取代基的苯甲酰萘（苯）胺衍生和，测定它们在非极性溶剂环己烷中的荧光发射光谱，发现系列合成产物具有双重荧光，其长滤发射具有电荷转移特性，其长波发射态能量与不同取代基的苯甲酰萘（苯）胺衍生物的失（得）电子能力，即给（受）体的氧化还原电位之间符合Weller方程。     

Synthesis and spectral characteristics of two novel intramolecular charge transfer fluorescent dyes

The synthesis and absorption/fluorescence properties of two novel intramolecular charge transfer (ICT) compounds of (fluorene-2-yl)-(9-ethylcarbazole-3-yl) ketene and 1-phenyl-3-(fluorenone-2-yl)-5-(9-ethylcarbazole-3-yl)-2-pyrazoline were reported. The primary structure of the target compounds was characterized by IR and ¹H NMR. The systems contained a fluorenone or a propenon group as an electron acceptor (A) and an N-ethylcarbazole and a pyrazoline group as electron donors (D). From the emissive properties it was concluded that the electronic coupling between D and A was sufficient to allow charge transfer in these molecules. The ICT maximal emission displayed a large wavelength shift and Stokes shifts increased in response to the increase of the solvent polarity. The highly solvatochromic properties made the two compounds of great interest as new classes of fluorescent probes, electroluminescent and electrofax materials.     

Guest-responsive intramolecular charge transfer of viologen-crown ether conjugate

Viologen-benzocrown ether conjugate (1) was prepared, in which a phenyl unit in benzocrown ether was incorporated into the nitrogen atom of a bypiridinium unit through a sigma bond. 1 showed a yellow color associated with an intramolecular charge transfer (CT) that responds to alkali and alkaline earth metal ions, especially to Ca²⁺.     

Synthesis of new viologen macrocycles with intramolecular charge transfer

The syntheses of three new macrocycles composed of an acceptor (viologen) and a donor (dioxoaryl) are reported. These compounds exhibit intramolecular charge transfer and their X-ray analyses revealed that the aromatic systems are situated in parallel planes with a mean interplanar distance of 3.32 Å.     

Rational design of a colorimetric and ratiometric fluorescent chemosensor based on intramolecular charge transfer (ICT)

A simple colorimetric and ratiometric fluorescent anion sensor 1, 3,6-dichloro-1,8-dinitrocarbazole, was rationally designed and synthesized on basis of the mechanism of intramolecular charge transfer (ICT). In DMSO solutions of 1, the presence of AcO⁻, F⁻ and H₂PO₄⁻ gave birth to the formation of a 2:1 host-to-guest complex, which was synchronously accompanied by a ‘naked-eye’ color change from light yellow to purple, a red-shift of the absorption spectrum and a blue-shift of the emission spectrum.     

A colorimetric chemosensor for fast detection of thiols based on intramolecular charge transfer

A TCNQ-based triphenylamine derivative (1) with strong intramolecular charge transfer (ICT) character was designed as a colorimetric sensor for thiols. Upon addition of thiols, the absorption spectrum of sensor 1 in aqueous solution was remarkably changed because the adduct of 1 with thiol decreased its ICT character. Sensor 1 showed highly selective and sensitive sensing ability toward thiols over other analytes. This selectivity could be easily observed by naked eyes, indicating that sensor 1 is a potential colorimetric sensor for thiols.     

Rapid and easy protein staining for SDS-PAGE using an intramolecular charge transfer-based fluorescent reagent

High-performance staining for 1-D and 2-D SDS-PAGE was carried out using a novel protein-binding fluorophore (Dye 1), which noncovalently interacts with proteins and provides a fluorescence emission response to proteins by intramolecular charge transfer. In order to achieve the high-throughput analysis of proteins for SDS-PAGE, the general protocols for in-gel protein staining (SDS-PAGE, fixation, staining, washing, and detection) were simplified to produce an easy and rapid protocol (SDS-PAGE together with staining, washing, and detection). This method was performed by preparation of an electrophoresis buffer containing Dye 1 under optimum conditions, and by the binding of Dye 1 to proteins in the gel during the SDS-PAGE. As a result, this study required only 15 min for protein staining as a minimum time. On the other hand, it takes several hours for the general protein staining method, such as SYPRO Ruby staining (18 h) and CBB staining (105 min). Moreover, the protein-to-protein variation was low, and the detection limit was 7.0 ng/band of BSA (S/N = 3.0) in this method, which was as sensitive as the short-protocol silver staining methods. On the basis of these results, this rapid and easy protocol for SDS-PAGE using Dye 1 may be widely applicable and convenient for users in the various scientific and medical fields.     

The sensing mechanism of fluoride anion for a novel molecule D2: Desilylation and intramolecular charge transfer

In this work, the sensing mechanism of a new fluoride chemosensor 12‐([tert‐butyldiphenylsilyl]oxy)‐8a,13a‐dihydro‐7H‐benzo[de]benzo[4,5]imidazo[2,1‐a]‐isoquinolin‐7‐one (abbreviated as D2) is investigated using density functional theory (DFT) and time‐dependent DFT (TDDFT) methods. The theoretical electronic spectra (vertical excitation energies and fluorescence peak) reproduced previous experimental results (D. Li et al., Spectrochim. Acta A Mol. Biomol. Spectrosc. 2017 , 185, 173), which confirms the rationality of the theoretical level used in this work. The constructed potential energy curve of the desilylation process suggests that the low barrier could be responsible for the rapid response to fluoride anions. Analyses of the binding energies show that only fluoride anion can be detected by D2 chemosensor in dimethylsulfoxide (DMSO). In view of the excitation process, the strong intramolecular charge transfer (ICT) process of the S₀ → S₁ transition explains the red shift of the absorption peak of the D2 sensor with the addition of fluoride anions. This work not only presents a straightforward sensing mechanism of sensing of the fluoride anion by the D2 chemosensor but should also play an important role in the synthesis and design of fluorescent sensors in future.     

A boronic acid based intramolecular charge transfer probe for colorimetric detection of hydrogen peroxide

Many oxidative stress related diseases and adverse health conditions have been associated with the negative effects of hydrogen peroxide and other similar reactive oxygen species in human body. Therefore, increasing attention has been attracted to the detection and monitoring of hydrogen peroxide in living organisms and food items. In this work, a simple, inexpensive colorimetric method for the quantitative determination of hydrogen peroxide in aqueous sample is described. This method utilizes the de-protection of aryl boronic acid to yield a strongly colored water-soluble dye, which is capable of absorbing and emitting in the red region of the spectrum. The mechanism is faster in alkaline condition and utilizes the intramolecular charge transfer between strong phenolate donor and TCF acceptor, thus allowing a naked eye detection of hydrogen peroxide within seconds. The method is unaffected by the presence of various salts, metal ions, and other interfering species, and it can provide a limit of detection as low as ~1 ppm in aqueous samples. This unique way of generating a fluorogenic donor-acceptor pair holds a potential of this dye and other related derivatives for understanding the role of hydrogen peroxide in physiology and pathology.     

Piezofluorochromism of triphenylamine-based triphenylacrylonitrile derivative with intramolecular charge transfer and aggregation-induced emission characteristics

New triphenylacrylonitrile derivative (DPPA) with triphenylamine moiety as electron donor group has been synthesized. Its emission wavelengths were strongly affected by solvent polarity, indicating intramolecular charge transfer (ICT) transitions. It was found that DPPA was almost non-emissive in tetrahydrofuran (THF), and the emission could be intensified obviously when a great amount of H₂O was added, illustrating aggregation induced emission property. It is interesting that the pristine crystal of DPPA emitted green light, and the ground made its emitting color to change into orange, which could be recovered under fumed with dichloromethane (DCM) vapor. The piezofluorochromic behavior might be switched reversibly under the stimulus of external force because of crystalline-amorphous phase transformation, which could be confirmed from the results of PXRD patterns and DSC curves in different solid states. This work might open a new strategy to provide a broad perspective for the development of AIE PFC materials.     

Hg sensing in aqueous solutions: an intramolecular charge transfer emission quenching fluorescent chemosensors

Compounds 4a and 4b, comprising an anthracene moiety as the fluorophore and a pair of dithiocarbamate functionalities as ligating groups, were designed as fluorescent chemosensors for Hg(II). In aqueous solvent systems, upon excitation, in addition to the normal emission bands of locally excited (LE) state of anthracene, both compounds show a prominent pH-independent intramolecular charge transfer (ICT) emissive band, which can be modulated by Hg²⁺ binding. The systems can be exploited to develop a fluorescent sensitive probe for Hg²⁺.     

Theoretical investigation on dual fluorescence and intramolecular charge transfer of 5-phenyl-5H-phenanthridin-6-one

Quantum-chemical calculations with the time-dependent density function theory (TDDFT) have been carried out for 5-phenyl-5H-phenanthridin-6-one (PP). For this molecule, dual fluorescence and in- tramolecular charge transfer (ICT) were experimentally observed. The B3LYP functional with 6-311 G (2d, p) basis set has been used for the theoretical calculations. The solvent effects have been described within the polarizable continuum model (PCM). Ground-state geometry optimization reveals that the phenyl/phenanthridinone dihedral angle equals 90.0°, a nearly perpendicular structure. Vertical ab- sorption energy calculations characterize the lower singlet excited states both in gas phase and in solvents. It can be found that the lower excited states have locally excitation (LE) feature. Through constructing the potential energy curves of both isolated and solvated systems describing the LE→ICT reaction and fluorescence emission, we obtain the enthalpy difference ΔH between the LE and ICT states, energy barrier Ea, and energy difference δEFC, indicating the structural changes taking place during the ICT reaction. Potential curve and calculated emission energies for both isolated and sol- vated systems show a dual fluorescence phenomenon, consisting of a LE emission band and a red-shifted ICT band. Our calculations including the solvent effects indicate that the dual fluorescence is brought about by the change in molecular structure connected with the planarization of the twisted N-phenylphenanthridinone during the ICT reaction.     

分子内电荷转移双重荧光体识别阴离子研究

设计合成阴离子受体是近年来超分子化学中一个颇为活跃的研究领域[1～ 7] .其中荧光法以其高灵敏度和高选择性等特点使发光受体的设计合成备受关注 [6 ,7] .分子内电荷转移 (Intramolecular charge transfer,ICT)原理已被成功地用于构筑阳离子荧光传感体系[8] ,但将其应用于阴离子识别的研究尚鲜见报道[9～ 12 ] .本文设计合成了 ICT荧光体对二甲氨Scheme 1　 The structures of anion receptors基苯甲酰肼 (DMABH,结构见 Scheme 1 ) ,研究了 DMABH与阴离子如 HSO- 4,Ac O- ,H2 PO- 4,Cl O- 4,NO- 3,Cl- 和 Br- 等结合后的光…     

Spectral and photophysical properties of intramolecular charge transfer fluorescence probe: 4'-dimethylamino-2,5-dihydroxychalcone

The spectral and photophysical properties of a new intramolecular charge transfer (ICT) probe, namely 4′-dimethylamino-2,5-dihydroxychalcone (DMADHC) were studied in different solvents by using steady-state absorption and emission spectroscopy. Whereas the absorption spectrum undergoes minor change with increasing polarity of the solvents, the fluorescence spectrum experiences a distinct bathochromic shift in the band position and the fluorescence quantum yield increases reaching a maximum before decrease with increasing the solvent polarity. The magnitude of change in the dipole moment was calculated based on the Lippert–Mataga equation. These results give the evidence about the intramolecular charge transfer character in the emitting singlet state of this compound.     

Ultrafast intramolecular charge transfer and internal conversion with tetrafluoro-aminobenzonitriles.

The five 2,3,5,6-tetrafluoro-4-aminobenzonitriles XABN4F with a dimethyl-amino (DMABN4F), diethyl-amino (DEABN4F), azetidinyl (AZABN4F), methyl-amino (MABN4F) or amino (ABN4F) group undergo ultrafast intramolecular charge transfer (ICT) at room temperature, in the polar solvent acetonitrile (MeCN) as well as in the nonpolar n-hexane. ICT also takes place with the corresponding non-fluorinated aminobenzonitriles DMABN, DEABN and AZABN in MeCN, whereas for these molecules in n-hexane only minor (DMABN, DEABN) or no (AZABN) ICT fluorescence is detected. For the secondary (MABN) and primary (ABN) amines, an ICT reaction does not occur, which makes ABN4F the first electron donor/acceptor molecule with an NH(2) group for which ICT is observed. The ICT state of the XABN4Fs has a dipole moment of around 14 D, clearly smaller than that of DMABN (17 D). This difference is attributed to the electron withdrawing from the CN group to the phenyl ring, exerted by the four F-substituents. The reaction from the initially prepared locally excited (LE) to the ICT state in n-hexane proceeds in the sub-picosecond time range: 0.35 ps (DMABN4F), 0.29 ps (DEABN4F) and 0.13 ps (AZABN4F), as determined from femtosecond transient absorption measurements. In the highly polar solvent MeCN, an ICT reaction time of around 90 fs is observed for all five XABN4Fs, irrespective of the nature of their amino group. This shows that with these molecules in MeCN the ICT reaction rate is limited by the solvent dielectric relaxation time of MeCN, for which a value of around 90 fs has been reported. It is therefore concluded that, during this ultrashort ICT reaction, a large-amplitude motion such as a full 90 degrees twist of the amino group is unlikely to occur in the XABN4Fs. The ICT state of the XABN4Fs is strongly quenched via internal conversion (IC), with a lifetime tau'(0) (ICT) down to 3 ps, possibly by a reaction passing through a conical intersection made accessible due to a deformation of the phenyl group by out-of-plane motions induced by vibronic coupling between low-lying pisigma* and pipi* states in the XABN4Fs.     

Spectral properties of intramolecular charge transfer fluorescence probe 1-keto-2-(p-dimethylaminobenzal)-tetrahydronaphthalene

The photophysical properties of a new compound 1-keto-2-(p-dimethylaminobenzal)-tetrahydronaphthalene in various solvents at room temperature were characterized by the absorption and steady-state fluorescence technique. The bathochromic shift on the emission spectra, the broad halfwidth of the fluorescence band and the increase in the excited state dipole moment occurred. These results gave the evidence about the intramolecular charge transfer (ICT) character in the emitting singlet state of the compound.     

Photo-excited intramolecular charge transfer and excited state intramolecular proton transfer behaviors for HPIBT system: A theoretical investigation

Given facile synthetic route and excellent photo stability, excited state intramolecular proton transfer (ESIPT)-active luminous materials have gained more and more attention. Here, we focus on photo-induced excitation process and the ESIPT reaction process for the novel 5-benzothiazol-2-yl-6-hydroxy-2-methyl-isoindole-1,3-dione (HPIBT) molecule. On the level of chemical geometries and infrared spectra, we verify that O─H⋯N of HPIBT should be enhanced. We find that a proton is likely to be attracted by enhanced electronic densities around N, that is, charge transfer impetus ESIPT trend. Combing potential energy curves and searching for transition state, we clarify the ultrafast ESIPT mechanism of HPIBT due to a low barrier, which legitimately explains previous experimental characteristics.     

First experimental evaluation of partial charge transfer during anion adsorption

The partial charge transfer during anion adsorption cannot be measured in electrochemical experiments or reliably estimated by ab initio quantum-chemical and DFT calculations. However, it is directly involved in the adsorbate charge that is experimentally accessible by in situ contact electric resistance technique. We present the first quantitative evaluation of charge transfer during halides adsorption on silver from aqueous solutions in dependence on the electrode potential. Partial charge transfer from adsorbed bromide and iodide ions to the silver electrode increases with the positive potential shift and may reach complete charge transfer resulting in adatom creation. Chloride adsorption on silver occurs with much lower charge transfer, but on some stainless superalloys it proceeds with substantial charge transfer owing to their specific electronic structure.