Intramolecular Charge Transfer Phenomenon Research Articles

Experimental and theoretical study of the Favipiravir association in water solvent

Favipiravir, also known as T-705, is an antiviral prodrug that was first developed against the influenza virus and was later found to be effective against other RNA viruses, including arenaviruses, bunyaviruses, Zika, Ebola, Lassa, and COVID-19 viruses, in addition to influenza A and B. Due to the global prevalence of SARS-COV-2 in 2019, Favipiravir was used as an antiviral drug for treating COVID-19, but the challenges facing it, including its solubility, tablet ability, and bioavailability, remain. It is critical and challenging to develop a drug with appropriate bioavailability, improved oral absorption, and increased solubility without interfering with other functions and preventing the consumption of high daily doses. For this purpose, in the present study, the interactions of Favipiravir-Favipiravir and Favipiravir-H2O and the association of the Favipiravir molecules were investigated experimentally and theoretically. The theoretical results showed that under normal conditions, all structures were stable, but the most stable structure based on calculations of electronic energy, Gibbs, and solvation Gibbs free energies (minimum value), both in the gas phase and in the aqueous phase, is related to the B-enol isomer. Also, the change in dipole moment in the solvation process for this isomer was less than others. Also, the intense intermolecular hydrogen bonds O-H…O and N-H…O between the Favipiravir and water molecules showed that Favipiravir…Favipiravir interactions are stronger than Favipiravir…H2O interactions in aqueous solutions. These interactions indicate that Favipiravir can participate in the aggregation phenomena in high concentrations. Also, Stokeʼs shift values slightly increased with the decreasing the drug concentration in water (intramolecular charge transfer phenomenon).

Enhanced efficiency of DSSCs by co-sensitizing dyes with complementary absorption spectra

In order to understand the mechanism of molecular improvement by dye co-sensitization at the microscale, a co-sensitized molecular system is simulated using density functional theory and time-dependent density functional theory. The single molecules AJ502 and TZ101 are first evaluated globally, with AJ502 having better spectral response performance and higher light absorption efficiency. The AJ502 molecule has a strong electron accept ability and intramolecular charge transfer phenomenon. These factors make the short circuit current density and photoelectric conversion efficiency of AJ502 have a very prominent performance. At the same time, the co-sensitization properties of AJ502 and TZ101 are investigated, finding that the overall molar extinction coefficient and charge transfer phenomenon of the co-sensitized system are enhanced. Most importantly, a detailed comparison of the effects of the two co-sensitized conformations on dye-sensitized solar cell devices shows that the H-H conformation is the most advantageous due to its more robust structure, pronounced red shift in the absorption spectrum and larger amount of intermolecular charge transfer.

Sustainable natural chlorogenic acid as a functional molecular sensor toward viscosity detection in liquids.

Liquids are perishable at ease during the long-term transportation and storage processes, non-invasive and in situ inspection method is urgent to be developed. In consideration of the important role of viscosity, one kind of sustainable natural product chlorogenic acid (CA) extracted from honeysuckle has been used as a versatile optical sensor for viscosity determination during the liquid spoilage process. The natural molecule was conducted by the O-diphenyl and carboxylic acid ester groups in coincidence, a typical twisted intramolecular charge transfer phenomenon was formed. This sensor features wide adaptability, high selectivity, good sensitivity, and excellent photo stability in various liquids. And CA displays a larger Stokes shift, high viscosity sensitive coefficient (0.62), and narrower energy band. The rotatable conjugate structure can be acted as the recognition site, and the bright fluorescent signal of CA is specifically activated when in the high viscous micro-environment. Inspired by this objective phenomenon, CA has been applied to detect the thickening efficiency of various food thickeners. More importantly, the viscosity fluctuations during the deterioration stage of liquids can be screened through non-invasive and in situ monitoring. We expected that more natural products can be developed as molecular tools for liquids safety investigation, and fluorescent analytical methods can be expanded toward interdisciplinary research.

Intramolecular charge transfer-based spirobifluorene-coupled heteroaromatic moieties as efficient hole transport layer and host in phosphorescent organic light-emitting diodes

In this study, we report two efficient intramolecular charge transfer (ICT) compounds with versatile functionality as hole transporting layers (HTL) and hosts in emission layer (EML) of phosphorescent organic light emitting diodes (Ph-OLEDs) with donor-acceptor-donor structures. In both molecules, 9,9′-spirobifluorene (SBF) was employed as a common electron acceptor, while phenoxazine (PXZ) or phenothiazine (PTZ) were used as donors. The molecules 2,7-di(10H-phenoxazin-10-yl)-9,9′-spirobi[fluorene] (SBF-PXZ) and 2,7-di(10H-phenothiazin-10-yl)-9,9′-spirobi[fluorene] (SBF-PTZ) were synthesized via a Buckwald-Hartwig cross-coupling reaction in a single step that exhibited typical ICT phenomena. The extremely twisted geometrical configurations of SBF-PXZ and SBF-PTZ may allow for effective intramolecular charge-transfer. Both molecules exhibited strong absorption and emission characteristics in the visible region in solution as well as in the thin film form; significant positive solvatochromism was also observed for both compounds. The replacement of PTZ donor with the PXZ donor caused a bandgap reduction together with an improved ionization potential (IP). The deeper IP (>5.1 eV), greater glass transition temperature, and higher hole mobility extracted from the hole only devices of both molecules revealed them as superior candidates for HTL applications (with/without exciton blocking layers) in Ph-OLEDs. It is further corroborated by the enhanced half-life time of Ph-OLEDs with SBF-PXZ/SBF-PTZ HTLs. Moreover, the OLED performances with SBF-PTZ and SBF-PXZ as EMLs and hosts for phosphorescent dopant OLEDs have exemplified the versatility of the proposed ICT compounds.

Hydrogen bonding interactions induced excited state proton transfer and fluoride anion sensing mechanism for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐5‐carboxylicacid

AbstractThe present work explores and reports photo‐induced behavior and excited state intramolecular proton transfer (ESIPT) process for the novel 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐5‐carboxylicacid (DICH) compound. Our theoretical investigation implies that two intramolecular hydrogen bonds (O1─H2···N3 or O4─H5···O6) of DICH form are strengthening in the first excited state by comparing bond lengths, bond angles, and infrared (IR) spectra, which may facilitate the ESIPT process effectively. Particularly, the changes of O1─H2···N3 are bigger than O4─H5···O6, which demonstrates that the ESIPT is more likely to happen along with O1─H2···N3. Within the framework of MOs analysis, intramolecular charge transfer phenomenon can be found, which could be a reasonable evidence for confirming the occurrence of the ESPT process in the S1 state. We theoretically construct the potential energy curves for DICH system based on fixing both O1─H2 and O4─H5 bond lengths and optimizing structures in both S0 and S1 states. Through the comparisons of potential barriers among stable configurations, we confirm the S1‐state DICH‐PT1 (proton‐transfer tautomer along with O1─H2···N3) should be the most reasonable configuration ascribed to previous experimental emission peak. Furthermore, we also predict and explain the fluoride‐sensing mechanism for DICH system that the deprotonation reaction bringing from fluoride anion inhibits the initial ESIPT process of DICH, which results in the novel changes of ultraviolet‐visible (UV‐Vis) spectra that plays the roles in fluorescence response. We sincerely hope this work could provide essential insights into the design and function of ESIPT as well as florescence sensor for optoelectronic applications.

Molecular Origins of the Nonlinear Optical Responses of a Series of α-(X-2-Pyridylamino)-o-cresol Chromophores from Concerted X-ray Diffraction, Hyper-Rayleigh Scattering, and Ab Initio Calculations

Faster transmission rates are desperately needed in the telecommunications industry, given that global demand for signal transmission already outstrips supply. New organic nonlinear optical (NLO) materials offer a prospective solution for the telecommunications industry given that they exhibit shorter optical response times compared to their inorganic counterparts. α-(X-2-Pyridylamino)-o-cresol-type motifs with their donor−π–acceptor (D−π–A) architecture and high level of π-conjugation are expected to afford high levels of intramolecular charge transfer (ICT). Such ICT phenomena will contribute to these types of molecules having faster optical response times and large (hyper)polarizabilities. The linear and second-order NLO properties of three new α-(X-2-pyridylamino)-o-cresol motifs (X = 4-CH3 (1); 5-Cl (2); 3,5-Cl (3)) were hence evaluated. NLO structure–function relationships were established in terms of their ICT characteristics and molecular hyperpolarizabilities (β). Given the typically large errors...

Theoretical investigation on the excited state intramolecular proton coupled charge transfer phenomenon for a novel fluorophore

AbstractWe theoretically investigate the excited state behaviors of the novel fluorophore tetraphenylethene‐2‐(2′‐hydroxyphenyl)benzothiazole (TPE‐HBT), which was designed based on the intersection of TPE and HBT, using density functional theory and time‐dependent density functional theory methods. Compared with previous experimental results about fluorescence peaks, our calculated results are in good agreement with experimental data, which further confirms that the theoretical level we used is reasonable. Furthermore, our results confirm that the excited state intramolecular proton transfer (ESIPT) process happens upon photoexcitation, which is distinctly monitored by the infrared spectra and the potential energy curves. In addition, the calculation of highest occupied molecular orbital and lowest unoccupied molecular orbital reveals that the electron density change of proton acceptor because of the intramolecular charge transfer (ICT) process in the S1 state induces the ESIPT. Moreover, the transition density matrix is worked out to facilitate deeper insight into the ESIPT coupled ICT process. It is hoped that the present work not only elaborates the ESIPT coupled ICT phenomenon and corresponding mechanisms for the TPE‐HBT but also may be helpful to design and develop new materials and applications involved in TPE‐HBT systems in future.

Li+-Induced fluorescent metallogel: a case of ESIPT-CHEF and ICT phenomenon

A fluorescent metallogel (1% w/v) has been synthesized from non-fluorescent ingredients viz. the smallest possible low molecular weight aromatic symmetrical ligand H2SA (1) and LiOH in a chloroform and methanol mixture. The chelation of Li+ is not only responsible for the inhibition of excited state intramolecular proton transfer (ESIPT) or the origin of fluorescence through chelation enhanced fluorescence (CHEF) in 1, but also for aggregation leading to gelation. The metallogel obtained from 1/Li+ reveals a fibrous morphology while 1 with other, bigger size, alkali metal ions like Na+/K+/Cs+ demonstrates the growth of crystals with different shapes. The effect of the size of the alkali metal ion over gel formation is well explored by FTIR, UV-vis, fluorescence, average lifetime measurements, SEM and PXRD. The metallogel shows multi-stimuli responsive behaviour towards thermal and mechanical stress as well as reswelling properties. The regioisomer H2PBA (2) also shows emission upon treatment with LiOH due to the presence of intramolecular charge transfer (ICT), this is well established by various experiments. The mechanism of gel formation is well established by FTIR, 1H NMR, UV-vis, fluorescence, lifetime measurements, SEM and single crystal and powder XRD instrumental techniques. The involvement of various phenomena in gel formation has been further supported by other synthesized model compounds viz. H2MBA (3), PMO (4), H2SEA (5) and H2SPA (6). True gel phase material is proved by detailed rheological experiments.

Spectroscopic and theoretical investigations on intramolecular charge transfer phenomenon in 1-3-dioxolane derivative

High fluorescence quantum yield (FQY) and large Stokes shift (SS) cannot be easily achieved simultaneously by traditional PICT or TICT fluorescent probe. However, an 1-3-dioxolane derivative named 5-methyl-8,9-dihydro-5H-[1,3]dioxolo[4,5-b]carbazol-6(7H)-one (MDDCO) features both high FQY and large SS. The purpose of this study is to search the mechanism behind this phenomenon by theoretical method. Simulated structure changes and charge transfer suggest ICT process in MDDCO is similar to PLICT (Planarized Intramolecular Charge Transfer) process. Calculated UV–Vis spectra and fluorescence spectra show that PLICT-like state (S1 state) of MDDCO leads to large SS. Computed transient-absorption spectra and radiative decay rates indicate that PLICT-like state is key factor for high FQY of MDDCO. These findings suggest that PLICT-like state in 1,3-dioxolane derivatives can achieve both large SS and high FQY, which presents a new method for high-performance fluorescent probe design.

Proton Induced Modulation of ICT and PET Processes in an Imidazo-phenanthroline Based BODIPY Fluorophores.

BODIPY fluorophores linked with an imidazo-phenanthroline donor at α and β positions have been synthesized. Intriguing intramolecular charge transfer phenomenon is observed in both the dyes which has been extensively investigated using UV-vis absorption, steady-state and time-resolved fluorescence measurements. H-bonding and intrinsic polarity of the solvents has modulated the absorption and emission bands of these fluorophores strongly causing significant increase in the Stokes shifts. In spite of having difference only in terms of the position of donor subunit, the photophysics of these dyes are not only significantly different from each other, but contradictory too. Interestingly, acidochromic studies revealed the shuttling mechanism between ICT and PET processes for BDP 2. Quantum chemical calculations have been employed further to support experimental findings. DFT and TD-DFT method of analysis have been used to optimize ground and excited state geometries of the synthesized dyes.

Functional organic click-materials: application in phosphorescent organic light emitting diodes

1,2,3-Triazole has been applied as a novel linker in donor–acceptor materials to control intramolecular charge transfer phenomena.

Structure-Property Relationships in Click-Derived Donor-Triazole-Acceptor Materials.

To shed light on intramolecular charge-transfer phenomena in 1,2,3-triazole-linked materials, a series of 1,2,3-triazole-linked push-pull chromophores were prepared and studied experimentally and computationally. Investigated modifications include variation of donor and/or acceptor strength and linker moiety as well as regioisomers. Photophysical characterization of intramolecular charge-transfer features revealed ambipolar behavior of the triazole linker, depending on the substitution position. Furthermore, non-centrosymmetric materials were subjected to second-harmonic generation measurements, which revealed the high nonlinear optical activity of this class of materials.

Intramolecular charge transfer character in tetrathiafulvalene-annulated porphyrinoids: effects of core modification and protonation.

The synthesis, characterization, and photophysical and electrochemical properties of a novel tetrathiafulvalene (TTF)-annulated core-modified porphyrin (1) and its expanded rubyrin analogue (2) are described. The sulfur core modifications in 1 and 2 allow a feasible intramolecular charge transfer from the TTF fragments to the central conjugated core as inferred from comparative spectroscopic and electrochemical measurements. DFT calculations also support the intramolecular charge transfer nature of 1 and 2 upon excitation. Further the electronic perturbation of the TTF-annulated porphyrins was achieved by protonation, giving rise to a drastic change in the optical features with an extremely low energy band in the NIR region. The pronounced electron accepting ability of the macrocyclic core of the dicationic species (H21(2+) and H22(2+)) resulted in the thermally excited electron transfer occurring at room temperature as elucidated by EPR spectroscopy.

Photoinduced intramolecular charge transfer phenomena in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid

A donor acceptor substituted aromatic system 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid (DMAPPDA) has been synthesized and its spectral properties have been explored on the basis of steady state absorption and fluorescence spectroscopy. Spectral features point largely towards a possible occurrence of photoinduced intramolecular charge transfer process from the donor NMe2 group to the acceptor acid group. Solvent dependency of the large Stokes’ shifted emission band and the calculated large excited state dipole moment support the polar character of the charge transfer excited state. Quantum yield calculations and effect of addition of acid and base on the steady state spectra were also performed to further scrutinize the excited state CT character.

1‐Azaadamantanes: Pharmacological Applications and Synthetic Approaches

AbstractFor Abstract see ChemInform Abstract in Full Text.

1-Azaadamantanes: pharmacological applications and synthetic approaches.

1-Azaadamantane (1-azatricyclo [3.3.1.1(3,7)]decane) was synthesized in 1953, and the derivatives have been used as rigid models for studies on intramolecular charge transfer phenomena, fluorescence excitation Rydberg states, highly twisted amides, solid electrolyte gas sensors, basicities, and self-organization systems. These structures have also been attracting considerable interest due to their pharmacological activities. The substituted 1-azaadamantanes as conformationally restricted amines have great potential for the therapeutic utilization as anticholinergic agents, serotonergic agents, and squalene synthase inhibitors. However, many steps have been needed for the synthesis of 1-azaadamantanes, and the concise synthetic approaches have been developed. Though double or triple Mannich reactions yield 1-azaadamantanes in moderate yields, the reduction steps are necessary. Our recent research has revealed that trifluoromethanesulfonic anhydride is available for the convenient synthesis of 1-azoniaadamantanes and 1-azaadamantanes without reduction. The new tools for the discovery of novel drugs such as quantitative structure-activity relationship (QSAR) analysis and vibrational circular dichroism (VCD) spectroscopy have also been discussed.

Synthesis and Characterization of a Novel Hyperbranched Oligomer with 1,3,5-trisphenylbenzene as Cores

A novel hyperbranched oligomer with 1,3,5-trisphenyl benzene ring as cores and trisphenyl amino moieties as connecting groups was synthesized. It was characterized by FTIR, 1 H-NMR and 13 C-NMR, The intramolecular charge transfer phenomenon was found in its excited state, its emission color could be tuned by changing only the ratio of the mixed solvent.

Elongated push–pull diphenylpolyenes for nonlinear optics: molecular engineering of quadratic and cubic optical nonlinearities via tuning of intramolecular charge transfer

Push–pull polyenes are of particular interest for nonlinear optics (NLO) as well as model compounds for long-distance intramolecular charge transfer (ICT). In order to tune the ICT phenomenon and control the linear and nonlinear optical properties, we have synthesized and investigated several series of soluble push–pull diphenylpolyenes of increasing length and having various donor (D) and acceptor (A) end groups. Their linear and NLO properties have been studied by performing electro-optical absorption measurements (EOAM) and third-harmonic generation (THG) experiments in solution. Each push–pull molecule exhibits an intense ICT absorption band in the visible characterized by an increase in dipole moment upon excitation (Δ μ). By lengthening the polyenic chain, linear increases in excited-state dipoles are achieved while the ground-state dipole is maintained constant. The polyenic chain thus allows for long-distance intramolecular charge transfer. In addition, tuning of the magnitude of the ICT phenomenon and of the nonlinear responses is achieved by varying the donor and acceptor end groups: increasing the D/A strength leads to concomitant enhancements of Δ μ, quadratic ( β) and cubic ( γ) hyperpolarizabilities values. Giant Δ μ values (up to more than 30 D) and enhanced non-resonant quadratic and cubic NLO molecular responses (i.e. β(0)=500×10 −30 esu and γ(0)=8000×10 −36 esu) have been attained while maintaining suitable solubility, stability and transparency.

Electronic spectra of jet-cooled 1-phenylpyrrole: Large-amplitude torsional motion and twisted intramolecular charge-transfer phenomenon

The fluorescence excitation spectrum and the single vibronic level dispersed fluorescence spectra in the region of the S0⇆S1 transition were measured for jet-cooled 1-phenylpyrrole. The 0–0 band was observed at 35 493 cm−1. Long and low-frequency progressions with somewhat irregular intensity distributions appeared on both spectra, and were assigned to torsional motion. The torsional energy levels in the S0 and S1 states were obtained up to 25 and 16 quanta, respectively. The torsional potentials in both states could be determined from the sufficient number of energy levels observed. In the S0 state the most stable conformation was determined to be a twisted form with a dihedral angle of 38.7°, where the planar barrier height was calculated to be 457 cm−1, and the perpendicular to be 748 cm−1. On the other hand, it was discovered that 1-phenylpyrrole in the S1 state also had a twisted form with a somewhat smaller dihedral angle of 19.8°, and that the barrier to planarity was 105 cm−1 and to perpendicularity, 1526 cm−1. These facts indicated that the electronic excitation caused 1-phenylpyrrole to be rigid to twist. 1-Phenylpyrrole and its derivatives have been reported as a group of twisted intramolecular charge-transfer (TICT) molecules. No indication of TICT appeared on the shape of the S1-state torsional potential determined. The relation between torsional potential and TICT is discussed based on the results of this study.

Photophysical behaviour of some pyrenylethylene derivatives and its implication on trans → cis photoisomerisation reactions

The fluorescence properties of some pyrenylethylene derivatives capable of exhibiting twisted intramolecular charge transfer phenomenon havebeen studied as a function of solvent polarity. The solvent polarity dependent change in the fluorescence quantum yield has been interpreted in terms of intramolecular retational relaxations. The trans → cis photoisomerization data of the compounds indicate that the twist around the ethylenic double bond is accelerated in polar solvents.