Intramolecular Charge Transfer Interactions Research Articles

Towards Designer Photocatalysts: Structure‐Property Relationships in 2,6‐Diaryl‐pyryliums

Fully organic photocatalyst systems are highly attractive, not merely because they are transition‐metal free, but more importantly due to their unique and often potent reactivity. A detailed understanding of the various redox states, both ground and excited state, and specifically what structural parameters control them is therefore crucial for harnessing the full potential of these systems in organic synthesis. However, unlike their organometallic counterparts, detailed structure‐property relationships for organic photocatalysts are largely absent from the literature. In this study, we demonstrate linear free‐energy relationships across a range of key photophysical and electrochemical properties of 2,6‐diarylpyryliums. Electronic absorption and emission maxima can be carefully tuned over the ranges of 83 nm and 102 nm respectively. Intramolecular charge transfer (ICT) interactions were revealed in cases of substitution with polarizable heavy‐atoms. A strong linear dependence of ground state reduction potentials on substituent electronics was observed. Notably, the excited state reduction potential, E*red, could be controlled over a range of nearly 1000 mV. Systematic errors in computational modeling of ground and excited state redox potentials were identified and corrected. We believe the quantitative structure‐property relationships identified here provide foundational tools for rational and predictive organic photocatalyst design.

Manipulating Intramolecular Charge Transfer in Terpyridine Derivatives towards "Turn-On" Fluorescence Chemosensors for Zn2.

A series of donor-acceptor (D-A) terpyridine derivatives with various intramolecular charge transfer interactions have been successfully synthesized bearing phenyl, methoxyphenyl, N-butyldiphenylamine (DPA), and triphenylamine (TPA) as electron-donors and terpyridine (TPY), 2,6-di(pyrazin-2-yl)pyridine (PYDPZ), and N,N-dimethylated PYDPZ (PYDPZ-2CH3) as electron acceptors. Upon the introduction of pyrazine rings instead of pyridine ones and further selective N,N'-dimethylation, the intramolecular D-A interactions are significantly enhanced, resulting in the remarkable reduced intramolecular charge transfer (ICT) transitions and quenched PL emissions in CH2Cl2 solution. However, their ICT emissions are clearly recovered upon adding Zn2+. Especially, for double positively charged compound 12, the Zn2+-induced "turn-on" green emission (λmax, em = 518 nm, Φ = 0.24) with excellent sensitivity (I/I0 = 77) and selectivity (IZn/ICd = 23) is detected. Under the optimized experimental condition (EtOH-H2O (9:1, v/v), containing 0.05 M HEPES buffer (pH = 7.4)), this probe is used to quantitative determination of Zn2+ in a water sample with an average recovery of 97.5%. Furthermore, the probe is applied to imaging of Zn2+ ions in HeLa cells and its mechanism is confirmed by the molecular dynamics simulation, in which lower coulomb potential for membrane surface adsorption and energy barrier for membrane translocation can be found.

Constructing Donor–Acceptor-Linked COFs Electrolytes to Regulate Electron Density and Accelerate the Li+ Migration in Quasi-Solid-State Battery

HighlightsDonor–acceptor-linked covalent organic framework (COF)-based electrolyte can not only fulfill highly-selective Li+ conduction, but also offer a crucial opportunity to understand the role of electronic density in quasi-solid-state Li metal batteries.Donor–acceptor-linked COF electrolyte results in Li+ transference number 0.83, high ionic conductivity 6.7 × 10–4 S cm−1 and excellent cyclic ability in Li metal batteries.In situ characterizations, density functional theory calculation and time-of-flight secondary ion mass spectrometry are adopted to expound the mechanism of the rapid migration of Li+ in the “donor–acceptor” electrolyte system.

Biomimetic Entropy-Dominant Molecular Hinges with Picomolar Affinity.

Molecular hinges are ubiquitous in both natural and artificial supramolecular systems. A major challenge to date, however, has been simultaneously achieving high thermodynamic and kinetic stability. Here, we employ host-enhanced intramolecular charge-transfer interactions to mediate entropy-favored complexation between a flexible AB2-type guest and a macrocyclic host, forming a new type of molecular hinge with an ultrahigh picomolar binding affinity (Ka > 1012 M-1). This entropy-promoted hinge modulates photoisomerization, exhibiting a substantial preference for the E-isomer, which is further demonstrated to mirror the natural retinal-opsin cycle, promoting the sensitization of visible light. This work unveils an efficient approach to exploit entropy-dominant architectures for the design of hierarchical molecular systems.

Recent Advances in Fluorescent Polyimides.

Polyimide (PI) refers to a type of high-performance polymer containing imide rings in the main chain, which has been widely used in fields of aerospace, microelectronic and photonic devices, gas separation technology, and so on. However, traditional aromatic PIs are, in general, the inefficient fluorescence or even no fluorescence, due to the strong inter- and intramolecular charge transfer (CT) interactions causing unavoidable fluorescence quenching, which greatly restricts their applications as light-emitting functional layers in the fabrication of organic light-emitting diode (OLED) devices. As such, the development of fluorescent PIs with high fluorescence quantum efficiency for their application fields in the OLED is an important research direction in the near future. In this review, we provide a comprehensive overview of fluorescent PIs as well as the methods to improve the fluorescence quantum efficiency of PIs. It is anticipated that this review will serve as a valuable reference and offer guidance for the design and development of fluorescent PIs with high fluorescence quantum efficiency, ultimately fostering further progress in OLED research.

Design of Triphenylamine-based D-π-A Systems for Efficient Ternary WORM Memory Devices.

The impact of various substituent moieties on the molecular framework of a conjugated D-A system in resistive switching memory property has been scrutinized through an array of novel D-π-A molecules. The synthesized molecules with triphenylamine (TPA) as the electron donor and dicyanovinylindanone (IC) as the electron acceptor demonstrated substantial non-volatile WORM (Write-Once Read-Many) memory behaviour with appreciable ON/OFF current ratios up to 105 and a lowest recorded threshold voltage of -0.80 V. The well-balanced combination of these potent electron donating and accepting units culminated in exceptional intramolecular charge transfer interactions and minimal band gap values (1.82-2.31 eV) for the molecules, as demonstrated by photophysical and electrochemical investigations. These factors, coupled with the thin-film morphological studies, corroborated the superior performance of the fabricated devices. A longer retention time of 2000s and an endurance of 100 cycles mark the substantial stability of the memory devices. Moreover, conversion from binary to ternary WORM memory was achieved by the effective tuning of the electronic properties of the D-A systems by various substituent moieties. Molecular simulation studies revealed that the resistive switching phenomenon arises from a synergistic interplay of charge transfer and charge trapping processes within these D-A systems.

Supramolecular Assembly of Nitrogen-Containing Curved π-Conjugated Molecules to Polar Crystal

The chemistry of curved π-conjugated molecules has been extensively studied because of the development of their synthetic approach. Among the numerous studies, we have been engaged in nitrogen-containing curved π-conjugated molecules. These molecules have extended optical properties, redox-active behaviors, and electron-donating ability due to the electron-rich nature of nitrogen atoms. Recently, we have focused on the supramolecular assembling behavior of these compounds. For example, we have reported buckycatcher consisted of two azabuckybowls, providing two-photon absorbing host-guest complexes with fullerenes. In this presentation, we would like to show the packing behavior using π-extended azahelicenes and azabuckybowls. Our group has developed π-extended aza[5]helicene derivatives, showing brilliant emissive features. Recently, we succeeded in the synthesis of unsymmetrically substituted azahelicenes. We found that their stackings in the crystal were dependent on the substituent. X-ray diffraction analysis for all products showed π-stacked conformation with each other in the crystal (Figure 1b). In particular, azahelicenes with triisopropylsilyl groupswere found to align their dipole moments to form a one-dimensional columnar structure in the crystal. Polar crystals are expected to have applications in ferroelectric, piezoelectric, and nonlinear optical response materials. This is the first example of a polar crystal with helicenes, paving the way for novel piezoelectric organic materials.The second topic is related to azabuckybowl. In the crystal, azabuckybowl forms a face-to-face dimer by concave-convex interaction. In this study, we prepared two types of azabuckybowl perylene bisimide (PBI) dyads connected with alkyne linkages. PBIs have also been reported to show columnar stacking in solution. We anticipated that the segregate stacking should be achieved by recognizing the difference in structures between the bowl and planar geometry. The UV/vis absorption spectra revealed the presence of intramolecular charge-transfer interaction. In addition, the concentration-dependent absorption spectra and 1H NMR spectra indicated PBI and azabuckybowl units stacked with each other independently in solution (Figure 1a). Here, we would like to discuss about the effect of the effect of molecular shape on the supramolecular assembly with the data obtained using these compounds. Figure 1

Multi‐Resonance TADF Conjugated Polymers toward Highly Efficient Solution‐Processible Narrowband Green OLEDs

AbstractDue to the extended conjugation along the polymeric backbone and the scarcity of suitable multi‐resonance (MR) emitting units for polymerization, precisely adjusting the colors of MR‐thermally activated delayed fluorescence (MR‐TADF) conjugated polymers to green and red region remains to be a formidable challenge. Herein, this work develops a series of green MR‐TADF polymers for the first time by attaching MR emitting moiety as pendant to an acceptor triphenyltriazine while simultaneously embedding acceptor moiety into polycarbazole backbone. Benefitting from the enhanced intramolecular charge transfer (ICT) interaction by introducing acceptor on the para‐carbon position of boron (B) atom of the MR unit, as well as extended conjugation along backbone, all polymers exhibit red‐shifted emissions with emission peaks of 505–517 nm and full‐width at half maximums (FWHMs) of below 48 nm compared to the pendant bluish‐green MR unit peaking at 484 nm. The solution‐processed devices based on these polymers exhibit excellent performances with maximum quantum efficiency (EQE) of 22.2%, emission peak at 511 nm and FWHM of 44 nm, which represents the state‐of‐the‐art performance among the MR‐TADF polymer‐based narrowband OLEDs.

Interdisciplinary insights into (1′R,3S,3′R)-1'-(4-chlorobenzoyl)-5′,6′,7′,7a′-tetrahydro-1′H dispiro[indoline-3,2′-pyrrolizine-3′,3″-indoline]-2,2″-dione: Structural, electronic, and molecular dynamics perspectives

In the field of heterocyclic compounds, the spiro-pyrrolidine and oxindole ring systems are highly esteemed due to their distinctive structural scaffold that is present in numerous pharmacologically significant alkaloids. Interdisciplinary research has been increasingly important in recent years for deciphering the intricate characteristics and behaviors of novel organic compounds. The current work uses quantum chemical computational techniques to study the structural stability and nonlinear optical (NLO) activity of (1′R,3S,3′R)-1'-(4-chlorobenzoyl)-5′,6′,7′,7a′-tetrahydro-1′H dispiro[indoline-3,2′-pyrrolizine-3′,3″-indoline]-2,2″-dione (DSOIP-Cl). The study combines molecular biology, computational chemistry, and theoretical chemistry knowledge to create a comprehensive picture of this fascinating organic compound. This study employed the density functional theory (DFT) B3LYP method to compute the electronic properties and molecular geometry. The basis set for the computations was 6–311++G(d,p). The IEFPCM solvation method is used to investigate the behavior of the head compound in different solvents. Understanding the interaction between organic compounds and the solvent phase is crucial because the majority of interactions in biological systems occur in solution. UV–Vis spectral analysis of the molecule in different solvents is performed using the TD-DFT method. The compound exhibits more excellent absorption in polar solvents such as water, while its absorption is lower in the gaseous phase. Assessing NLO properties revealed optoelectronics applications. DSOIP-Cl has 5.25 times the first-order hyperpolarizability of urea. Different solvents have higher dipole moments and first-order hyperpolarizability than gases. To identify the inter- and intramolecular charge transfer interactions, intermolecular hydrogen bonding, and hyperconjugative interactions that stabilize the structure, natural bond orbital (NBO) analysis is performed. A stabilization energy of 9.99 kcal/mol is obtained for π(C32–C33) → σ*(C33–C34) due to strong intramolecular hyperconjugative interactions. Frontier molecular orbital (FMO) analysis helps determine the global reactivity parameters and the charge transfer interaction. The van der Waals interaction and steric effect within the molecule are identified using RDG analysis. The pharmacokinetic properties, adherence to drug-likeness criteria, and easily controllable synthesis process were evaluated through ADME analysis, establishing it as an up-and-coming candidate for subsequent drug development. Ultimately, to determine the biological activity and the ability of the title compound to inhibit aldose reductase, a series of computational techniques are employed, including molecular docking study, molecular dynamic (MD) simulation, and MM-PBSA binding energy calculations. −7.86 kcal/mol was reported as the docking score. Hydrophobic interactions play an essential role in the efficiency of protein-ligand binding. The remarkable energetic contribution of DSOIP-Cl to the MM-PBSA binding dynamics highlights its unique association with the AR protein, with a binding energy of −79.81 kJ/mol.

White light-emissive triphenylamine-based triazole derivatives: Fluorescence switching response to volatile acid

Two triphenylamine-based tris and bis-triazole molecules (TTA and BTA) were reported, exhibiting significant fluorescence in the solid and solution states. TTA and BTA were highly sensitive towards trifluoroacetic acid (TFA) vapor by visible color change as the triazole nitrogen can easily be protonated. Triazoles show extreme sensitivity because of the reliable intramolecular charge transfer (ICT) interactions; the protonation of triazole moieties resulted in a bathochromic shift in UV–visible and fluorescence spectra. These spectra alterations were reversible when the base triethylamine (TEA) was added. When protonated, the fluorescence changed from blue to cyan, returning to blue on TEA addition (deprotonation). TTA displayed an Aggregation-Induced Enhanced Emission (AIEE) effect in the water: acetonitrile (7:3) combination. Density Functional Theory (DFT) calculations were utilized to calculate the energy gap between the HOMO-LUMO of TTA and BTA and their protonated forms. Both the triazoles were highly stable in a di-protonated state. Aside from acid sensitivity, TTA and BTA emitted white light with a high Color Rendering Index (CRI) of 87 % and 98 %, respectively, in the solid and the polymer composite thin film because of their multiple emission bands.

Understanding the impact of thiazole unit sequence in π-bridge on the performance of small molecule donor materials

Energy level regulation and crystallization optimization of materials are the key ideas to improve the performance of organic solar cells. In this work, based on clarifying small molecule structure, we introduce thiazole into different positions of π-bridge and investigate its effect on the properties of small molecule donors (SMDs) and related device performance. As thiazole gradually moves towards BDT, the electron clouds of these three SMDs (BTTTzR, BTTzTR and BTzTTR) tend to be divided on the framework, gradually deepened the energy level, and enlarged band gaps. In terms of device performance, the BTTzTR:Y6 device shows good inhibition of charge recombination and phase separation performance, and the efficiency of the related OSCs is 7.87 %. Morphological analysis shows that BTTTzR is prone to form nanoscale microcrystals after thermal annealing treatment, with slightly decreased performance of 6.79 %. BTzTTR is affected by difficult intramolecular charge transfer and weak intermolecular interactions, shows the worst performance of 5.77 %. This work is conducive to a deeper understanding of the electron-deficient substitution of the π-bridge in SMDs.

Dissolved organic matter isolates obtained by solid phase extraction exhibit higher absorption and lower photo-reactivity: Effect of components

Notable differences in photo-physical and chemical properties were found between bulk water and solid phase extraction (SPE) isolates for dissolved organic matter (DOM). The moieties extracted using modified styrene divinylbenzene cartridges, which predominantly consist of conjugated aromatic molecules like humic acids, contribute mainly to light absorption but exhibit lower quantum yields of fluorescence and photo-produced reactive intermediates (PPRIs). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed lignin as the moieties displaying most significant variance in abundance. In Van Krevelen-Spearman plot, we observed molecules positively or negatively correlated with DOM's optical and photochemical properties (including SUVA254, steady-state concentrations of ·OH, 1O2 quantum yield, etc.) were confined to specific regions, which can be delineated using a threshold modified aromaticity index (AImod) of 0.3. Based on the relationships between optical properties and PPRI production, it is suggested that the energy gap between ground state and excited singlet state (△ES1→S0), governing the inner conversion rate, serves as a determinant for apparent quantum yield of PPRIs in DOM, with intra-molecular charge transfer (CT) interactions potentially playing a pivotal role. Regarding DOM's photoreactivity with pollutants, this study has revealed, for the first time, that protein/amino sugars/amino acids could act as antioxidant groups in addition to phenols on the photolysis of sulfadiazine. These findings provide valuable insights into DOM photochemistry and are expected to stimulate further research in this area.

Appending Coronene Diimide with Carbon Nanohoops Allows for Rapid Intersystem Crossing in Neat Film.

The development of innovative triplet materials plays a significant role in various applications. Although effective tuning of triplet formation by intersystem crossing (ISC) has been well established in solution, the modulation of ISC processes in the solid state remains a challenge due to the presence of other exciton decay channels through intermolecular interactions. The cyclic structure of cycloparaphenylenes (CPPs) offers a unique platform to tune the intermolecular packing, which leads to controllable exciton dynamics in the solid state. Herein, by integrating an electron deficient coronene diimide (CDI) unit into the CPP framework, a donor-acceptor type of conjugated macrocycle (CDI-CPP) featuring intramolecular charge-transfer (CT) interaction was designed and synthesized. Effective intermolecular CT interaction resulting from a slipped herringbone packing was confirmed by X-ray crystallography. Transient spectroscopy studies showed that CDI-CPP undergoes ISC in both solution and the film state, with triplet generation time constants of 4.5 ns and 238 ps, respectively. The rapid triplet formation through ISC in the film state can be ascribed to the cooperation between intra- and intermolecular charge-transfer interactions. Our results highlight that intermolecular CT interaction has a pronounced effect on the ISC process in the solid state, and shed light on the use of the characteristic structure of CPPs to manipulate intermolecular CT interactions.

Manipulating Intramolecular Charge Transfer and Supramolecular Interaction in D-A-D Conjugated Systems by Regioisomerization.

Three new donor-acceptor-donor (D-A-D) architecture regioisomers comprising a large planar electron-withdrawing core tribenzo[a,c,i]phenazine and two identical electron-donating triphenylamines with different substitution patterns were designed and synthesized. Employing this regioisomerization strategy, the intramolecular charge-transfer interactions are effectively tuned and result in a significant bathochromic shift of photoluminescence maximum over 100 nm, which induces the corresponding emission band extending into the near-infrared region as well as giving a high solid-state quantum yield of 25%. Meanwhile, it is found that the supramolecular interactions of this series of regioisomers with planar electron-donor pyrene are greatly affected by the substitution pattern.

Substituent Position Dependent Photophysical Properties of Indole – Barbituric and Thiobarbituric Acid based Molecular Rotors

AbstractA series of 2‐ and 3‐methylindole (MI)‐based barbituric acid (BA) and thiobarbituric acid (TBA) derivatives (2MIBA, 2MITBA, 3MIBA and 3MITBA) in Donor (D)‐π‐Acceptor (A) configuration having strong intramolecular charge transfer (ICT) interactions were synthesized by the simple and efficient route. Methyl substituent at the 2‐ and 3‐ position alters the coplanarity of the DA systems leaving 2MI derivatives as nonplanar whilst 3MI derivatives as planar one and the latter forms an intramolecular hydrogen bond between indole N−H and −C=O of BA or TBA, which facilitates the excited state intramolecular proton transfer (ESIPT) emission in 3MIBA and 3MITBA. Comparing the UV‐visible absorption spectra in the solution phase reveals that the ICT band of 2MITBA and 3MITBA are red‐shifted from the 2MIBA and 3MIBA due to the stronger electron‐accepting nature of C=S than the C=O. Since these molecules exert photo‐induced intramolecular charge transfer followed by a rotation around the bridging methylene group, only weak fluorescence is noted. Nevertheless, in an aggregated state, both 3MIBA and 3MITBA exhibit significant aggregation‐induced enhanced emission (AIEE) characteristics in their THF/water mixture, but the effect is not promising for 2MIBA and 2MITBA. Further, melamine‐3MITBA co‐assembly aided through an intermolecular hydrogen bonding network can also be used as a solid‐state emitter.

Tuning sensing efficacy of anthraimidazoledione-based charge transfer dyes: nitro group positioning impact.

Anthraimidazoledione-based optical sensors have been designed by varying the position of the nitro functional group. All three positional isomers showed highly colored, photostable optical signals owing to intramolecular charge transfer interactions. Despite having the same anion-binding site (imidazole unit), the selectivity and sensitivity of the compounds depend on the positioning of the nitro group. The selectivity was fairly good for the meta isomer, followed by the ortho and para isomers, respectively. In contrast, the sensitivity towards anions followed a completely opposite trend, with the para isomer being the most sensitive one towards anions. Interestingly, the color changing response along the turn-on fluorescence signal was observed only with CN- ions in a semi-aqueous environment. Though the introduction of water as a co-solvent could improve the selectivity, the sensitivity was found to be slightly less than that observed in pure organic medium. Mechanistic studies indicated hydrogen bonding interactions between the imidazole -NH proton and cyanide, which further facilitated the extent of intramolecular charge transfer.

Low bandgap fused-ring electron acceptors based on π-expended asymmetric benzotrithiophene core: Regulating aggregation and photovoltaic performance by side chain isomerization

Asymmetric molecular design strategy has received increasing attention in the development of fused-ring electron acceptors (FREAs). Benzo [2,1-b: 3,4-b’: 5,6-b”] trithiophene (asym-BTT) with intrinsically asymmetric and electron-rich π-plane is an ideal unit to construct asymmetric FREAs, whereas asym-BTT-based FREAs are still very limited. Herein, two asymmetric FREAs based on the π-expended asym-BTT fused-core with para-hexylphenyl and meta-hexylphenyl side chains (p-FABTT and m-FABTT) have been developed. Owing to strong electron-donating ability and planar configuration of π-expended asym-BTT fused-core, two acceptors exhibit effective intramolecular charge transfer and intermolecular interaction, leading to near infrared absorption above 900 nm with narrow bandgaps of around 1.34 eV. Although the same π-conjugated backbones of two acceptors afford the nearly identical energy levels and solution absorptions, side chain isomerization leads to significant differences in film absorption, molecular stacking orientation and crystallinity. In neat film, the m-FABTT with meta-hexylphenyl side chains exhibits slightly redshifted absorption with stronger 0-0 absorption peak from J-aggregation compared to p-FABTT with para-hexylphenyl side chains. More orderly molecular stacking and stronger π-π interactions with shorter π-π stacking distance in both the neat film and active layer can be observed for m-FABTT. When blended with donor polymer D18, m-FABTT exhibits broadened spectral region and proper phase separation morphology for effective exciton dissociation and charge transport. Therefore, the OSCs device based on m-FABTT achieves an optimal PCE of 7.14 % with a higher JSC of 15.39 mA cm−2 and an improved FF of 57.96 % as comparing with p-FABTT-based device (a PCE of 4.81 % with a JSC of 11.67 mA cm−2 and a FF of 48.51 %).

Enhancing the photo-stability of narrow-bandgap acceptors via non-covalent interactions

It is widely acknowledged the significant impact of narrow-bandgap non-fullerene acceptors (NFAs) in the field of organic electronics. However, most NFAs suffer from stability issues, attributed to their strong intra-molecular charge transfer interaction (ICT) effect and large conjugated plane. The exo-cyclic double bond between the end group and donor core is particularly susceptible. Herein, 4-IF4F and 6-IF4F were designed and synthesized with diverse configurations of π-bridge units to study the effect of non-covalent interaction on the photo-stability. Although the device based on 4-IF4F shows a slight low photovoltaic performance compared with 6-IF4F, the photostability of 4-IF4F is much better, attributed to its non-covalent interaction between the fluorine atom of the π-bridge and the hydrogen atom of the exocyclic double bond. Briefly, this work systematically investigated the incorporation of FTT units in NFAs and their photovoltaic performance, further demonstrating that it is a promising strategy by using non-covalent interaction to improve the stablility of narrow-bandgap NFAs.

Eco-friendly synthesis, structural elucidation, computational investigation and in vitro antioxidant activity of a new N-tosylated benzimidazole derivative

Synthesis of 2-(diethoxymethyl)-1-tosyl-1H-benzo[d]imidazole 5 in excellent yield was achieved from 2-(1-ethoxypropyl)-1H-benzo[d]imidazole by ionic liquid supported eco-friendly green protocol. The precursor, 2-(diethoxymethyl)-1H-benzo[d]imidazole was prepared from o-phenylenediamine in good yield. The compound 5 was characterized by 1H, 13C and mass spectroscopic analyses. Also, its structure was further confirmed by X-ray single crystal analysis. From Hirshfeld calculations, it was clear that the H…H (51.1 %), H…C (21.6 %), O…H (18.9 %) and N…H (6.3 %) interactions were the most dominant in the solid-state structure of compound 5. The crystal stability was controlled by the short distance of O3…H7 (2.556 Å), N2…H6 (2.555 Å) and H11C…H11C (1.964 Å). Natural bond orbital (NBO) calculations were used to calculate the different intramolecular charge transfer interactions in the synthesized benzimidazole molecule 5. In addition, the DFT calculations were used to predict its electronic and reactivity descriptors. Furthermore, the synthesized compound was examined for its antioxidant properties and it was found that the compound 5 exhibited potent antioxidant activity (IC50 value of 42.32 µM) when compared to the standard drug butylated hydroxyanisole (BHA) (IC50 value of 58.6 µM). In addition, the compound 5 showed significant tuberculosis activity (3.12 µg/mL) against Mycobacterium tuberculosis H37Rv when compared to the standard drug, ethambutol (1.56 µg/mL). The docking simulation was also performed for compound 5 which correlated well with the in vitro findings.

Uncovering the substituted-position effect on excited-state evolution of benzophenone-phenothiazine dyads.

Photofunctional materials based on donor-acceptor molecules have drawn intense attention due to their unique optical properties. Importantly, Systematic investigation of substitution effects on excited-state charge transfer dynamics of donor-acceptor molecules is a powerful approach for identifying application-relevant design principles. Here, by coupling phenothiazine (PTZ) at the ortho-, meta-, and para-positions of the benzene ring of benzophenone (BP), three regioisomeric BP-PTZ dyads were designed to understand the relationship between substituted positions and excited-state evolution channels. Ultrafast transient absorption is used to detect and trace the transient species and related evolution channels of BP-PTZ dyads at excited state. In a non-polar solvent, BP-o-PTZ undergoes the through-space charge transfer process to produce a singlet charge-transfer (1CT) state, which subsequently proceeds the intersystem crossing process and transforms into a triplet charge-transfer (3CT) state; BP-m-PTZ experiences intramolecular charge transfer (ICT) process to generate the 1CT state, which subsequently transforms into the 3CT state by the intersystem crossing (ISC) and finally converts into the local-excited triplet (3LE) state; as for BP-p-PTZ, only 3LE states can be detected after the ISC process from the 1CT state. On the other hand, the twisted ICT states are generated via twisted motion between the donor and acceptor for all BP-PTZ dyads or planarization of the PTZ unit in high polar solvents. The excited-state theoretical calculations unveil that the features of ICT and intramolecular interaction between the three dyads play a decisive role in determining the through-bond charge transfer and through-space charge transfer processes. Also, these results demonstrate that the excited-state evolution channels of PTZ derivatives could be modified by tuning the substituted positions of the donor-acceptor dyads. This study provides a deep perspective for the substitute-position effect on donor-acceptor-type PTZ derivatives.