Study of the microscopic mechanism of stepwise charge injection in co-sensitive DSSCs in the framework of a D-π-A dye and chlorophyll.

The newly synthesized dye molecules TY6 and CXC22 were selected to explain the influence of anthracene and acetylene groups on the power conversion efficiency (PCE) of the molecules at the microscopic level. Theoretical simulation was carried out to understand the properties of the two molecules, including frontier molecular orbitals, absorption spectra, light absorption efficiency, intramolecular charge transfer (ICT), dye regeneration, I-V prediction, etc. The results suggest that for CXC22, adding an anthracene and acetylene group in the conjugate bridge greatly enhances the molecule's absorption wavelength and molar extinction coefficient; CXC22 also has significant advantages in the intramolecular charge transfer and comparatively better dye regeneration and electron injection. These parameters cause CXC22 to have a higher PCE. Subsequently, CXC22 and the chlorophyll molecule (CHL7) were selected for co-sensitization to regulate performance. The stable structure in the co-sensitization configuration was screened, and the absorption spectrum characteristics and charge transfer mechanisms were revealed for the co-sensitization system. The designed evaluation model predicted that the PCE of CO1 (the cosensitive system of CXC22 and TY6 in H-H configuration is referred to as CO1) could reach 16.78%. This work provides an idea for developing an efficient dye-sensitized solar cell system.

Nonlinear optical properties and optimization strategies of D-π-A type phenylamine derivatives in the near-infrared region.

Modifying simple molecular structures to significantly improve nonlinear optical (NLO) performance is a primary prerequisite for scientific research. Based on the four phenylamine derivatives reported in previous studies, we designed four organic nonlinear molecules by changing the acceptor group and π-linker. (Time-dependent) density functional theory (DFT/TD-DFT) was performed on molecular geometry optimization, the contribution of π electrons to the bond order, linear and two-photon absorption (TPA) spectra, the intra-molecular charge transfer matrix (CTM), and NLO coefficients. These aspects were considered to analyze in detail how the structural modification of acceptors and π-linkers affects NLO characteristics. The three modification methods were: adding a carbonyl group at the junction of the π-linker and the acceptor group, adding a carbonyl group and a nitrogen atom to the acceptor group, and replacing the quinolinone with a pyrenyl group as the π-linker. The latter two methods can significantly reduce the excitation energy and enhance the intensity of intra-molecular charge transfer during the two-photon transition. The maximum TPA cross-sections and wavelengths of the designed molecules are DPPM (84722.6 GM, 815.7 nm) and DDPM (21600.6 GM, 781.3 nm). These two molecules have large TPA cross-sections in the near-infrared region, which renders them as possible NLO materials with broad application prospects.

Unveiling the influence of atomic electronegativity on the double ESIPT processes of uralenol: A theoretical study.

In this work, the effects of atomic electronegativity (O, S, and Se atoms) on the competitive double excited-state intramolecular proton transfer (ESIPT) reactions and photophysical characteristics of uralenol (URA) were systematically explored by using the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The calculated hydrogen bond parameters, infrared (IR) vibrational spectra, reduced density gradient (RDG) scatter plots, interaction region indicator (IRI) isosurface and topology parameters have confirmed the six-membered intramolecular hydrogen bond (IHB) O4H5…O3 is the stronger one in all the three studied compounds. Subsequently, frontier molecular orbitals (FMOs) and natural bond orbital (NBO) population analysis essentially uncover that the electron redistribution has induced the ESIPT process. Besides, the constructed potential energy curves (PECs) have indicated that the ESIPT process prefers to occur along the O4H5…O3 rather than the O1H2…O3 and the proton-transfer energy barrier is gradually decreased with the weakening of atomic electronegativity from URA to URA-S and URA-Se. In a conclusion, the attenuating of atomic electronegativity has enhanced the IHBs of URA and thereby promoting the ESIPT reaction, which is helpful for further developing novel fluorophores based on ESIPT behavior in the future.

Tactfully unveiling the effect of solvent polarity on the ESIPT mechanism and photophysical property of the 3-hydroxylflavone derivative.

In this contribution, the solvent effects on the excited-state intramolecular proton transfer (ESIPT) and photophysical properties of 2-(4-(diphenylamine)phenyl)-3-hydroxy-4H-chromen-4-one (3HF-OH, Dyes Pigm. 2021, 184, 108865) in the dimethylsulfoxide (DMSO), acetonitrile (ACN), dichloromethane (DCM) and cyclohexane (CYH) phases have been comprehensively explored by using the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The obtained bond lengths, bond angles and infrared (IR) vibration analysis related to the intramolecular hydrogen bond (IHB) reveal that the IHB intensity of 3HF-OH is weakened as the solvent polarity increased. Besides, the ESIPT process changes from the endothermic to the exothermic with the enlargement of solvent polarity, and the reaction barrier increases gradually. It is worth noting that the molecular configuration torsion of 3HF-OH is gradually intensified with the decline of solvent polarity, which aggravates the twisted intramolecular charge transfer (TICT) state and thereby partially attenuates the short-wavelength fluorescence of 3HF-OH in the CYH solvent. In addition to these, the structural torsion has restrained the occurrence of the ESIPT behavior by means of elevating the energy barrier. This theoretical research would provide valuable guidance for regulating and controlling the photophysical behavior of compounds via the strategy of changing solvent polarity.

Photovoltaic performance and power conversion efficiency prediction of double fence porphyrins.

To explore high efficiency dye-sensitized solar cells (DSSCs), two experimentally derived (single fence and double fence porphyrins) and two theoretically designed zinc porphyrin molecules with D-D-π-A-A configurations were studied. Density functional theory and time-dependent density functional theory were employed to simulate these two experimental dyes and dye@TiO2 systems to understand why the double fence porphyrin molecule exhibits better photovoltaic performance than the single fence porphyrin molecule. For the short-circuit current (JSC), the various parameters that affected the experimental magnitude of JSC were analyzed from different aspects of absorption, charge transfer and chemical parameters as well as an electron injection process. The almost equal open-circuit voltages (VOC) in the experiment were predicted by theoretical VOC calculations. Our model predicted power conversion efficiencies (PCEs) of 1.993% and 10.866% for the single and double fence molecules, respectively, which are in accordance with the experimental values of 3.48% and 10.69%, respectively. In addition, one designed two new molecules based on the double fence porphyrin molecule with a 2-methyl-2H-benzo[d][1,2,3]triazole (BTA) unit bearing one fluorine and two fluorine atoms as the guest acceptor, respectively. Compared to the original molecules, the engineered molecules significantly improved the photovoltaic parameters, JSC and VOC, thereby causing excellent PCEs. The most outstanding designed molecule reached a PCE of 12.155%, and is considered a candidate dye for high-efficiency DSSC. This study provides insights into the photoelectric properties of single and double fence porphyrins. It also demonstrated that the strong electron-withdrawing ability of fluorine atoms would enhance the photovoltaic performance and provide a guideline for the further design of double fence porphyrins.

Improving the antioxidant activity of natural antioxidant honokiol by introducing the amino group.

Exploring and synthesizing the compounds with stronger antioxidant activity have always been the goal of researchers. Herein, the substitution effects of the amino (NH2-) group with the excellent electron-donating ability in different positions on the antioxidant activity of Honokiol (Hon) were systematically explored by using the quantum chemistry calculation based on the density functional theory method. The three possible antioxidant mechanisms of Hon and its four NH2-substituted derivatives (Hon1-Hon4), containing the hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET), were explored in depth considering the gas and solvent phases. In addition, the frontier molecular orbital energies, natural bond orbital (NBO) charge population, and global descriptive parameters were used to study their antioxidant activity. The results indicate that compared with the original molecule Hon, the NH2 substituents would have the stronger antioxidant activity. Moreover, the radical scavenging process of Hon and its derivatives has a disposition to the HAT and SPLET mechanisms in the gas and solvent phases, respectively. Meaningfully, owing to the lowest bond dissociation enthalpy and proton affinity values, Hon4 would show the most prominent antioxidant activity by comparison with the other compounds. In conclusion, this work will provide the purposeful reference for designing and synthesizing the antioxidants with more outstanding performance.

Novel Triarylamine-Based Hole Transport Materials: Synthesis, Characterization and Computational Investigation.

Three novel triarylamine-based electron-rich chromophores were synthesized and fully characterized. Compounds 1 and 2 were designed with electron-rich triphenylamine skeleton bearing two and four decyloxy groups namely, 3,4-bis(decyloxy)-N,N-diphenylaniline and N-(3,4-bis(decyloxy)phenyl)-3,4-bis(decyloxy)-N-phenylaniline, respectively. The well-known electron-rich phenothiazine was introduced to diphenylamine moiety through a thiazole ring to form N,N-bis(3,4-bis(decyloxy)phenyl)-5-(10H-phenothiazin-2-yl)thiazol-2-amine (Compound 3). These three novel compounds were fully characterized and their UV-vis absorption indicated their transparency as a favorable property for hole transport materials (HTMs) suitable for perovskite solar cells. Cyclic voltammetry measurements revealed that the HOMO energy levels were in the range 5.00-5.16 eV for all compounds, indicating their suitability with the HOMO energy level of the perovskite photosensitizer. Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used to investigate the possibility of the synthesized compounds to be utilized as HTMs for perovskite solar cells (PSCs). The computational investigation revealed that the hole mobility of Compound 1 was 1.08 × 10-2 cm2 V-1 s-1, and the substitution with two additional dialkoxy groups on the second phenyl ring as represented by Compound 2 significantly boosted the hole mobility to reach the value 4.21 × 10-2 cm2 V-1 s-1. On the other hand, Compound 3, in which the third phenyl group was replaced by a thiazole-based phenothiazine, the value of hole mobility decreased to reach 5.93 × 10-5 cm2 V-1 s-1. The overall results indicate that these three novel compounds could be promising HTMs for perovskite solar cells.

Effect of Polymerization on the Charge-Transfer Mechanism in the One (Two)-Photon Absorption Process of D-A-Type Triphenylamine Derivatives.

To investigate the effect of polymerization (n = 1, 2, 3, and 4) on the charge-transfer (CT) mechanisms in the one (two)-photon absorption (OPA and TPA) process of D-A-type triphenylamine derivatives, charge density difference is used to graphically represent the CT characteristics. A transition density matrix is utilized to reveal the direction of CT on different groups quantitatively. With the n increasing, electrons are mainly transferred between the groups in the middle position of the molecular chain during OPA and TPA processes. Simulated results show that the energy gap and excitation energy have a good linear relationship with the reciprocal of the polymerization degree. Importantly, the polymerization effect can effectively increase the electronic transmission capability, TPA performance, and second hyperpolarizability. Besides, the simplified sum over state model reveals the variation factor of the TPA cross-section and the second static hyperpolarizability. The McRae formula and Bakhshiev formula are used to estimate the difference of dipole moments, which is an important parameter of the second hyperpolarizability. The comprehensive analysis of the nonlinear optical (NLO) parameters of triphenylamine derivatives can provide some significant guidance for molecular design and improve the NLO performance of D-A molecular materials. Also, the thermodynamic parameters can provide some theoretical supports for solving practical problems.

Enhancement of one- and two-photon absorption and visualization of intramolecular charge transfer of pyrenyl-contained derivatives.

To further improve the pyrenyl-contained derivatives two-photon absorption (TPA) and third-order nonlinear optical (NLO) properties, three steps of optimization are employed based on experimental molecule PCVS-B: heteroatomic substitution, exchanging the position of double bonds and adding a branch. The contributions of π electrons to localized orbital locators and Mayer bond orders (LOL-π and IABπ) show that the second step can enhance the chemical interaction between pyrenyl and the branched-chain. Two visual methods of charge density difference (CDD) and transition density matrix (TDM) are combined to intuitively analyze the intramolecular charge transfer (ICT) process of one (two) photon absorption; results show that both following two steps can increase the degree of ICT on the conjugated plane of the pyrenyl. The sum over state (SOS) model was used to find out the dominant two-photon transition process. The difference between the dipole moments obtained by the McRae equation is applied to the three-state model, revealing the inherent law of the second static hyperpolarizability.

Theoretical Investigation on Photophysical Properties of Triphenylamine and Coumarin Dyes.

Organic molecules with donor and acceptor configures are widely used in optoelectronic materials. Triphenylamine dyes (TPCTh and TPCRh) are investigated via density functional theory (DFT) and time-dependent DFT. Some microscopic parameters related to light absorption and photoelectric formation are calculated to interpret the experimental performance in dye-sensitized solar cells (DSSCS). Considering that coumarin derivatives (Dye 10 and Dye 11) have good donor and acceptor structures, they also have a COOH group used as an anchoring group to connect with semiconductors. Thus, the two dyes' photophysical and photoelectric properties are analyzed to estimate the performance and application in DSSCs.

Characterization and Evaluation of the Solubility and Oral Bioavailability of Rutin-Ethanolate Solvate.

Rutin has many biological activities, but poor solubility and absorption limit its oral application. This study aimed to investigate the characterization of metastable rutin-ethanolate and its solubility and oral bioavailability. In this research, a soluble rutin/CH3CH2OH solvate (Form Π) was prepared by solvent crystallization. High-performance liquid chromatography, gas chromatograph, and 1H-NMR showed that Form Π was formed by rutin and ethanol in a molar ratio of 1:1. The changes of Fourier transform infrared spectroscopy and 1H-NMR spectrum and the density functional theory (DFT) calculation predicted hydrogen bond formation between 4'-O of rutin and -OH of ethanol. The results of morphology, solid state CP/MAS 13C-NMR, X-ray diffraction, and differential scanning calorimetry (DSC) revealed that Form Π is a novel polymorph that differs from Form Ι (rutin trihydrate). Form Π can be stored for a long time under sealed and dry conditions at 40°C but would gradually transform into Form Ι under humid conditions. Although Form Π is a new metastable polymorph relative to Form Ι, Form Π has better solubility and faster dissolution rate. Moreover, the bioavailability of Form Π was 2.04 times higher than that of Form Ι. This outcome implied that Form Π would be a prospective raw material of oral preparation.

Effect of graphene between photoanode and sensitizer on the intramolecular and intermolecular electron transfer process.

The main goal of this work is to investigate the effects of a graphene layer between the photosensitive layer and semiconductor substrates on the electron transport performance of dye-sensitized solar cells from the perspective of intramolecular arrangement and interfaces. The benzothiadiazole sensitizer YKP-88 is used as the photosensitive layer and the influence of the graphene layer on the short-circuit current density (Jsc) and open-circuit voltage (Voc) is also discussed by exploring the frontier molecular orbitals, intramolecular charge transfer, weak interaction, interfacial electron dynamic propagations and other microscopic parameters after the anchoring of the graphene layer. The results demonstrate that the graphene layer can accelerate the electron injection of dye molecules into the semiconductor substrate, which not only has a qualitative reduction in injection time, but also has a qualitative change in the increase of the injection amount. In addition, it is also found that the graphene layer increases the stereoscopic effect, the absorption of long wavelength (>700 nm) photon flu and the amount of electron injection into the photoanode, which benefits the intramolecular charge transfer and increases the Jsc and Voc of solar cells. The combination of intermolecular and interfacial perspectives indicates that the appropriate configuration of graphene layers can effectively improve the photoelectric conversion efficiency of dye-sensitized solar cells.

Screening of functional monomers and solvents for the molecular imprinting of paclitaxel separation: a theoretical study.

The interactions between the template molecule paclitaxel (PTX) and seven functional monomers containing methacrylic acid (MA), acrolein (AC), 4-vinylbenzoic acid (4VA), acrylonitrile (AN), 2-vinylpyridine (2VP), 2,6-bisacrylamide pyridine (BAP) and methyl methacrylate (MM) were systematically investigated adopting the density functional theory (DFT) method. Moreover, the different binding sites on PTX and solvents embracing chloroform, acetone, ethanol, methanol, and acetonitrile were considered. The calculated solvent energies (ΔEsolvent) and template-monomer binding energies (ΔEb) suggest that the chloroform is the most suitable solvent for the molecular imprinting reaction of PTX among the studied five solvents. Furthermore, from the obtained ΔEb, we can find that the monomer 4VA combining with PTX in the form of the specific intermolecular hydrogen bonds would present the most stable structure among the investigated monomers. These results can provide valuable theoretical guidance for the efficient extraction of PTX by the molecular imprinting technique in experiments. Graphical abstracts.

Second-Order Nonlinear Optical Switch Manipulation of Photosensitive Layer by an External Electric Field Coupled with Graphene Quantum Dots.

The main purpose of this work is to explore the effect of graphene quantum dots (GR) filling the photosensitive layer. The multibranched dye JH-1 as the photoactive layer material was used to analyze the non-negligible role of graphene quantum dots from the perspectives of optimized structure, electrochemical parameters, optical properties, nonlinear optical (NLO) switch, and external electric field. The results demonstrated that the graphene quantum dots not only improve the optical properties of solar cells but also control the electron transfer in the photosensitive layer molecules under the manipulation of a specific external electric field. When the external electric field intensity is below 20 × 10-4 au, the excess electron orbital does not change. When the external electric field reaches 25 × 10-4 au, the excess electron orbital on the graphene quantum dots evolves. This discovery allows the electron transfer from the photosensitive layer, which should be controlled by the NLO switch. In addition, the optical properties of sensitizers showed regular evolution in the external electric field, which provides an effective way to improve the performance. Comprehensive analysis indicated that the doping of graphene quantum dots with the photosensitive layer can be used as a new way to improve the photoelectric conversion efficiency of solar cells.

Modification of NFA-Conjugated Bridges with Symmetric Structures for High-Efficiency Non-Fullerene PSCs.

As electron acceptors, non-fullerene molecules can overcome the shortcomings of fullerenes and their derivatives (such as high cost, poor co-solubility, and weak light absorption). The photoelectric properties of two potential non-fullerene polymer solar cells (PSCs) PBDB-T:IF-TN (PB:IF) and PBDB-T:IDT-TN (PB:IDT) are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT). Based on the optimized structure of the ground state, the effects of the electron donor (D) and electron acceptor (A) (D/A) interfaces PBDB-T/IF-TN (PB/IF) and PBDB-T/IDT-TN (PB/IDT) are studied by a quantum-chemical method (QM) and Marcus theory. Firstly, for two non-fullerene acceptors (NFAs) IF-TN and IDT-TN, the NFA IDT-TN has better optical absorption ability and better electron transport ability than IF-TN. Secondly, for the D/A interfaces PB/IF and PB/IDT, they both have high optical absorption and electron transfer abilities, and PB/IDT has better optical absorption and lower exciton binding energy. Finally, some important parameters (open-circuit voltage, voltage loss, fill factor, and power conversion efficiency) are calculated and simulated by establishing the theoretical model. From the above analysis, the results show that the non-fullerene PSC PB:IDT has better photoelectric characteristics than PB:IF.

Tunable electron transfer rate in a CdSe/ZnS-based complex with different anthraquinone chloride substitutes.

We use femtosecond transient absorption spectroscopy to study ultrafast electron transfer (ET) dynamics in a model donor and acceptor system using CdSe/ZnS core/shell structure quantum dots (QDs) as donors and anthraquinone (AQ) molecules as acceptors. The ET rate can be enhanced by decreasing the number of chlorine substituents in the AQ molecules because that increases the driving force, which is the energy level offset between the conduction band energy of CdSe/ZnS and the lowest upper molecular orbital potential of AQ derivatives, as confirmed by cyclic voltammetry measurements. However, the electronic coupling between the QDs and AQ derivatives, and the sum of reorganization energy of AQ molecules and solvent calculated by density functional theory are not the main reasons for the change in ET rate in three systems. Our findings provide new insights into selecting an acceptor molecule and will be useful in tuning ET processes for advanced QD-based applications.

Molecular engineering mechanism of organic photoactive layer by alkyl chains, 4-butoxyphenyl and cyanogroup.

The three organic dye molecules (JY31, JY32 and JY33) were applied to the photoactive layer in solar cells. Photophysical and photochemical characteristic have been investigated with natural bond orbital (NBO), frontier molecular orbital, ionization potentials, electron affinities, absorption properties, reorganization energies, static first hyperpolarizability, emission characteristics, IR spectra, charge density difference; the influence of alkyl chains and 4-butoxyphenyl on properties were revealed; Subsequently, three new molecules JY33-1, JY33-2 and JY33-3 were designed by inserting the electron withdrawing group -CN into the acceptor part of JY33 in order to understand molecular engineering mechanism. The results show that the three original molecules have relatively high molar extinction coefficients, and the molecule of JY33 with a 4-butoxyphenyl group enables a bathochromic shift in absorption spectrum and is beneficial to improve the hole transport, injection capacity and ICT properties as well as better energy levels matching. The current study provides an effective channel for manipulating performance in materials design of solar cells.

Effects of nitro- and amino-group on the antioxidant activity of genistein: A theoretical study.

Five novel compounds (Gen-NO2, Gen-2NO2, Gen-NH2, Gen-2NH2 and Gen-6NH2) have been designed via introducing an electron-withdrawing group -NO2 and an electron-donating group -NH2 into the structure of genistein. The effects of -NO2 and -NH2 groups on the antioxidant ability of genistein were investigated via quantum chemistry method in gas and methanol phases. The crucial parameters related to three antioxidant mechanisms were calculated. Moreover, the frontier molecular orbital, natural bond orbital and global descriptive parameters were calculated to evaluate the reactivity of genistein and its derivatives. Calculated results indicate the antioxidant process of genistein and its derivatives inclines to the hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms in gas and methanol phases, respectively. Moreover, introducing -NH2 group into genistein can improve its antioxidant activity owing to the outstanding activities of amino-substituents of genistein, which will provide valuable guidance for the synthesis of new antioxidants experimentally.

Design, Electron Transfer Process, and Opto-Electronic Property of Solar Cell Using Triphenylamine-Based D-π-A Architectures.

A series of D-π-A type dyes were designed based on the experimentally synthesized A1 by introducing different functional groups on the donor and π-spacer, and the optical and electrical properties were calculated by using density functional theory (DFT) and time-dependent DFT (TD-DFT). P1⁻P6 present highest light harvesting efficiency (LHE), driving force of electron injection ( Δ G i n j e c t ), reorganization energy ( Δ G r e g ) and e V O C . These critical parameters have a close relationship with the short-circuit current density ( J S C ) and open-circuit photovoltage ( V O C ), and lead to P1⁻P6 will exhibit higher efficiency. D4 also exhibit superior properties in the driving force of electron injection ( Δ G i n j e c t ), reorganization energy ( Δ G r e g ), which will lead to a higher short-circuit current density ( J S C ). We hope that these results will be helpful for experiments to synthesize new and highly efficient dyes.

Photoactuated Properties of Acetylene-Congeners Non-Metallic Dyes and Molecular Design for Solar Cells.

This paper theoretically simulated (using DFT and TD-DFT in N,N-dimethylformamide (DMF) solvent) the photodynamic properties of three non-metallic dye molecules with D-π-A1-π-A2 structure. The total photoelectric conversion efficiency (PCE) could be evaluated by the following parameters: the geometric structures, the electronic structures, and the absorption spectra, the analyses of charge difference density (CDD) and natural bond orbitals (NBO), the analyses of ionization potential (IP) and electron affinity (EA) from electronic contribution capacity, the reorganization energies (λh, λe, and λtotal), and the chemical reaction parameter (h, ω, ω-, and ω+) for intramolecular charge transfer (ICT) processing, the excited lifetime (τ) and the vertical dipole moment (µnormol). The ∆Ginject, the ∆Gdyeregen, the light harvesting efficiencies (LHE) and the excited lifetime (τ) were used to explain experimental JSC. The experimental trend of VOC was explained by the calculation of ∆ECB and µnormol. Moreover, the 15 dyes were designed by adding the electron-donor groups (⁻OH, ⁻NH2, and ⁻OCH3) and the electron-acceptor groups (⁻CF3, ⁻F, and -CN) to the LS-387 molecular skeleton, which improved electronic contribution, intramolecular charge transfer (ICT), and optoelectronic performance.