Auxiliary Donor Research Articles

Theoretical study of the effects of modifying the structures of organic dyes based on N,N-alkylamine on their efficiencies as DSSC sensitizers.

In this work, we carried out a theoretical study in which DFT and TD-DFT calculations of a series of six new organic dyes that incorporate N,N-alkylamine as an electron donor and a cyanoacrylic acid group as an electron acceptor and anchoring group were performed. In each dye, the donor and the acceptor were bridged by six different π-conjugated spacers consisting of an auxiliary donor group (3,4-ethylenedioxythiophene, EDOT) or an auxiliary acceptor group (benzothiadiazole, BTZ or diketopyrrolopyrrole, DPP) that was linked to either thiophene or phenyl. EHOMO, ELUMO, Egap, λmax, Eex, the open-circuit photovoltage (Voc), the light-harvesting efficiency (LHE), and the free injection energy (ΔGinject) were calculated for all of the dyes to compare their photovoltaic performance. The effects of the incorporation of an additional acceptor group (DPP or BTZ) or an additional donor group (EDOT) into the π-bridge on the geometry, electronic structure, and photovoltaic performance of each designed dye were explored. The study shows that modifying the dye skeleton can greatly improve the performance of the dye and increase its power conversion efficiency. It also reveals that all of the studied dyes are promising candidates for an effective DSSC sensitizer, especially those that include the acceptor group DPP in the π-bridge.

Rhodanine-3-acetic acid containing D-π-A push-pull chromophores: Effect of methoxy group on the performance of dye-sensitized solar cells

Abstract Three organic photosensitizers (TPA-R9, J-R9, CAR-R9) comprising of triphenylamine, julolidine and carbazole with methoxy group as an additional auxiliary donor and rhodanine-3-acetic acid as an acceptor were synthesized, and used in dye-sensitized solar cells application. The impact of the different donors with additional methoxy group on the photophysical, electrochemical, and photovoltaic properties are studied. The electron transfer kinetics are investigated by transient absorption spectroscopy and impedance spectroscopy. At a fixed VOC, the electron lifetime increases in the order of donors: julolidine

First theoretical probe for efficient enhancement of nonlinear optical properties of quinacridone based compounds through various modifications

In this study, first attempt has been made for theoretical designing of quinacridone (QA) dye and new QA-based compounds (QA-1 to QA-9) were proposed by installing auxiliary donors (dimethylvinyl, methoxy, and N,N-dimethylamine), donor (diphenylamine) and acceptors (cyanoacrylic acid, CN and NO2) segments into fixed π-bridge QA. DFT and TDDFT calculations with B3LYP/6-31G(d,p) and CAM-B3LYP/6-31G(d,p) functional were used to shed light on the promising structure, charge transport and NLO properties. Introduction of auxiliary donors/donor and acceptor successfully modified the structure which led to superior NLO properties. An eye-catching NLO response was observed in all designed compounds. Interestingly, QA-9 exhibits appealingly large enhancement in NLO properties through ICT process with <α> and βtot computed to be 716.02 (a.u) and 128082.15 (a.u) respectively. UV–Vis results indicates the QA-9 most red shifted among all studied compounds with λmax = 489.02 nm. QA-1 to QA-9 showed narrow HOMO-LUMO energy gap as compared to QA which results in enhanced NLO response. NBO analysis confirms the formation of charge separation state in QA-1 to QA-9 due to successful migration of electrons from auxiliary donors/donor to acceptors via π-bridge. The present research evokes the scientific interest regarding the development of QA based tempting NLO compounds that can be beneficial in modern hi-tech applications.

Systematic Study of the Effect of Auxiliary Acceptors in D–A′−π–A Sensitizers Used on Dye-Sensitized Solar Cells

We perform a systematic quantum chemical investigation to elucidate the effect of auxiliary acceptors (A′) on the electronic properties of D–A′−π–A dyes used in dye-sensitized solar cells. A large set of dyes (380) are considered to achieve robust conclusions. Our calculations indicate that the auxiliary acceptor modulates, as expected, the lowest unoccupied molecular orbital level of the dye, except for very poor acceptors. More surprisingly, some auxiliary acceptors also modify the highest occupied molecular orbital level of the dye and its excited states effectively act as auxiliary donors as well. The study of the data set reveals that the effect of changing the π-bridges is highly systematic and predictable. Despite the variability in the geometry between the connected fragments, the frontier molecular orbital energy levels of dyes are very closely related to the energy levels of the component fragments, e.g., it is easy to predict the change in the electronic structure of a dye due to the change of ...

New D–D′–A Configured Dye for Efficient Dye-Sensitized Solar Cells

D−π–A, D–A−π–A, and other configuration-based organic dyes have shown great potential in the field of dye-sensitized solar cells (DSCs). Compared with traditional configurations, D–D′–A offers several advantages such as enrichment of the electron-donating ability, absorption spectral region, and molar extinction coefficient and inhibits dye aggregation. Hence, in this work, a novel D–D′–A-type dye has been designed and synthesized for DSC applications. In this configuration, substituted imidazole has been used as a primary donor, phenothiazine as an auxiliary donor, and cyanoacetic acid as an acceptor/anchoring group. Structural characterizations of a D–D′–A-type dye were done by using NMR and electron ionization–mass spectrometry. Photophysical, electrochemical, and computational studies were systematically performed to evaluate its electronic transitions, light-harvesting property, highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels, and redox behavior. The photop...

Dye-sensitized solar cells based on (D−π−A)3L2 phenothiazine dyes containing auxiliary donors and flexible linkers with different length of carbon chain

Four (D−π−A)3L2 phenothiazine dyes (PTZTB1−4) and a reported reference dye (R−SB) with a mono D−π−A chain were utilized as photosensitizers for dye-sensitized solar cells. In the skeleton of the dyes PTZTB1−4, three D−π−A chains (D−π−A)3 were connected by flexible linker of n-hexyl or n-dodecyl group (L2) to build the (D−π−A)3L2 configuration. The effect of both the auxiliary donors and linkers with different length of carbon chains upon the photophysical, electrochemical as well as photovoltaic properties of the (D−π−A)3L2 dyes were further investigated. Results reveal that the dyes PTZTB3−4 containing the auxiliary donor of 4-octyloxyphenyl group show a higher molar extinction coefficient, a broader IPCE response region, and a higher HOMO value than those of PTZTB1−2 and R−SB. Among all of the devices, the cells based on PTZTB2 and PTZTB4 exhibit a higher open circuit voltage due to that the charge recombination is blocked significantly by the n-dodecyl linkers. Meanwhile, a maximal power conversion efficiency of 6.66% is achieved by the device fabricated with PTZTB3. Besides, it is noteworthy that the (D−π−A)3L2 dyes possess a superior adsorbed stability on TiO2 interface than that of the reference dye as a result of the three anchors in a molecule of the former.

Effect of methoxy group on NLOphoric properties of fluorescent 7-arylstyryl-2-methoxyphenylimidazo[1,2-a]pyridine - Solvatochromic and computational method

Extensively conjugated donor-π-acceptor-donor (D-π-A-π-D) type fluorescent styryl dyes bearing imidazo[1,2-a]pyridine units have been investigated for their nonlinear optical properties (NLO). Enhanced Stokes shift (2486–2843 cm−1) brought about by replacing methoxy group by diethyl, dimethyl, cyclohexylamino substituents at C-2 and C-7 positions of imidazo[1,2-a]pyridine core in styryl dyes have been understood in elucidating the electronic structures. The position of methoxy group acting as auxiliary donor largely influences the nonlinear optical (NLO) properties of imidazo[1,2-a]pyridine derivatives. Polarizabilities and hyperpolarizabilies were estimated by solvatochromic and DFT method using BHandHLYP and CAM-B3LYP functionals with the 6-311 + G(d,p) basis set. Imidazo[1,2-a]pyridine derivatives showed minimum ten-fold higher NLO parameters compared to reminiscent of charge transfer contribution of donor groups. The dyes have two-photon cross-section values 66–189 GM and comparable with commercial two photon absorbing styryl dyes.

Design and synthesis of phenothiazine based push-pull organic sensitizers with benzimidazole as an auxiliary donor for DSC’s

Design and synthesis of phenothiazine based push-pull organic sensitizers with benzimidazole as an auxiliary donor for DSC’s

Rational tailoring of C275 towards promising organic dyes: Enhancing light absorption and charge separation

Designed with electron-donating and electron-withdrawing moieties as donors and acceptors, respectively, a series of novel organic dyes for dye-sensitized solar cells (DSCs) are simulated using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods The interacting dye/TiO2 systems are also studied to further explore the interfacial injection process of photo-excited electron. The model dye C275 is featured with donor/acceptor (D/A) molecular architecture, which is primary to achieve the easy charge-transfer excitation and suitable energy levels alignment. To date, considerable efforts are devoted to the design and synthesis of D/A type organic dyes, and the initial configurations are typically comprised of N-annulated perylene donor, porphyrin linker, and carboxylic acid acceptor. Our results show that, the electronic levels and optical absorption properties can be tuned gradually by introducing auxiliary donor units or electron-deficient spacer in acceptor groups. Moreover, the designed dyes also exhibit good performance in terms of photoinduced charge transfer, electron injection, and dye regeneration, etc. Through structural modification of donor moieties, the new tailored dyes provide appropriate energy levels, strong light-harvesting and easy charge separation. Meanwhile, the distinct red-shift of optical absorption and large amount of transferred charges are also obtained by structural tailoring of acceptor groups, whereas the large values of injection time may be harmful for the interfacial photoelectron injection. Therefore, comparing with donor modification, it should be more carefully to choose appropriate acceptor group with the balance of various energetic and kinetic factors for the rational design of high-efficient organic dyes.

Auxiliary Methoxy Aided Triphenylamine and Dicyanoisophorone Based Flurophores with Viscosity and Polarity Sensitive Intramolecular Charge Transfer

Novel, multibranched “triphenylamine based donor with added auxiliary methoxy donor and dicyanovinyl acceptor” based fluorescent molecules are developed. The dicyanoisophorone moiety is used as a configurationally locked polyene system for π-conjugation linking between donor and acceptor, to control the unnecessary intramolecular rotations in the molecule, which can to act as a rotor. The synthesized dyes show good fluorescent molecular rotor properties and strong emission solvatochromism. Auxiliary methoxy donors shift both the absorption and emission maxima towards longer wavelengths compared to known analogues, along with increased Stokes shifts. Fluorescent molecular rotor properties of the dyes are influenced by a local excited state to twisted intramolecular charge transfer state transition, which is discussed in terms of emission solvatochromism and Lippert–Mataga, Weller and Rettig polarity plots. Three different viscous solvent systems i.e., paraffin oil–dichloromethane, polyethylene glycol-400–dichloromethane and polyethylene glycol-400–N,N-dimethylformamide are used to investigate the sensitivity of rotors towards the viscosity of the environment. A maximum 16-fold enhancement in emission intensity and 0.616 × value is achieved for rotor Dye-3. The polarity effect of a binary viscous solvent system, by the virtue of intramolecular charge transfer, on the viscosity sensing properties of rotors is explained by constructing the Weller and Rettig’s plots for different viscous systems.

Reaction mixture analysis by ESI-MS: Mercury(II) and dicysteinyl tripeptide complex formation

Current clinical treatment for mercury poisoning generally depends on the complexation of mercury ions with dithiol compounds. Although mercury is known to have a high binding affinity for the soft sulfur donor atoms, further understanding of its complex formation tendencies in the presence of auxiliary donor atoms is necessary to enhance its immobilization and detoxification. In order to evaluate the effect of auxiliary binding groups on mercury complex formation, two dicysteinyl tripeptides, CXC, where C is cysteine and X is glycine (CGC) or glutamic acid (CEC) were reacted with mercury(II) chloride. These peptides provide the structural differences to evaluate the role of an added gamma carboxylate group in complex formation. The reaction mixtures were studied by Electrospray Ionization Mass Spectrometry (ESI-MS). Low micromolar mercury(II) solutions consisting of mercury(II) to peptide molar ratio of 1:2, 1:1, and 1:0.5 were analyzed for changes in complex speciation after mixing. The results show that the major complex formed is the 1:1 Hg(peptide) complex for both dithiol peptide ligands. Other complexes include 1:2 Hg(peptide)2, 2:2 Hg2(peptide)2, 2:3 Hg3(peptide)2 and 4:2 Hg4(peptide)2. But the CEC ligand also readily forms higher order peptide complexes such as 1:3 Hg(CEC)3, 2:3 Hg2(CEC)3, and 3:3 Hg3(CEC)3.Computational modeling using electronic structure methods was used to predict the structures and energetics of some candidate complexes. These calculations show that the thiol sulfur of the cysteine residues is the most important mercury coordination site. However, auxiliary binding groups including the carboxylate and amide groups in these peptides also play a significant role in stabilizing complexes through interaction with mercury(II) or hydrogen bonding.ESI-MS and computational data provide corroborating evidences that auxiliary donor atoms play an important role in mercury-dithiol complex formation and speciation. These results will be useful toward the rational design of dithiols for optimal mercury chelation.

Effect of π-linkers on phenothiazine sensitizers for dye-sensitized solar cells

Eleven new dyes have been synthesized in order to investigate the effect of five different π-spacers and two different auxiliary donors in phenothiazine-based sensitizers for dye-sensitized solar cells. The target molecules were synthesized in 5–7 steps from 10H-phenothiazine. Evaluation of the photovoltaic performance revealed that introducing a π-spacer does not necessarily increase the power conversion efficiency. Still, dyes with a furan π-spacer were found to be slightly more efficient compared to their thiophene counterparts, and more efficient than no spacer. Dyes with phenyl based π-spacers resulted in less efficient solar cells, and especially so when incorporating two fluorine atoms. Surprisingly, introducing an additional electron donating group in the auxiliary donor had no pronounced effect on the photovoltaic performance of the dyes.

Effect of Flexible, Rigid Planar and Non-Planar Donors on the Performance of Dye-Sensitized Solar Cells

A systematic design and synthesis of three push–pull metal-free organic dyes employing N-alkylated diphenylamine (D1), carbazole (D2), and phenothiazine (D3) as donor moieties are presented in this paper. While, vinylbenzene, methoxybenzene, and cyanoacrylic acid were used as π-linker, auxiliary donor, and acceptor moieties, respectively for all three dyes. The study focusses on identifying the best donor among the three in terms of simple molecular design. TiO2-based dye-sensitized solar cells (DSSC) were fabricated with these dyes. Further, dyes and their deprotonated forms were investigated using density functional theory (DFT) and time-dependent DFT analyses to characterize their electronic and optical properties. The variation in power conversion efficiency (PCE) was observed owing to change in coplanarity from freely rotating diphenylamine, fused planar carbazole, and nonplanar phenothiazine. Cyclic voltammetry was performed on D1, D2, and D3 indicated that the substitution at C3 position is effective in stabilizing the radical cation formed upon exposure to light, thereby preventing it from dimerization and degradation. Results illustrated that the dye-containing carbazole as donor (D2d) delivered the best PCE, viz., 3.7%. This was further enhanced to 4.2% on addition of chenodeoxycholic acid as a coadsorbent.

First principles study on interface between dual-channel anchorable organic dyes and TiO2 for dye-sensitized solar cells

Four A-D-A-D-A organic dyes with different auxiliary acceptor or donor groups have been theoretically investigated by first principle as potential photosensitizers in dye-sensitized solar cells. Judging from the isolated dyes, 2PZ-SP with diphenyl-substituted pyrido[3,4-b]pyrazine-2,5-thiophene as auxiliary acceptor is not suitable to be taken as organic dye in DSSCs because of the inappropriate electron density distribution. However, it is difficult to distinguish the performance of other three dyes since no one has all superiorities. After the dye is adsorbed on TiO2 surface, the deviation between LUMO energy level of dye and conduction band of TiO2 (101) surface is further enlarged, which is favorable for the electron injection. Moreover, 2PZ-PP stands out because of the smallest H-L energy gap and the shortest injection time. Finally, a new D-π-A dye with the identical donor, π group, and acceptor groups is designed to compare with 2PZ-BT. It is found that 2PZ-BT has the absolute advantage to be potential dye for DSSCs. Besides the suitable groups, the appropriate configuration is more critical aspect to determine the performance.

Investigation of new carbazole based metal-free dyes as active photo-sensitizers/co-sensitizers for DSSCs

Herein, we report the molecular design, synthesis and characterization of three new D-D-π-A configured metal-free chromophores D1-3 for their application in DSSCs as sensitizers as well as co-sensitizers. The new entities comprise carbazole as donor scaffold, 4-methoxyphenyl group as auxiliary donor and three different units, viz. cyanoacetic acid, 2, 4-thiazolidinedione and barbituric acid as acceptor/anchoring groups. Their photochemical, electrochemical and theoretical studies were carried out in order to assess their feasibility as active sensitizers. Further, D1-3 were exploited as co-sensitizers along with NCSU-10 dye. Their photoelectrochemical performances and charge transport properties in fabricated DSSCs were studied. The results revealed that D1 sensitizer displayed the highest PCE of 2.20% among the three dyes. D3 when co-sensitized with NCSU-10 displayed an improved PCE of 8.32% (JSC = 19.25 mA.cm−2, VOC = 0.680 V, FF = 63.7%) while NCSU-10 alone exhibited PCE of 8.25% (JSC = 20.41 mA.cm−2, VOC = 0.667 V, FF = 60.6%).

Strategies for the synthesis of HBGl3, a glutamic acid derived ligand bearing phenolic and azacarboxylate donor groups at the nitrogen atom

The development of a route applicable to the preparation of acyclic glutamic acid-based chelating ligands bearing two different auxiliary donor groups linked to the nitrogen atom by methylene spacers is described and applied to the synthesis of the new polydentate ligand HBGl3, the first example of such a structure. The synthesis is accomplished using a strategy employing reductive amination and t-butyl ester protected intermediates. The most basic pKa values for the HBGl3 ligand have been estimated via potentiometric and UV–Visible titration techniques.

Formation of tyrosine radicals in photosystem II under far-red illumination

Photosystem II (PS II) contains two redox-active tyrosine residues on the donor side at symmetrical positions to the primary donor, P680. TyrZ, part of the water-oxidizing complex, is a preferential fast electron donor while TyrD is a slow auxiliary donor to P680+. We used PS II membranes from spinach which were depleted of the water oxidation complex (Mn-depleted PS II) to study electron donation from both tyrosines by time-resolved EPR spectroscopy under visible and far-red continuous light and laser flash illumination. Our results show that under both illumination regimes, oxidation of TyrD occurs via equilibrium with TyrZ• at pH 4.7 and 6.3. At pH 8.5 direct TyrD oxidation by P680+ occurs in the majority of the PS II centers. Under continuous far-red light illumination these reactions were less effective but still possible. Different photochemical steps were considered to explain the far-red light-induced electron donation from tyrosines and localization of the primary electron hole (P680+) on the ChlD1 in Mn-depleted PS II after the far-red light-induced charge separation at room temperature is suggested.

The impact of adjusting auxiliary donors on the performance of dye-sensitized solar cells based on phenothiazine D-D-π-A sensitizers

Three new D-D-π-A sensitizers ZHG5, ZHG6 and ZHG7 have been prepared by gradually improving the steric hindrance of auxiliary donors and the power conversion efficiencies (PCE) are 5.64%, 5.32% and 2.74%. UV–Vis absorption indicates that the molar extinction coefficients decrease with the increased steric hindrance of auxiliary donors. X-ray photoelectron spectroscopy (XPS) indicates that the tilt angles of ZHG5 and ZHG6 anchored on the TiO2 film are similar and ZHG7 is almost standing rather vertical on the TiO2 film with the smallest tilt angle. The results of dye desorption and XPS experiments indicate that the dye loading amount of ZHG6 with larger steric hindrance is lower than that of ZHG5, ZHG7 with largest auxiliary donor has the maximum loading amount probably due to its smallest tilt angle. Larger auxiliary donor of ZHG6 leads to higher open circuit voltage (Voc = 734 mV) but lower shorter circuit current (Jsc = 12.63 mA cm−2) compared with that of ZHG5 (Voc = 730 mV, Jsc = 12.06 mA cm−2). However, dense packing of dye ZHG7 anchored on the TiO2 leads to more serious intermolecular π-π aggregation effects. Perhaps this effect and lowest molar extinction coefficient are the reason that DSSC based on ZHG7 have the lowest PCE. So above results indicate that auxiliary donor with overlarge steric hindrance will have smaller tilt angle of dye anchored on TiO2 and may lead to more dye loading amount but serious intermolecular π-π aggregation effects.

Controlling Near-Infrared Chromophore Electronic Properties through Metal-Ligand Orbital Alignment.

Transition-metal complexes of radical ligands can exhibit low-energy electronic transitions in the near-infrared (NIR) spectral region. NIR band energy and intensity sensitively depend on the degree of electronic coupling of the chromophore. Using the example of open-shell complexes derived from platinum and a 1,4-terphenyldithiophenol, we present a novel approach toward spectroscopically distinct NIR dyes for which the degree of electronic coupling correlates with the relative orientation of radical ligand and metal orbitals. Ligand/metal orbital alignment is modulated by auxiliary phosphine donors and selectively results in electron localized Class II-III or delocalized Class III structures that display distinct NIR transitions at 6500 and 4000 cm-1.

OPTOELECTRONIC PROPERTIES OF TRIPHENYLAMINE BASED DYES FOR SOLAR CELL APPLICATIONS. A DFT STUDY

Abstract: Dye-sensitized solar cells (DSSCs) based on triphenylamine (TPA) as a donor group linked with the acceptor cyanoacrylic acid electron acceptor by 2,2’-bithiophene as π-bridged (D-π-A) has been investigated by Density Functional Theory (DFT) at the B3LYP/6-311G(d,p) level of theory, to establish the conformational orientation of cyanoacrylic acid group as well as evaluate the effect of planarizing the 2,2’-bithiophene unit in position 3 and 3’ by electron withdrawing or donor groups on the electronic structure properties of ground and doping(n,p) states. Also, the Time Dependent Density Functional Theory (TD-DFT) at the CPCM-TD-CAM-B3LYP//CAM-B3LYP/6-311G(d,p) level of theory were selected to modulate the electronic absorption spectra and charge-transfer capabilities of the molecules analyzed in the present work. The results indicate that adding an auxiliary donor or withdrawing group to the 2,2’-bithiophene in the (D-π-A) arrangement allow to modify the LUMO’s energy of the dyes, while the HOMO's energy is slightly affected.