Acceptor Fragments Research Articles

Diketopyrrolopyrrole based highly conjugated small molecules for organic solar cells

A series of three donor molecules (DPP-B, DPP-N and DPP-P) based on diketopyrrolopyrrole (DPP) sharing the similar backbone of D-π-A-π-D have been investigated. In these molecules, substituents such as pyrene, naphthalene and benzene act as the electron donating end groups, DPP as the central core unit and thiophene has been used as a bridge between donor and acceptor fragments. Theoretical calculations have been carried out with the help of density functional theory (DFT) and time-dependent functional theory (TD-DFT). For the optimization of geometry of investigated molecules, DFT functional B3LYP/6-31g(d) has been used and TD-B3LYP/6-31g(d) has been used to obtain the best results of calculations inexcited state. DPP-P has been considered a suitable donor molecule among all investigated molecules as it manifests the suitable value of Eg of 2.24 eV and showed the stronger absorption λmaxof 611 nm. Hence, this study reveals that investigated donor molecules are suitable for high performance organic solar cell devices

DFT/TDDFT Investigation on donor-acceptor triazole-based copolymers for organic photovoltaics

Using density functional theory (DFT) method, we studied several triazole-based donor-acceptor (DA) π-conjugated molecules and evaluated their lowest unoccupied molecular orbital (LUMO) energies. Our results shows that bithiophene-substituted triazole-based acceptors with short and non-bulky substituents tend to be co-planar and hence exhibit stronger conjugation and electron delocalization, thereby leading to lower orbital energies of LUMO. Introduction of heteroatom such as S and Se within the chemical structure of triazole-based acceptor also significantly reduces the bandgap by lowering the LUMO energies. Among the donor fragments studied, a dithieno [3,2-b:2′,3′-d]phosphole donor fragment (Y4) led to donor-acceptor (DA) pairs with comparatively lower highest occupied molecular orbitals (HOMO, (-5.01 to -4.69 eV) along with higher VOC (>1.29 eV) without much compromise in its bandgap energy. This makes such DA-based polymers promising for bulk heterojunction solar cell applications. TD-DFT calculations were further used to simulate the absorption spectra of the DA monomers and showed that most pairs gave meaningful absorption from 400 to 1100 nm. More interestingly, the addition of long aromatic substituents in the acceptor fragment tends to give broader absorption spectra. Further studies on trimers with DDA repeating unit revealed that copolymers bearing Y4 and a benzo [1,2-d;4,5-d’]bitriazole X1 (or X6) exhibits close to ideal band gap of 1.37 eV (1.36 eV) with favorable open circuit voltage 1.23 eV, though absorption by Y4-Y4-X1 takes place in Infrared scope with higher oscillator strength. All in all, we identified a polymer comprising Y4 donor and X1 acceptor fragment to be a promising material for heterojunction organic solar cell application.

Influence of Substitution Effect on MMCT in Mixed‐Valence Cyanido‐Bridged FeII−CN−Ru2III,III−NC−FeII System

AbstractThis work reports the designed synthesis and characterization of nine tetranuclear mixed valence cyanido‐bridged complexes [CpMen(dppe)FeIICNRu2III,III(X‐DMBA)4NCFeII(dppe)CpMen][PF6]2 (1–9: CpMen=polymethylcyclopentadienyl, n=0, 4, 5; DMBA=N,N’‐dimethylbenzamidinate, X= H, MeO, CF3). The regular variation of crystallographic data, IR and UV/Vis/NIR spectra for complexes 1–9 demonstrates that the substitution effect of the ligand at the donor or acceptor fragment has explicit influence on the MMCT properties. Moreover, the electrochemical measurement might suggest the existence of long‐range electronic coupling between the two terminal FeII in this FeII−CN−Ru2III,III−NC−FeII array.

Narrow-Bandgap Single-Component Polymer Solar Cells with Approaching 9% Efficiency.

Two narrow-bandgap block conjugated polymers with a (D1-A1)-(D2-A2) backbone architecture, namely PBDB-T-b-PIDIC2T and PBDB-T-b-PTY6, are designed and synthesized for single-component organic solar cells (SCOSCs). Both polymers contain same donor polymer, PBDB-T, but different polymerized nonfullerene molecule acceptors. Compared to all previously reported materials for SCOSCs, PBDB-T-b-PIDIC2T and PBDB-T-b-PTY6 exhibit narrower bandgap for better light harvesting. When incorporated into SCOSCs, the short-circuit current density (Jsc ) is significantly improved to over 15mA cm-2 , together with a record-high power conversion efficiency (PCE) of 8.64%. Moreover, these block copolymers exhibit low energy loss due to high charge transfer (CT) states (Ect ) plus small non-radiative loss (0.26eV), and improved stability under both ambient condition and continuous 80°C thermal stresses for over 1000 h. Determination of the charge carrier dynamics and film morphology in these SCOSCs reveals increased carrier recombination, relative to binary bulk-heterojunction devices, which is mainly due to reduced ordering of both donor and acceptor fragments. The close structural relationship between block polymers and their binary counterparts also provides an excellent framework to explore further molecular features that impact the photovoltaic performance and boost the state-of-the-art efficiency of SCOSCs.

Vibronic exciton model for low bandgap donor-acceptor polymers.

A vibronic exciton model is introduced to describe the excited state band structure and associated absorption spectra of low bandgap donor-acceptor conjugated polymers. The Hamiltonian is represented in a diabatic basis consisting of Frenkel-like donor and acceptor fragment excitations as well as charge-transfer (CT) excitations between neighboring fragments. States are coupled to each other through electron and hole transfer as well as Coulombically, through interacting fragment transition dipole moments. Local vibronic coupling involving the prominent aromatic-quinoidal vibrational mode, which is responsible for pronounced vibronic progressions in most conjugated oligomers and polymers, is also included. The DAD repeat unit is shown to behave like a J-aggregate trimer, driven by both the sizable in-phase electron and hole transfer integrals between donor and acceptor fragments as well as negative Coulomb coupling between donor and acceptor fragment excitations. The J-aggregate behavior is enhanced in the polymer limit through inter-repeat unit coupling, with the 0-0 vibronic peak significantly enhanced in the lowest-energy near-IR band. In addition, the radiative rate is enhanced by the number of coherently connected repeat units. The near-IR band is shown to possess roughly equal admixtures of CT and Frenkel-like excitations. Applications are made to the polymer PffBT4T-2DT, with the simulated absorption spectrum quantitatively capturing the salient features of the measured spectrum.

Rational Design of π-Conjugated Tricoordinated Organoboron Derivatives With Thermally Activated Delayed Fluorescent Properties for Application in Organic Light-Emitting Diodes.

A series of donor–acceptor (D–A) tricoordinated organoboron derivatives (1–10) have been systematically investigated for thermally activated delayed fluorescent (TADF)-based organic light-emitting diode (OLED) materials. The calculated results show that the designed molecules exhibit small singlet-triplet energy gap (ΔEST) values. Density functional theory (DFT) analysis indicated that the designed molecules display an efficient separation between donor and acceptor fragments because of a small overlap between donor and acceptor fragments on HOMOs and LUMOs. Furthermore, the delayed fluorescence emission color can be tuned effectively by introduction of different polycyclic aromatic fragments in parent molecule 1. The calculated results show that molecules 2, 3, and 4 possess more significant Stokes shifts and red emission with small ΔEST values. Nevertheless, other molecules exhibit green (1, 7, and 8), light green (6 and 10), and blue (5 and 9) emissions. Meanwhile, they are potential ambipolar charge transport materials except that 4 and 10 can serve as electron and hole transport materials only, respectively. Therefore, we proposed a rational way for the design of efficient TADF materials as well as charge transport materials for OLEDs simultaneously.

Theoretical description of the electronic properties and intrinsic chemical reactivity of organic compounds derived from 1,3-Benzoxazole

The electronic and intrinsic chemical reactivity properties of four single ring chain structure organic compounds derived from 1,3-Benzoxazole, based on to mono- and bi-substitution of acceptor and donor fragments of electrons. This theoretical study was motivated by the need to inquire specifically about the effect of electric charge transfer individual and simultaneous of the substitutes into one of the parent compound phenyl rings. The amino and nitro groups were used as fragments, respectively. The results found from this study are important because it provides key aspects to understand mechanisms for the design of novel structures for the development of new materials with appropriate properties and explore their potential use as biomarkers, active media for tunable lasers, or active layers for solar cells and suggest their possible use for these applications based on 27-Phenyl-30-Oxazol-2-Phenyl-1,3-Benzoxazole from the comparative study of their electronic and chemical reactivity properties of 27-Phenyl-30-Oxazol-2-Phenyl-1,3-Benzoxazole and compounds derived. The Gaussian 03 software suite was used as a computer calculation tool, while the calculations were computed by using the hybrid functional that combines Becke’s three-parameter exchange functional with Lee Yang Parr’s correlation functional.

Twist-Bend Nematogenic Supramolecular Dimers and Trimers Formed by Hydrogen Bonding

A selection of novel non-symmetric supramolecular liquid crystal dimers and trimers formed by hydrogen-bonding have been prepared and their phase behaviour characterised by polarised optical microscopy, X-ray diffraction and temperature-dependent Fourier-transform infrared spectroscopy. We mix the bent twist-bend nematogen 4-[6-(4’-cyanobiphenyl-4-yl) hexyloxy]-benzoic acid (CB6OBA) with a series of small stilbazole-based compounds 4-[(E)-2-(n-alkoxyphenyl)ethenyl]pyridines (nOS) of varying terminal chain length (n) to obtain the CB6OBA:nOS complexes. Complexes with n ≤ 7 exhibit nematic and twist-bend nematic behaviour, followed on cooling by a smectic C phase for n = 4–7, and finally, a hexatic-type smectic X phase for n = 3–7. Mixtures with n = 8–10 exhibit a smectic A phase below the conventional nematic phase, and on further cooling, a biaxial smectic Ab phase and the same hexatic-type SmX phase. Supramolecular trimers, CB6OBA:CB6OS and CB6OBA:1OB6OS, formed between CB6OBA and dimeric stilbazoles [(E)-2-(4-{[6-(4’-methoxy[1,1’-biphenyl]-4-yl)hexyl]oxy}phenyl)ethenyl]pyridine (1OB6OS) or 4-[(E)-4’-(6-{4-[(E)-2-(pyridin-4-yl)ethenyl]phenoxy}hexyl)[1,1’-biphenyl]-4- carbonitrile (CB6OS), exhibit nematic and twist-bend nematic phases, and are the first hydrogen-bonded trimers consisting of unlike donor and acceptor fragments to do so.

Unravelling the impact of thiophene auxiliary in new porphyrin sensitizers for high solar energy conversion

The performance of conjugated donor-π-Acceptor (D-π-A) sensitizers with the modification of thiophene auxiliary acceptors depends critically on their mesoscopic ordering that enables improved photon harvesting and charge transfer processes. This idea has been implemented here by reporting photocatalytic hydrogen production performance in the incremental order of 2691, 6641 and 7396 μmol g−1 h−1 by altering thiophene (LG-5) to thieno-thiophene (LG-tT) to dithieno- thiophene (LG-DtT) auxiliaries. New sensitizers, LG-tT and LG-DtT are making it possible to achieve an impressive power conversion efficiency of (PCE) of 8.25 % and 7.05 %, respectively in dye-sensitized solar cell applications. The high onset of Q-band absorption of both sensitizers (720−750 nm) is resulting in effective harvesting of sunlight. DFT studies suggest the photoexcited electron transfer process took place intramolecularly from donor phenothiazine to acceptor cyanoacrylic acid via porphyrin macrocycle. This strategy of molecular engineering at donor and acceptor fragments led to competitive results compared to many reported sensitizers for both DSSC and photocatalytic hydrogen generation.

Donor-Acceptor-Appended Triarylboron Lewis Acids: Ratiometric or Time-Resolved Turn-On Fluorescence Response toward Fluoride Binding.

Triarylboron Lewis acid compounds (CzmBoT (1c) and DPAmBoT (2c)), in which carbazole (Cz) or diphenylamine (DPA) donors are linked with a triazine acceptor in the ortho position of the phenylene ring are prepared and characterized. The treatment of 1c and 2c with the fluoride anion produces the corresponding fluoride adducts [1cF]- and [2cF]- as a tetraethylammonium salt. An X-ray diffraction study of [1cF]- reveals a twisted conformation between the Cz and phenylene rings. The Cz-containing 1c shows a ratiometric fluorescence change upon fluoride binding, while the DPA-containing 2c exhibits a turn-on fluorescence response in tetrahydrofuran. In particular, both fluoride adducts exhibit thermally activated delayed fluorescence (TADF) properties with microsecond-range lifetimes. Electrochemical and theoretical analysis suggests that the intramolecular charge-transfer transition from the donor to a conjugated acceptor fragment is switched to the donor to a triazine transition after fluoride binding. Theoretical analysis further demonstrates the twisted structure, effective highest occupied molecular orbital-lowest unoccupied molecular orbital separation, and the small energy splitting between the excited singlet and triplet states for the fluoride adducts, with all supporting the observed TADF. The time-resolved fluorescence measurements of 2c in the presence of both fluoride and a competitive fluorescent dye (Coumarin 6) effectively eliminate the short-lived fluorescence of a dye, retaining long-lived fluorescence signals originating only from [2cF]-.

Twisted acceptors in the design of deep-blue TADF emitters: crucial role of excited-state relaxation in the photophysics of methyl-substituted s-triphenyltriazine derivatives

A series of twisted triaryl-s-triazine derivatives are used as acceptor fragments in design of deep-blue TADF emitters for OLED. Comprehensive photophysical investigations indicate high impact of structural relaxation on the TADF color and efficiency.

Cruciform Molecules Bearing Bis(phenylsulfonyl)benzene Moieties for High‐Efficiency Solution Processable OLEDs: When Thermally Activated Delayed Fluorescence Meets Mechanochromic Luminescence

AbstractFour crucifix‐shaped molecules, named TPA‐BPSB, DMAc‐BPSB, MTPA‐BPSB and MDMAc‐BPSB, bearing the same acceptor fragment of bis(phenylsulfonyl)benzene (BPSB) and different donor segments (TPA and MTPA are the diphenylamine derivatives while DMAc and MDMAc are the 9,9‐dimethylacridine derivatives) are synthesized and characterized by NMR, mass spectra, and single crystal X‐ray crystallography. The molecular structure–property relationship of these crucifix‐shaped molecules is systematically explored. All compounds display thermally activated delayed fluorescence (TADF) in the region of 500–550 nm. In addition, charming mechanochromic luminescence properties are observed for all these TADF molecules under external stimuli, such as grinding and exposure to CH2Cl2 vapor. Four TADF molecules are used as the emitters in organic light‐emitting diodes (OLEDs) fabricated via solution process. MTPA‐BPSB‐based device presents a best performance with a highest external quantum efficiency of ≈21%, which is among the highest efficiencies for reported BPSB‐based solution‐processable OLEDs so far. This research has an important significance in designing high‐efficiency multifunctional TADF molecules.

Phenoxazines having various electron acceptor or donor fragments as new host materials for green phosphorescent OLEDs

We report on the synthesis and characterization of a new series of phenoxazine-based compounds as potential host materials of phosphorescent OLEDs. The derivatives are thermally stable materials as it was demonstrated by thermogravimetric analysis. Electron photoemission spectra of thin layers of the materials show ionization potentials in the range of 5.24–5.56 eV. Some of the developed materials formed homogenous amorphous layers with high glass transition temperatures and were used as hosts for bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III), Ir(ppy)2(acac), guest in green phosphorescent organic light-emitting diodes. Results indicated that a device with 3-[bis(9-ethylcarbazol-3-yl)methyl)-10-hexylphenoxazine host exhibited superior performance with external quantum efficiency exceeding 5.9%, maximum current efficiency of 18.3 cd/A, maximum brightness of 5366 cd/m2 and low turn on voltage of 3.1 V.

Coordination Chemistry of P4 S3 and P4 Se3 towards the Iron Fragments [Fe(Cp)(CO)2 ]+ and [Fe(Cp)(PPh3 )(CO)

The complexes Ag(L)n[WCA] (L=P4S3, P4Se3, As4S3, and As4S4; [WCA]=[Al(ORF)4]− and [F{Al(ORF)3}2]−; RF=C(CF3)3; WCA=weakly coordinating anion) were tested for their performance as ligand‐transfer reagents to transfer the poorly soluble nortricyclane cages P4S3, P4Se3, and As4S3 as well as realgar As4S4 to different transition‐metal fragments. As4S4 and As4S3 with the poorest solubility did not yield complexes. However, the more soluble silver‐coordinated P4S3 and P4Se3 cages were transferred to the electron‐poor Fp + moiety ([CpFe(CO)2]+). Thus, reaction of the silver salt in the presence of the ligand with Fp−Br yielded [Fp−P4S3][Al(ORF)4] (1 a), [Fp−P4S3][F(Al(ORF)3)2] (1 b), and [Fp−P4Se3][Al(ORF)4] (2). Reactions with P4S3 also yielded [FpPPh3−P4S3][Al(ORF)4] (3), a complex with the more electron‐rich monophosphine‐substituted Fp + analogue [FpPPh3]+ ([CpFe(PPh3)(CO)]+). All complex salts were characterized by single‐crystal XRD, NMR, Raman, and IR spectroscopy. Interestingly, they show characteristic blueshifts of the vibrational modes of the cage, as well as structural contractions of the cages upon coordination to the Fp/FpPPh3 moieties, which oppose the typically observed cage expansions that lead to redshifts in the spectra. Structure, bonding, and thermodynamics were investigated by DFT calculations, which support the observed cage contractions. Its reason is assigned to σ and π donation from the slightly P−P and P−E antibonding P4E3‐cage HOMO (e symmetry) to the metal acceptor fragment.

Optoelectronic Properties of C60 and C70 Fullerene Derivatives: Designing and Evaluating Novel Candidates for Efficient P3HT Polymer Solar Cells.

Ten novel fullerene-derivatives (FDs) of C60 and C70 had been designed as acceptor for polymer solar cell (PSC) by employing the quantitative structure-property relationship (QSPR) model, which was developed strategically with a reasonably big pool of experimental power conversion efficiency (PCE) data. The QSPR model was checked and validated with stringent parameter and reliability of predicted PCE values of all designed FDs. They were assessed by the applicability domain (AD) and process randomization test. The predicted PCE of FDs range from 7.96 to 23.01. The obtained encouraging results led us to the additional theoretical analysis of the energetics and UV-Vis spectra of isolated dyes employing Density functional theory (DFT) and Time-dependent-DFT (TD-DFT) calculations using PBE/6-31G(d,p) and CAM-B3LYP/6-311G(d,p) level calculations, respectively. The FD4 is the best C60-derivatives candidates for PSCs as it has the lowest exciton binding energy, up-shifted lowest unoccupied molecular orbital (LUMO) energy level to increase open-circuit voltage (VOC) and strong absorption in the UV region. In case of C70-derivatives, FD7 is potential candidate for future PSCs due to its strong absorption in UV-Vis region and lower exciton binding energy with higher VOC. Our optoelectronic results strongly support the developed QSPR model equation. Analyzing QSPR model and optoelectronic parameters, we concluded that the FD1, FD2, FD4, and FD10 are the most potential candidates for acceptor fragment of fullerene-based PSC. The outcomes of tactical molecular design followed by the investigation of optoelectronic features are suggested to be employed as a significant resource for the synthesis of FDs as an acceptor of PSCs.

The Intriguing Case of the One‐Photon and Two‐Photon Absorption of a Prototypical Symmetric Squaraine: Comparison of TDDFT and Wave‐Function Methods

AbstractWe face the challenging description of the excited states responsible for one photon (OPA) and two photon (TPA) absorption in squaraine dyes, adopting both time‐dependent density functional theory and a large variety of post Hartree Fock methods, including coupled cluster and adiabatic diagrammatic construction methods (ADC, to the second and third order), symmetry adapted cluster configuration interaction (CI), CASSCF including second‐order perturbative corrections (PT2) with standard CASPT2 recipe and according to n‐electron valence PT2 (NEVPT2) approach, and an additional multireference CI with PT2 corrections (CI‐MRPT2). We selected a small prototypical symmetric squaraine dye for which these accurate computations are feasible and experimental data are available. We show that while all methods reasonably reproduce the OPA spectrum, an acceptable description and assignment of the states responsible for TPA is only possible through ADC(3) and multireference calculations, due to the strong involvement of double‐excitations. The nature of ground state and OPA and TPA states is investigated with a rigorous reading of the CASSCF wavefunctions in terms of localized molecular orbitals on the donor and acceptor fragments, showing that these states arise from a balance of many different contributions including biradical configurations, local excitations and charge‐transfer states where both side aromatic rings and the carbonyls of the squarylium moiety act as donors.

Solution-Processed Highly Efficient Bluish-Green Thermally Activated Delayed Fluorescence Emitter Bearing an Asymmetric Oxadiazole-Difluoroboron Double Acceptor.

Difluoroboron (BF2)-containing dyes have attracted great interest owing to their exceptionally high luminescence efficiency and good electron-withdrawing properties. However, only a few reports on difluoroboron-based thermally activated delayed fluorescence (TADF) have been addressed. In this contribution, a novel BF2-containing TADF molecule of BFOXD, which contains two acceptor fragments of oxadiazole (OXD) and BF2 and one donor unit of 9,9-dimethylacridine, was synthesized and characterized. For comparison, the precursor of OHOXD bearing one acceptor unit was also investigated. Both molecules clearly show TADF characteristics with sky-blue emission in solution and film state. Additionally, OHOXD undergoes excited-state intramolecular proton transfer-coupled intramolecular charge transfer processes. Using 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi) as the host, the organic light-emitting diodes fabricated via a solution process show maximum external quantum efficiency (EQE) of 2.98 and 13.8% for OHOXD- and BFOXD-based devices, respectively. While the bipolar TADF host of 10-(4-((4-(9H-carbazol-9-yl)phenyl)sulfonyl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (CzAcSF) is utilized instead of CzSi, the OHOXD- and BFOXD-based devices exhibit better performances with the maximum EQEs of 12.1 and 20.1%, respectively, which render the most efficient and the bluest emission ever reported for the BF2-based TADF molecules. This research demonstrates that introduction of one more acceptor unit into the TADF molecule could have a positive effect on emission efficiency, which opens a new way to design high-efficiency TADF molecules.

Glass-forming non-symmetric bis-styryl-DWK-type dyes for infra-red radiation amplification systems

A series of D-π-A type organic dyes with bulky triphenylmethyl moiety containing 2,6-bis-(4-substituted)styryl-4H-pyran-4-ylidene donor (D) fragments and different electron acceptors (A) were synthesized and investigated, mostly for potential applications in organic solid-state lasers as infra-red (IR) radiation amplification medium. Dye glass transition temperature is above 99 °C with thermal stability in the region from 173 °C to 326 °C which was slightly influenced by the electron acceptor fragment attached to the 4H-pyrane ring in 4-position. Introducing substituents in 4-position within one of the styryl-fragments with stronger electron withdrawing properties decreased ASE excitation threshold values (Eth) up to 180 μJ/cm2 in dye spin-cast neat films and shifted photoluminescence and amplified spontaneous emission (ASE) processes into the infra-red (IR) region. Although more studies are required, some of the investigated non-symmetric bis-styryl-DWK-dyes show potential as a solution-processable gain medium for IR radiation amplification.

Photogalvanic eff ect in porphyrin-pyrrolo[3′,4′:1,9]-(C60-Ih)[5,6]fullerene-2′,5′-dicarboxylate systems

The influence of molecular structural factors of covalently bound porphyrin-fullerene dyads and porphyrin—fullerene binary mixtures on photocurrent in model photoelectrochemical cells was studied. It was found that the photocurrent increased either by introducing solubilizing alkyl groups into the donor (porphyrin) or acceptor (fullerene) fragments, or by covalent binding porphyrin and fullerene into a donor-acceptor dyad.

Supramolecular interactions and self-assembling in adducts of cymantrenecarboxylic acid with amino derivatives of five- and six-membered heterocyclic N-bases

The structures of eleven new derivatives of cymantrenecarboxylic acid with heterocyclic N-bases as well as with ethanolamine were characterized by X-ray analysis. Depending on the strength of the bases, the complexes are either ionic salts in which the N atoms of the aromatic ring are protonated, or supramolecular adducts in which the carboxylic acid protons form hydrogen bonds. In the structures of compounds, the various supramolecular interactions take place due both to the specific geometry of the cymantrene fragment and to the geometry of the N-base. It was shown that the location of the H-bond donor and acceptor fragments of the base molecules is a factor determining the self-assembly. The crystal structure of the triclinic modification of cymantrenecarboxylic acid was described for the first time.