Donor Molecules Research Articles

End group modulation of A-D-A type small donor molecules for DTP based organic photovoltaic solar cells: a DFT approach.

Here, five new acceptor-donor-acceptor (A-D-A) type small donor molecules C1-C5, have been designed based on the central D unit, dithieno[3,2-b:2',3'-d]pyrrole (DTP). Besides, five different A units, viz. 1,1-dicyano-methylene-5,6-dimethyl-3-indanone, 1,1-dicyano-methylene-5,6-difluoro-3-indanone, 1,1-dicyano-methylene-5,6-dichloro-3-indanone, 1,1-dicyano-methylene-5-nitro-3-indanone, and 1,1-dicyano-methylene-5,6-diamino-3-indanone are selected for these designed compounds C1-C5, respectively. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods have been employed to study the influence of different A units on the geometric, electronic, optical, charge transport and photovoltaic properties of the designed donor molecules. The results reveal that the performance of the designed donor molecules have been improved on attachment of the strong electron withdrawing A units. The observed reorganization energy (λ) values infer the electron donating nature of the designed compounds. Moreover, the absorption properties of the designed compounds manifest that compound C4 possesses the high values of maximum wavelength (λmax) in both gas and solvent phases. The properties of the D/A blends reveal that all designed blends C1-C5/C60-CN, have the capacity to promote charge carrier separation at the D/A interface. Further, the photovoltaic performance of the D/A complexes also reveal that complex C4/C60-CN, with a theoretical PCE of 18%, can be considered as the most promising candidate for application in OSCs.

Impact of donor halogenation on reorganization energies and voltage losses in bulk-heterojunction solar cells

The introduction of halogen atoms in the donor molecules in organic solar cells leads to a decrease in the reorganization energy, which in turn results in reduced non-radiative voltage losses and an improved open-circuit voltage in the devices.

A supramolecular artificial light-harvesting system based on a luminescent platinum(II) metallacage.

A trigonal luminescent metallacage was constructed by the coordination-driven self-assembly of m-pyridine-modified tetraphenylene ligands with organic Pt(II) acceptors, which exhibited excellent Aggregation-Induced Emission (AIE) properties. An efficient artificial light-harvesting system was successfully constructed by selecting the metallacage as the donor and the hydrophobic fluorescent dye Nile Red (NiR) as the donor molecule in a system of acetone/water (1/9, v/v), The absorption spectra of NiR and the emission spectra of the metallacage showed considerable overlap, achieving energy transfer from the metallacage to NiR.

Electronic structure and energetics of a heterodimeric BChl g'/Chl a' special pair generated by exposure of Heliomicrobium modesticaldum to dioxygen.

Heliobacteria are anoxygenic phototrophs that have a Type I homodimeric reaction center containing bacteriochlorophyll g (BChl g). Previous experimental studies have shown that in the presence of light and dioxygen, BChl g is converted into 81-OH-chlorophyll aF (hereafter Chl aF), with an accompanying loss of light-driven charge separation. These studies suggest that the reaction center only loses the ability to transfer electrons once both BChl g' molecules of the P800 special pair have been converted to Chl aF'. The present work confirms that the partially converted BChl g'/Chl aF' special pair remains functional in samples exposed to dioxygen by demonstrating its presence using hyperfine couplings obtained from Q-band 1H ENDOR, 2D 14N HYSCORE and DFT methods. The DFT calculations of the BChl g'/BChl g' homodimeric primary donor, which are based on the recently published X-ray crystal structure, predict that the unpaired electron spin is equally delocalized over both BChl g' molecules and provide an excellent match to the experimental hyperfine couplings of the anaerobic samples. Exposure to dioxygen leads to substantial changes in the hyperfine interactions, indicative of greater localization of the unpaired electron spin. The measured hyperfine couplings are reproduced in the DFT calculations by replacing one of the BChl g' molecules of the primary donor with a Chl aF' molecule. The calculations reveal that the spin density becomes localized on BChl g' in the heterodimeric primary donor. Time-dependent DFT calculations demonstrate that conversion of either or both of the accessory BChl g molecules and/or one of the BChl g' molecules of P800 to Chl aF' results in minor effects on the energy of the charge-separated states. In contrast, if both of the BChl g' molecules of P800 are converted a large increase in the energy of the charge-separated state occurs. This suggests that the reaction center remains functional when only one half of the dimer is converted, however, conversion of both halves of the P800 dimer leads to loss of function.

Voltage-dependent excitation dynamics in UV-absorbing organic photovoltaics with efficient charge transfer exciton emission

Voltage-dependent characterizations of organic solar cells with brightly-emitting charge-transfer excitons reveal excitation dynamics and trends as a function of donor molecule.

Metallo-dithiaporphyrin pigments for bulk-heterojunction solar cell applications: ab initio investigation of structural and optoelectronic properties.

Metallo-dithiaporphyrin small molecules have been designed by substituting Ru(ii) with various transition metals at the same oxidation state (M = Mn, Fe, Ni, Cu) as donor materials for Bulk Heterojunction Organic Solar Cells (BHJ-OSCs). Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used to study the optoelectronic properties of metallo-dithiaporphyrin at various functionals and basis sets. We discovered that the open-circuit voltage (VOC) value increases when Ru(ii) in Ru(S2TTP)Cl2 (S2TTP = tetra-p-tolyldithiaporphyrin) is substituted. In addition, the light harvesting efficiency (LHE) of nickel, manganese, and iron complexes was found to be similar to that of ruthenium, and the iron complex furthermore presented a comparable charge transfer in the excited state corresponding to the Q-band, compared to Ru(S2TTP)Cl2. Hence M(S2TTP)Cl2 (M = Mn, Fe, Ni) appear to be potential low cost candidate donor molecules within a bulk heterojunction solar cell. We further propose suitable engineered acceptor pigments, fitted to provide a good overall solar cell efficiency.

Device engineering of organic solar cells based on a boron subphthalocyanine electron donor molecule

A boron subphthalocyanine molecule has been employed as a novel electron donor in organic solar cells (OPVs), and optimized in terms of composition and device structure in small molecule solar cells. It is demonstrated that the power conversion efficiency (PCE) of the devices obtained by solution-processing in bulk heterojunction solar cells could be improved by one order of magnitude by changing the fabrication method to vacuum deposition, which promotes a better morphology in the OPV active layers. Importantly, upon insertion of an additional pristine C70 thin interlayer between the active layer and the hole transport layer the PCE was further improved, highlighting the importance of interfacial layer engineering in such subphthalocyanine small molecule OPVs.

Advanced Theory and Simulations in 2022 – Growing in Volume and Breadth

<i>Advanced Theory and Simulations</i> in 2022 – Growing in Volume and Breadth

Stereo-controlled cyclopropanation catalysis within the confined pores of porphyrin MOFs

Three Rh-porphyrin MOF catalysts show a MOF topology independent stereoselectivity enhancement for styrene derivatives with coordinating functionalities. Upon donor molecule addition, the activity is increased facilitating Rh-carbene formation.

Donor–acceptor–donor molecules for high performance near ultraviolet organic light-emitting diodesviahybridized local and charge-transfer processes

Two bipolar molecules were designed with outstanding thermal stabilities. The molecules possess hybridized local and charge-transfer characteristics and exhibit high performance near ultraviolet electroluminescence with excellent color purity.

A density functional study of the coronene-pyrrole system in relation to its possible application as NO2 and NH3 sensors

According to recent research on the application of graphene materials as sensors and particularly polypyrrole-graphene materials, which are especially promising, the functionalization of graphene with a pyrrole molecule might be considered a viable alternative as a NO2 and NH3 sensor. In this way, a graphene sheet simulated as a coronene molecule was used in order to test whether this kind of functionalization could be useful for detecting the NO2 and NH3 toxic gases with a relatively high sensitivity. NO2 was studied as an example of an electron acceptor molecule, and NH3 as an electron donor molecule. Both molecules were adsorbed on two different regions of the functionalized adsorbent, and the energy ranges found for adsorption were reported and compared with those of the pristine graphene. The results indicated that in the coronene-pyrrole system, pyrrole tends to lie almost parallel to the coronene sheet in a π-π stacking interaction between the two conjugated systems, being the closest distances of 3.0 and 3.2 Å. The use of Δ (ΔHOMO-LUMO) as a descriptor confirmed that the coronene-pyrrole system is a good option as a NO2- and NH3-sensor; therefore, it might be an easy and suitable descriptor for characterizing the performance of a sensor; all calculations were made using a Density Functional formalism, through a functional M06-2X in combination with the 6-31G(d,p) basis set.

Plasmon effect on triplet-singlet energy transfer in the dye-doped Langmuir-Blodgett films

The effect of silver plasmonic nanoparticles on triplet-singlet energy transfer in the donor-acceptor pair of organic dyes was studied. Layered dye films were prepared on the surface of glass and island silver films using the Langmuir-Blodgett method. Amphiphilic analogs of Rose bengal and polymethine dye were used as donor and acceptor of energy. A polymer monolayer was deposited between monolayers of donor and acceptor molecules to exclude the competing triplet-triplet energy transfer. The spectra of delayed fluorescence and phosphorescence of donor-acceptor films and the delayed luminescence lifetime of donor in these films have been measured. It is shown that a threefold increase in the fluorescence intensity and a twofold increase in the donor phosphorescence intensity are observed on silver island films. The successful triplet-singlet energy transfer is evidenced by both the quenching of donor centers and appearance of sensitized delayed fluorescence of the acceptor with the duration close to the donor triplet lifetime. In the presence of silver nanoparticles, in addition to enhancement in the intensity of the donor emission, an increase in the efficiency of tripletsinglet energy transfer was observed. The obtained results can be used in various optical devices.

Nonpolymer Organic Solar Cells: Microscopic Phonon Control to Suppress Nonradiative Voltage Loss via Charge-Separated State.

Recent remarkable developments on nonfullerene solar cells have reached a photoelectric conversion efficiency (PCE) of 18% by tuning the band energy levels in small molecular acceptors. In this regard, understanding the impact of small donor molecules on nonpolymer solar cells is essential. Here, we systematically investigated mechanisms of solar cell performance using diketopyrrolopyrrole (DPP)-tetrabenzoporphyrin (BP) conjugates of C4-DPP-H2BP and C4-DPP-ZnBP, where C4 represents the butyl group substituted at the DPP unit as small p-type molecules, while an acceptor of [6,6]-phenyl-C61-buthylic acid methyl ester is employed. We clarified the microscopic origins of the photocarrier caused by phonon-assisted one-dimensional (1D) electron-hole dissociations at the donor-acceptor interface. Using a time-resolved electron paramagnetic resonance, we have characterized controlled charge-recombination by manipulating disorders in π-π donor stacking. This ensures carrier transport through stacking molecular conformations to suppress nonradiative voltage loss capturing specific interfacial radical pairs separated by 1.8 nm in bulk-heterojunction solar cells. We show that, while disordered lattice motions by the π-π stackings via zinc ligation are essential to enhance the entropy for charge dissociations at the interface, too much ordered crystallinity causes the backscattering phonon to reduce the open-circuit voltage by geminate charge-recombination.

End-group engineering of non-fused benzothiadiazol derivatives with thiophene rings based small donor molecules for tuning the photovoltaic properties via DFT approach

In this study, seven new small-donor molecules (U1-U7) with an A2-(D-A1)2-D-A2 configuration, were developed by end-groups manipulations for the betterment of photon absorption, charge mobility and morphology of photovoltaic molecules. The CAM-B3LYP functional, along with 6-31G(d,p) basis set had been exploited to probe the optical, as well as electronic characteristics of UR and U1-U7molecules. In addition, the solvent state calculations were analyzed by employingthe time-dependent approach (TD-DFT) of the theoretically used density functional theory (DFT). It was observed that all the newly developed molecules (U1-U7) possessed a redshift in their λmax, and also had smaller bandgap with better charge mobility for electrons due to their lower RE energy of λe than the reference molecule (UR). Additionally, several optoelectronic characteristics of the examined molecules were compared tothose of the well-known Y6 fused ring-based acceptor. All the newly created molecules exhibited lesser excitation energy, as well as greater oscillator strength than UR molecule. Another optical property, the light harvesting efficiency (LHE) had a range of 0.99935–0.99985 for all studied molecules. Open circuit voltage (VOC) was estimated by forming a combination of the newly developeddonor moleculeswith PC61BM. Some of the developed compounds revealed an increase in open circuit voltage, as well as the fill factor (FF), and consequently the estimated power conversion efficiencies (PCEs). Among all other newly developed molecules, U1 exhibited excellent optoelectronic properties such as maximum absorption, smallest Eg, charge mobility, and highest FF. Therefore, these end-capped manipulated compounds, especially U1, mightbe considered in the manufacturing of exceptionally competent organic solar cells in the near future.

Synthesis of TSF Donors Substituted with the meso-Dimethylethylenedithio Group: Structures and Conducting Properties of (meso-DM-BETS)2X (X− = PF6− and AsF6−)

Abstract Synthesis and X-ray structure analysis of TSF-based donors substituted with the meso-dimethylethylenedithio group (meso-DM-EDT-TSF and meso-DM-BETS) were successfully performed. The donor molecules in (meso-DM-BETS)2X (X− = PF6− and AsF6−) formed a dimerized face-to-face π-stack, and the packing pattern could be classified as β-type. A tight-binding band calculation suggested that the meso-DM-BETS salts have a two-dimensional Fermi surface with a wide bandwidth. Both salts exhibited metallic conductivities down to low temperatures with σr.t. = 45–46 S cm−1.

Selenoxides as Excellent Chalcogen Bond Donors: Effect of Metal Coordination.

The chalcogen bond has been recently defined by the IUPAC as the attractive noncovalent interaction between any element of group 16 acting as an electrophile and any atom (or group of atoms) acting as a nucleophile. Commonly used chalcogen bond donor molecules are divalent selenium and tellurium derivatives that exhibit two σ-holes. In fact, the presence of two σ-hole confers to the chalcogen bonding additional possibilities with respect to the halogen bond, the most abundant σ-hole interaction. In this manuscript, we demonstrate that selenoxides are good candidates to be used as σ-hole donor molecules. Such molecules have not been analyzed before as chalcogen bond donors, as far as our knowledge extends. The σ-hole opposite to the Se=O bond is adequate for establishing strong and directional ChBs, as demonstrated herein using the Cambridge structural database (CSD) and density functional theory (DFT) calculations. Moreover, the effect of the metal coordination of the selenoxide to transition metals on the strength of the ChB interaction has been analyzed theoretically. The existence of the ChBs has been further supported by the quantum theory of atoms in molecules (QTAIM) and the noncovalent interaction plot (NCIPlot).

Environmentally affable and highly efficient donor material based on cyclopentadithiophene (CPDT) framework for remarkable organic solar cells

The quantum chemical exploration of highly conjugated D-π-A type molecules based on cyclopentadithiophene (CPDT) core is anticipated to recommend novel organic materials for efficient organic solar cells (OSCs). Five new conjugated molecules (C1–C5) were designed by drafting of reference CR through thiophene bridged end caped acceptors and their geometric, as well as optoelectronic properties, were investigated at MPW1PW91/6-31G (d,p) functional. All the newly tailored chromophores (C1–C5) proclaimed lower energy gap values (ranging from 1.95 to 2.19 eV) than the reference CR (3.18 eV). TD-DFT calculations of all the newly designed molecules revealed higher λmax in the range 500–514 nm than the reference CR (483.2 nm) in dichloromethane solvent. Lower excitation energies (1.79–1.94 eV) and higher dipole moment (4.84–18.37 D) for all the drafted compounds (C1–C5) than reference CR were observed which proclaimed efficient charge transfer. Simulations of global reactivity parameters like hardness, chemical potential, softness and electrophilicity manifested all these molecules (C1–C5) to be reactive and thermally stable. The small values of reorganization energies for electron and hole exhibited high electron-hole mobilities and low charge recombination. The power conversion efficiency (PCE) parameters were simulated by scaling the HOMO of designed molecules acting as a donor with LUMO of PC61BM acceptor. All the designed molecules (C1–C5) demonstrated high open circuit voltage (0.67–0.92 V) than the reference (0.49 V) which is favorable for enhancement of PCE. Also, the higher values of fill factor (FF) ranging from 0.8417 to 0.8677 for newly designed chromophores increased the PCE than reference CR (0.8015). The results demonstrated the suitability of these donor molecules designed by deliberated technique, opening a new path for the development of donor's contributors to OSCs and may prove efficient materials for fabrication of future OSCs.

Quantum mechanical modeling of fused rings-based small-donor molecules with enhanced optoelectronic attributes for high performance organic photovoltaic cells

Seven small molecule donors (S1–S7) have been theoretically formulated by the end-capped modeling of acceptors of reference SR. Through density functional and its time-dependent theory, different photo-physical, morphological, and opto-electronic aspects of the newly reported molecules were analyzed with reference to the SR molecule. Amongst the different studied features were the absorption maxima (λmax), transition density matrix, frontier molecular orbitals, reorganization energies of hole and electron, excitation energies, bandgaps, fill factor, and open circuit voltage (VOC), etc. Individually, the S4 molecule had the smallest bandgap and electron reorganization energy, the highest ionization potential and λmax, as well as the smallest excitation energy in the analyzed gas and chloroform phases. While the smallest interaction coefficient was seen to be of S1. The VOC of all the donor molecules computed with respect to PC61BM acceptor revealed the greatest VOC and fill factor of S1 and S4 molecules. So, it could be understood that these molecules, with special reference to S1 and S4, might outperform SR in a variety of ways, and hence are suggested to experimentalists for future innovations of organic photovoltaic cells.

Photochemical Nitric Oxide Release from S‐Nitrosothiol‐Functionalized Chitosan

AbstractS‐nitrosothiols (RSNOs) are nitric oxide (NO) donor molecules with potential biomedical applications since they mimic NO biological functions, such as vasodilation and inflammatory process regulation. In this work, chitosan (CS), a natural biopolymer widely used as a biomaterial, is functionalized with thioglycolic acid (TGA) or mercaptosuccinic acid (MSA) in reactions mediated by a carbodiimide, yielding CS with thiol contents of 88 µmol g–1 (CS‐TGA) and 126 µmol g–1 (CS‐MSA). The subsequent S‐nitrosation of CS‐TGA and CS‐MSA generates the corresponding S‐nitroso derivatives, CS‐TGA(SNO) and CS‐MSA(SNO). The UV–Vis spectral changes associated with the S‐NO bond cleavage of CS‐TGA(SNO) and CS‐MSA(SNO), monitored in solution over 18 days of storage in a common refrigerator, reveal that these S‐nitroso CS derivatives display enhanced thermal stability in the dark, with half‐life values of 36.1 for CS‐TGA(SNO) and 16.1 days for CS‐MSA(SNO). Conversely, CS‐TGA(SNO) and CS‐MSA(SNO) can release NO photochemically on‐demand under visible light irradiation in a first‐order process triggered by photon absorption that leads to a half‐life of 33 min for both S‐nitroso CS. These results show that CS‐TGA(SNO) and CS‐MSA(SNO) may emerge as new CS‐based biomaterials for providing light‐triggered local NO release in biomedical applications.

Computational Study of New Small Molecules based Thiophene as Donor Materials for Bulk Heterojunction Photovoltaic Cells.

In this research work, we study the structural, optical, electronic, and photovoltaic properties of eight thiophene-based π-conjugated organic molecules using quantum methods namely time-dependent density functional theory. In particular, we identify the relationships between the chemical structure of these π-conjugated organic molecules and their optoelectronic properties. Moreover, we calculate and compare the highest energy occupied molecular orbital and lowest energy unoccupied molecular orbital energy levels of these compounds which act as donor with the ones of the acceptorphenyl-C61-butyric acid methyl ester. As a result, the investigated molecules show a low band gap, suitable open-circuit voltage and appropriate alignment energy level between the engineered donor molecules and the acceptor phenyl-C61-butyric acid methyl ester. This theoretical study shows that these new molecules have potential properties for the development of organic heterojunction photovoltaic cells.