Search

The calculation of the power conversionefficiency (PCE) valuefor a bulk heterojunction (BHJ) organic solar cell is complex dueto the wide number of parameters involved in the processes. This studyfocuses the attention on the molecular parameters involved into theopen circuit voltage and the PCE definitions and in particular onthe electronic coupling and on the lowest unoccupied molecular orbital(LUMO) of the acceptor. A simplified model system composed by a polymeras donor and a novel class of molecules (9,9′-bisfluorenylidenederivatives) as acceptor has been proposed as prototype to simulatethe BHJ organic solar cell interface. Several substituents on differentpositions are tested and the chemical nature/position of substituentshave a relevant influence on the electronic coupling and energy levelvalues. Geometrical and electronic properties are obtained using densityfunctional theory (DFT) and time-dependent (TD)-DFT calculations,respectively. A new hypothesis suggests that the minimization of theelectronic coupling between the LUMO of the acceptor and the highestoccupied molecular orbital (HOMO) of the donor can enhance the PCEreducing the recombination interface processes and calculations showingthe possibility to minimize this parameter and fine-tune acceptorenergy level through the acceptor functionalization. An accurate balancebetween electronic coupling and on the LUMO of the acceptor allowsto propose the more performing candidate as electron acceptor in aP3HT/99′BF derivative BHJ solar cell. [ABSTRACT FROM AUTHOR]

Highlights: [•] We study the electronic structure of Co, Ni, and Cu impurities in SrTiO3 crystals. [•] Differences between DFT and DFT+ U electronic structures are only quantitative. [•] Impurities generate defect states in the gap. [•] Impurities favor the formation of oxygen vacancies, and attract them. [•] Simple substitutionals prefer low-spin states, whereas vacancy-impurity complexes have higher multiplicities. [Copyright &y& Elsevier]

We present a computational study based on accurate DFTand TD-DFTmethods on model bioinspired donor–acceptor dyads, formed bya carotenoid covalently linked to a tetraphenylporphyrin (TPP) atthe ortho position of one of the TPP phenyl rings. Dyadic systemscan be used in the construction of organic solar cells and developmentof efficient photocatalytic systems for the solar energy conversion,due to the unique advantages they offer in terms of synthetic feasibility.This study aims to describe the influence of chemical modificationson the absorption spectra, in particular on the lowest energy chargetransfer bands. Effects of different metals of biological interest,i.e., Mg, Fe, Ni, and Zn, and of H2O and histidine moleculescoordinated to the metals in different axial positions are rationalized. [ABSTRACT FROM AUTHOR]

n this work we present an effective and flexible computational approach, which is the result of an ongoing development in our groups, allowing the complete a priori simulation of the ESR spectra of complex systems in solution. The usefulness and reliability of the method are demonstrated on the very demanding playground represented by the tuning of the equilibrium between 310- and α-helices of polypeptides by different solvents. The starting point is the good agreement between computed and X-ray diffraction structures for the 310-helix adopted by the double spin-labelled heptapeptide Fmoc-(Aib-Aib-TOAC)2-Aib-OMe. Next, density functional computations, including dispersion interactions and bulk solvent effects, suggest another energy minimum corresponding to an a-helix in polar solvents, which, eventually, becomes the most stable structure. Computation of magnetic and diffusion tensors provides the basic ingredients for the building of complete spectra by methods rooted in the Stochastic Liouville Equation (SLE). The remarkable agreement between computed and experimental spectra at different temperatures allowed us to identify helical structures in the various solvents. The generality of the computational strategy and its implementation in effective and user-friendly computer codes pave the route toward systematic applications in the field of biomolecules and other complex systems. [ABSTRACT FROM AUTHOR]

The structural, electronic, and spectroscopic properties of high- and intermediate-spin transition metal phthalocyaninato complexes (MPc; M = V, Cr, Mn and Fe) have been theoretically investigated to look into the origin, symmetry and strength of the M–Pc bonding. DFT calculations coupled to the Ziegler's extended transition state method and to an advanced charge density and bond order analysis allowed us to assess that the M–Pc bonding is dominated by σ interactions, with FePc having the strongest and most covalent M–Pc bond. According to experimental evidence, the lightest MPcs (VPc and CrPc) have a high-spin ground state (GS), while the MnPc and FePc GS spin is intermediate. Insights into the MPc unoccupied electronic structure have been gained by modelling M L2,3-edges X-ray absorption spectroscopy data from the literature through the exploitation of the current Density Functional Theory variant of the Restricted Open-Shell Configuration Interaction Singles (DFT/ROCIS) method. Besides the overall agreement between theory and experiment, the DFT/ROCIS results indicate that spectral features lying at the lowest excitation energies (EEs) are systematically generated by electronic states having the same GS spin multiplicity and involving M-based single electronic excitations; just as systematically, the L3-edge higher EE region of all the MPcs herein considered includes electronic states generated by metal-to-ligand-charge-transfer transitions involving the lowest-lying π* orbital (7eg) of the phthalocyaninato ligand. [ABSTRACT FROM AUTHOR]

The interest for heterometallic lanthanide- d or- p metal (Ln-M) complexes is growing because of a potential cooperative or synergistic effect related to the proximity of two different metals in the same molecular architecture affording special tunable physical properties. To exploit the potentiality of Ln-M complexes, suitable synthetic approaches, and the in-depth understanding of the effect of each building block on their properties are mandatory. Here, we report the study on a family of heterometallic luminescent complexes [Ln(hfac) 3 Al(L) 3 ], Ln= Eu 3+ and Tb 3+ . Using different L ligands, we investigated the effect of the steric and electronic properties of the Al(L) 3 fragment, highlighting the general validity of the employed synthetic route. A marked difference in the light emission of [Eu(hfac) 3 Al(L) 3 ] and [Tb(hfac) 3 Al(L) 3 ] complexes has been observed. Thanks to photoluminescence experiments and Density Functional Theory calculations, Ln 3+ emissions are explained with a model involving two non-interacting excitation paths through hfac or Al(L) 3 ligands., Competing Interests: The authors declare no competing interests., (© 2023 The Author(s).)

The relative stability of trans -[(η 5 -C 5 H 5 )Fe(η 1 -CO)(μ-CO)] 2 ( trans -I) and cis -I tautomers in a vacuum and in solvents with different dielectric constants ( ε ) has been investigated by exploiting density functional theory (DFT). Theoretical results indicate that, in agreement with experimental evidence, trans -I is more stable than cis -I in a vacuum (∼1.5 kcal mol -1 ; ε = 1), while the opposite is true in media with ε > 7. Differently from solution, DFT outcomes pertaining to the vapor-phase cis -I ⇆ trans -I equilibrium at T = 368 K, the temperature at which the Fe L 2,3 -edges and the C and O K-edge X-ray absorption spectroscopy (XAS) data of I have been recorded, ultimately indicate the trans -I predominance (∼93%). Compositions, oscillator strengths ( f ) and excitation energy ( EE ) values of cis -I transitions substantially mirror those of trans -I; nevertheless, the weighted cis -I f ( EE ) distributions negligibly contribute to the diverse simulated XA spectra of I.

A series of Gd 3+ complexes ( Gd1 - Gd3 ) with the general formula GdL 3 (EtOH) 2 , where L is a β-diketone ligand with polycyclic aromatic hydrocarbon substituents of increasing size ( 1 - 3 ), was studied by combining time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy and DFT calculations to rationalize the anomalous spectroscopic behavior of the bulkiest complex ( Gd3 ) through the series. Its faint phosphorescence band is observed only at 80 K and it is strongly red-shifted (∼200 nm) from the intense fluorescence band. Moreover, the TR-EPR spectral analysis found that triplet levels of 3 / Gd3 are effectively populated and have smaller | D | values than those of the other compounds. The combined use of zero-field splitting and spin density delocalization calculations, together with spin population analysis, allows us to explain both the large red shift and the low intensity of the phosphorescence band observed for Gd3 . The large red shift is determined by the higher delocalization degree of the wavefunction, which implies a larger energy gap between the excited S 1 and T 1 states. The low intensity of the phosphorescence is due to the presence of C-H groups which favor non-radiative decay. These groups are present in all complexes; nevertheless, they have a relevant spin density only in Gd3 . The spin population analysis on NaL models, in which Na + is coordinated to a deprotonated ligand, mimicking the coordinative environment of the complex, confirms the outcomes on the free ligands.

Due to its unique magnetic properties offered by the open-shell electronic structure of the central metal ion, and for being an effective catalyst in a wide variety of reactions, iron phthalocyanine has drawn significant interest from the scientific community. Nevertheless, upon surface deposition, the magnetic properties of the molecular layer can be significantly affected by the coupling occurring at the interface, and the more reactive the surface, the stronger is the impact on the spin state. Here, we show that on Cu(100), indeed, the strong hybridization between the Fe d-states of FePc and the sp-band of the copper substrate modifies the charge distribution in the molecule, significantly influencing the magnetic properties of the iron ion. The Fe II ion is stabilized in the low singlet spin state (S=0), leading to the complete quenching of the molecule magnetic moment. By exploiting the FePc/Cu(100) interface, we demonstrate that NO 2 dissociation can be used to gradually change the magnetic properties of the iron ion, by trimming the gas dosage. For lower doses, the FePc film is decoupled from the copper substrate, restoring the gas phase triplet spin state (S=1). A higher dose induces the transition from ferrous to ferric phthalocyanine, in its intermediate spin state, with enhanced magnetic moment due to the interaction with the atomic ligands. Remarkably, in this way, three different spin configurations have been observed within the same metalorganic/metal interface by exposing it to different doses of NO 2 at room temperature., (© 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

A theoretical protocol combining density functional theory (DFT) and multireference (CAS) calculations is proposed for a Eu 3+ complex. In the complex, electronic levels of the central Eu 3+ ion are correctly calculated at the CASPT2 level of theory, and the effect of introducing different numbers of states in the configuration interaction matrices is highlighted as well as the shortcomings of DFT methods in the treatment of systems with high spin multiplicity and strong spin-orbit coupling effects. For the 5 D 0 state energy calculation, the inclusion of states with different multiplicity and the number of states considered for each multiplicity are crucial parameters, even if their relative weight is different. Indeed, the addition of triplet and singlets is important, while the number of states is relevant only for the quintets. The herein proposed protocol enables a rigorous, full ab initio treatment of Eu 3+ complex, which can be easily extended to other Ln 3+ ions.

The unoccupied electronic structures of three closed-shell, highly popular organoiron complexes ([Fe(CO) 5 ], [(η 5 -C 5 H 5 )Fe(CO)(μ-CO)] 2 , and [(η 5 -C 5 H 5 ) 2 Fe]; 0 , I , and II , respectively) have been investigated both experimentally and theoretically by combining original gas-phase X-ray absorption spectroscopy (XAS) outcomes recorded at the C and O K-edge with results of scalar relativistic time-dependent density functional calculations carried out within the zeroth order regular approximation. Experimental evidence herein discussed complement the Fe L 2,3 -edges XAS ones we recently recorded, modeled, and assigned for the same complexes (Carlotto et al. Inorg. Chem. 2019, 58, 5844). The first-principle simulation of the C and O K-edge features allowed us to univocally identify the electronic states associated to the ligand-to-metal charge transfer (LMCT) transitions both in I and in II . At variance to that, LMCT transitions with sizable oscillator strengths do not play any role in determining neither the C nor the O K-edge spectral pattern of 0 . The higher π-acceptor capability of the CO ligand, regardless of its terminal or bridging coordination, with respect to [(η 5 -C 5 H 5 )] - is herein ultimately confirmed.

Model peptides relevant to hCtr1 transchelate CuI from the anti-tumour [CuI(PTA) 4 ] + complex before metal internalization into tumor cells. ESI(+)MS experiments corroborated by DFT calculations indicate that tetracoordinated-Cu II and linear-Cu I arrangements of in situ generated copper-peptide products play a crucial role in promoting the transfer of copper from the terminal MDH portion into adjacent HSH peptide sequence.

Correction for 'New light on an old debate: does the RCN-PtCl 2 bond include any back-donation? RCN ← PtCl 2 backbonding vs. the IR ν C[triple bond, length as m-dash]N blue-shift dichotomy in organonitriles-platinum(ii) complexes. A thorough density functional theory - energy decomposition analysis study' by Girolamo Casella et al., Dalton Trans., 2019, DOI: 10.1039/c9dt02440a.

For a series of organonitrile [RCN (R = Me, CF 3 , Ph, CH 3 Ph, CF 3 Ph)] ligands, the nature of the N-Pt bond in the related cis-/trans-(RCN) 2 PtCl 2 complexes has been computationally investigated by Density Functional Theory. A fragment based bond analysis has been performed in the canonical Kohn-Sham molecular orbitals framework, and it has been ultimately assessed that this bond is characterized both by N→Pt σ and by N←Pt π contributions. Voronoi Deformation Density charges further confirms the occurrence of N←Pt π interactions. Moreover, the Energy Decomposition Analysis-Natural Orbital for Chemical Valence (EDA-NOCV) method shows that the strength of the N←Pt π interaction is not negligible by contributing to about 30-40% of the total orbital interaction. Finally, the well-known ν C[triple bond, length as m-dash]N blue-shift occurring upon coordination to Pt II , has been thoroughly investigated by exploiting the EDA-NOCV and by evaluating ν C[triple bond, length as m-dash]N and force constants. The origin of the ν C[triple bond, length as m-dash]N blue-shift in these systems has been discussed on the basis of the CN bond polarization. N←Pt π backbonding causes only a systematic decrease of the observed ν C[triple bond, length as m-dash]N blue-shift when compared to the one calculated for RCN-X (X = H + , alkaline, Lewis acids) herein reported (X = purely σ acceptors).

The occupied and unoccupied electronic structures of three highly popular, closed shell organoiron complexes ([Fe(CO) 5 ], [(η 5 -C 5 H 5 )Fe(CO)(μ-CO)] 2 , and [(η 5 -C 5 H 5 ) 2 Fe]) have been theoretically investigated by taking advantage of density functional theory (DFT) calculations coupled to the isolobal analogy ( Elian et al. Inorg. Chem. 1976 , 15 , 1148 ). The adopted approach allowed us to look into the relative role played by the ligand → Fe donation and the Fe → ligand back-donation in title molecules, as well as to investigate how CO- (terminal or bridging) and [(η 5 -C 5 H 5 )] - -based π* orbitals compete when these two ligands are simultaneously present as in [(η 5 -C 5 H 5 )Fe(CO)(μ-CO)] 2 . Insights into the nature and the strength of the bonding between Fe and the C donor atoms have been gained by exploiting the Nalewajski-Mrozek bond multiplicity index ( Nalewajski et al. Int. J. Quantum Chem. 1994 , 51 , 187 ), which have been found especially sensitive even to tiny bond distance variations. The bonding picture emerging from ground state DFT results proved fruitful to guide the assignment of original, high-resolution, gas-phase L 2,3 -edges X-ray absorption spectra of the title molecules, which have been modeled by the two-component relativistic time-dependent DFT including spin orbit coupling and correlation effects and taking advantage of the full use of symmetry. Assignments alternative to those reported in the literature for both [Fe(CO) 5 ] and [(η 5 -C 5 H 5 ) 2 Fe] are herein proposed. Despite the high popularity of the investigated molecules, the complementary use of symmetry, orbital, and spectroscopy allowed us to further look into the metal-ligand symmetry-restricted-covalency and the differential-orbital covalency, which characterize them.

Mn(acac)2 (I) and Co(acac)2 (II) L2,3-edge absorption spectra have been modeled using the DFT/ROCIS method. In addition to the agreement between experiment and theory, the combined use of the B3LYP exchange-correlation functional and the def2-TZVP(-f) basis set provided useful information about the coordinative geometry around the M(ii) ions as well as about the nature and the strength of the Mn-O and Co-O interaction. The lower excitation energy (EE) side of both (I)(/)(II)L3 and (I)(/)(II)L2 intensity distributions mainly includes states having ground state spin multiplicity (S = 5/2 in I and S = 3/2 in II), whereas states with lower spin multiplicity (S = 3/2 in I and S = 1/2 in II) significantly contribute to the higher EE side of both (I)(/)(II)L3 and (I)(/)(II)L2. Hence, the occurrence of states involving metal to ligand charge transfer transitions in the presence of ligands with low lying empty π* orbitals on the L3 and L2 higher EE sides is herein confirmed.