@article{7968, abstract = {Organic materials are known to feature long spin-diffusion times, originating in a generally small spin–orbit coupling observed in these systems. From that perspective, chiral molecules acting as efficient spin selectors pose a puzzle that attracted a lot of attention in recent years. Here, we revisit the physical origins of chiral-induced spin selectivity (CISS) and propose a simple analytic minimal model to describe it. The model treats a chiral molecule as an anisotropic wire with molecular dipole moments aligned arbitrarily with respect to the wire’s axes and is therefore quite general. Importantly, it shows that the helical structure of the molecule is not necessary to observe CISS and other chiral nonhelical molecules can also be considered as potential candidates for the CISS effect. We also show that the suggested simple model captures the main characteristics of CISS observed in the experiment, without the need for additional constraints employed in the previous studies. The results pave the way for understanding other related physical phenomena where the CISS effect plays an essential role.}, author = {Ghazaryan, Areg and Paltiel, Yossi and Lemeshko, Mikhail}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {21}, pages = {11716--11721}, publisher = {American Chemical Society}, title = {{Analytic model of chiral-induced spin selectivity}}, doi = {10.1021/acs.jpcc.0c02584}, volume = {124}, year = {2020}, } @article{17941, abstract = {How heteroatomic substitutions affect electron transport through π-conjugated hydrocarbons has been the subject of some debate. In this paper we investigate the effect of heteroatomic linkers in a molecular junction on the electron-transmission spectrum, focusing on the occurrence of quantum interference (QI) close to the Fermi level, where conductivity can be significantly suppressed. We find that the substitution or addition of heteroatoms to a carbon skeleton at the contact positions does not change the main feature of QI due to the underlying carbon skeleton. QI in the overall system thus remains a robust feature. This empirical observation leads us to derive, in two mathematical ways, that these findings can be generalized. We note that addition or substitution of a carbon atom by a heteroatom at the contact positions will increase or decrease the number of electrons in the π-system, which will lead to a change in the alignment of the molecular orbitals of the isolated system relative to the electrode Fermi level. Both Hückel and density functional theory calculations on model systems probe the effect of this Fermi level change and confirm qualitatively the implications of the underlying mathematical proofs.}, author = {Tsuji, Yuta and Stuyver, Thijs and Gunasekaran, Suman and Venkataraman, Latha}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {27}, pages = {14451--14462}, publisher = {American Chemical Society}, title = {{The influence of linkers on quantum interference: A linker theorem}}, doi = {10.1021/acs.jpcc.7b03493}, volume = {121}, year = {2017}, } @article{17977, abstract = {Primary amines can interact with neighbor molecules or with a metal substrate via weak bonds involving the electron lone pair of their amino functional group. Near edge X-ray absorption spectra (NEXAFS) on the N 1s edge show that the structure of the empty molecular orbitals localized on the nitrogen atom is very sensitive to these interactions. Here we investigate the origin of these changes by means of theoretical calculations. NEXAFS spectra are simulated for the 1,4-benzenediamine (BDA) molecule in its free, crystalline, and monolayer on Au(111) forms. We identify the electronic states which are affected by these amino-based interactions. In the case of the molecular layer grown on the gold substrate, we show how the results of the calculations can be used to identify intermolecular interactions influencing adsorption geometries in molecular monolayers.}, author = {Balducci, Gabriele and Romeo, Michele and Stener, Mauro and Fronzoni, Giovanna and Cvetko, Dean and Cossaro, Albano and Dell’Angela, Martina and Kladnik, Gregor and Venkataraman, Latha and Morgante, Alberto}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {4}, pages = {1988--1995}, publisher = {American Chemical Society}, title = {{Computational study of amino mediated molecular interaction evidenced in N 1s NEXAFS: 1,4-diaminobenzene on Au (111)}}, doi = {10.1021/jp512146t}, volume = {119}, year = {2014}, } @article{7301, abstract = {Several problems arise at the O2 (positive) electrode in the Li-air battery, including solvent/electrode decomposition and electrode passivation by insulating Li2O2. Progress partially depends on exploring the basic electrochemistry of O2 reduction. Here we describe the effect of complexing-cations on the electrochemical reduction of O2 in DMSO in the presence and absence of a Li salt. The solubility of alkaline peroxides in DMSO is enhanced by the complexing-cations, consistent with their strong interaction with reduced O2. The complexing-cations also increase the rate of the 1-electron O2 reduction to O2•– by up to six-fold (k° = 2.4 ×10–3 to 1.5 × 10–2 cm s–1) whether or not Li+ ions are present. In the absence of Li+, the complexing-cations also promote the reduction of O2•– to O22–. In the presence of Li+ and complexing-cations, and despite the interaction of the reduced O2 with the latter, SERS confirms that the product is still Li2O2.}, author = {Li, Chunmei and Fontaine, Olivier and Freunberger, Stefan Alexander and Johnson, Lee and Grugeon, Sylvie and Laruelle, Stéphane and Bruce, Peter G. and Armand, Michel}, issn = {1932-7447}, journal = {The Journal of Physical Chemistry C}, number = {7}, pages = {3393--3401}, publisher = {ACS}, title = {{Aprotic Li–O2 battery: Influence of complexing agents on oxygen reduction in an aprotic solvent}}, doi = {10.1021/jp4093805}, volume = {118}, year = {2014}, } @article{17994, abstract = {Charge transfer through noncovalent interactions is crucial to a variety of chemical phenomena. These interactions are often weak and nonspecific and can coexist, making it difficult to isolate the transfer efficiency of one type of bond versus another. Here, we show how core-hole clock spectroscopy can be used to measure charge transfer through noncovalent interactions. We study the model system 1,4-benzenediamine molecules bound on an Au surface through an Au–N donor–acceptor bond as these are known to provide a pathway for electronic conduction in molecular devices. We study different phases of the molecule/Au system and map charge delocalization times from carbon and nitrogen sites on the molecule. We show that charge delocalization across Au–N donor–acceptor bond occurs in less than 500 as. Furthermore, the Au–N bond also enhances delocalization times from neighboring carbon sites, demonstrating that fast charge transfer across a metal–organic interface does not require a covalently bonded system.}, author = {Kladnik, Gregor and Cvetko, Dean and Batra, Arunabh and Dell’Angela, Martina and Cossaro, Albano and Kamenetska, Maria and Venkataraman, Latha and Morgante, Alberto}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {32}, pages = {16477--16482}, publisher = {American Chemical Society}, title = {{Ultrafast charge transfer through noncovalent Au–N interactions in molecular systems}}, doi = {10.1021/jp405229b}, volume = {117}, year = {2013}, } @article{6370, abstract = {The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a “push–pull” π-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the “nonlinearity-thermal stability trade-off”. The HOSE calculation also reveals a correlation between the quinoidal resonance contribution to the overall structure of OH1 and the UV–vis absorption peak wavelength in the wider family of configurationally locked polyene framework materials. Solid-state tensorial coefficients of the molecular dipole, polarizability, and the first hyperpolarizability for OH1 are derived from the first-, second-, and third-order electronic moments of the experimental charge-density distribution. The overall solid-state molecular dipole moment is compared with those from gas-phase calculations, revealing that crystal field effects are very significant in OH1. The solid-state hyperpolarizability derived from this charge-density study affords good agreement with gas-phase calculations as well as optical measurements based on hyper-Rayleigh scattering (HRS) and electric-field-induced second harmonic (EFISH) generation. This lends support to the further use of charge-density studies to calculate solid-state hyperpolarizability coefficients in other organic NLO materials. Finally, this charge-density study is also employed to provide an advanced classification of hydrogen bonds in OH1, which requires more stringent criteria than those from conventional structure analysis. As a result, only the strongest OH···NC interaction is so classified as a true hydrogen bond. Indeed, it is this electrostatic interaction that influences the molecular charge transfer: the other four, weaker, nonbonded contacts nonetheless affect the crystal packing. Overall, the establishment of these structure–property relationships lays a blueprint for designing further, more NLO efficient, materials in this industrially leading organic family of compounds.}, author = {Lin, Tze-Chia and Cole, Jacqueline M. and Higginbotham, Andrew P and Edwards, Alison J. and Piltz, Ross O. and Pérez-Moreno, Javier and Seo, Ji-Youn and Lee, Seung-Chul and Clays, Koen and Kwon, O-Pil}, issn = {1932-7447}, journal = {The Journal of Physical Chemistry C}, number = {18}, pages = {9416--9430}, publisher = {American Chemical Society (ACS)}, title = {{Molecular origins of the high-performance nonlinear optical susceptibility in a phenolic polyene chromophore: Electron density distributions, hydrogen bonding, and ab initio calculations}}, doi = {10.1021/jp400648q}, volume = {117}, year = {2013}, } @article{18015, abstract = {We investigate the binding and energy level alignment of 2,3,5,6-tetramethyl-1,4-benzenediamine (TMBDA) on Au(111) through a combination of helium atom scattering (HAS), X-ray photoemission (XPS), and scanning tunneling microscopy (STM). We show that TMBDA binds to step edges and to flat Au (111) terraces in a nearly flat-lying configuration. Through combination of HAS and STM data, we determine that the molecules are bound on step edges with an adsorption energy of about 1.2 eV, which is about 0.2 eV stronger than the adsorption energy we measure on flat surface. Preferential bonding to the under-coordinated Au atoms on step edges suggests that the molecules bind to Au through the nitrogen lone pair. Finally, STM measurements on TMBDA in these two different adsorption configurations show that the highest-occupied molecular orbital is deeper relative to Fermi for the more strongly bound molecules on step edges, confirming that the nitrogen bonds through charge donation to the Au.}, author = {Kamenetska, M. and Dell’Angela, M. and Widawsky, J.R. and Kladnik, G. and Verdini, A. and Cossaro, A. and Cvetko, D. and Morgante, A. and Venkataraman, Latha}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {25}, pages = {12625--12630}, publisher = {American Chemical Society}, title = {{Structure and energy level alignment of tetramethyl benzenediamine on Au(111)}}, doi = {10.1021/jp202555d}, volume = {115}, year = {2011}, } @article{18036, abstract = {We measured conductance traces while breaking gold point contacts in a solution of molecules containing the μ-p-phenylenediethynyl X−C⋮C−C6H4−C⋮C−X unit, with eight different capping X groups:  Au−P(OMe)3 (1), H (2), SiMe3 (3), Au−P(cy)3 (4), Au−PMe2Ph (5), Au−PMePh2 (6), Au−PMe3 (7), and Au−PPh3 (8). Our goal with this work was to achieve a direct Au−C link with a conjugated organic group, potentially forming a molecular junction without chemical link groups that typically decrease junction conductances, such as thiols or amines. Conductance traces collected in the presence of molecules 1, 2, 3, 5, and 7 reveal additional steps at conductances as high as 0.1 G0 (G0 = 2e2/h) down to the measurable limits of the experimental setup. Conductance histograms generated from these traces therefore show a broad increase of counts when compared to a control histogram collected in the solvent alone suggesting the binding of the molecules to the broken Au contacts. The histograms for molecules 1, 5, 7, and 2 were not distinguishable, although that of molecule 3 had considerably fewer counts over the entire conductance range, suggesting that the steric bulk of the SiMe3 prevented frequent junction formation. The histograms collected in a solution of molecules 4, 6, or 8 did not differ from that of the control histogram probably because of the steric bulk of the Au−PR3 capping groups prevented the formation a molecular junction.}, author = {Millar, David and Venkataraman, Latha and Doerrer, Linda H.}, issn = {1932-7455}, journal = {The Journal of Physical Chemistry C}, number = {47}, pages = {17635--17639}, publisher = {American Chemical Society}, title = {{Efficacy of Au−Au contacts for scanning tunneling microscopy molecular conductance measurements}}, doi = {10.1021/jp0756101}, volume = {111}, year = {2007}, }