scholarly journals Ratchet effect in brownian photomotors: symmetry constraints and going beyond them

2021 ◽  
Vol 12 (2) ◽  
pp. 124-134
Author(s):  
M. L. Dekhtyar ◽  
◽  
V. M. Rozenbaum ◽  
N. G. Shkoda ◽  
M. I. Ikim ◽  
...  
Keyword(s):  
Charge Distribution ◽  
Molecular Design ◽  
Dipole Moments ◽  
Directed Motion ◽  
Ratchet Effect ◽  
Brownian Particles ◽  
Order Of Magnitude ◽  
Symmetry Constraints ◽  
Donor Acceptor ◽  
Predominant Factor

The symmetry conditions have been derived for the occurrence of the ratchet effect in Brownian photomotors. To this end, spatiotemporal symmetry operations in vector transformations, coordinate and time shifts, and in the overdamped regime were applied to the average photomotor velocity taken as a functional of the coordinate- and time-dependent potential energy. As established, individual Brownian particles (molecules) can move directionally only provided a symmetrically distributed charge fluctuates in them and they are placed on the substrates with an antisymmetric charge distribution or, vice versa, they are characterized by antisymmetrically distributed charge fluctuations and are placed on symmetric substrates. The collective directed motion of orientation-averaged particles is possible only in the former case. If a particle charge distribution is described by a time dependence with the universal type of symmetry (i.e., simultaneously symmetric, antisymmetric, and shift-symmetric), an additional symmetry constraint on the ratchet functioning arises: the ratchet effect is ruled out in the overdamped regime but allowed for inertial moving particles if the charge distributions in both the particle and the substrate are neither symmetric nor antisymmetric. The effect of the universal type of symmetry is exemplified by dipole photomotors derived from donor-acceptor conjugated organic molecules. With a specific type of molecular photoexcitation and a specific relationship of the dipole moments in the ground and excited states, the ratchet effect becomes symmetry-forbidden. The forbiddenness can be removed by molecular polarization effects, which in this case become the predominant factor governing the direction of the motion and average velocity of photomotors. The estimated velocities of polarization photomotors are an order of magnitude larger than for known motor proteins and dipole Brownian photomotors. These results can be helpful in the purposeful molecular design of dipole photomotors.

Molecular Tetrominoes: Selective Masking of Donor pi-face to Control Configuration of Donor-Acceptor Complex

2021 ◽  
Author(s):  
Jenna L Sartucci ◽  
Arindam Maity ◽  
Manikandan Mohanan ◽  
Jeffery A. Bertke ◽  
Miklos Kertesz ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Organic Electronics ◽  
Molecular Design ◽  
Design Rules ◽  
Acceptor Complex ◽  
Donor Acceptor ◽  
Doping Mechanism ◽  
Control Configuration

Understanding the doping mechanism in organic semiconductors and generating molecular design rules to control the doping process is crucial to improve the performance of organic electronics. Even though controlling the...

Dipole moments induced in larger molecule. Long-chain aliphatic esters

1982 ◽  
Vol 47 (1) ◽  
pp. 29-34 ◽  
Author(s):  
Otto Exner ◽  
Ayfer Bapçum
Keyword(s):  
Benzene Solution ◽  
Dipole Moments ◽  
Straight Chain ◽  
Basic Assumptions ◽  
Donor Acceptor ◽  
Eyring Theory ◽  
Aliphatic Esters ◽  
Long Chain

Dipole moments of straight-chain aliphatic esters Ia-Ic and IIa-IIf were measured in benzene solution. The observed trends are poorly reproduced by the classical Smith-Eyring theory; the reason may be partly the unknown conformation, partly even donor-acceptor complexes with the solvent. No deviations were observed with the highest members of the series, attributable to violation of some basic assumptions of the theory of dielectrics.

scholarly journals Phosphorene–Fullerene Nanostructures: A First-Principles Study

2021 ◽  
Author(s):  
Diego Cortes-Arriagada ◽  
Daniela E. Ortega
Keyword(s):  
Active Sites ◽  
Short Range ◽  
Density Functional ◽  
Dipole Moments ◽  
Molecular Size ◽  
Bandgap Engineering ◽  
Donor Acceptor ◽  
The Stability ◽  
Strong Repulsion ◽  
Intermolecular Distances

Hybrid materials formed by carbon fullerenes and layered materials have emerged due to their advantages for several technological applications, and phosphorene arises as a promising two-dimensional semiconductor for C60 adsorption. However, the properties of phosphorenefullerene hybrids remain mainly unexplored. In this work, we employed density functional theory to obtain structures, adsorption energies, electronic/optical properties, binding (AIM, NBO), and energy decomposition analyses (ALMO-EDA) of nanostructures formed by phosphorene and fullerenes (C24 to C70). We find fullerenes form covalent and non-covalent complexes with phosphorene depending on the molecular size, showing remarkable stability even in solution. Two classes of covalent complexes arise by cycloaddition-like reactions: the first class, where short-range effects (charge-transfer and polarization) determines the stability; and the second one, where short-range effects decay to avoid steric repulsion, and balanced longrange forces (electrostatics and dispersion) favors the stability. Otherwise, high-size fullerenes (C50 to C70) only form non-covalent complexes due to strong repulsion at shorter intermolecular distances and lack of dissociation barriers. In terms of electronic properties, fullerenes act as mild p-dopants for phosphorene, increasing its polar character and ability to acquire induced dipole moments (polarizability). Also, small energy-bandgap fullerenes (<0.8 eV) largely increase the phosphorene metallic character. We also note fullerenes retain their donor/acceptor properties upon adsorption, acting as active sites for orbital-controlled interactions and maximizing the phosphorene light absorbance at the UV-Vis region. Finally, we strongly believe our study will inspire future experimental/theoretical studies focused on phosphorene-fullerene uses for storage, anode materials, sensing, phosphorene bandgap engineering, and optoelectronics.<br>

scholarly journals Molecular design strategy for practical singlet fission materials: The charm of donor/acceptor decorated quinoidal structure

CCS Chemistry ◽  
2021 ◽  
pp. 1-17
Author(s):  
Long Wang ◽  
Xiaomei Shi ◽  
Shishi Feng ◽  
WanZhen Liang ◽  
Hongbing Fu ◽  
...  
Keyword(s):  
Molecular Design ◽  
Design Strategy ◽  
Singlet Fission ◽  
Donor Acceptor

Charge moderated preplanetary growth from single grains to giant aggregates

2021 ◽  
Author(s):  
Felix Jungmann ◽  
Jens Teiser ◽  
Maximilian Kruss ◽  
Tobias Steinpilz ◽  
Kolja Joeris ◽  
...  
Keyword(s):  
Cross Sections ◽  
Planet Formation ◽  
Dipole Moments ◽  
Copper Plate ◽  
Net Charge ◽  
Electrostatic Charges ◽  
Ongoing Work ◽  
Astrophysical Journal ◽  
Stable Clusters ◽  
Order Of Magnitude

&lt;p&gt;In early phases of planet formation, bouncing and fragmentation barriers still represent major obstacles. Beginning at micrometer, dust can readily grow to sub-millimeter size in collisions due to cohesion before bouncing prevails. Later, streaming instabilities trigger further growth which might finally results into planetesimal formation by gravitational collapse. However, for streaming instabilities sub-millimeter grains might be too small, therefore there is gap of at least 1 order of magnitude in size which needs to be bridged.&lt;/p&gt; &lt;p&gt;Here, we present our ongoing work how to bridge this gap by charge moderated aggregation [1]. When two (dielectric) grains collide they charge. This tribocharging or collisional charging is omnipresent in nature. We designed drop tower experiments in which we generated charges on glass and basalt grains by collisions in a shaker. In microgravity, the particle trajectories and collisions were observed, and charges were measured by applying an electric field.&lt;/p&gt; &lt;p&gt;In early work, we analyzed millimeter-sized glass grain collisions with a copper plate. The coefficient of restitution increased with the charge on a single grain due to mirror charge forces. That means highly charged grains tend to stick more easily to surfaces than uncharged grains. The velocity where sticking is possible was increased by a factor of 100 up to several dm/s [2].&lt;br /&gt;&amp;#160;&lt;br /&gt;More recently, we used half millimeter basalt spheres and observed sticking events at several cm/s among grains themselves [3]. This is also way higher than predicted by adhesion. In a number of cases, we could observe the sequential formation of aggregates of up to ten single grains. During approach the grains are accelerated due to net charge Coulomb forces but likely also due to higher order charges on the surfaces in agreement to earlier measurements of strong permanent dipole moments [4]. Attraction increases collision cross-sections and the growth is sped up. Growth only stopped by the end of microgravity [3].&amp;#160;&lt;/p&gt; &lt;p&gt;To observe the formation of still larger aggregates we developed a new setup, in which a dense cloud of 150 &amp;#181;m diameter basalt grains was continuously agitated slightly under microgravity and in vacuum. Here, the growth of a giant aggregate of centimeter size was observed collecting nearly all material in one cluster [5].&lt;/p&gt; &lt;p&gt;To conclude, in experiments under various conditions, we see strong evidence that electrostatic charges on grains are able to conquer the bouncing barrier. We observed the bottom-up growth tracking individual particles, stable clusters emerging from dense regions and the formation of giant clusters during agitation. These are all bricks in the wall giving evidence that collisional charging might play a crucial role in planet formation.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt; &lt;p&gt;[1] Steinpilz, T.; Joeris, K.; Jungmann, F.; Wolf, D.; Brendel, L.; Teiser, J.; Shinbrot, T.; Wurm, G. Nature Physics 2020a, 16, 225-229.&lt;/p&gt; &lt;p&gt;[2] Jungmann, F.; Steinpilz, T.; Teiser, J.; Wurm, G. Journal of Physics Communications 2018, 2 095009, 095009.&lt;/p&gt; &lt;p&gt;[3] Jungmann, F.;Wurm, G. Astronomy and Astrophysics 2021, DOI: https://doi.org/10.1051/0004-6361/202039430.&lt;/p&gt; &lt;p&gt;[4] Steinpilz, T.; Jungmann, F.; Joeris, K.; Teiser, J.; Wurm, G. New Journal of Physics 2020b, 22, 093025.&lt;/p&gt; &lt;p&gt;[5] Teiser, J.; Kruss, M.; Jungmann, F.; Wurm, G. The Astrophysical Journal Letters 2021, 908, L22.&lt;/p&gt;

The Electrostatic Moments of a Charge Distribution

1997 ◽  
Author(s):  
Philip Coppens
Keyword(s):  
Dipole Moment ◽  
Charge Distribution ◽  
Dipole Moments ◽  
Practical Importance ◽  
Diffraction Method ◽  
Quadrupole Moments ◽  
Charge Densities ◽  
Moment Vector ◽  
Experimental Values ◽  
A Charge

The moments of a charge distribution provide a concise summary of the nature of that distribution. They are suitable for quantitative comparison of experimental charge densities with theoretical results. As many of the moments can be obtained by spectroscopic and dielectric methods, the comparison between techniques can serve as a calibration of experimental and theoretical charge densities. Conversely, since the full charge density is not accessible by the other experimental methods, the comparison provides an interpretation of the results of the complementary physical techniques. The electrostatic moments are of practical importance, as they occur in the expressions for intermolecular interactions and the lattice energies of crystals. The first electrostatic moment from X-rays was obtained by Stewart (1970), who calculated the dipole moment of uracil from the least-squares valence-shell populations of each of the constituent atoms of the molecule. Stewart’s value of 4.0 ± 1.3 D had a large experimental uncertainty, but is nevertheless close to the later result of 4.16 ± 0.4 D (Kulakowska et al. 1974), obtained from capacitance measurements of a solution in dioxane. The diffraction method has the advantage that it gives not only the magnitude but also the direction of the dipole moment. Gas-phase microwave measurements are also capable of providing all three components of the dipole moment, but only the magnitude is obtained from dielectric solution measurements. We will use an example as illustration. The dipole moment vector for formamide has been determined both by diffraction and microwave spectroscopy. As the diffraction experiment measures a continuous charge distribution, the moments derived are defined in terms of the method used for space partitioning, and are not necessarily equal. Nevertheless, the results from different techniques agree quite well. A comprehensive review on molecular electric moments from X-ray diffraction data has been published by Spackman (1992). Spackman points out that despite a large number of determinations of molecular dipole moments and a few determinations of molecular quadrupole moments, it is not yet widely accepted that diffraction methods lead to valid experimental values of the electrostatic moments.

Ground and excited state dipole moments of planar vs. twisted p-N,N-(dimethylamino)benzonitrile systems: maximum charge transfer for minimum overlap

1992 ◽  
Vol 70 (7) ◽  
pp. 1932-1938 ◽  
Author(s):  
Hemant K. Sinha ◽  
S. Muralidharan ◽  
Keith Yates
Keyword(s):  
Excited State ◽  
Charge Transfer ◽  
Degrees Of Freedom ◽  
Theoretical Calculations ◽  
Dipole Moments ◽  
Torsional Angle ◽  
Dimethylamino Group ◽  
Maximum Charge ◽  
Donor Acceptor ◽  
Excited State Dipole Moments

Electric field induced change in the absorption spectrum (electrochromism) has been employed to obtain the ground and excited state dipole moments of planar and sterically hindered (twisted) p-N,N-(dimethylamino)benzonitriles in dioxane solution. These studies support the twisted intramolecular charge transfer (TICT) hypothesis and provide additional insight to the TICT concept. The charge transfer nature of the excited state has been found to directly depend on the torsional angle of the N,N-dimethylamino group with respect to the benzonitrile moiety. It is suggested that solvent coupling is essential to initiate twisting by affecting the intramolecular degrees of freedom and the existence of the highly dipolar excited state is a result of such twisting of the donor–acceptor bond. Theoretical calculations have been performed to explain the observed changes in dipole moment values.

Strukturen ladungsgestörter oder räumlich überfüllter Moleküle, 80 [1 - 3] Strukturänderungen von p-Benzochinon durch Donator- und Akzeptor-Substituenten

1996 ◽  
Vol 51 (2) ◽  
pp. 153-171 ◽  
Author(s):  
Hans Bock ◽  
Sabine Nick ◽  
Wolfgang Seitz ◽  
Christian Näther ◽  
Jan W. Bats
Keyword(s):  
Charge Distribution ◽  
Quantum Chemical Calculations ◽  
Satisfactory Agreement ◽  
Quantum Chemical ◽  
Structural Changes ◽  
Structural Data ◽  
Semiempirical Calculations ◽  
Reduction Potentials ◽  
Donor Acceptor ◽  
Structural Summary

Abstract The structures of seven di- or tetrasubstituted p-benzoquinone derivatives O=C(XC=CH )2C=O and O=C(XC=CX)2C=O with substituents X = -OCH3, -N(CH2)5, - N(CH2CH2)2O, -Cl, -CN and -⊕N(HC=CH)2C-N(CH3)2 are presented and discussed in comparison with published ones substituted by X = -Si(CH3)3, -C6H5, -N(CH3)2, -⊕N(HC=CH)2CN(CH3)2, -O⊖ , and - NO2. Based on the introduction, in which halfwave-reduction potentials, geometry-optimized quantum-chemical calculations on substituent perturbation and known structural data of p-benzoquinone derivatives are used to characterize their molecular ground states. The structural changes indicate how substituent perturbations might be rationalized. Of the categories defined - imperturbed, donor, donor/acceptor and acceptor perturbed - the donorsubstituted p-benzoquinones do exhibit the largest differences, often called cyanine distorsion. In very satisfactory agreement with extensive semiempirical calculations, all effects determined experimentally are discussed in terms of varying charge distribution. With respect to the biochemical importance of p-benzoquinone derivatives, this first structural summary points out important facets.

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