Excitation Dynamics and Relaxation in a Molecular Heterodimer

The exciton dynamics in a molecular heterodimer is studied as a function of differences in excitation and reorganization energies, asymmetry in transition dipole moments and excited state lifetimes. The heterodimer is composed of two molecules modeled as two-level systems coupled by the resonance interaction. The system-bath coupling is taken into account as a modulating factor of the energy gap of the molecular excitation, while the relaxation to the ground state is treated phenomenologically. Comparison of the description of the excitation dynamics modeled using either the Redfield equations (secular and full forms) or the Hierarchical quantum master equation (HQME) is demonstrated and discussed. Possible role of the dimer as an excitation quenching center in photosynthesis self-regulation is discussed. It is concluded that the system-bath interaction rather than the excitonic effect determines the excitation quenching ability of such a dimer

Fine control of chlorophyll-carotenoid interactions defines the functionality of light-harvesting proteins in plants

V.B. and C.D.P.D. acknowledge the support from the Leverhulme Trust RPG-2015-337. This research utilized Queen Mary’s MidPlus computational facilities, supported by QMUL Research-IT and funded by EPSRC grant EP/K000128/1. W.P.B acknowledges support from the Photosynthetic Antenna Research Center (PARC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DE-SC0001035 for initial development of the TDC calculation code, as well as support from Army Research Office (ARO-MURI) Award W911NF1210420 for further development

CP / MAS, 13 C AND 17 O NMR STUDIES OF PROTON TRANSFER AND DYNAMICS OF CYANOPYRIDINE HYDROGEN-BOND COMPLEX WITH TRICHLOROACETIC ACID IN CRYSTAL AND IN SOLUTION *

The hydrogen bond (H-bond) in the complex of cyanopyridine (4-pyridincarbonitrile, C6H4N2, further CyPy) with trichloroacetic acid (TCA) was investigated in the solid state and in the solution (1 M in CH3CN). The 13 C CP / MAS results as well as X-ray and neutron diffraction reveal a complete proton transfer (CPT) for the CyPy·TCA complex. An experimental criterion of the threshold of CPT is proposed. Reorientational dynamics of 'free' and 'bonded' CyPy molecules in solution were investigated by 17 O and 13 C NMR relaxation time and nuclear Overhauser effect (NOE) factor measurements. The rotational diffusion even of 'free' CyPy molecules is anisotropic, with a corresponding correlation time of 3 ps for rotation and that of 6 ps for tumbling at 293 K. The formation of the CyPy·TCA H-bond complex causes a general slowdown of the overall rotational motion with a very slight increase in its anisotropy (7 ps for rotation and 17 ps for tumbling, respectively). The results are compared with similar data on H-bonding in pyridine N-oxide/acid systems

Influence of Sr Content on CMR Effect in Polycrystalline La1−xSrxMnO3La_{1-x}Sr_{x}MnO_{3} Thin Films

The magnetoresistance of thin polycrystalline $La_{1-x}Sr_{x}MnO_{3}$ films deposited on lucalox substrate using metal organic chemical vapor deposition technique was investigated in pulsed magnetic fields up to 18 T in the temperature range 100-320 K. The influence of film preparation conditions, ambient temperature variation and Sr content is analyzed in order to determine the optimal conditions for the design of CMR-B-scalar magnetic field sensor based on thin manganite film, operating at room temperature

Magneto- and Electroresistance of Ultrathin Anisotropically Strained La-Sr-MnO Films

The magnetoresistance anisotropy of ultrathin La$\text{}_{0.83}$Sr$\text{}_{0.17}$Mn O$\text{}_{3}$ films deposited on NdGaO$\text{}_{3}$ substrate by metalorganic chemical vapour deposition technique was investigated. The electric-field-induced resistance change was studied up to electric fields of 10 kV/cm using ns duration electrical pulses. It was found that in ultrathin (< 10 nm) and thin (< 50 nm) films the origin of electric-field-induced resistance change is thermal. However, the films with thicknesses of about 20 nm, exhibit negative electric-field-induced resistance change, having a pure electronic nature. This effect is explained in terms of two-layer systems with imperfections located at the interface between the layers

Arylmethylene-1,3-indandione based molecular glasses: Third order optical non-linearity

The synthesis and new optical features of three indan-1,3-dione class structures is reported. The simple arylmethylene-1,3-indandione structure 2-(4-diethylaminobenzylidene)indan-1,3-dione was used to design two linked structures: 1,3-bis-{3-hydroxy-4-[4-diethylamino-1-(1,3-dioxoindan-2- ylmethylene)benzen-3-yloxy]-1-thiabuthyl}benzene and 4,4′-bis-{{3-hydroxy- 4-[4-diethylamino-1-(1,3-dioxoindan-2-ylmethylene)benzen-3-yloxy]-1-thiabutyl} phenyl}sulfide. In contrast to the simple compound, which readily crystallized, the linked derivatives remained in an amorphous phase and are considered as molecular glasses with respective glass transition temperatures 88 and 100°C. For non-linear optical investigations samples were prepared as a guest-host system in polycarbonate matrix (10%). The Maker-fringe technique was used to investigate the third harmonic generation at a wavelength of 355 nm (YAG laser). Third-order non-linear susceptibility χ (3) values were extracted 5.75·10 -21 m 2 V -2, 8.60·10 -21 m 2 V -2, 16.85·10 -21 m 2 V -2 for these respective indandiones while modeling the experimental results. To evaluate the susceptibility of the indan-1,3-dione derivatives third harmonic generation a comparative experiment for a reference azodye in polycarbonate was performed. The results show an important feature - higher molecular second order hyperpolarizability for the linked structures. NMR, MS, IR, UV-VIS, XRD and elemental analysis were used to structurally characterize the new compounds and ellipsometry was applied to interpret the non-linear optical results. © 2012 Elsevier Ltd. All rights reserved