The effect of torsion angle on the rate of intramolecular triplet energy transfer

Benniston, Andrew C.; Harriman, Anthony; Li, Peiyi; Patel, Pritesh V.; Sams, Craig A.

doi:10.1039/b512307k

Cited by 50 publications

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“…Consequently, we can conclude that efficient energy transfer occurs from Ru-terpy to Os-terpy at ambient temperature in fluid solution. This behaviour is similar to that found in a glassy matrix, [15] but the dynamics are faster in solution. On cooling a solution of the Ru-Os mixed-metal complexes in butyronitrile, and using an excitation wavelength of 480 nm at which the Ru-terpy unit absorbs 65 % of incident photons, the total emission intensity increases progressively.…”

Section: Resultssupporting

confidence: 76%

“…We have previously reported electron exchange in these same molecules at low temperature [15] at which conformational motion is severely retarded. Results similar to those reported for single-molecule conductance were noted, [9] with an 80-fold variation in the rates for planar and orthogonal geometries.…”

Section: Introductionmentioning

confidence: 96%

“…The spacer is composed of a strapped 2,2'-dialkoxybiphenyl unit in which the length of the strap controls the torsion angle between the two phenyl rings. [14] Although these straps collapse into the lowestenergy conformation in a low temperature glass, thereby A C H T U N G T R E N N U N G facilitating a correlation between torsion angle and rate of electron exchange, [15] a wider range of torsion angles is to be expected in fluid solution. The main objective of this study is to establish if the global rate constant for electron exchange in such dyads still remembers the mean torsion angle pertaining to the lowest-energy conformer.…”

Section: Introductionmentioning

confidence: 98%

“…At this temperature, it is reasonable to suppose that the strap adopts the lowest-energy conformation and the behaviour found at 170 K tends to confirm the situation already known to exist in the glassy matrix in which k TET is highly dependent on the dihedral angle. [15] The large uncertainty associated with the measured F LUM values and the limited information that be extracted from a single temperature [16] preclude detailed analysis of these results in terms of their exact correlation with f.…”

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confidence: 99%

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Electron Exchange in Conformationally Restricted Donor–Spacer–Acceptor Dyads: Angle Dependence and Involvement of Upper‐Lying Excited States

Benniston

Harriman

et al. 2008

Chemistry A European J

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The rate constant for triplet energy transfer (k(TET)) has been measured in fluid solution for a series of mixed-metal Ru-Os bis(2,2':6',2''-terpyridine) complexes built around a tethered biphenyl-based spacer group. The length of the tether controls the central torsion angle for the spacer, which can be varied systematically from 37 to 130 degrees . At low temperature, but still in fluid solution, the spacer adopts the lowest-energy conformation and k(TET) shows a clear correlation with the torsion angle. A similar relationship holds for the inverse quantum yield for emission from the Ru-terpy donor. Triplet energy transfer is more strongly activated at higher temperature and the kinetic data require analysis in terms of two separate processes. The more weakly activated step involves electron exchange from the first-excited triplet state on the Ru-terpy donor and the size of the activation barrier matches well with that calculated from spectroscopic properties. The pre-exponential factor derived for this process correlates remarkably well with the torsion angle and there is a large disparity in electronic coupling through pi and sigma orbitals on the spacer. The more strongly activated step is attributed to electron exchange from an upper-lying triplet state localized on the Ru-terpy donor. Here, the pre-exponential factor is larger but shows the same dependence on the geometry of the spacer. Strangely, the difference in coupling through pi and sigma orbitals is much less pronounced. Despite internal flexibility around the spacer, k(TET) shows a marked dependence on the torsion angle computed for the lowest-energy conformation.

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Section: Resultssupporting

confidence: 76%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 98%

mentioning

confidence: 99%

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Electron Exchange in Conformationally Restricted Donor–Spacer–Acceptor Dyads: Angle Dependence and Involvement of Upper‐Lying Excited States

Benniston

Harriman

et al. 2008

Chemistry A European J

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“…Quantum control of a large amplitude torsional angle has been the subject of several recent investigations [2][3][4][5][6][7].…”

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confidence: 99%

Rotation-Induced Breakdown of Torsional Quantum Control

2011

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Control of the torsional angles of nonrigid molecules is key for the development of emerging areas like molecular electronics and nanotechnology. Based on a rigorous calculation of the rotation-torsion-Stark energy levels of nonrigid biphenyl-like molecules, we show that, unlike previously believed, instantaneous rotation-torsion-Stark eigenstates of such molecules, interacting with a strong laser field, present a large degree of derealization in the torsional coordinate even for the lowest energy states. This is due to a strong coupling between overall rotation and torsion leading to a breakdown of the torsional alignment. Thus, adiabatic control of changes on the planarity of this kind of molecule is essentially impossible unless the temperature is on the order of a few Kelvin.Quantum control of molecular degrees of freedom is becoming an important field of research that promises important technological developments. In the last few years impressive progress on the control of molecular alignment and orientation has been achieved [1]. However, control of internal degrees of freedom remains in its infancy due, among other things, to the elusive character of intramolecular vibrational relaxation processes which are prevalent even in relatively small polyatomic molecules. Quantum control of a large amplitude torsional angle has been the subject of several recent investigations [2][3][4][5][6][7].Control of torsional angles is key for the development of new miniaturized communication systems based on energy transfer along molecular wires [2,3]. For example, it has been established that the rate of electron exchange in a ruthenium (Il)-osmium (II) binuclear complex depends on the conformation of a biphenyl bridge [4]. Ramakrishna and Seideman [5] showed that torsional control by an intense laser pulse should be achieved for several nonrigid molecules displaying internal rotation. In the case of biphenyl, using a model where the two phenyl rings can rotate about a fixed axis perpendicular to the direction along which the laser field is propagating, their calculation predicts that the two rings become localized in the same plane for a circularly polarized laser field of intensity around 10 10 W/cm 2 and temperatures up to 77 K. In their time dependent experiments, Madsen and co-workers [6,7] showed that for the similar 3, 5-difluoro-3', 5'-dibromobiphenyl molecule, torsional control of the internal rotation can be achieved using two laser pulses. The first pulse adiabatically aligns the C-C bond between the phenyl rings along its polarization axis. The second pulse imparts a kick to the molecule that is able to initiate torsional motion. These experimental results were corroborated [6,7] using a theoretical model analogous to that of Ref. [5].In conventional spectroscopic studies, large amplitude motions have been traditionally difficult to analyze due to the existence of strong couplings with the overall rotation and with other low-frequency vibrations [8]. Contrarily. dynamics approaches tend to neglect these coupli...

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Wires and Related Systems

Balzani

Venturi

2008

Molecular Devices and Machines

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The effect of torsion angle on the rate of intramolecular triplet energy transfer

Cited by 50 publications

References 19 publications

Electron Exchange in Conformationally Restricted Donor–Spacer–Acceptor Dyads: Angle Dependence and Involvement of Upper‐Lying Excited States

Electron Exchange in Conformationally Restricted Donor–Spacer–Acceptor Dyads: Angle Dependence and Involvement of Upper‐Lying Excited States

Rotation-Induced Breakdown of Torsional Quantum Control

Wires and Related Systems

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