1
|
Ree J, Ko KC, Kim YH, Shin HK. Excitation of NH Stretching Modes in Aromatic Molecules: o-Toluidine and α-Methylbenzylamine. J Phys Chem B 2023; 127:7276-7282. [PMID: 37566790 DOI: 10.1021/acs.jpcb.3c03968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/13/2023]
Abstract
Selectively excited o-toluidine and α-methylbenzylamine have been studied with quasi-classical trajectory procedures to determine the extent and timescales of intramolecular energy flow. The initial excitation is in the stretching mode of the para-CH bond, and its flow is initiated by interaction with an argon atom. Energy flow to the NH stretching mode is the dominant relaxation pathway, and its effectiveness is enhanced strongly by the methyl-NH interaction. Energy flow characteristics in both molecules are similar, but the flow is more effective in o-toluidine than in α-methylbenzylamine because the methyl group bonded to the benzene ring exerts stronger perturbation on the energy-flow pathway than the group bonded to the side chain. The relaxation of the initially excited CH completes on a timescale of several picoseconds, but the main part of energy flow to the NH occurs on a subpicosecond scale. In o-toluidine, carbon-carbon overtone modes lead to ring-CC bonds gaining and transporting more energy than high-frequency CH bonds, but they all gain far less energy than the NH stretching mode.
Collapse
Affiliation(s)
- J Ree
- Department of Chemistry Education, Chonnam National University, Gwangju 61186, Korea
| | - K C Ko
- Department of Chemistry Education, Chonnam National University, Gwangju 61186, Korea
| | - Y H Kim
- Department of Chemistry, Inha University, Incheon 22212, Korea
| | - H K Shin
- Department of Chemistry, University of Nevada, Reno, Nevada 89557, United States
| |
Collapse
|
2
|
Shin HK. Influence of a Methyl Group on the Unidirectional Flow of Vibrational Energy in an Adenine-Thymine Base Pair. J Phys Chem B 2023; 127:163-171. [PMID: 36594729 DOI: 10.1021/acs.jpcb.2c07416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The role of a methyl group in intramolecular vibrational energy redistribution (IVR) of the hydrogen-bonded adenine-thymine base pair has been studied using classical dynamics procedures. Energy transferred to the doorway bond thymine-NH from the vibrationally excited H2O(v) efficiently redistributes among various bonds of the base pair through vibration-to-vibration coupling, depositing a large fraction of the available energy in the terminal bond adenine-NH. On the other hand, the extent of energy flow in the reverse direction from the excited adenine-NH to thymine-NH is insignificant, indicating IVR in adenine-thymine resulting from the intermolecular interaction with a vibrationally excited H2O molecule, is direction-specific. The unidirectional flow is due to the coupling of stretch-torsion vibrations of a methyl group with conjugated bonds on the thymine ring, when the methyl rotor is present and is adjacent to the vibrationally excited thymine-NH. The insignificance of energy flow from the terminal-to-terminal bond in the reverse direction is attributed to the absence of a methyl group on the adenine moiety, even though the molecule has many CC and CN bonds coupled to their neighbors.
Collapse
Affiliation(s)
- H K Shin
- Department of Chemistry, University of Nevada, Reno, Nevada89557, United States
| |
Collapse
|
3
|
Wang JJ, Gong J, McGaughey AJH, Segal D. Simulations of heat transport in single-molecule junctions: Investigations of the thermal diode effect. J Chem Phys 2022; 157:174105. [PMID: 36347668 DOI: 10.1063/5.0125714] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
With the objective of understanding microscopic principles governing thermal energy flow in nanojunctions, we study phononic heat transport through metal-molecule-metal junctions using classical molecular dynamics (MD) simulations. Considering a single-molecule gold-alkanedithiol-gold junction, we first focus on aspects of method development and compare two techniques for calculating thermal conductance: (i) The Reverse Nonequilibrium MD (RNEMD) method, where heat is inputted and extracted at a constant rate from opposite metals. In this case, the thermal conductance is calculated from the nonequilibrium temperature profile that is created at the junction. (ii) The Approach-to-Equilibrium MD (AEMD) method, with the thermal conductance of the junction obtained from the equilibration dynamics of the metals. In both methods, simulations of alkane chains of a growing size display an approximate length-independence of the thermal conductance, with calculated values matching computational and experimental studies. The RNEMD and AEMD methods offer different insights, and we discuss their benefits and shortcomings. Assessing the potential application of molecular junctions as thermal diodes, alkane junctions are made spatially asymmetric by modifying their contact regions with the bulk, either by using distinct endgroups or by replacing one of the Au contacts with Ag. Anharmonicity is built into the system within the molecular force-field. We find that, while the temperature profile strongly varies (compared with the gold-alkanedithiol-gold junctions) due to these structural modifications, the thermal diode effect is inconsequential in these systems-unless one goes to very large thermal biases. This finding suggests that one should seek molecules with considerable internal anharmonic effects for developing nonlinear thermal devices.
Collapse
Affiliation(s)
- Jonathan J Wang
- Chemical Physics Theory Group, Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S 3H6, Canada
| | - Jie Gong
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Alan J H McGaughey
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Dvira Segal
- Chemical Physics Theory Group, Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S 3H6, Canada
| |
Collapse
|
4
|
Leong TX, Collins BK, Dey Baksi S, Mackin RT, Sribnyi A, Burin AL, Gladysz JA, Rubtsov IV. Tracking Energy Transfer across a Platinum Center. J Phys Chem A 2022; 126:4915-4930. [PMID: 35881911 PMCID: PMC9358659 DOI: 10.1021/acs.jpca.2c02017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
![]()
Rigid, conjugated alkyne bridges serve as important components
in various transition-metal complexes used for energy conversion,
charge separation, sensing, and molecular electronics. Alkyne stretching
modes have potential for modulating charge separation in donor–bridge–acceptor
compounds. Understanding the rules of energy relaxation and energy
transfer across the metal center in such compounds can help optimize
their electron transfer switching properties. We used relaxation-assisted
two-dimensional infrared spectroscopy to track energy transfer across
metal centers in platinum complexes featuring a triazole-terminated
alkyne ligand of two or six carbons, a perfluorophenyl ligand, and
two tri(p-tolyl)phosphine ligands. Comprehensive
analyses of waiting-time dynamics for numerous cross and diagonal
peaks were performed, focusing on coherent oscillation, energy transfer,
and cooling parameters. These observables augmented with density functional
theory computations of vibrational frequencies and anharmonic force
constants enabled identification of different functional groups of
the compounds. Computations of vibrational relaxation pathways and
mode couplings were performed, and two regimes of intramolecular energy
redistribution are described. One involves energy transfer between
ligands via high-frequency modes; the transfer is efficient only if
the modes involved are delocalized over both ligands. The energy transport
pathways between the ligands are identified. Another regime involves
redistribution via low-frequency delocalized modes, which does not
lead to interligand energy transport.
Collapse
Affiliation(s)
- Tammy X Leong
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Brenna K Collins
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, United States
| | - Sourajit Dey Baksi
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, United States
| | - Robert T Mackin
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Artem Sribnyi
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Alexander L Burin
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - John A Gladysz
- Department of Chemistry, Texas A&M University, College Station, Texas 77842, United States
| | - Igor V Rubtsov
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| |
Collapse
|
5
|
Maitra A, Sarkar S, Leitner DM, Dawlaty JM. Electric Fields Influence Intramolecular Vibrational Energy Relaxation and Line Widths. J Phys Chem Lett 2021; 12:7818-7825. [PMID: 34378946 DOI: 10.1021/acs.jpclett.1c02238] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Intramolecular vibrational energy relaxation (IVR) is fundamentally important to chemical dynamics. We show that externally applied electric fields affect IVR and vibrational line widths by changing the anharmonic couplings and frequency detunings between modes. We demonstrate this effect in benzonitrile for which prior experimental results show a decrease in vibrational line width as a function of applied electric field. We identify three major channels for IVR that depend on electric field. In the dominant channel, the electric field affects the frequency detuning, while in the other two channels, variation of anharmonic couplings as a function of field is the underlying mechanism. Consistent with experimental results, we show that the combination of all channels gives rise to reduced line widths with increasing electric field in benzonitrile. Our results are relevant for controlling IVR with external or internal fields and for gaining a more complete interpretation of line widths of vibrational Stark probes.
Collapse
Affiliation(s)
- Anwesha Maitra
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0001, United States
| | - Sohini Sarkar
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0001, United States
| | - David M Leitner
- Department of Chemistry, University of Nevada Reno, Reno, Nevada 89519, United States
| | - Jahan M Dawlaty
- Department of Chemistry, University of Southern California, Los Angeles, California 90089-0001, United States
| |
Collapse
|
6
|
Nawagamuwage SU, Qasim LN, Zhou X, Leong TX, Parshin IV, Jayawickramarajah J, Burin AL, Rubtsov IV. Competition of Several Energy-Transport Initiation Mechanisms Defines the Ballistic Transport Speed. J Phys Chem B 2021; 125:7546-7555. [PMID: 34185993 PMCID: PMC8287563 DOI: 10.1021/acs.jpcb.1c03986] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
The ballistic regime
of vibrational energy transport in oligomeric
molecular chains occurs with a constant, often high, transport speed
and high efficiency. Such a transport regime can be initiated by exciting
a chain end group with a mid-infrared (IR) photon. To better understand
the wavepacket formation process, two chemically identical end groups,
azido groups with normal, 14N3-, and isotopically
substituted, 15N3-, nitrogen atoms, were tested
for wavepacket initiation in compounds with alkyl chains of n = 5, 10, and 15 methylene units terminated with a carboxylic
acid (-a) group, denoted as 14N3Cn-a and 15N3Cn-a. The transport
was initiated by exciting the azido moiety stretching mode, the νN≡N tag, at 2100 cm–1 (14N3Cn-a) or 2031 cm–1 (15N3Cn-a). Opposite to the
expectation, the ballistic transport speed was found to decrease upon 14N3 → 15N3 isotope
editing. Three mechanisms of the transport initiation of a vibrational
wavepacket are described and analyzed. The first mechanism involves
the direct formation of a wavepacket via excitation with IR photons
of several strong Fermi resonances of the tag mode with the νN=N + νN–C combination state
while each of the combination state components is mixed with delocalized
chain states. The second mechanism relies on the vibrational relaxation
of an end-group-localized tag into a mostly localized end-group state
that is strongly coupled to multiple delocalized states of a chain
band. Harmonic mixing of νN=N of the azido
group with CH2 wagging states of the chain permits a wavepacket
formation within a portion of the wagging band, suggesting a fast
transport speed. The third mechanism involves the vibrational relaxation
of an end-group-localized mode into chain states. Two such pathways
were found for the νN≡N initiation: The νN=N mode relaxes efficiently into the twisting band
states and low-frequency acoustic modes, and the νN–C mode relaxes into the rocking band states and low-frequency acoustic
modes. The contributions of the three initiation mechanisms in the
ballistic energy transport initiated by νN≡N tag are quantitatively evaluated and related to the experiment.
We conclude that the third mechanism dominates the transport in alkane
chains of 5–15 methylene units initiated with the νN≡N tag and the wavepacket generated predominantly at
the CH2 twisting band. The isotope effect of the transport
speed is attributed to a larger contribution of the faster wavepackets
for 14N3Cn-a or to the different
breadth of the wavepacket within the twisting band. The study offers
a systematic description of different transport initiation mechanisms
and discusses the requirements and features of each mechanism. Such
analysis will be useful for designing novel materials for energy management.
Collapse
Affiliation(s)
| | - Layla N Qasim
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Xiao Zhou
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Tammy X Leong
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Igor V Parshin
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | | | - Alexander L Burin
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| | - Igor V Rubtsov
- Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States
| |
Collapse
|