Ballistic energy transport along PEG chains: distance dependence of the transport efficiency

Abstract

Dual-frequency relaxation-assisted two-dimensional infrared (RA 2DIR) spectroscopy was used to investigate energy transport in polyethylene glycol (PEG) oligomers of different length, having 0, 4, 8, and 12 repeating units and end-labeled with azido and succinimide ester moieties (azPEGn). The energy transport initiated by excitation of the N≡N stretching mode of the azido group in azPEGn in CCl(4) at ca. 2100 cm(-1) was recorded by probing the C=O stretching modes (reporters) of the succinimide ester moiety. Sensitive to the excess energy delivered to the reporter modes, RA 2DIR permits observation of both the through-bond and through-solvent energy transport contributions. The cross-peak data involving the reporter modes with different thermal sensitivity and the data for mixtures of compounds permitted concluding that through-bond energy transport is the dominant mechanism for most cross peaks in all four azPEGn compounds. The through-bond energy transport time, evaluated as the waiting time at which the cross peak maximum is reached, was found to be linearly dependent on the chain length of up to 60 Å, suggesting a ballistic energy transport regime. The through-bond energy transport speed determined from the chain-length dependence of T(max) in CCl(4) is found to be ca. 450 m s(-1). The cross-peak amplitude at the maximum decays exponentially with the chain length; a characteristic decay distance is found to be 15.7 ± 1 Å. The cross-peak amplitude at zero waiting time, determined by the end-to-end distance distribution, is found to decay with the chain length (L) as ∼L(-1.4), which is close to predictions of the free flight chain model. The match indicates that the end-group interaction does not strongly perturb the end-to-end distribution, which is close to the ideal random coil distribution with the Gaussian probability density.

Photogeneration of charge carriers in a weakly disordered π-conjugated polymer at high photon energies of exciting light

“…It has been established that in polyatomic molecules the vibrational excitation is not evenly distributed among a large number of intramolecular vibrations, but it is transferred, for example, through a chain consisting of 12-26 CH 2 units [21,22] and between moieties linked by 4-8 conjugated bonds [23]. Using the method of the two-dimensional (2D) infrared spectroscopy [23], Lin et al have shown that transport of the intramolecular vibration energy in the polyethylene glycol (PEG) oligomers of different length, having 4, 8, and 12 repeating units [24], and in perfluoroalkane oligomers with various chain lengths [25] occurs in a ballistic energy transport regime. In the ballistic regime the energy is transferred by vibrational states delocalized over the whole transport region [24].…”

“…Using the method of the two-dimensional (2D) infrared spectroscopy [23], Lin et al have shown that transport of the intramolecular vibration energy in the polyethylene glycol (PEG) oligomers of different length, having 4, 8, and 12 repeating units [24], and in perfluoroalkane oligomers with various chain lengths [25] occurs in a ballistic energy transport regime. In the ballistic regime the energy is transferred by vibrational states delocalized over the whole transport region [24]. The energy transport speed was found to be 450 m/s for the PEG oligomers in CCl 4 [24] and 1150 m/s for perfluoroalkane oligomers in chloroform [25].…”

“…In the ballistic regime the energy is transferred by vibrational states delocalized over the whole transport region [24]. The energy transport speed was found to be 450 m/s for the PEG oligomers in CCl 4 [24] and 1150 m/s for perfluoroalkane oligomers in chloroform [25]. These values are close to a speed of propagation (950 m/s) of the heat burst in a monolayer of long-chain hydrocarbon molecules anchored to metal substrates that was measured by using the method of the sum-frequency generation spectroscopy [21].…”

Initial spatial distribution of geminate charge carriers photogenerated in doped conjugated polymers

“…These values are close to a speed of propagation (950 m/s) of the heat burst in a monolayer of longchain hydrocarbon molecules anchored to metal substrates that was measured by using the method of the sum-frequency generation spectroscopy [23]. It has been found that the vibrational energy transport time increases with increasing the chain length and reaches about 15 ps at the chain length of 6 nm [26].…”

“…Using the method of the twodimensional infrared spectroscopy [25], Rubtsov and co-workers have shown that transport of the intramolecular vibration energy in the polyethylene glycol (PEG) oligomers of different lengths [26] and in perfluoroalkane oligomers with various chain lengths [27] occurs in a ballistic energy transport regime, in which the energy is transferred by vibrational states delocalized over the whole transport region [26]. The energy transport speed was found to be 450 m/s for the PEG oligomers in CCl 4 [26] and 1150 m/s for perfluoroalkane oligomers in chloroform [27]. These values are close to a speed of propagation (950 m/s) of the heat burst in a monolayer of longchain hydrocarbon molecules anchored to metal substrates that was measured by using the method of the sum-frequency generation spectroscopy [23].…”