“…The log−log plots of I F or I P against time t from the end of the photoirradiation show straight lines; both decays of I F and I P for the ITL obeyed the t -1 law for all the polymer matrices used . The t -1 law has been reported in the field of radiation chemistry. − This decay kinetics is often theoretically explained using the long-range electron transfer model on the basis of electron tunneling, − because it is independent of the temperature. , We observed the ITL at a temperature as low as 20 K where even the side-chain motion of a polymer seems to be almost frozen. Therefore, the ITL is also considered to take place through charge recombination via electron tunneling. 4 Dependence of the fluorescence intensity I F (open circles), the phosphorescence intensity I P (closed circles), and the intensity ratio I P / I F (open squares) on time change for the ITL at 20 K of the TMB chromophore doped in a PnBMA film.…”
Section: Resultsmentioning
confidence: 63%
“…There have been various investigations on the ITL for irradiated organic glasses or polymer solids at a low temperature. The ITL decay kinetics is reported to obey the t -1 law: the ITL intensity is proportional to an inverse power function of time t . − In most cases, the kinetics is independent of temperature. , Thus, many authors explained the ITL decay in terms of a long-range electron transfer by electron tunneling. − In this model, the trap depth is assumed to be unique and constant with time. However, the direct evidence for the assumptions is lacking because of the difficulty of the absorption measurements of the transient ionic species.…”
Section: Introductionmentioning
confidence: 99%
“…4 There have been various investigations on the ITL for irradiated organic glasses or polymer solids at a low temperature. The ITL decay kinetics is reported to obey the t -1 law: the ITL intensity is proportional to an inverse power function of time t. [5][6][7][8] In most cases, the kinetics is independent of temperature. 7,8 Thus, many authors explained the ITL decay in terms of a longrange electron transfer by electron tunneling.…”
The behavior of a photoejected electron with the parent
cation formed through two-photon
ionization of a dopant chromophore in poly(alkyl methacrylate)s
and polystyrene was studied by
measurement of the emission spectra of the charge recombination
luminescence, i.e., isothermal
luminescence (ITL) at 20 K and thermoluminescence (TL) at temperatures
from 20 to 300 K. The ITL
spectral shape remained the same between 10 min and 10 h after the
photoirradiation. On the other
hand, the intensity ratio of phosphorescence
(I
P) to fluorescence
(I
F),
I
P/I
F in the TL spectra
increased for
poly(alkyl methacrylate)s above a temperature where small scale
motions of the main chain are released
but was almost constant for polystyrene in the temperature range
examined. These findings show that,
for poly(alkyl methacrylate)s, the photoejected electrons change
into more stable anion species with a
motional relaxation of the polymer. From the TL spectral change,
the depth of the deeper trap at higher
temperatures was estimated to be more than 1.8 eV.
“…The log−log plots of I F or I P against time t from the end of the photoirradiation show straight lines; both decays of I F and I P for the ITL obeyed the t -1 law for all the polymer matrices used . The t -1 law has been reported in the field of radiation chemistry. − This decay kinetics is often theoretically explained using the long-range electron transfer model on the basis of electron tunneling, − because it is independent of the temperature. , We observed the ITL at a temperature as low as 20 K where even the side-chain motion of a polymer seems to be almost frozen. Therefore, the ITL is also considered to take place through charge recombination via electron tunneling. 4 Dependence of the fluorescence intensity I F (open circles), the phosphorescence intensity I P (closed circles), and the intensity ratio I P / I F (open squares) on time change for the ITL at 20 K of the TMB chromophore doped in a PnBMA film.…”
Section: Resultsmentioning
confidence: 63%
“…There have been various investigations on the ITL for irradiated organic glasses or polymer solids at a low temperature. The ITL decay kinetics is reported to obey the t -1 law: the ITL intensity is proportional to an inverse power function of time t . − In most cases, the kinetics is independent of temperature. , Thus, many authors explained the ITL decay in terms of a long-range electron transfer by electron tunneling. − In this model, the trap depth is assumed to be unique and constant with time. However, the direct evidence for the assumptions is lacking because of the difficulty of the absorption measurements of the transient ionic species.…”
Section: Introductionmentioning
confidence: 99%
“…4 There have been various investigations on the ITL for irradiated organic glasses or polymer solids at a low temperature. The ITL decay kinetics is reported to obey the t -1 law: the ITL intensity is proportional to an inverse power function of time t. [5][6][7][8] In most cases, the kinetics is independent of temperature. 7,8 Thus, many authors explained the ITL decay in terms of a longrange electron transfer by electron tunneling.…”
The behavior of a photoejected electron with the parent
cation formed through two-photon
ionization of a dopant chromophore in poly(alkyl methacrylate)s
and polystyrene was studied by
measurement of the emission spectra of the charge recombination
luminescence, i.e., isothermal
luminescence (ITL) at 20 K and thermoluminescence (TL) at temperatures
from 20 to 300 K. The ITL
spectral shape remained the same between 10 min and 10 h after the
photoirradiation. On the other
hand, the intensity ratio of phosphorescence
(I
P) to fluorescence
(I
F),
I
P/I
F in the TL spectra
increased for
poly(alkyl methacrylate)s above a temperature where small scale
motions of the main chain are released
but was almost constant for polystyrene in the temperature range
examined. These findings show that,
for poly(alkyl methacrylate)s, the photoejected electrons change
into more stable anion species with a
motional relaxation of the polymer. From the TL spectral change,
the depth of the deeper trap at higher
temperatures was estimated to be more than 1.8 eV.
“…Power law kinetics in this form have been observed for electron transfer recombination dynamics in frozen glass [94][95][96] and in other rigid environments. [97][98][99] Power law kinetics have also been reported for electron injection and/or recombination between surface-bound dye molecules and semiconductor metal oxide surfaces.…”
In semi-rigid PEG-DMA550 films with added reductive quenchers, electron transfer quenching of the metal-to-ligand charge transfer excited state(s) of [Ru(bpy)3](2+) (bpy = 2,2'-bipyridine) occurs by both rapid, fixed-site, and slow, diffusional, quenching processes. Stern-Volmer analysis of diffusional quenching reveals diffusion-controlled quenching both in the fluid and film with the latter greatly inhibited by the high viscosity of the medium. The data for fixed-site quenching are consistent with electron tunneling with the expected exponential distance dependence. Based on this analysis long-range electron transfer occurs with a distance attenuation factor β of ∼0.47 Å(-1) with a notable decrease, β = 0.16 Å(-1), when the quencher is incorporated into the PEG backbone. Fixed-site electron transfer quenching varies with driving force. Back electron transfer is complex, as expected for a distribution of fixed sites, and varies with power law kinetics.
“…This type of luminescence decay has earlier been observed in organic glasses at 4. 2 K and 77 K (Ershov and Kieffer 1973, Kieffer, LapersonneMeyer andRigant 1974), and was interpreted in terms of tunnelling of an electron through the Coulomb barrier separating it from a positive ion . The rateconstant a depends on the distance between the electron and the ion and the height of the energy barrier separating them .…”
For DNA films, X-irradiated at 77 K, a comparative study was performed on (a) light emission (fluorescence and phosphorescence) during irradiation, (b) afterglow and thermoluminescence, (c) optical absorption after irradiation, and (d) free-radical reactions in similar gamma-irradiatied DNA samples. Spectra are reported for the various kinds of light emission and for the optical absorption. From temperature-dependence studies, it was concluded that the light-emission phenomena are unrelated to the reactions of the free radicals as studied by electron paramagnetic resonance. The optical absorption on the other hand, is strongly correlated to the presence of free radicals in the DNA. Some mechanisms possibly involved in the observed luminescence reactions are discussed.
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