Carrier generation process on photoconductive polymer films as studied by magnetic field effects on the charge-transfer fluorescence and photocurrent.

The journal of physical chemistry. B · 2005 · Mixed · Insufficient evidence

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MixedInsufficient evidencePaper 3570

Study snapshot

PublicationThe journal of physical chemistry. B · 2005

Study typein_vitro

Reported directionMixed

Evidence ratingInsufficient

Abstract

We have studied the magnetic field effects (MFEs) on the charge-transfer fluorescence and transient photocurrent of a 1,2,4,5-tetracyanobenzene-doped poly(N-vinylcarbazole) film, which reflect the recombination and escape yields of the carriers, respectively. The recombination yield dependence of the external magnetic field (B) clearly shows two types of the MFEs, growth with increasing B due to the hyperfine mechanism (HFM) and a negative dip due to the level-crossing mechanism (LCM). On the other hand, the escape yield indicates complementary MFEs with a sharp decrease in yield with increasing B and then a positive dip. Simultaneous observation of the HFM- and LCM-MFEs proves the stepwise hole-hopping mechanism rather the long-range hole-jumping one. The quantitative analysis of the recombination and escape MFEs is performed using the stochastic Liouville equations (SLE) for a one-dimensional lattice model in which the stepwise hole hops take place between the nearest neighbor carbazole units with spin conservation. The SLE analysis provides the recombination and hole transfer rate constants of 7.0 x 10(7) and 4.5 x 10(8) s(-1), respectively. The boundary site number for the ion pairs in the one-dimensional model is estimated by the best fit to the experimental results. The interionic distance of the boundary ion pair in the one-dimensional model including eight sites agrees with the thermalization distance in the Onsager model. Hence, it is concluded that the elementary processes in the Onsager model applied to molecular amorphous solids are the stepwise hole hops rather than a long-range hole jump.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typein_vitro

Effect directionmixed

PopulationNot supplied

Sample sizeNot supplied

ExposureNot supplied

Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

Magnetic field effects on charge-transfer fluorescence and transient photocurrent in tetracyanobenzene-doped poly(N-vinylcarbazole) films showed two components in recombination yield (increase with field attributed to a hyperfine mechanism and a negative dip attributed to a level-crossing mechanism), while escape yield showed complementary effects (sharp decrease with increasing field and then a positive dip). Modeling with stochastic Liouville equations for a 1D nearest-neighbor hopping model fit the data and yielded recombination and hole transfer rate constants of 7.0×10^7 s^-1 and 4.5×10^8 s^-1, supporting stepwise hole hopping rather than long-range hole jumping.

Outcomes measured

charge-transfer fluorescence (recombination yield)
transient photocurrent (escape yield)
magnetic field effects (hyperfine mechanism; level-crossing mechanism)
estimated recombination rate constant
estimated hole transfer rate constant
boundary site number / interionic distance estimates in 1D lattice model

Limitations

Magnetic field strength (B) values not provided in the abstract
In vitro/materials study on polymer films; no human/animal health outcomes reported
Exposure parameters beyond presence of an external magnetic field are not specified in the abstract

View raw extracted JSON

{
  "study_type": "in_vitro",
  "exposure": {
    "band": null,
    "source": "external magnetic field",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "charge-transfer fluorescence (recombination yield)",
    "transient photocurrent (escape yield)",
    "magnetic field effects (hyperfine mechanism; level-crossing mechanism)",
    "estimated recombination rate constant",
    "estimated hole transfer rate constant",
    "boundary site number / interionic distance estimates in 1D lattice model"
  ],
  "main_findings": "Magnetic field effects on charge-transfer fluorescence and transient photocurrent in tetracyanobenzene-doped poly(N-vinylcarbazole) films showed two components in recombination yield (increase with field attributed to a hyperfine mechanism and a negative dip attributed to a level-crossing mechanism), while escape yield showed complementary effects (sharp decrease with increasing field and then a positive dip). Modeling with stochastic Liouville equations for a 1D nearest-neighbor hopping model fit the data and yielded recombination and hole transfer rate constants of 7.0×10^7 s^-1 and 4.5×10^8 s^-1, supporting stepwise hole hopping rather than long-range hole jumping.",
  "effect_direction": "mixed",
  "limitations": [
    "Magnetic field strength (B) values not provided in the abstract",
    "In vitro/materials study on polymer films; no human/animal health outcomes reported",
    "Exposure parameters beyond presence of an external magnetic field are not specified in the abstract"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "magnetic field effects",
    "charge-transfer fluorescence",
    "photocurrent",
    "photoconductive polymer film",
    "poly(N-vinylcarbazole)",
    "tetracyanobenzene",
    "hyperfine mechanism",
    "level-crossing mechanism",
    "stochastic Liouville equations",
    "Onsager model",
    "hole hopping"
  ],
  "suggested_hubs": []
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1021/jp0453212
PubMed: 16852031

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