Permittivity Threshold and Thermodynamics of Integer Charge-Transfer Complexation for an Organic Donor–Acceptor Pair
Journal Article
·
· Journal of Physical Chemistry. B
- Johns Hopkins Univ., Baltimore, MD (United States); Johns Hopkins University
- Johns Hopkins Univ., Baltimore, MD (United States)
Molecular or chemical-based charge doping provides a means to change the properties (e.g. conductivity) of a material through a complete or partial transfer of charge between its constituents. Understanding how local material environment impacts this process is thus important for controlling the properties of organic materials. This paper presents spectroscopic investigations of molecular charge transfer interactions between a pair of common charge-doping and -transporting materials (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, F4TCNQ, and N,N’-Diphenyl-N-N’-di-p-tolylbenzene-1,4-diamine, MPDA). Equilibrium constants associated with charge transfer were determined for donor-acceptor pairs dissolved in a series of solvents covering a range of values of permittivity. A threshold for highly favorable charge separation was observed to occur at a permittivity of ~8-9, with more and less favorable charge separation observed in solvents of higher and lower permittivity, respectively, but with chloroform (permittivity=4.81) exhibiting an anomalously favorable charge separation. Temperature-dependent studies were undertaken to assess the thermodynamics of charge separation. In 1,2- dichloroethane (permittivity=10.36) and chlorobenzene (permittivity=5.62), charge transfer was observed to be both enthalpically and entropically favorable. Charge separation in chloroform is exothermic and entropically disfavored, indicating that specific, inner-shell solvent-solute interactions stabilize the charge-separated complex and result in a net increase in local solution structure. Furthermore, our results provide insight on how modification to the chemical environment may be utilized to support stable charge transfer for molecular doping applications and requiring only modest changes in local permittivity.
- Research Organization:
- Johns Hopkins Univ., Baltimore, MD (United States)
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- FG02-07ER46465
- OSTI ID:
- 1962363
- Journal Information:
- Journal of Physical Chemistry. B, Journal Name: Journal of Physical Chemistry. B Journal Issue: 12 Vol. 127; ISSN 1520-6106
- Publisher:
- American Chemical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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