Charge recombination via intercolumnar electron tunneling through the lipid-like mantle of discotic hexa-alkyl-hexa-peri-hexabenzocoronenes.
The recombination of the mobile charge carriers formed in pulse-ionized hexa-alkyl-substituted hexa-peri-hexabenzocoronenes occurs mainly via intercolumnar electron tunneling through the intervening hydrocarbon mantle. This is evidenced as a dramatic increase in the time scale of the decay of the radiation-induced conductivity from a few hundred nanoseconds to close to a millisecond as the peripheral alkyl substituents increase in size from 8 to 24 carbon atoms with corresponding disk diameters, D, from 23.4 to 36.6 A. The decay kinetics are a function only of the total number of peripheral carbon atoms with no evidence for specific effects of chain branching. The 1/e decay time, tau(e), increases exponentially with D according to tau(e) = tau(e)(0) exp(betaD) with tau(e)(0) = 48 fs and beta = 0.63 A(-1). Taking into account the tilted columnar configuration of the molecules in the solid phase leads to a beta value of ca. 0.8 A(-1) for the distance dependence of intercolumnar electron tunneling. In contrast to the orders of magnitude changes in the time scale for intercolumnar charge recombination, the intracolumnar charge hopping times vary by only a factor of 4, between 40 and 160 fs, with no systematic dependence on the nature of the alkyl substituents. On the basis of the results, the time scale estimated for electron tunneling across a 40 A thick lipid membrane is estimated to be close to 1 ms.
Warman
John M
JM
Optoelectronic Materials Section, DelftChemTech, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands.
Piris
Jorge
J
Pisula
Wojciech
W
Kastler
Marcel
M
Wasserfallen
Daniel
D
Müllen
Klaus
K
D004553:Electric Conductivity; D004583:Electrons; D007700:Kinetics; D008055:Lipids / Q000737:chemistry*; D016252:Microscopy, Scanning Tunneling; D015394:Molecular Structure; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D011083:Polycyclic Compounds / Q000737:chemistry; D013997:Time Factors
D008055:Lipids; D011084:Polycyclic Aromatic Hydrocarbons; D011083:Polycyclic Compounds; C012256:coronene