Ultrafast Light-Induced Electron-Hole Pair Separation Along Oriented Molecular Clusters in a Langmuir-Blodgett Film

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Abstract
Supermolecules TA(4)P, i.e. 4-[p-N-methyl-N-[4-(3-perylenyl)-butyl]amino-phenyl]-2,6-diphenyl-thiopyrylium perchlorate, of elongated shape were synthesized consisting of a hydrophilic aromatic head unit and two consecutive hydrophobia aromatic moeities. Light-induced electron-hole pair separation was started from the lowest excited singlet state delocalized over the elongated TA subunits. Aligned clusters of the TA(4)P Supermolecules were formed in a Langmuir-Blodgett film with their long axes pointing in about the direction of the desired unidirectional charge transfer across the LB film. Ultrafast hole transfer was measured as fluorescence decay from room temperature to 80 K. Hole transfer was measured directly at room temperature as hole injection from the perylene part of the TA(4)P clusters into an α-perylene single crystal. The observed signals suggest an adiabatic activation free reaction path for light-induced electron-hole pair separation in the TA(4)P clusters, though a case at the borderline to a non-adiabatic reaction path cannot be ruled out completely.