Sulfur-Bridged Diazulenylmethyl Cations: Formation of Charge-Segregated Assembly with High Charge-Carrier Mobility

Sulfur-bridged diazulenylmethyl cations were synthesized and exhibited high stability even under basic conditions (pH 10) due to the delocalization of positive charge over the whole pai-conjugated skeleton. As a result of the effective delocalization and the absence of orthogonally oriented bulky substituents, the cationic pai-conjugated skeletons formed a pai-stacked array with short interfacial distances. A derivative with SbF6 as a counter anion formed a charge-segregated assembly in the crystalline state, rather than the generally favored charge-by-charge arrangement of oppositely charged species based on electrostatic interactions. Theoretical calculations suggested that the destabilization caused by electrostatic repulsion between two positively charged pai-conjugated skeletons is compensated by the dispersion forces. In addition, the counter anion SbF6 played a role in regulating the molecular alignment through F…H-C and F…S interactions, which resulted in the charge-segregated alignment of the cationic pai-skeletons. This characteristic assembled structure gave rise to a high charge-carrier mobility of 1.7 cm2V-1s-1 as determined using flash-photolysis time-resolved microwave conductivity and photocurrent measurements.