Langmuir-Blodgett films of amphiphilic bis(tetrathiafulvalene) macrocycles with four alkyl chains

Amphiphilic bis(tetrathiafulvalene) [bis(TTF)] macrocycles with four alkyl chains were fabricated as novel electrically active Langmuir-Blodgett (LB) films. Two TTF units were linked via [24]crown-8, [21]-crown-7, and [18]crown-6 macrocycles, forming charge-transfer (CT) salts with 2,3,5,6-tetrafluoro-7,7,8, 8-tetracyano-p-quinodimethane (F₄-TCNQ) at the air-water interface and on solid substrates. The CT salt of the amphiphilic bis(TTF)-macrocycle having a [24]crown-8 ring system formed a uniform surface morphology on mica. Using single-crystal X-ray structural analysis, the layer structure between the hydrophobic chains and the one-dimensional π-π stack of the CT salt was confirmed. Our results show that the bis(TTF)-macrocycle was folded at the flexible [24]crown-8 moiety, forming intramolecular π-π dimer structures and one-dimensional intermolecular π-π stacks with F₄-TCNQ dimers. The open-shell electronic structure of the LB films was determined by electronic spectra, electrical conductivity, and electron spin resonance analyses. Asymmetry was introduced into the bis(TTF)-macrocycle by changing the ring size from [24]crown-8 to [21]crown-7. The surface morphology of the CT salts with F₄-TCNQ was established as two-dimensional round-shape domains on mica. Further reduction of the macrocyclic ring from [21]crown-7 to [18]crown-6 resulted in a CT salt of the bis(TTF)-macrocycle with F ₄-TCNQ with a leaf-shape domain morphology and a typical dimension of ∼1 μm² on mica. In general, decreasing the macrocyclic ring size from [24]crown-8 to [21]crown-7 or [18]crown-6 affected the inter- and intramolecular interactions and the surface morphologies of LB films.