An aryl-fused redox-active tetrathiafulvalene with enhanced mixed-valence and radical-cation dimer stabilities
H.V. Schröder, F. Witte, M. Gaedke, S. Sobottka, L. Suntrup, H. Hupatz, A. Valkonen, B. Paulus, K. Rissanen, B. Sarkar, C.A. Schalley – 2018
Molecular recognition of stable organic radicals is a relatively novel, but important structural binding motif in supramolecular chemistry. Here, we report on a redox-switchable veratrole-fused tetrathiafulvalene derivative VTTF which is ideally suited for this purpose and for the incoorporation into stimuli-responsive systems. As revealed by electrochemistry, UV/Vis measurements, X-ray analysis, and electrocrystallisation, VTTF can be reversibly oxidised to the corresponding radical-cation or dication which show optoelectronic and structural propterties similar to tetrathiafulvalene and tetrakis(methylthio)-tetrathiafulvalene. However, theoretical calculations, variable temperature EPR, and NIR spectroscopy indicate that the dispersion-driven binding in the mixed-valence dimer (VTTF2)●+ (KMV = 69 M-1 in CH2Cl2) and the radical-cation dimer (VTTF●+)2 (KRC = 38 M-1 in CH3CN) is significantly enhanced by the additional veratrole π-surface in comparison to pristine tetrathiafulvalene.