Development of N-Alkyl-Substituted Bis(pyrrolo3,4-d)tetrathiafulvalenes as Organic Semiconductors for Solution-Processible Field-Effect Transistors

摘要

A series of N-alkyl-substituted bis(pyrrolo3,4-d)tetrathiafulvalenes(PyTTFs,alkyl = n-butyl,n-octyl,n-dodecyl,n-cetyl,and n-icosyl,3-7)were synthesized as highly soluble tetrathiafulvalene(TTF)derivatives.Their solid-state structures were characterized by X-ray diffraction,and their suitability for use as semiconductors for solution-processible organic field-effect transistor(OFET)devices was evaluated.Whereas the solubility of the TTF derivatives was enhanced with the introduction of alkyl groups,very long alkyl groups,such as the n-icosyl group,reduced the solubility probably due to intermolecular hydrophobic interactions between the very long alkyl groups.The solid-state structure was also influenced by the length of the alkyl groups;molecules 5-7 having n-dodecyl or longer alkyl groups tended to assume two-dimensional(2-D)molecular ordering both in the bulk single crystals and in the spin-coated thin films.In contrast,3 and 4,having short n-butyl and n-octyl groups,did not take on a 2-D interactive structure in the solid state.Consistent with the solid-state structure of the PyTTF derivatives,field-effect transistor(FET)characteristics of the solution-processed OFETs markedly depended on the length of the afkyl groups.In contrast to spin-coated thin films of 3 and 4,which were relatively inferior semiconducting layers(mu_(FET)= ~10~(-5)cm~2 V~(-1)s~(-1)or no reproducible field effect),OFET devices consisting of spin-coated thin films of 5-7 showed typical p-channel FET characteristics,namely,hole mobilities of ~10~(-2)cm~2 V~(-1)s~(-1)and current on/off ratios of ~10~4.The results indicate that an appropriate combination of a pi-conjugated core with long alkyl groups could provide soluble organic semiconductors that are applicable to solution-processible OFETs.