Even and odd oligothiophene-bridged bis-naphthalimides for n-type and ambipolar organic field effect transistors

The synthesis and characterization of a new family of thiophene bridged bis-naphthalimides (2NDI-XT) are presented here. These semiconductors have been designed to have an even or an odd number of thiophene rings, with the aim of studying molecules with varying and alternant molecular dipolar moments, which are expected to significantly impact molecular packing. Following a theoretical analysis, the stability of a series of p-dimers showing either parallel or antiparallel packing dispositions has been predicted. Our results point out to a molecular packing motif in which both the NDI and oligothiophene fragments are cofacial for all the semiconductors investigated, regardless of their estimated molecular dipole moments. These, in principle, unexpected results are in good agreement with the field-effect mobilities measured in a bottom-gate top-contact transistor architecture, which show no straightforward correlation between device performance and dipolar moment. Ambipolar field-effect mobilities are recorded for the most extended p-systems, 5,5 '-bis(2-hexyldecylbenzo[lmn] thieno[3 ',4 ': 4,5] imidazo[2,1-b][ 3,8] phenanthroline-1,3,6(2H)-trione-10-yl)-2,2 '-bithiophene, 2NDI-4T and 5,5 "-bis(2-hexyldecylbenzo[ lmn] thieno[3 ',4 ': 4,5] imidazo[2,1-b][3,8] phenanthroline-1,3,6(2H)-trione-10-yl)-2,2 ': 5 ',2 "-terthiophene, 2NDI-5T, with the latter showing quite balanced electron and hole mobilities of 1.8 x 10(-3) cm(2) V-1 s(-1) and 8.4 x 10(-3) cm(2) V-1 s(-1), respectively.