Abstract
Benzo[4,5]cyclohepta[1,2-b] fluorene (5a), a new pi-conjugated polycyclic hydrocarbon containing linearly fused six-, five-, six-, seven- and six-membered rings (C-6-C-5-C-6-C-7-C-6), was designed and its stable derivatives 5b and 5c were synthesized. With 22 pi electrons, 5a is an isomer of pentacene with quinoidal, dipolar ionic and diradical resonance forms. Molecules 5b and 5c were experimentally investigated with cyclic voltammetry, electronic absorption spectroscopy and X-ray crystallographic analysis, and theoretically studied by calculating the NICS value, diradical character and dipole moment. A comparison of 5a-c with pentacene and other pentacene analogues containing linearly fused five-or seven-membered rings was also conducted and discussed. It was found that 5b behaved as a p-type organic semiconductor in solution-processed thin film transistors with a field effect mobility of up to 0.025 cm(2) V-1 s(-1).