Exploiting Substituent Effects for the Synthesis of a Photooxidatively Resistant Heptacene Derivative

Substituent effects have been exploited to produce an unusually persistent heptacene derivative. In total, four new heptacene derivatives with varying levels of photooxidative resistance (1 < 2 < 3 < 4) have been synthesized. A combination of p-(t-butyl)thiophenyl substituents at positions 7 and 16 (i.e., arylthio substituents attached to the most reactive ring) and o-dimethylphenyl substituents at positions 5, 9, 14, and 18 (i.e., steric resistance on neighboring rings) make heptacene derivative 4 especially resistant to photooxidation. It persists for weeks as a solid, for 1-2 days in solution if shielded from light, and for several hours in solution when directly exposed to both light and air. Heptacene derivative 4 has been fully characterized. It possesses a small HOMO-LUMO gap of 1.37 eV.