Synthesis, molecular and electron transport properties of 2-alkyltrinitrofluoren-9-ones

2-Alkyltrinitrofluoren-9-ones 2 were conveniently synthesized by controlled nitration of 2-alkylfluoren-9-ones 5 with a mixture of red fuming HNO3 and concentrated H2SO4 at 0–25 °C. The precursors 5 were derived from the corresponding 2-acylfluorenes by appropriate reduction of the acyl function, followed by base-catalysed O2-oxidation at the C-9 position. The regiochemistry of nitration was interesting: with a sterically bulky substituent in 5, nitration occurred at C-4, -5, and -7 positions, affording 2-alkyl-4,5,7-trinitrofluoren-9-one in over 35% yield; on the other hand, 5 with a primary alkyl function underwent nitration predominantly at C-3, -5, and -7 positions. By virtue of its alkyl function, 2-alkyltrinitrofluoren-9-one 2 displayed better solubility and polymer compatibility characteristics than its non-alkylated analog, TNF. However, the charge transfer interactions of 2 with electron donors were weaker than those of TNF, despite the fact that they both have the same electron affinity. Both 2 and TNF exhibited good electron transport properties in poly(N-vinylcarbazole) matrices.