Easily oxidizable triarylamine materials with naphthalene and binaphthalene core: structure–properties relationship

We devised and synthesized a series of electron-rich compounds featuring diphenylamine, carbazole or dibenzo[c,g]carbazole connected via phenylacetylene linkers to an aromatic central unit. The key synthetic step was a high yielding cross coupling reaction between halogenated (bi)naphthalene and organometallic reagents prepared in situ from terminal alkynes (side-arms). By masking one of the iodo functions with a diethyltriazenyl group in the side-arm precursors, we efficiently circumvented the formation of doubly aminated by-products. Although one step longer, this approach led to higher yields of terminal alkynes than the direct coupling route. Spectroscopic and electrochemical measurements supported by computational evidence revealed that conjugation in the 1,4-disubstituted naphthalene backbone is superior to the 1,5 or 2,6 substituted cores. The diphenylamine derivative gets oxidized more readily when compared to its carbazole analogs. Expanding the core to binaphthalene did not alter electronic properties, but influenced the physical characteristics significantly.