[2+2] Cycloaddition-retroelectrocyclization reactivity and thin film transistor performances of carbazole-based platinum polyyne polymers

Carbazole-based platinum polyyne polymers are a good platform for the postfunctional formation of donoracceptor type narrow band gap polymers by the [2 + 2] cycloaddition-retroelectrocyclization reaction with tetracyanoethylene (TCNE). The TCNE reactivity depends on the connectivity pattern of the carbazole. The 3,6cabazole-based polymer shows a higher reactivity than the corresponding 2,7-carbazole-based polymer due to the p-positions with respect to the sp3 nitrogen atom. The connectivity pattern leads to the regioregularity difference in the resulting polymers. When TCNE is added to one of the alkynes of the 3,6-diethynylcarbazole unit, the electron-donating nature of the carbazole is lowered and the second TCNE addition does not occur. Accordingly, the regioregular polymer is formed from the 3,6-carbazole-based polymer, which is revealed from the 1H NMR spectrum. In contrast, the TCNE addition of the 2,7-carbazole-based polymer is mainly governed by the platinum atom, which produces a regiorandom structure. Finally, the charge carrier transporting properties of the precursor polymers are evaluated in thin film transistors. The 3,6-carbazole-based polymer displays a one order higher hole mobility than the corresponding 2,7-carbazole-based polymer. This result suggests that the shallower HOMO level of the former polymer facilitates the hole injection.