Efficient synthesis of conjugated 2-(9H-fluoren-7-yl)-9H-fluorene via Br elimination in 2-bromofluorene using electron beam-irradiation

This study demonstrates the synthesis of conjugated 2-(9H-fluoren-7-yl)-9H-fluorene using electron beam irradiation within 3 min in place of the conventional catalytic cross-coupling reactions. 2-bromofluorene was irradiated at various doses (10, 30, 50, 70, 90, and 100 kGy), resulting in the elimination of Br from the 2-position and the formation of C–C bonds between the Br-eliminated fluorenes. The yield of 2-(9H-fluoren-7-yl)-9H-fluorene increased with higher absorbed doses, reaching 65% at 100 kGy. UV–Vis absorption of synthesized 2-(9H-fluoren-7-yl)-9H-fluorene showed an onset at 357 nm and a maximum absorption peak at 325 nm, and blue emission ranging from 340 to 450 nm in photoluminescence (PL). The results of UV–Vis absorption and PL indicated expanded conjugation of 2-(9H-fluoren-7-yl)-9H-fluorene due to the formation of C–C bonds between 2-bromofluorene through the electron beam-induced coupling reaction. Electron beam irradiation offers the potential to significantly reduce the reaction times for synthesis of conjugated organic compounds.