Bridging the gap between polyfluorene and ladder-poly-p-phenylene: Synthesis and characterization of poly-2,8-indenofluorene

We present here a new derivative of poly-p-phenylene (PPP), the poly-2,8-in denofluorene ( 8a,b), to bridge the gap between 2,7-poly-9,9'-dialkylfluore ne (PF) (2) and ladder-poly-p-phenylene (LPPP) (4). The monomer 7a,b was sy nthesized starting from 6,12-dihydroindeno[1,2b]fluorene (5), which was fou r times alkylated, brominated with copper(II) bromide on an aluminum oxide matrix, and polymerized via a Ni(0)-mediated coupling reaction (M-n similar to (3.3-3.9) x 10(4) (tuluene, polystyrene standards)). As expected, the w avelength data for absorption and emission are intermediate to those of PF and LPPP and prove the suitability of the polymer to be used as blue-light- emitting material in polymer light-emitting diodes. The polymer 8a,b is sta ble up to 380 degrees C and shows thermotropic liquid crystalline behavior at high temperatures (250-300 degrees C). Oligomers of the 6,6',12,12'-tetr aoctylindenofluorene (6a) have been synthesized by Ni(0)-induced coupling o f monobromo and dibromo (7a) compounds, to determine the effective conjugat ion length (n(infinity,abs) = 6-7, n(infinity,em) = 5-6).