Palladium catalysis has been found to offer an effective solution-phase alternative to gas-phase flash vacuum pyrolysis as a method for converting the planar ring system of 7, 10-di(2-bromophenyl)fluoranthene (4) to that of the C(28)H(14) bowl-shaped fullerene fragment dibenzo[a,g]corannulene (5).

This communication describes the synthesis of a novel low band gap hydrocarbon polymer, poly(indenofluorene), PIF, composed of 3,9-di-tert-butylindeno[1,2-b]fluorene building blocks. The polymer, with high degrees of polymerization (DP > 20), was generated by coupling alkylated 6,6,12,12-tetrachloro-6,12-dihydroindeno[1,2-b]fluorene monomers by means of low-valent transition metal [e.g. chromium(0) and nickel(0)] compounds as dehalogenating agents. The cross-conjugated coupling product exhibits a widely red shifted longest wavelength absorption maximum (λmax of up to 799 nm). This fact can be interpreted as resulting from the contribution of quinoid states to the electronic ground state. Oligomeric products possessing similar structures were also generated by dehydrohalogenation polymerization, starting from the corresponding 6,12-dihalo-6,12-dihydroindeno[1,2-b]fluorenes.

A new class of polycyclic aromatic hydrocarbons--oligoindenopyrenes--has been synthesized featuring a Pd-catalyzed Suzuki-Heck coupling cascade. The oligoindenopyrenes are robust, highly colored substructures of C(70) and have properties that might prove useful in new organic materials or devices. After excitation, the tetraindenopyrene derivative 3d undergoes efficient deactivation (99%) by internal conversion to the ground state. The small fluorescence quantum yield (0.004) is in accordance with the short (0.6 ns) fluorescence decay time.

Poly(indenofluorene) shows a strong degenerate four-wave mixing (DFWM) response when it is excited with 100-fs pulses at 800 nm. The DFWM signal scales with the 1.5 power of the input intensity, which we interpret as being due to absorption saturation phenomena. The saturation was studied by open-aperture Z scan in dilute solutions of poly(indenofluorene) in chloroform. The changes in the absorption coefficient alpha are described by the formula alpha = alpha(0)/[1 + (I/I(sat))(1/2)], where I(sat) is the saturation intensity, which is found to be of the order of 100>MW/cm(2).