Luminescent π-conjugated poly(aryleneethynylene)s consisting of plural aromatic units: Preparation and systematic studies on their optical properties

A series of π-conjugated poly(aryleneethynylene)s (PAEs) containing two or three different arylene units in the main chain have been prepared by palladium-catalyzed coupling reactions. The PAEs consist of 2,5-dihexyloxy-1,4-phenylene diethynylene (-CC-C6H2(OC6H13)2-p-CC-; C6H13 = hexyl) units with alternating arylene (-Ar-) units. Various kinds of arylenes, including 9,10-dihydrophenanthrene-2,7-diyl (Phen), pyridine-2,5-diyl (Py), thiophene-2,5-diyl (Th), anthracene-9,10-diyl (Ant), and 2,1,3-benzothiadiazole-4,7-diyl (BTdz), are used as the -Ar- units. The obtained PAEs were soluble in organic solvents by virtue of the attached hexyloxy side chains, and were characterized by NMR, IR, GPC, and UV-vis absorption and photoluminescence (PL) spectroscopy. The cooperation of different polymer segments induces variations in the electronic structure of the PAEs that show π-π∗ absorption peaks in the range of 380-530 nm and PL emission peaks in the range of 430-610 nm with quantum yields of 5-55% in their solutions. The UV-vis and PL peaks of the PAEs shifted to a longer wavelength in films and in colloidal solutions, indicating the occurrence of intermolecular electronic interactions by aggregation. In Ant-containing PAEs, the PL of the polymer chain was entirely replaced with a red-shifted PL emission assignable to the Ant segments due to intramolecular energy transfer.