Photo-physical and electro-optical properties of polythiophenes bearing tetrahydropyran side groups

Photo-physical and electro-optical properties of regio-regular polythiophenes functionalized with tetrahydropyran (THP) moieties tethered to the main chain by alkyl spacers are reported. Three sets of polymers were characterized. One consisted of polythiophenes in which THP groups were attached by either ethyl or undecyl side chains. The former exhibited solid state quantum yield of photoluminescence (Φ_pl) of 12%, while the undecyl analog exhibited a value of only 2.7%. Non-optimized polymer LEDs displayed orange and red emission for the ethyl and undecyl analogs, respectively. A second series of polymers investigated was based on random copolymers of 3-(2-(2-tetrahydropyranyloxy)ethyl)thiophene) and 3-hexyl, dodecyl or hexadecyl-thiophene. Polymers possessing shorter alkyl chains possessed shorter solid-state absorption and emission wavelengths but greater quantum yields of luminescence. The third series was based on random copolymers 3-(2-(2-tetrahydropyranyloxy)ethyl)thiophene) with various amounts of 3-hexylthiophene. As the 3-hexylthiophene content was reduced, the solid-state absorption and emission wavelengths decreased, while quantum yields of luminescence increased. Differences in luminescent properties are explained on the basis of extent of interchain aggregation induced by π–π intermolecular interactions and/or local ordering/disordering of alkyl chains.