Effects of chemical modifications on photophysics and exciton dynamics of π-conjugation attenuated and metal-chelated photoconducting polymers

Effects of two types of chemical modifications on photoconducting polymers consisting of polyphenylene vinylene (PPV) derivatives are studied by static and ultrafast transient optical spectroscopy as well as semi-empirical ZINDO calculations. The first type of modification inserts 2,2′-bipyridyl-5-vinylene (bpyV) units in the PPV backbone, and the second type involves metal-chelation with the bpy sites. Photoluminescence (PL) and exciton dynamics of polymers 1 and 2 with PV:bpyV ratios of 1 and 3 were examined in solution, and compared with those of the homo-polymer, poly(2,5-bis(2′-ethylhexyloxy)-1,4-phenylene vinylene) (BEH-PPV). Similar studies were carried out for several metal-chelated polymers. These results can be explained by changes in π-conjugation throughout the polymer backbone. The attenuation in π-conjugation by the chemical modifications transforms a conducting polymer from one-dimensional semiconductor to molecular aggregates.