LPPPs defect emission

That even low levels of defects can produce strong emission is exemplified by the case of Ph-LPPP (108). The PL emission from 108 is very similar to that from 106 with maxima at 460 and 490 nm. However, the EL spectrum shows an additional long wavelength band. This is not a broad featureless band as seen for the defect emission from 5 or 106, but one with well-resolved maxima at 600 and 650 nm. Photophysical investigation of this emission showed the feature at 600 nm to be emission from a triplet exciton (phosphorescence) with a vibronic shoulder at 650 nm [158]. Elemental analysis of the polymer showed it contained 80 ppm of palladium (cf. <2 ppm in 106). It was therefore proposed that residues of the palladium catalyst used to make the precursor polymer 103 reacted with the phenyllithium and the polymer to introduce covalently bound palladium centres onto the polymer chain. These then act as sites for phosphorescent emission. 

That even low levels of defects can produce strong emission is exemplified by the case of Ph-LPPP (71). The synthesis (Scheme 32) is similar to that of Me-LPPP (66), except that complete ring closure of the polyalcohol 71 could not be obtained using boron trifluoride [119]. As a result, other reagents had to be tested and it was found that complete ring closure could be obtained by using aluminium chloride [149]. 

---