Photophysical properties of N -acylated linear polyethylenimine and dehydroalanine main-chain polymers containing carbazole or pyrene groups in side chains

Abstract

A comparison of the UV absorption spectra of a carbazole-substituted N -acylated linear polyethylenimine (PEI) ( 5, 6 ) with its monomer ( 1, 2 ) and dimer ( 3, 4 ) model compounds shows the presence of local conformational order of the carbazole groups in 3, 5 , and 6 since these compounds exhibit hypochromism. The UV absorption spectra of carbazole-substituted N -acrylated dehydroalanine main-chain polymer (PDA) ( 12, 13 ) and monomer ( 10, 11 ) model compounds indicate that the extent of local conformational order of the carbazole groups is reduced in 12 and 13 compared to that in 5 and 6 . The UV absorption spectra of a pyrene-substituted PEI ( 9 ) and PDA ( 15 ) and those of their monomer model compounds ( 7, 14 ) indicate that the extent of local conformational order of the pyrene groups is greater in 9 than in 15 and furthermore the pyrene-substituted polymers ( 9, 15 ) show more local conformational order than analogous carbazole-substituted polymers ( 5, 12 ). The emission spectra of 5 and 12 show carbazole monomer emission, while those of 9 and 15 are dominated by pyrene excimer emission. The formation of excimer emission is more efficient in 9 than in 15 . Fluorescence lifetime measurements indicate interactions of excited carbazole groups in 5 and 13 but not in 12 . The quenching of carbazole fluorescence by dimethyl terephthalate is more efficient in 5 than that in 12 , indicating more efficient transfer of electronic energy in 5 . These measurements show that the PEI main-chain polymers are conducive to interactions of the pendant groups.