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

Abstract

AbstractA 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.