EXCIMER FORMATION IN STERICALLY HINDERED POLY(9-VINYLCARBAZOLE) AND ITS DIMER MODEL COMPOUNDS

The fluorescence properties, especially the excimer formation process, in poly(3,6-di-tert-butyl-9-vinylcarbazole) (PBVCz) and its dimeric model compounds, meso- and rac-2,4-bis(3,6-di-terf-butyl-9-carbazolyl)pentanes (meso- and rac-BCzPe), have been investigated. The molecular structure of poly(9-vinylcarbazole) (PVCz) was modified by bulky tert-butyl substituents on the carbazole ring. PBVCz and rac-BCzPe show broad excimer emission at wavelengths slightly shifted from the excited monomer band. Since sandwich excimer formation is hindered by the bulky groups, this polymer exhibits a unique excimer formed by the syndiotactic diads. To investigate the excimer formation process, :H NMR analysis and calculation of conformational energies were carried out for rac-BCzPe. The result indicates that a partially overlapping arrangement of the carbazole rings is attained by parallel rotation of two aromatic planes from the stable TT conformation, but the extent of overlapping is quite small. These data show that the carbazole excimer has fairly continuous energy levels, depending on the degree of overlapping of the aromatic planes. © 1990, American Chemical Society. All rights reserved.