Excimer emission in protonated pyridine systems—4. Effect of molecular weight on dimer-like excimer formation of poly-2-vinylpyridine in rigid glass solution in the presence of trifluoroacetic acid at 77 K

✍ Scribed by Yoshio Utena; Hirofumi Yajima; Tadahiro Ishii; Takahashi Handa

• Publisher: Elsevier Science
• Year: 1987
• Tongue: English
• Weight: 413 KB
• Volume: 23
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(87)90012-7

✦ Synopsis

The fluorescenc~ectra of samples of poly-2-vinylpyridine (P2VP) with various average degrees of polymerization (DP) have been measured in tetrahydrofuran-methanol-methyltetrahydrofuran (4:3: I by volume) rigid glass solutions in the presence of saturated trifluoroacetic acid (TFA) at 77 K. All protonated P2VPs predominantly exhibited a dimer-like excimer fluorescence around 325 nm. The rate constants of the dimer-like excimer formation, radiative and non-radiative processes were determined from the ratio of the dimer-like excimer to the monomer band intensities and lifetimes of the monomer and dimer-like excimer fluorescence. The rate constant of the dimer-like excimer formation exhibits a DP dependence below 95 but is constant at higher values. On the other hand, the rate constants of the radiative and non-radiative processes are almost independent of DP. These results indicate that the dimer-like excimer can be formed more easily in protonated P2VP with DP ~> 95 than when DP ~< 57. The singlet excitation energy for protonated P2VP with D--P I> 95 migrates along the polymer chain and is effectively trapped at the dimer-like excimer forming sites, satisfying the requirements for the dimer-like excimer formation prior to the initial excitation step.