Emission of Macrocyclic and Linear Poly(2-vinylnaphthalene): Observation of Two Excimer Populations in Macrocycles

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• 作者：Gennadi G. Nossarev ; Jerainne Johnson ; Stephen E. Bradforth ; Thieo E. Hogen-Esch
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：May 23, 2013
• 年：2013
• 卷：117
• 期：20
• 页码：10244-10256
• 全文大小：530K
• 年卷期：v.117,no.20(May 23, 2013)
• ISSN：1932-7455

文摘

Macrocyclic vinyl aromatic polymers, particularly at small degrees of polymerization (DP), exhibit properties that diverge from linear polymers. A series of matched DP linear and macrocyclic polymers are prepared for one such model system, poly(2-vinylnaphthalene), and their spectroscopic properties (electronic absorption, steady-state and picosecond time-resolved emission) are compared. It is found that small macrocycles exhibit pronounced differences in their excited state dynamics compared to their linear analogues: as the DP decreases, the ratio of monomer to excimer emission is strongly enhanced as is the overall emission quantum yield, and the excimer emission is increasingly blue-shifted. Moreover, time-resolved data shows the formation of excimers in the DP_n = 12 macrocycle is at least an order of magnitude faster than that for the matching linear polymer but there are at least two excimer populations for the cycles whereas the linear polymer shows only one. It is suggested that the strained macrocycle conformation tends to splay the pendent chromophores pseudoequatorial, leading to a greater number of preconfigured excimer sites, but that these are shallower traps with both faster formation and dissociation time scales. Overall, this leads to longer overall exciton lifetimes, explaining the greater overall monomer emission. By reducing the impact of trapping and potentially keeping the excitons mobile, these results suggest that macrocyclic architectures have potential advantages for light harvesting.