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

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 DPn = 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 macro...