Abstract
Poly[oxy-2,2-(1-pyrenylmethyl)(4-N,N-dimethylaminobenzyl)propyleneoxysebacoyl] (III) (DP (degree of polymerization) ≲38) and its reference polymer, poly[oxy-2,2-(1-pyrenylmethyl)(benzyl)propyleneoxysebacoyl] (V) were prepared by polycondensation of the corresponding 1,3-propanediol with thiophenyl sebacate. The effects of solvents and the concentration on the inter- and intramolecular exciplex formation by III were examined in three solvents and compared with the monomer model compounds, 1,3-Diacetoxy-2-(4-N,N-dimethylaminobenzyl)-2-(1-pyrenylmethyl) propane (IV) and 1,3-diacetoxy-2-benzyl-2-(1-pyrenylmethyl)propane (VI). The ratio of the exciplex emission intensity (Fe) to the monomer emission intensity of pyrenyl groups (Fm) increased with concentration in a region below 10−5 M, suggesting the interpolymer exciplex formation of III, whereas the exciplex by IV was concentration independent. The degree of interpolymer exciplex formation was higher in 1,2-dichloroethane (good solvent) than in mesitylene or o-xylene (poor solvent). The optimum DP for interpolymer exciplex formation was observed. On the other hand, the intrapolymer exciplex intensity ((Fe/Fm)c→0) of III increased monotonously with DP, suggesting non-neighboring group participation in the intrapolymer exciplex formation, since the excimer formation by V is entirely an intrapolymer event and VI emits fluorescence from the locally excited state of pyrene alone. The driving force for the intermolecular association in the polymeric systems was attributed to the weak ground state interactions between the electron donor (N,N-dimethylanilino group, DMA) and the electron acceptor (pyrenyl group, Py). The quantum yield of the exciplex emission by III in 1,2-dichloroethane was as high as 0.4. The factors determining the interpolymer association are also qualitatively discussed.
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