EXCIPLEX BY PYRENE‐N,N‐DIMETHYLANILINE PAIR BONDED TO POLYMERS IN AQUEOUS MEDIA

Abstract— Emission spectra of poly[2‐(4‐N,N‐dimethylaminobenzyl)‐2‐(l‐pyrenylmethyl)ethyl methacryl‐ate] (I) and the copolymers with vinyl‐benzyltriethylammonium chloride (II) or sodium p‐styrenesulfo‐nate (III) were studied in extremely polar media such as dimethylformamide (DMF) and water. While the emission by the monomer model compound (2‐(4‐N,N‐dimethylaminobenzyl)‐2‐(l‐pyrenylmethyl)‐ethyl isobutyrate(IV)) scarcely showed exciplex emission in DMF or aqueous DMF, exciplex by I was clearly observed in the same solvents. Furthermore, the ratio of exciplex intensity (F_e) to monomer intensity (F_m) increased by the addition of water to the DMF solution up to 60 vol%. This abnormal spectral behavior of increasing exciplex emission intensity with solvent polarity was interpreted as being due to shrinking of polymer chain. The peaking wavelength of exciplex shifted towards blue in the presence of water, indicating that the solvation of exciplex was hindered and/or the hydrophobic domain was organized. This interpretation was supported by the exciplex emission of II in water. No exciplex was detected from III in water. This is the first example of exciplex emission in homogeneous aqueous solution. In comparison with the published results of micellar systems, the exciplex emission of the polycation indicated that the hydrophobic domain in the polycation was so strong that the solvation of exciplex was considerably hindered. The peaking wavelength of exciplex at 480 nm also lends support to the presence of a non‐polar microenvironment.