Photoluminescence from Amino-Containing Polymer in the Presence of CO2: Carbamato Anion Formed as a Fluorophore

Abstract

Organic photoluminescent materials are important to many applications especially for diagnosis and detection, and most of organic photoluminescent materials contain fluorophores with extended conjugated structures. Recently some of amino-containing polymers without fluorophores with extended conjugated structure are observed to be photoluminescent, and one possible cause of the photoluminescence is oxidation of the amines. Here we show that photoluminescence can be produced by exposing a typical amino-containing polymer, polyethylenimine, to carbon dioxide. We demonstrate that carbamato anion formed via the reaction between the amine and carbon dioxide is a fluorophore; and the loosely-bound protonated water molecule can increase UV absorption but reduce the photoluminescence emission. Also carbamato anion shows solvent- and excitation wavelength-dependent emission of photoluminescence. The photoluminescence profile of carbamoto anion was discussed. These results will facilitate the understanding of photoluminescence observed from amino-containing materials and the design of new fluorophores.

Photoluminescence from Chitosan for Bio-Imaging

“…A maximum emission is observed from the excitation at 336 nm, which is close to the excitation wavelength leading to a strong photoluminescence of carbamato anion. [50] Fig. 1a, curve B, shows the excitation spectrum of chitosan at 404 nm emission with a peak at ,340 nm that agrees with the observation from emission.…”

“…In our previous study, [50] it was reflected that the carbamato anion via the reaction of CO 2 and the amines of polymers contributed to fluorescence observed from amino-containing polymers. Therefore, the aqueous solution of chitosan was treated with CO 2 for 3 h and aged for two days.…”

“…After the treatment of chitosan solution via CO 2 bubbling for 3 h followed by two days of aging, the intensity of the peak at ,171 ppm increases with reference to the peak at ,174 ppm, and two new peaks at ,125 ppm and 160 ppm appear with the peak at 125 ppm being attributed to the dissolved CO 2 . [50] The reaction between the amines of chitosan and CO 2 can form a carbamato anion together with the complex of the carbamato anion and loosely bound protonated water; and the peak attributed to the complex of the carbamato anion and loosely bound protonated water in the 13 C NMR spectrum is broad and is usually less obvious. [50] The content of amine in chiotsan is much lower than that in PEI.…”

“…[50] The reaction between the amines of chitosan and CO 2 can form a carbamato anion together with the complex of the carbamato anion and loosely bound protonated water; and the peak attributed to the complex of the carbamato anion and loosely bound protonated water in the 13 C NMR spectrum is broad and is usually less obvious. [50] The content of amine in chiotsan is much lower than that in PEI. Hence, it is reasonable that the peaks attributed to the complex of the carbamato anion and loosely bound protonated water should be difficult to be observed, and the formation of HCO 3 À should be possible.…”

“…Here, as a continuing effort, we indicate that carbamato anion from the reaction between the amines of chitosan and CO 2 is the fluorophore of the photoluminescence observed similar to the results reported in our previous work. [50] The fluorescence profile and the potential bio-imaging application of chitosan are investigated.…”