Ratiometric fluorescent chemosensor based on the block copolymer of poly(N-isopropylacrylamide)-b-poly(N-vinylcarbazole) containing rhodamine 6G and 1,8-naphthalimide moieties

We have synthesized an amphiphilic block copolymer poly(N-isopropylacrylamide)-b-poly(N-vinylcarbazole) containing 1,8-naphthalimide and spirolactam rhodamine 6G moieties via reversible addition-fragmentation chain transfer radical polymerization. The photoluminescence (PL) spectrum of the poly(N-vinylcarbazole) block well matches the absorption spectrum of the 1,8-naphthalimide moiety and the enhanced emission with a peak at 510 nm from the 1,8-naphthalimide moiety is found in the block copolymer film for excitation at 330 nm. The 560-nm emission from the rhodamine 6G moiety is observed as the block copolymer film sprayed by Britton-Robinson (B-R) buffers or Fe3+ aqueous solutions for excitation at 330 and 400 nm. The PL intensity at 560 nm is markedly increased for the pH value of the B-R buffer lower than 3.0 or the Fe3+ concentration in water higher than 5 x 10(-4) M. The 560-nm PL intensity is much higher for the block copolymer film photoexcited at 330 nm than that photoexcited at 400 nm due to double-step resonance energy transfer. The PL intensity ratio of 560 to 510 nm (I-560/I-510) is dependent on the resonance energy transfer from 1,8-naphthalimide to rhodamine 6G, which is sensitive to the concentrations of H+ and Fe3+ ions in water.

Automated summary

An amphiphilic block copolymer containing 1,8-naphthalimide and spirolactam rhodamine 6G moieties was synthesized via reversible addition-fragmentation chain transfer radical polymerization. The photoluminescence properties were found to be influenced by the energy transfer between the two moieties.