Conjugated polyelectrolytes with pH-dependent conformations and optical properties.
We report here the synthesis and characterization of two new conjugated polymers: poly{2,5-bis[3-(N,N-diethylammonium acetate)-1-oxapropyl]-1,4-phenylenevinylene} (P1') and poly{2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene} (P2). Both polymers exhibit unique pH-dependent optical properties in aqueous solution. These pH-dependent optical properties are attributed to the mutual electrostatic repulsions of positive charges pendent on the benzene rings. This electrostatic repulsion leads to an increased or decreased torsional angle in the conjugated backbone, thus affecting the effective conjugation length of these polymers. The UV-vis spectra of P1 in various pH solutions exhibit a near-isosbestic point, which indicates changes in the composition of the two distinct conformations (the charged and the neutral forms). The transition between the highly charged state and the neutral state was clearly observed in the UV-vis and photoluminescence studies on both P1 and P2. This transition is particularly sensitive in the pH range from 6.2 to 7.0, a range that would allow the detection of minor environmental changes. P2 has a quantum efficiency of 14% in water, which is considered to be relatively high among water-soluble PPVs.
Gao
Yuan
Y
Physical Chemistry and Spectroscopy, Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Wang
Chun-Chih
CC
Wang
Leeyih
L
Wang
Hsing-Lin
HL
D015374:Biosensing Techniques / Q000379:methods*; D004573:Electrolytes / Q000138:chemical synthesis*; D006863:Hydrogen-Ion Concentration; D008163:Luminescent Measurements; D008956:Models, Chemical; D008968:Molecular Conformation; D055095:Optics and Photonics; D000644:Quaternary Ammonium Compounds / Q000138:chemical synthesis*; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet; D055672:Static Electricity; D013499:Surface Properties; D014753:Vinyl Compounds / Q000138:chemical synthesis*; D014867:Water / Q000737:chemistry
D004573:Electrolytes; D000644:Quaternary Ammonium Compounds; D014753:Vinyl Compounds; C522652:poly(2,5-bis(3-(N,N,N-triethylammonium bromide)-1-oxapropyl)-1,4-phenylenevinylene); C522651:poly(2,5-bis(3-(N,N-diethylammonium acetate)-1-oxapropyl)-1,4-phenylenevinylene); D014867:Water