Surface-induced chromism and enhanced fluorescence of the soluble polydiacetylene, poly(4-butoxycarbonylmethylurethane), at a solid/solution interface: An evanescent-wave induced fluorescence study

Using evanescent-wave induced fluorescence (EWIF) spectroscopy, from the soluble polydiacetylene, poly(4-butoxycarbonylmethylurethane) (poly-4BCMU), has been studied in solutions of 2-methyltetrahydrofuran and a chloroform-hexane mixture, in contact with a fused silica surface. The system requires up to 4 h to attain equilibrium, at which point the EWIF emission intensity is observed to be 20 and 60 times greater than expected for the yellow (Y) and red (R) form solutions, respectively. This has been interpreted as adsorption of the polymer onto the glass surface which leads to a reduction in the efficiency of the non-radiative, internal conversion deactivation mechanism of the excited state, with consequent increase in the fluorescence quantum yield. In the case of a Y-form poly-4BCMU solution, at times less than 10 min, following the introduction of the solution to the surface, the EWIF spectrum resembles the R-form of the polymer. This spectrum grows in with a rate constant of ca. 0.7 min^-1 and is attributed to a transient effect induced by a hydrophilic, non-solvent-conditioned glass surface, causing the equilibrium between the Y- and R-forms of the polymer to be shifted in favour of the R-form. The spectrum then disappears with a rate constant of 0.025 min^-1 as equilibrium is reattained and the glass surface becomes conditioned, or 'solvated'. The kinetic data support the theory of an intramolecular fringed micellar structure for the R-from of poly-4BCMU in solution.