Brent R. Crenshaw

Self-assembly of chromogenic dyes—a new mechanism for humidity sensors

The design, fabrication and characterization of a novel type of humidity sensing polymer are presented. The new material was prepared by incorporating a chromogenic, cyano-substituted oligo(p-phenylene vinylene) dye into a polyamide by quenching the blend from the melt. Exposure of these kinetically trapped, molecularly mixed blends to water plasticizes the amorphous phase and leads to aggregation of the dye molecules, concomitant with pronounced and irreversible changes of the materials absorption and fluorescence color.

Absorption and fluorescence of single molecules

Simultaneous detection of single molecules by absorption and fluorescence is demonstrated using confocal microscopy at cryogenic temperature. Dynamical processes such as blinking and spectral jumping of single emitters are observed in both detection channels. The relative magnitude of fluorescence and absorption varies between molecules. In particular, we observe molecules that do not emit detectable Stokes-shifted fluorescence but show a strong absorption signal. The fact that coherent resonant scattering underlies the absorption process is demonstrated by a correlation between small linewidth and large absorption amplitude.