Surface Absorption Polarization Sensors (SAPS), Final Technical Report, Laser Probing of Immobilized SAPS Actuators Component

Joseph I. Cline

关键词: ABSORPTION;    ABSORPTION SPECTROSCOPY;    ACTUATORS;    DETECTION;    DOSEMETERS;    EFFICIENCY;    ELECTRON DENSITY;    LASERS;    MONITORING;    POLARIZATION;   

DOI  :  10.2172/977056
RP-ID  :  DOE/NA/26973-1
PID  :  OSTI ID: 977056
Others  :  TRN: US201010%%438

美国|英语

来源: SciTech Connect

【 摘 要 】

A novel hypothesized detection scheme for the detection of chemical agents was proposed: SAPS ``Surface-Adsorbed Polarization Sensors''. In this technique a thin layer of molecular rotors is adsorbed to a surface. The rotors can be energized by light absorption, but are otherwise locked in position or alternatively rotate slowly. Using polarized light, the adsorbed rotors are turned as an ensemble. Chemical agent (analyte) binding that alters the rotary efficiency would be detected by sensitive polarized absorption techniques. The mechanism of the SAPS detection can be mechanical, chemical, or photochemical: only a change in rotary efficiency is required. To achieve the goal of SAPS detection, new spectroscopic technique, polarized Normal Incidence Cavity Ringdown Spectroscopy (polarized NICRDS), was developed. The technique employs very sensitive and general Cavity Ringdown absorption spectroscopy along with the ability to perform polarized absorption measurements. Polarized absorption offers the ability to measure the angular position of molecular chromophores. In the new experiments a thin layer of SAPS sensors (roughly corresponding to a monolayer coverage on a surface) immobilized in PMMA. The PMMA layer is less than 100~nm thick and is spin-coated onto a flat fused-silica substrate. The new technique was applied to study the photoisomerization-driven rotary motion of a family of SAPS actuators based on a family of substituted dibenzofulvene rotors based upon 9-(2,2,2- triphenylethylidene)fluorene. By varying the substitution to include moieties such as nitro, amino, and cyano the absorption spectrum and the quantum efficiency of photoisomerization can be varied. This SAPS effect was readily detected by polarized NICRDS. The amino substituted SAPS actuator binds H+ to form an ammonium species which was shown to have a much larger quantum efficiency for photoisomerization. A thin layer of immobilized amino actuators were then shown by polarized NICRDS to have a propensity for the angular control of rotary motion to be strongly influenced by the presence of the H+ analyte: the SAPS actuators can readily detect the presence of a H+ analyte at 1 equivalent concentration. Because the total number of SAPS actuators in the probe volume of the film is small, the amount of analyte detectable can be very low. A variety of SAPS actuator structures based on dibenzofulvene rotors are possible that could bind other analytes. It appears that analyte binding that alters the electron density in the dibenzofulvene ring is sufficient to create a detectable change in the rotary efficiency. If the analyte is strongly bound to the rotor, the SAPS actuator behaves in a dosimeter mode. Weak, reversible binding would allow for monitoring of varying concentrations.