Triad-sequestered Polymer Encapsulated Reverse Micelle Composite Materials as Optically Addressable Magnetic Field Sensors
Published on: 2017-08-09
In past reports, Donor-Chromophore-Acceptor (D-C2+-A2+) triad species have served as molecular level sensors which can optically detect magnetic fields. Upon photoexcitation of the chromophore (C2+), a series of electron transfer steps occur which generate a biradical cation Charge Separated State (CSS, D+•-C2+-A+•). A fluid solution environment is required in order for the CSS to form. The CSS can be detected and monitored by time-resolved transient absorption spectroscopy. The lifetime of the photoexcited CSS (CSS) exhibits a corresponding magnetic field effect (MFE), wherein it increases and becomes strongly bi-exponential with increasing field strength. In this work, the ?CSS is observed upon incorporating the D-C2+-A2+ triads in polymer encapsulated reverse micelle composite (PERMC) materials. The D-C2+-A2+ triads are sequestered inside the micellar fluid domains within the macroscopic solid. Such PERMCs are prepared by the radical polymerization of the styrene:divinylbenzene nonpolar phase of composite precursor reverse micellar solutions (CPRMSs). The radii of AOT micelles that sequester triads in the CPRMSs are on the order of 4.0 nm as determined by elevated temperature dynamic light scattering (DLS) particle sizing. Tapping mode-atomic force microscopy (TM-AFM) imaging on cryo-cut PERMCs shows the presence of spherical-shaped micellar imprints which confirms that the micelles are still intact even after the nonpolar phase of the CPRMS is polymerized. Under no applied field, the ?CSS of triad sequestered-PERMCs is increased by a factor of ten relative to that of bulk solution conditions. This is plausibly due to the expected lower frequency of collisional encounters between the oxidized donor (D+•) and reduced acceptor (A+•) constituting the ?CSS within the reverse micelle. A fraction of the ?CSS population corresponding to the triad-sequestered PERMCs exhibits a MFE wherein the slow component of the ?CSS increases by an order of magnitude at fields of 500 mT with respect to those of 0 mT. The relative difference in magnitude of this response is analogous to that observed in bulk solution.
Polymer encapsulated reverse micelle; Composite material; Solidified reverse micellar solutions; Optical detection of magnetic fields; Organic magnetic field sensor