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Abstract Cr²⁺and Cr³⁺ions are shown to mediate the formation, morphology, and organization of arachidic acid (AA) Langmuir‐Blodgett (LB) monolayers. This finding, based on cyclic voltammetry (CV), linear sweep voltammetry (LSV) and fluorescence recovery after photobleaching (FRAP) measurements, show that Langmuir monolayer formation depends on subphase pH and metal ion concentration. Following monolayer deposition on indium tin oxide (ITO), the LB monolayer organization can be modified reversibly through control of the Cr oxidation state, which has not been shown before by other monolayers formed with other divalent metal ions. The dynamics and the mobility of a chromophore (perylene) incorporated into the monolayer sense changes in Cr oxidation state‐dependent organization of the LB monolayer. Demonstrating reversible changes in monolayer organization provides an opportunity to control chemical and electron access to the interface support. 

Deep eutectic solvents (DESs) exhibit dynamic heterogeneity, where the intricate and dynamic hydrogen bonding within the DES mediates dynamic spatial variation in the DES local environment. The Type III DES composed of choline chloride and glycerol (ChCl:Gly) exhibits this effect prominently, and we report on the observed local organization and its dependence on system composition using the time-resolved reorientation dynamics of three illustrative chromophores of different polarities: perylene (neutral, nonpolar), oxazine 725 (cation, polar) and rose bengal (dianion, polar). Our findings demonstrate that the environments sensed by all three chromophores are markedly different than that predicted by the bulk viscosity of the DES, and that these local environments exhibit remarkably little change as the mole ratio of the DES constituents is varied. Taken collectively, these data provide clear evidence of short-range organization that bears very little resemblance to the longer-range structural organization that determines DES bulk properties.