**1. Introduction**

Chemical toxicants such as pesticides and toxic industrial chemicals have the potential to contaminate material surfaces for extended periods of time. Often the natural attenuation of toxic substances through evaporation and degradation in ambient environments occurs slowly due to low vapor pressure, poor solubility, and resistance to hydrolysis [1]. Due to this persistence, surfaces on which toxic chemicals reside pose human exposure risks that require application of decontamination solutions to completely render a surface safe. However, decontamination solutions and procedures are cumbersome, expensive, and often damaging to the contaminated substrate [2].

Polymeric coatings are typically applied to many surfaces to improve aesthetics and provide corrosion or weathering protection; therefore, they provide an ideal substrate to incorporate coating additives to impart continuous self-decontaminating behavior at the surface and reduce subsequent contamination. A minimal loading concentration of additive is ideal so that the properties beneficial for the originally intended purpose of the polymer coating are maintained. Specifically, polyurethanes are of the broadest interest owing to their properties such as chemical resistance and durability [3].

Several recent research developments have investigated the incorporation of novel reactive additives into various urethane coating formulations in attempts to create coatings that self-decontaminate. Antimicrobial coatings have been successfully created by imparting additives such as nonionic biocides [4], quaternary ammonium biocides [5,6], surface concentrating biocides [7], functionalized coatings [8,9], and antimicrobial peptides [10]. While these are successful biocidal additives, less success has been achieved in chemical decontaminating coatings. One reason is that additives for chemical decontamination are limited to only a few modes of action such as absorption, hydrolysis, and oxidation. Of these, oxidation offers the greatest potential to completely detoxify a broad spectrum of chemical contaminants [11].

C60 fullerene molecules have also been observed to exhibit intriguing photochemical properties, including oxidative capabilities, which hold exciting potential for development of a self-decontaminating coating [12–15]. Upon exposure to visible light, C60 fullerene is first excited to its singlet state C60 (<sup>1</sup> C60), which then through intersystem crossing (ISC), forms the triplet state species of C60 (<sup>3</sup> C60). 3 C60 has a lifetime on the order of μs whereas 1 C60 exhibits a lifetime of several ns [12,16–18]. This triplet state species of fullerene has the ability to convert ground state triplet oxygen (<sup>3</sup> Ȉg <sup>í</sup>) into singlet oxygen (1 ǻg), a reactive oxygen species (ROS) [13,19]. The combination of a high quantum yield [13] and low rate of degradation of C60 fullerene by ROS [12] make this molecule extremely attractive as a photo-active coating additive.

Extensive studies have been conducted to analyze and characterize the photosensitivity of C60 in solution with varying degrees of success [16,19–24]. Various photosensitizers have been shown to exhibit antimicrobial activity when incorporated into polyurethane coating systems under specific conditions [25–27]. Similarly, antiviral systems have successfully been developed with the incorporation of fullerene as a solid-phase photosensitizer into biological fluid [28]. Recently, fullerenes modified with intercage constituents have displayed a remarkable ability to produce singlet oxygen as well as antimicrobial activity in polymeric adhesive films [29]. However, insertion of intercage constituents into fullerenes introduces additional cost and complexity that may be avoided by utilizing neat C60.

Incorporation of C60 fullerene into polymer matrices has been investigated for applications ranging from photovoltaics [30] to augmentation of polymer mechanical properties [31]. Covalent incorporation of C60 fullerene into polymers offers controlled distribution and reduced leaching, albeit often at the sacrifice of photoactivity [32,33]. In contrast, non-covalent incorporation of C60 fullerene offers simplified formulation and unaffected photophysical properties [34]. Furthermore, non-covalent incorporation of an amphiphilic fullerene species affords the potential for surface segregating photoactive additives. While synthetic modification of C60 into an amphiphilic species most likely will affect the photophysical properties of C60, increased concentration of a photoactive additive at the surface of a polymer due to its amphiphilic character should improve the decomposition of surface-residing chemical contaminants.

It can be assumed that when incorporated into a polymer matrix, the photoactivity of fullerene may be reduced due to a lack of molecular oxygen available to the fullerene molecule if it is encapsulated into the bulk of the polymeric coating. However, if one is able to overcome this limitation, significant activity should remain at the coating–air interface. It should then be expected that the production of ROS would result and subsequently react with any contamination that may be on the surface. Furthermore, an amphiphilic additive that automatically segregates to the polymer–air interface during a film cure would improve decontaminating efficiency. The hypothesis proposed herein is that the fullerene contained in the coating produces singlet oxygen from the atmosphere by the aforementioned mechanism and subsequently reacts with undesired contamination analytes that are present on the surface. If such analytes are hazardous, such as the case of pesticides or chemical warfare agents, then the action of the additive in the coating should reduce the hazard and subsequently present a surface free from contamination.
