Our work focuses on advancing the field of photocatalysis and photopolymerization, particularly through the development of novel catalytic systems for hydrosilation, a process with significant industrial applications and importance to local industry (Momentive Performance Materials or MPM, Schenectady NY). Research focuses on addressing the limitations of traditional thermal curing methods for silicone materials, which are time-consuming and energy intensive. We are investigating and optimizing UV-activated catalytic hydrosilation as an efficient, low-temperature, and eco-friendly alternative for crosslinking silicones to create robust materials used in various industries, from release coatings to medical devices. 

In the context of release coatings, presently many problems exist with thermal curing, in particular catalyst-inhibitor volatility leads to premature curing (short, dark bath life). High temperatures can curl and degrade coatings and substrates which therefore limits the range of release coatings that can be made (no thin-gauge polyolefin or PET liners). Lastly, thermal curing generates large amounts of volatile organics which present environmental and safety concerns.

New light-activated Pt catalyst systems are being designed, synthesized, and evaluated for their performance as UV cure catalysts for silicone paper release coatings. Our work is defined by several key questions and processes that we are trying to understand and improve: (A) Understanding and Optimizing Photocatalysis: A central goal is to improve efficiency and reduce the cost of UV-activated hydrosilation. While Pt complexes are known as highly active photoinitiators, e.g., MeCpPtMe3 (3M catalyst or Pt-99), high loading (i.e. cost) is needed to achieve production competitive with thermal curing processes. A key question we are addressing is how to reduce the amount of Pt required for photocuring. We’re exploring a two-pronged technical approach to this challenge: (1) External Photosensitizers (PSs) and (2) Novel Ligand Design. Briefly for (1), the use of PSs, are being investigated to understand the photophysics in relation to catalytic performance; excited state dimer (excimer) formation appears to hinder efficiency. Identifying and evaluating new PSs that have a lower propensity for excimer formation, enable higher PS concentrations and reduce the need for Pt catalyst. (B) Investigating Reaction Kinetics and Mechanisms: To effectively develop these new catalysts, we seek a deeper understanding of the polymerization process itself. We developed a novel Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) "well" strategy to monitor the kinetics of these reactions in real-time. This innovative method allows for the analysis of reactions in ultra-thin films, which is highly relevant to industrial applications like release coatings. The ATR-FTIR strategy, which tracks the disappearance of the Si-H bending absorption band, provides an efficient and high-fidelity way to benchmark the performance of new catalysts and photosensitizers against state-of-the-art systems. This fundamental research extends beyond the specific application of silicone curing and contributes to a broader understanding of photoactivated systems including other catalytic reactions leveraging PSs, as well as applications such as 3D printing. Novel PSs and light-harvesting PS-ligand scaffolds have the potential to optimize other photochemically supported reactions catalyzed by organometallics with different metals.

Dr. Bonitatibus is also interested in another area of homogeneous catalysis, specifically artificial water oxidation, for continued development of clean and sustainable energy technologies. An efficient synthetic catalyst must replicate complicated functional requirements of the natural process performed at the oxygen-evolving complex (OEC) of the multi-subunit membrane protein Photosystem II (PSII). PSII's ability to convert two water molecules into dioxygen, requires four-electron, four-proton transfer, and establishes a blueprint and formidable benchmark for synthetic chemistry. Water oxidation catalysis presents a substantial energy demand (113.5 kcal/mol), equivalent to a high redox potential of 1.23 V vs. normal hydrogen electrode (NHE). Consequently, any practical artificial system must overcome this thermodynamic hurdle by incorporating a strong oxidant to drive the reaction. Profound synthetic chemistry challenges also involve identifying an effective pathway for the egress of protons during the reaction and understanding a mechanism for the binding of the substrate water molecules.

The focus of our research is to optimize, gain scientific insights, and understand new patterns of reactivity in novel catalytic artificial water oxidation systems. We have designed a number of ruthenium catalysts based off a benchmark found in the literature, namely [Ru(pda)(pic)3] (pda = 2,6-pyridine diacetate; pic = 4-picoline). New tridentate ligands have been prepared and assessed for O2-evloution performance. We have characterized artificial water oxidation catalysts using NMR, UV-Vis, and single crystal x-ray diffraction. The x-ray crystal structures display unusually large O-Ru-O angles of ~178°, which suggests that the access of a water molecule to the metal center can be facilitated via a wide-open bite angle. A systematic comparison of the structural parameters of [Ru(pda)(pic)3] derivatives, along with O2-evloution studies, provides preliminary insight and data on the effects of ligand geometry, ancillary ligands, and increased metal ion accessibility on water oxidation catalysis.

Success in designing artificial catalysts enables the direct conversion of sunlight and water into a clean fuel—hydrogen—by providing the electrons and protons necessary for reduction reactions in a complete artificial photosynthetic system. We’re working to unlock a scalable, cost-effective method for solar fuel generation, promising a transformative shift in global energy infrastructure.