Advancing Light-Triggered Alkyd Paint Curing: (Cp)FeII(naphthalene)](PF6) Catalysts with Enhanced Photosensitivity and Increased Performance in Pigmented Alkyd Paints

The class of photoactive complexes [(Cp)Fe^II(arene)]⁺ (Cp = cyclopentadienyl, arene = C₆H₆, C₆H₅;Me) enable light-controlled alkyd paint curing, eliminating the need for anti-skinning agents. While [(Cp)Fe^II(benzene)](PF₆) (0.10 wt%) initiates curing under ambient light (116 Lux/1.7 mW/m²) within 6 h for transparent paints, it is ineffective in dark-colored formulations. Here, we demonstrate that the more photosensitive complexes [(Cp)Fe^II(L)](PF₆) (L = naphthalene, 5-methoxynaphthalene, 6-methoxy-naphthalene, 5,8-dimethoxynaphthalene) accelerate curing with lower loadings (0.05 wt%). Due to their higher extinction coefficients and red-shifted adsorption bands, these [(Cp)Fe^II(L)](PF₆) catalysts effectively cure dark-pigmented paints. Mössbauer spectroscopy reveals the formation of a high-spin Fe^II intermediate as the active species. TD-DFT calculations reveal a redshift in absorption, attributed to a transition from dz^[2]-d_xy*/d_yz* (arene/naphthalene) to L_π-d_xy*/d_yz* (methoxylated naphthalenes). Excitation of the complexes using wavelengths corresponding to these absorbance bands result in weakening of the Fe^II-η⁶C₆ bonds, facilitating light-induced dissociation. This advancement enhances latency originating from photoactivation while expanding applicability to pigmented systems.