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

[(Cp)Fe^II(naphthalene)](PF₆) catalysts are reported with improved curing efficiency of alkyd paints compared to [(Cp)Fe^II(arene)](PF₆), particularly in dark-pigmented formulations. Their improved photosensitivity enables faster drying at lower concentrations, presenting a promising alternative to conventional industrial driers under regulatory pressure. The photoactivatable iron driers are effective in challenging pigmented systems—such as blue and black paints—where light penetration is typically limited.

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.