Infrared Irradiation‐Lattice Vibration Coupling‐Initiated N→Π* Electronic Transition in Carbon Nitride Nanosheets for Increased Photocatalysis

Abstract Enabling n→π* electronic transition in graphitic carbon nitride (g‐CN) can significantly enhance its photocatalytic performance by extending visible light absorption. However, achieving this transition remains a grand challenge due to the selection rule that restricts it to planar tri‐s‐triazine units of g‐CN. Here, an effective strategy to induce the n→π* transition in g‐CN nanosheets by coupling infrared irradiation with lattice vibrations is presented. Theoretical simulations reveal two prominent vibration modes perpendicular to tri‐s‐triazine units at 219 and 737 cm −1 can promote the corrugation of tri‐s‐triazine units and facilitate the n→π* electronic transition when coupled with infrared irradiation. Additionally, these vibrational modes enable the efficient exfoliation of bulk g‐CN into 2D nanosheets by overcoming the interplanar binding energy. Through femtosecond transient absorption spectra (fs‐TAS), the n→π* transition prolongs the lifetime of photocatalytically active shallow electron trapping states and charge separation states in g‐CN is demonstrated. Accordingly, the activated n→π* electronic transition and prolonged lifetime of photocatalytically active charges lead to an H 2 generation rate of 2485 µmol h −1 g cat −1 , ≈40 times higher than that of the bulk counterpart. This work highlights the effectiveness of coupling lattice vibrations with infrared irradiation to drive the n→π* transition for enhanced visible‐light photocatalysis.