Photosensitizing Metasurface Empowered by Enhanced Magnetic Field of Toroidal Dipole Resonance

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2023-10, Vol.19 (42), p.e2302519-e2302519
• Main Authors: Hasebe, Hiroaki, Sugimoto, Hiroshi, Katsurayama, Yoshino, Furuyama, Taniyuki, Fujii, Minoru
• Format: Article
• Language: English
• Subjects: Arrays; Atomic energy levels; Electrons; Magnetic dipoles; Magnetic fields; Magnetic flux; Metasurfaces; Nanotechnology; Photochemical reactions; Resonance; Ruthenium; Silicon; Singlet oxygen
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202302519

Photochemical reaction exploiting an excited triplet state (T ) of a molecule requires two steps for the excitation, i.e., electronic transition from the ground (S ) to singlet excited (S ) states and intersystem crossing to the T  state. A dielectric metasurface coupled with photosensitizer that enables energy efficient photochemical reaction via the enhanced S →T magnetic dipole transition is developed. In the direct S →T transition, the photon energy of several hundreds of meV is saved compared to the conventional S → S →T transition. To maximize the magnetic field intensity on the surface, a silicon (Si) nanodisk array metasurface with toroidal dipole resonances is designed. The surface of the metasurface is functionalized with ruthenium (Ru(II)) complexes that work as a photosensitizer for singlet oxygen generation. In the coupled system, the rate of the direct S →T transition of Ru(II) complexes is 41-fold enhanced at the toroidal dipole resonance of a Si nanodisk array. The enhancement of a singlet oxygen generation rate is observed when the toroidal dipole resonance of a Si nanodisk array is matched with the direct S →T transition wavelength of Ru(II) complexes.