Red Light‐Gated Charge Transfer Enables Trace Oxygen Response in Dye‐Sensitized TiO 2 –Carbon Nanotube Hybrids

Abstract

ABSTRACT Light offers a powerful means of activating materials with spatial and temporal precision. However, translating excited‐state processes into chemically responsive electronic function in conductive solids remains challenging, particularly under low‐energy red illumination. Herein, we report red light‐gated charge transfer in dye‐sensitized single‐walled carbon nanotube–TiO 2 (SWCNT–TiO 2 ) hybrids that enables trace oxygen detection. Immobilization of red‐absorbing squaraine sensitizers on TiO 2 domains embedded within a conductive SWCNT network reversibly generates a photostationary charge‐transfer state under 628 nm excitation. Despite the low photon energy of red light, the hybrid architecture supports interfacial electron injection into TiO 2 and hole accumulation in the nanotube scaffold, while remaining electronically dormant in the dark. Interception of photogenerated electrons by O 2 perturbs this light‐induced state and converts excited‐state redox chemistry into a chemiresistive signal with ppb‐level sensitivity. This capability enables continuous monitoring of oxygen depletion in a sealed headspace during food spoilage. Electron paramagnetic resonance spectroscopy, energy‐level alignment analysis, and charge‐carrier inversion experiments show that O 2 triggers light‐activated changes in SWCNT carrier density. These findings demonstrate that low‐energy optical excitation can gate chemical response in dye‐sensitized SWCNT–TiO 2 hybrids, establishing a design strategy for temporally controlled sensing and photoresponsive electronic function.