Intramolecular Heterojunctions for Highly Sensitive Room-Temperature NO2 Sensing

Heterojunction materials achieve efficient charge transfer and carrier separation through built-in- electric fields at the interfaces, thereby substantially enhancing the sensitivity and selectivity of gas sensors. However, traditional particle-contact heterojunctions suffer from discontinuous interfaces and limited contact areas, resulting in low charge transport efficiency and restricted gas-sensing performance. Herein, we construct two intramolecular D-A heterostructured frameworks (CuBr-CuMND and CuI-CuMND) by directionally linking CuX chains (donor) and CuMND (acceptor) via Cu-S coordination bonds. The atomically continuous heterointerface achieves spatial highest occupied molecular orbital/lowest unoccupied molecular orbital separation and a strong internal built-in electric field (IEF). CuI-CuMND exhibits a record-low detection limit of 0.05 ppb and a response of 1315% toward 10 ppm of NO2, along with excellent long-term stability at room temperature without light assistance. Theoretical calculations reveal that, compared with CuBr-CuMND, CuI-CuMND exhibits a larger Fermi level disparity, which generates a stronger IEF that significantly enhances interfacial charge separation and transport, ultimately leading to a higher response value and faster response/recovery time toward NO2. This study establishes a molecular-scale intramolecular heterojunction engineering strategy for room-temperature trace-gas sensing.