Molecular shuttle, as a kind of molecular machines, is one of the research intriguing interest in supramolecular chemistry. Molecular shuttles are mostly based on the host-guest recognition. They have potential applications in many areas such as nano-structured functional materials, molecular switches, molecular logic gates, memory devices and so on. In this paper, the progress in molecular shuttles is systematically reviewed, including the conception, mechanisms and potential applications, focusing on the molecular shuttles driven by external-stimuli. According to the difference of external-stimuli, molecular shuttles can be classified into light-driven, pH-driven, redox-driven and multi-mode-driven molecular shuttles. The structure characteristics, motion law and progress of molecular shuttles driven by different external-stimuli, are elaborated. The problem of responsive molecular shuttles researches is analyzed, and the future development of responsive molecular shuttles is prospected.

Contents
1 Introduction
2 Mechanism of molecular shuttles
3 Molecular shuttles driven by different external-stimuli
3.1 Light-driven molecular shuttles
3.2 pH-driven molecular shuttles
3.3 Redox-driven molecular shuttles
3.4 Multi-mode-driven molecular shuttles
4 Potential applications of molecular shuttles
4.1 Potential applications in molecular logic gates
4.2 Potential applications in molecular switches
4.3 Potential applications in energy transfer
5 Prospects