The near-infrared(NIR)fluorescence imaging technologies have attracted considerable interest in recent years. They take great advantages for in vivo bioimaging because of their deep tissue penetration, minimum photo-damage to biological samples, and minimum interference from background auto-fluorescence by biomolecules in the living systems. It is still a crucial issue to develop NIR fluorescent dyes with high efficiency and low toxicity for fluorescence bioimaging technology. This article reviews the advances in the development of organic NIR fluorescent dyes including cyanines, BODIPYs, rhodamine analogues, squaraines, porphyrins; and the relationship between the structure and optical properties is highlighted to guide the design and preparation of NIR fluorescent dyes. In addition, We focus on discussing the main methodologies of functional modification to improve the biocompatibility and targeting capacities of organic NIR fluorescent dyes to realize multifunction and high performance. Finally, the future opportunities and challenges of NIR fluorescent dyes and NIR fluorescence imaging technologies are addressed to our understanding.

Contents
1 Introduction
2 Organic NIR fluorescent dyes
2.1 Cyanines
2.2 BODIPYs
2.3 Rhodamine analogues
2.4 Squaraines
2.5 Others
3 Functional modification and bioimaging applications
3.1 Functional modification
3.2 Fluorescence bioimaging
4 Conclusion and outlook