From Molecular Design and Materials Construction to Organic Nanophotonic Devices Chuang Zhang, Yongli Yan, Yong Sheng Zhao,* and Jiannian Yao* Beijing National Laboratory for Molecular Sciences (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China CONSPECTUS: Nanophotonics has recently received broad research interest, since it may provide an alternative opportunity to overcome the fundamental limitations in electronic circuits. Diverse optical materials down to the wavelength scale are required to develop nanophotonic devices, including functional components for light emission, transmission, and detection. During the past decade, the chemists have made their own contributions to this interdisciplinary field, especially from the controlled fabrication of nanophotonic molecules and materials. In this context, organic micro- or nanocrystals have been developed as a very promising kind of building block in the construction of novel units for integrated nanophotonics, mainly due to the great versatility in organic molecular structures and their flexibility for the subsequent processing. Following the pioneering works on organic nanolasers and optical waveguides, the organic nanophotonic materials and devices have attracted increasing interest and developed rapidly during the past few years. In this Account, we review our research on the photonic performance of molecular micro- or nanostructures and the latest breakthroughs toward organic nanophotonic devices. Overall, the versatile features of organic materials are highlighted, because they brings tunable optical properties based on molecular design, size-dependent light confinement in low-dimensional structures, and various device geometries for nanophotonic integration. The molecular diversity enables abundant optical transitions in conjugated π-electron systems, and thus brings specific photonic functions into molecular aggregates. The morphology of these micro- or nanostructures can be further controlled based on the weak intermolecular interactions during molecular assembly process, making the aggregates show photon confinement or light guiding properties as nanophotonic materials. By adoption of some active processes in the composite of two or more materials, such as energy transfer, charge separation, and exciton-plasmon coupling, a series of novel nanophotonic devices could be achieved for light signal manipulation. First, we provide an overview of the research evolution of organic nanophotonics, which arises from attempts to explore the photonic potentials of low-dimensional structures assembled from organic molecules. Then, recent advances in this field are described from the viewpoints of molecules, materials, and devices. Many kinds of optofunctional molecules are designed and synthesized according to the demands in high luminescence yield, nonlinear optical response, and other optical properties. Due to the weak interactions between these molecules, numerous micro- or nanostructures could be prepared via self-assembly or vapor-deposition, bringing the capabilities of light transport and confinement at the wavelength scale. The above advantages provide great possibilities in the fabrication of organic nanophotonic devices, by rationally combining these functional components to manipulate light signals. Finally, we present our views on the current challenges as well as the future development of organic nanophotonic materials and devices. This Account gives a comprehensive understanding of organic nanophotonics, including the design and fabrication of organic micro- or nanocrystals with specific photonic properties and their promising applications in functional nanophotonic components and integrated circuits. 1. INTRODUCTION The discovery of conductive polymers has encouraged the rapid growth in the research field of organic electronics and optoelectronics, including organic light-emitting diodes, 1 field- effect transistors, 2 and solar cells 3 from both molecular and polymeric materials. Their properties are highly tunable by changing the energy levels of ground and excited states in π- electron systems. The excited states in organic materials with low dielectric constants are Frenkel excitons, which have high binding energy and are localized within one or two molecules. This excitonic feature makes organics fundamentally different from their inorganic counterparts in both electronic and photonic aspects. Recently, photonics at the (sub)wavelength scale, namely, nanophotonics, has been developing rapidly during the rise of Received: May 24, 2014 Article pubs.acs.org/accounts © XXXX American Chemical Society A dx.doi.org/10.1021/ar500192v | Acc. Chem. Res. XXXX, XXX, XXX-XXX