Photoelectronic devices of organic semiconductors are of great interest recently because organic semiconductors have many fundamental advantages over their inorganic counterparts. For example, their low cost is ideal for large-area applications and their mechanical flexibility makes them naturally compatible with plastic substrates for lightweight and foldable products. The most attractive prospect, however, is their incorporation of functionality by molecular design. Phototransistors have much higher sensitivity and lower noise than photodiodes and use these advantages to combine light detection and signal magnification properties that realize greater functionality in a single device. This is an important aspect of optoelectronic integration. Since the first concept of a phototransistor was proposed by William Shockley in 1951, inorganic phototransistors have been quickly developed and used in a variety of applications. However, few reports in the literature have addressed phototransistors made of organic semiconductors, especially organic single crystals. Organic single crystals have important merits in the study of intrinsic properties and for the fabrication of high-quality devices and circuits. Here, we used an organic semiconductor, copper hexadecafluorophthalocyanine (F16CuPc), as the candidate to introduce single-crystalline photoswitches and phototransistors of organic semiconductors. F16CuPc was selected not only because of its remarkable air-stable, n-type properties but also because of its high thermal and chemical stability. Bao et al. first paid attention to this compound in 1998. Recently, Dosch and Barrena and co-workers carefully investigated its structure and self-organization properties on a solid surface. In addition, we synthesized single-crystalline sub-micro/nanoribbons of the compound by a physical vapor transport technique and studied its field-effect performance; we demonstrated its high field-effect mobility and on/ off ratio in transistors based on an individual ribbon. However, the optical properties of this air-stable, n-type material, are still unclear. In this Communication, we study these properties by using devices made of single-crystalline sub-micro/ nanometer ribbons of F16CuPc. Single-crystalline sub-micro/nanometer ribbons of F16CuPc were synthesized and transferred or in-situ patterned onto Si/ SiO2 (300 nm) substrates, as previously described. [6,7] Devices based on an individual sub-micro/nanometer ribbon were fabricated by the “multiple-times gold-wire mask moving” technique based on the asymmetrical drain/source electrode (Au/Ag) configuration shown in Figure 1—because such a configuration was beneficial for injection, transport, and collection. The ribbon thickness in the devices was measured carefully by atomic force microscopy. C O M M U N IC A TI O N