full papers www.MaterialsViews.com 3302 www.small-journal.com © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Remarkable Vapochromic Behavior of Pure Organic Octahedron Embedded in Porous Frameworks Linyi Bai, Avijit Jana, Huijun Phoebe Tham, Kim Truc Nguyen, Parijat Borah, and Yanli Zhao* different monitoring strategies were also explored, such as optical or electronic signal changes, mass spectrometry detec- tion, and ion mobility trapping technique. [6] Nevertheless, the technology simplification and unique synergy of the selec- tivity and sensitivity are still required in the further develop- ment of vapor sensors. Vapochromism is one of the promising approaches for vapor sensing, since the color or emission changes upon exposure to a certain volatile vapor could be directly trapped by an external monitoring method. [20,21] This vapochromic character effectively simplifies the monitoring operation. However, the vapochromic systems are still restricted by some drawbacks: (i) the vapochromic substrate is usually sim- plex and also unfriendly to the environment; [22–24] (ii) they suffer from poor stability, as these materials upon exposure to vapors for a long time could be degraded to result in low sensitivity and recyclability; [25–27] and (iii) strict operation conditions limit their applications in a large scope, [28,29] and most of them relies on the changes of hydrogen bonding, metal–metal, and π–π stacking interactions. [30] Therefore, further exploration of vapochromic systems with easy opera- tion, high stability, and simple response mechanism is in great demand, aiming at applying vapochromic materials more widely in gas sensing. Vapochromic behavior is employed to selectively monitor the vapor changes in surrounding environment, particularly for toxic gas leaking and floating detection. Thus, sensitive trapping and accurate response to different toxic vapors are critical factors in vapochromic sensing. In this work, a self-assembled hybrid that consists of fluorescent organic octahedron encapsulated by metal–organic polyhedron (MOP) is reported. The fluorescent octahedron is used as a responsive sensor to probe various solvent vapors, while the MOP is employed as a protector to prevent the corrosion of solvents to the organic octahedron. The hybrid exhibits remarkable vapochromic behavior to different solvents, and shows the highest selectivity and sensitivity specifically to acetone. In addition, acetone vapor under different conditions is utilized for further studying the response mechanism of the hybrid. This work presents a promising vapochromic sensor with good stability, selectivity, and sensitivity. The study is expected to open up the applicability of MOP-based hybrids for specific molecular capture, interim storage, controlled release, and advanced sensing. Sensors DOI: 10.1002/smll.201600437 L. Bai, Dr. A. Jana, H. P. Tham, Dr. K. T. Nguyen, Dr. P. Borah, Prof. Y. Zhao Division of Chemistry and Biological Chemistry School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link, Singapore 637371, Singapore E-mail: whni2012@sinano.ac.cn Prof. Y. Zhao School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798, Singapore 1. Introduction Air pollution has seriously threatened environment safety and human health. [1,2] In particular, toxic gas emissions and leaks could result in serious health problems. [3,4] Hence, developing fast response and accurate detection methods to these harmful gases is critical. In the past decade, various stimuli-responsive materials were designed and employed as chemical vapor sensors, [5,6] including gold or platinum nanoparticles, [7–10] fluorescent organic materials [11–13] or com- plexes, [14–16] and piezochromic materials. [17–19] Moreover, small 2016, 12, No. 24, 3302–3308