An inexpensive new material can quickly and accurately detect carbon dioxide (CO2) under a variety of circumstances, enabling the development of easy-to-use CO2 monitors. Methods to detect whether specific gases are present in the air already exist, but they come with many drawbacks, including high energy cost, slow detection speed, large size and sensitivity to humidity. Now, Kyoto University scientists have developed an inexpensive, reusable compound that gives off variable degrees of visible light that correspond to gas concentrations. Their findings, published online Sept. 4 in Nature Materials (doi: 10.1038/nmat3104), describe how the flexible crystalline material, or porous coordination polymer (PCP), transforms in accordance with changes in its environment. Once infused with distyrylbenzene (DSB), a fluorescent reporter molecule, the composite becomes sensitive specifically to CO2 and glows with an intensity that correlates to the concentration of that gas. The scientists set out to see whether their composite could differentiate between carbon dioxide and acetylene, a compound with similar physiochemical properties. They discovered that their PCP-DSB combination reacted very differently to the two gases, which confirmed that it could make accurate CO2 detection possible in a variety of applications. DSB exists as a long, flat molecule in its natural state, and it emits blue light. However, when absorbed by the PCP framework, DSB molecules twist, causing the PCP structure to become skewed and the glow of DSB to diminish significantly. They observed that the presence of CO2 causes the DSB molecules to revert to their flat, brightly fluorescent form, while also returning the PCP grid to its usual state. These steps could be reversed, however, without causing any significant changes to the composite. The team hopes to investigate combinations of host and guest materials to achieve more precise detection systems for gases or volatile organic compounds at much lower pressures and concentrations, said associate professor Takashi Uemura.