The lack of sensors for low cost, extensive, and continuous detection of vapor pollutants is a serious concern for health and safety in industrialized urban areas. Colorimetric sensors, such as distributed Bragg reflectors made of polymers, could achieve this task thanks to their low cost and easy signal transduction but are typically affected by low vapor permeability and lack of selectivity without chemical labeling. Here we demonstrate all-polymer Bragg multilayers for label-free selective detection of organic volatile compounds. The system exploits the ability of amorphous poly(p-phenylene oxide), PPO, to uptake large amount of guest molecules and to form cocrystalline phases with distinct optical properties. Bragg stacks embedding PPO active layers show selective colorimetric response to vapors of carbon tetrachloride and aromatic homologues, which can be revealed by the naked eye.

The lack of cost-effective systems for the extensive assessment of air pollutants is a concern for health and safety in urban and industrial areas. The use of polymer thin films as labelfree colorimetric sensors featuring specific interactions with pollutants would then represent a paradigm shift in environmental monitoring and packaging technologies, allowing to assess air quality, formation of byproducts in closed environment, and the barrier properties of the polymer themselves. To this end, all-polymer distributed Bragg reflectors promises reliable transducers for chemical stimuli, and effective colorimetric label-free selective detectors. We show selectivity attained by specific interaction of the polymeric components with the analytes. Such interactions drive the analyte intercalation trough the polymer structure and its kinetics, converting it in a dynamic optical response which is at the basis of the Flory-Huggins photonic sensors. Additionally, we demonstrate that such optical response can be used to esteem the diffusion coefficients of small molecules within the polymer media via simple UV-Vis spectroscopy retrieving data comparable to those obtained with state of the art gravimetric procedures. These results pave the way to an innovative, simple, and lowcost detection method integrable to in-situ assessment of barrier polymers used for the encapsulation of optoelectronic devices, food packaging, and goods storage in general. Currently, barrier properties of polymer thin films to vapors and gas are assessed via gravimetric 1 and pressure decay methods, 2-4 or by optical techniques based on microscopy 5 and infrared absorption, 6 which remained substantially unchanged for the last few decades. These methods need dedicated equipment and cannot be performed in-situ. In this scenario, research for new low-cost, simpler, and portable technologies to gather lab-on-chip devices is strongly pursued. In these regards, sensors based on the optical response of polymer distributed Bragg reflectors (DBR) represent a possible revolution in the field due to the high responsivity to analytes in the vapor phase. 7-9 DBRs are planar photonic crystals made of media with different refractive index stacked to form a dielectric lattice. The interaction between light and DBRs induces frequency regions where light propagation is forbidden. These frequencies are called photonic band gaps (PBGs), and are easily detectable via simple reflectance or transmittance spectroscopy. 10 In analogy with the energy-gap of semiconductors, the PBG properties depend on the lattice structure. Then, dielectric contrast among the lattice components, lattice parameters, and the number of layers affect the optical features generated by the DBR photonic structure. 11 Intuitively, a perturbation of

Thanks to their broadband emission and solution processability, 2D hybrid perovskite materials are promising for the realization of large area and flexible lighting devices. The deposition of 2D perovskites, however, requires wide range solvents that are incompatible with commodity polymers used for structural support and light management.Here we demonstrate coupling of broad-emitting 2,2-(ethylenedioxy)bis(ethylammonium)PbCl 4 perovskite with solution processed polymer distributed Bragg reflectors on both rigid fused silica and flexible polymer substrates. The optical functions of the chemically engineered perovskite were determined by ellipsometric measurements and used to design dielectric multilayer structures with photonic bandgap tunable over the entire visible range. The resulting photonic structures control directionality and spectral enhancement or suppression of the perovskite photoluminescence, in agreement with simple analytical optical models. These results pave the way to the development of a new generation of color-tunable light-emitting devices based on a single active material.