Hybrid photoactive materials, created by incorporating fluorescent dyes that are used in solution into channeled inorganic structures, could be used for a range of applications including biomedicine. The materials were found to protect the dye, thus rendering it more stable against degradation and increasing the useful service life of the materials. The photoactive materials were also found to increase the photophysical properties of the organic hosts (the dyes) and were found to respond differently depending on the direction of the polarization of the incident light. Channeled aluminophosphate with various encapsulated dyes emitting in the blue (acridine), green (pyronin Y) and red (LDS 722) regions of the spectrum, occluded separately (left) or simultaneously in the correct proportions to produce white light (right), under ultraviolet excitation light. Courtesy of Rebeca Sola. UPV/EHU. “Highly fluorescent materials in which the dyes are found to be ordered were obtained, thus providing a highly anisotropic response to the linearly polarized light,” said researcher Rebeca Sola, University of the Basque Country (UPV/EHU). In addition to allowing a single dye to be incorporated into the inorganic structure, the technology allows various dyes to be simultaneously encapsulated. “With two dyes whose response is complementary, we have obtained fluorescent particles that change color depending on the light polarization, and change from a blue fluorescent emission to a green one,” said Sola. “What is more, it is a reversible, reproducible process.” By incorporating a third, red-emission dye in the correct proportion, researchers were able to demonstrate a white-light emitting system. White-light emitters were also achieved by adding small organic molecules to metal organic frameworks (MOFs), and these emitters demonstrated ambient-temperature phosphorescence. “Phosphorescence is an emission process that routinely calls for very low temperatures to prevent the phosphorescent light from deactivating,” said Sola. The novel hybrid materials potentially offer a wide range of optical properties. For example, materials in which there is an artificial antenna effect with the ordering of the different dyes and a unidirectional energy transfer could be translated into particles with multicolored fluorescence, capable of picking up the energy from light at one end and transferring it to the opposite end. This could be of useful in the development of solar cells. A solid material that emits delayed fluorescence could be used in LED technologies. Materials capable of transforming incident laser light into light with double the amount of energy were developed. The researchers also developed fluorescent materials with photosensitizing substances, that could be used in bioimaging and photodynamic therapy. “The phototoxic action of these compounds is being explored by means of experiments in in vitro cell cultures, and although the results are promising, we are still in the early phases of the study," said Sola. According to Sola, it “is fairly straightforward” to synthesize these materials. “Crystalline structures in which the dye has already been occluded inside are obtained without any need to apply a diffusion process to insert the dye into the crystal.” The research was published in Chemistry — A European Journal (doi: 10.1002/chem.201701347).