Researchers Obtain Hybrid Photoactive Materials Using More Stable and Rigid Dyes

Researcher Rebeca Sola from the Department of Physical Chemistry in the UPV/EHU's Faculty of Science and Technology has created and characterized hybrid materials that react differently to light, and hold promise for potential use in a wide range of areas from optics to biomedicine.

Credit: UPV/EHU

One of the varieties of materials attained are inorganic, channeled structures that have combined into them fluorescent organic dyes in a structure that offers the dye stability and  the system rigidity, thus enhancing its photophysical properties.

Hybrid materials are those that integrate components of differing origins (inorganic and organic) so as to acquire materials diverse from conventional ones and which display new or better properties due to the synergistic effect between their components.

In the research conducted at the department, hybrid materials were acquired, among other things, by adding fluorescent dyes, which are regularly used in solution, into channeled inorganic structures. These materials primarily offer the dye protection, thus rendering it more stable against degradation and boosting the useful service life of the devices that include them, and secondarily, they offer the system rigidity, which is exciting as this has the potential to enhance the photophysical properties of the organic hosts (the dyes).

As the Researcher explained, "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". Simply put, materials that react in a different way based on the direction of the polarization of the incident light. Moreover, it "is fairly straightforward," to synthesize these materials said Sola. "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."

Various optical applications

The Researcher has thus acquired materials with a very extensive range of optical properties.

Of great interest are those in which there is an artificial antenna effect with the ordering of the different kinds of dye and a unidirectional energy transfer.

Rebeca Sola, Researcher, the Department of Physical Chemistry, Faculty of Science and Technology, UPV/EHU

This is translated into particles with multi-colored fluorescence, which can absorb the energy from light at one end and convey it to the opposite end. This could be of interest with regard to incorporating them into solar cells.

Another of the materials acquired is a solid material that discharges delayed fluorescence: rather than the fluorescence of the system switching off as soon as the excitation source is taken off, as is typically the case, it continues for tenths of a second and is clearly visible to the naked eye. "This kind of technology could be of interest in LED technologies," she explained. And materials capable of altering incident laser light into light with twice the quantity of energy were also achieved.

These materials not only permit the addition of a single dye into the inorganic structure, various dyes can also be concurrently encapsulated. "With two dyes whose response is complementary, we have obtained fluorescent particles that change colour depending on the light polarization, and change from a blue fluorescent emission to a green one," added Sola. “What is more, it is a reversible, reproducible process”. By incorporating a third, red-emission dye in the exact proportion, a white-light emitting system was also achieved, "once again of interest for illumination systems," she concluded.

White-light emitters were also acquired by incorporating small organic molecules to specific frameworks of metal ions and organic compounds known as Metal Organic Frameworks (MOFs); ambient-temperature phosphorescence was also acquired with them.

Phosphorescence is an emission process that routinely calls for very low temperatures to prevent the phosphorescent light from deactivating.

Rebeca Sola, Researcher, the Department of Physical Chemistry, Faculty of Science and Technology, UPV/EHU

Leap to biomedicine

The Researchers have revealed that hybrid materials could possibly have applications in other fields, such as biomedicine. To achieve this, they used photosensitizing substances appropriate for photodynamic therapy. These are materials that merge inorganic and organic fragments to create a kind of oxygen capable of causing the death of specific cells following excitation by light. Photodynamic therapy is a process used in dermatology, for instance, to treat a variety of skin diseases and even for various types of cancer.

Materials that not only produce this type of cytotoxic oxygen but which are also fluorescent have been acquired. And "that makes them very useful for bioimaging as well," added the Researcher. "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," she concluded.

Additional information

This research forms a part of the PhD thesis by Rebeca Sola-Llano (Barakaldo, 1989), entitled ‘Synergism between organic and inorganic moieties: in the search of new hybrid materials for optics and biomedicine'. Her supervisors were the Ramón y Cajal Researcher Virginia Martínez-Martínez and the UPV/EHU Professor Iñigo López-Arbeloa. Research groups at the Institute of Catalysis and Petrochemistry in Madrid, the Complutense University of Madrid, the University of Kyoto, the Katholieke Universiteit of Leuven and the Autonomous University of Madrid worked together in this thesis.

Bibliographic reference

M. J. Ortiz, E. Palao, R. Sola-Llano, A. Tabero, H. Manzano, A. R Agarrabeitia, A. Villanueva, I. López-Arbeloa, V. Martinez-Martinez.. ‘AcetylacetonateBODIPY−biscyclometalated Iridium(III) complexes: Effective strategy towards smarter fluorescent-photosensitizer agents'. Chem. Eur. J. 10.1002/chem.201701347 (2017).

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