New paper in Advanced Optical Materials – Solid Materials with NIR-Induced Fluorescence Modulation

New paper in Advanced Optical Materials – Solid Materials with NIR-Induced Fluorescence Modulation

20 Mar 2022

Recent publication in Advanced Optical Materials journal describing the use of phase change materials for the preparation of functional devices.

New publication in Advanced Optical Materials journal entitled “Tunable Thermofluorochromic Sensors Based on Conjugated Polymers” authored by our former PhD student Dr. Christian Bellacanzone, our PhD student Jaume Ramon Otaegui and led by Dr. Claudio Roscini and in collaboration with Dr. Jordi Hernando from Chemistry Department in the UAB. The review has been published in Open Access, thus allowing for free access to all interested researchers.

In this work, the authors have demonstrated another use of Phase Change Materials (PCM) to achieve thermofluorochromic materials. In this case, conjugated polymers were used as fluorophore, which are highly sensitive to the medium properties. They granted a very fine-tuning of the fluorescence emission properties, upon variation of PCM polarity, polymer concentration and conjugation length, covering a large part of the CIE 1931 color space. On the one hand, the authors employed conjugated polymers as emitters, which are emissive both in homogeneous solutions and in the aggregated state and, more importantly, show fluorescence properties that are highly dependent on the surrounding medium. On the other hand, the authors proposed the use of PCM as thermally responsive surrounding matrices. Up to now, organic nonpolymeric PCMs have been successfully combined with small molecular fluorophores to yield single-color emission switching (off/on or on/off), while multicolored thermal responses, with coarse color tunability, could only be accomplished by using different fluorescent molecules. Although conjugated polymers are known to manifest highly medium-dependent emission properties, the only so far reported examples of PCM-based thermofluorochromism using a semiconductive polymer (polydiphenylacetylene) only provided a single-color on/off fluorescence modulation, and/or it required additional chemical functionalization to improve its miscibility with the surrounding PCM.

Figure. a) Molecular structure of MEH-PPV. b) Emission spectra of a CHCl3 solution and a film of MEH-PPV. c) Scheme of a polymeric film loaded with solid lipid particles containing MEH-PPV chains. Depending on the solid or liquid state of the surrounding PCM, the MEH-PPV chains lie in their aggregated or nonaggregated forms within the particles, which provide different emission colors.

Interestingly, the published work describes the formation of PCM-based materials that can be structured as solid lipid microparticles, which upon incorporation into polymeric matrices enable obtaining free-standing films with thermofluorochromic behavior that could be directly used as temperature sensors.

ABSTRACT: Even though thermofluorochromic materials are eternal candidates for their use in multiple applications, they are still limited as they require complex synthetic strategies to accomplish tunable optical properties and/or provide optical changes only over a very wide temperature range. By taking advantage of the high sensitivity of the optical properties of conjugated polymers and oligomers to the external environment, herein phase change material (PCM)-based thermofluorochromic mixtures are created, where the solid-to-liquid transition of the PCM host triggers a sharp fluorescence color change of the dispersed polymers/oligomers. Fluorophore conjugation length, concentration, and PCM nature can be used to vary the spectral properties of the resulting materials along the visible region, covering a large part of the CIE 1931 color space. For the preparation of functional devices, this behavior can be directly transferred to the solid state by soaking or printing cellulose papers with the obtained thermofluorochromic mixtures as well as by structuring them into solid lipid particles that can be dispersed within polymer matrices. The resulting materials show very promising features as thermal sensors and anticounterfeiting labels.

Enjoy our article it’s in Open Access!

Funding: This work was supported by Grant Nos. RTI2018-098027-B-C21 and PID2019-106171RB-100 funded by No. MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe. The ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The ICN2 is supported by the Severo Ochoa Centres of Excellence programme, Grant No. SEV-2017-0706 funded by No. MCIN/AEI/10.13039/501100011033. This work was also supported by Generalitat de Catalunya (No. 2017 SGR00465 project). J.R.O. acknowledge the Generalitat de Catalunya (AGAUR) for his predoctoral FI fellowship.