[Seminar]"Temperature-induced effects in organic thin films comprising energy donor-acceptor systems" by Dr. Piotr Ślęczkowski

Temperature-induced effects in organic thin films comprising energy donor-acceptor systems

Dr. Piotr Ślęczkowski, Group Leader at International Centre for Research on Innovative Bio-based Materials (ICRI-BioM)-International Research Agenda, Lodz University of Technology, Poland

Abstract: Organic semiconductor dyes exhibiting so-called excited state intramolecular proton transfer (ESIPT) have demonstrated unique fluorescent properties, including dual-emission and large values of Stokes shift [1]. However, their application in thin films and related technologies is still limited and mainly focused on the realization of efficient white light organic light-emitting diodes (WOLEDs). In the frame of exploring new applications for ESIPT dyes, we have designed and synthesized two benzothiazole isomers, and we have further tailored their optical properties in thin films.
First, we have demonstrated that tuning of fluorescence emission wavelength and fluorescence quantum yield for those compounds resulted from modified intermolecular interactions in thin films. The latter were achieved by optimization of several parameters, including selection of solvent used for film deposition and by studying the effect of the annealing temperature [2]. Basing on this approach, we have also elaborated more advanced materials in form of two-component blends incorporating ESIPT molecules (panel a). It was achieved by doping one of the ESIPT analogue with a selected TADF dye emitting in far-red, thus realizing organic Förster resonance energy transfer (FRET) system (panel b). We have explored the role of the molecular interactions in this system by studying the morphology and fluorescent properties (panel c). Detailed analysis enabled us to demonstrate that resulting fluorescence is very sensitive to thermal post-treatment of the blended films. The irreversible structural changes were evidenced to determine the extent to which FRET occurs in the donor-acceptor materials developed. Finally, the application of thin films as thermal indicators was demonstrated for simple visual inspection and for ratiometric sensing, showing noticeable color changes every 10 °C and remarkable sensitivities of up to 14 % °C^-1 [3]..

References

[1] J. E. Kwon et al., Adv. Mater. 23, 3615 (2011).
[2] F. A. Soares et al., J. Phys. Chem. C 127, 17624 (2023).
[3] G. Martinez-Denegri et al., Adv. Optical Mater. 13, 2403073 (2025).