AUTHOR=Vasilev Aleksey , Kostadinov Anton , Kandinska Meglena , Landfester Katharina , Baluschev Stanislav 

TITLE=Tetrathienothiophene Porphyrin as a Metal-Free Sensitizer for Room-Temperature Triplet–Triplet Annihilation Upconversion

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.809863

DOI=10.3389/fchem.2022.809863

ISSN=2296-2646

ABSTRACT=Optically excited triplet states of organic molecules serve as energy pool for the subsequent processes, either photon energy downhill such as room temperature phosphorescence or photon energy uphill process – the triplet-triplet annihilation upconversion (TTA-UC). Manifestation of a high intersystem crossing coefficient is an unavoidable requirement for triplet state formation, following absorption of a single photon. This requirement is even more inevitable, if the excitation light is non-coherent, with moderate intensity and extremely low spectral power density, comparable with the light parameters of 1 Sun (1.5 AM). Coordination of a heavy atom increases substantially the probability for intersystem crossing. Nevertheless, having in mind the global shortage in precious- and rare-earths- metals, identification of metal-free organic moieties able to form triplet states becomes prerequisite for environmental friendly optoelectronic technologies. This motivates us to synthesize a metal-free thienothiophene containing porphyrin, based on a condensation reaction between thienothiophene-2-carbaldehyde and pyrrole in an acidic medium by modified synthetic protocol. The upconversion couple tetrathienothiophene porphyrin / rubrene when excited at 658 nm demonstrates bright, delayed fluorescence with emission maximum at 555 nm. This verify our hypothesis, that the ISC-coefficient in thienothiophene porphyrin is enough efficient in order to create even at room temperature and low-intensity optical excitation densely populated organic triplet ensemble, able for photon energy uphill processes, which makes this type of metal-free sensitizers even more important for optoelectronic applications