A [8]Cycloparaphenylene Derivative as Emitter in Triplet-Triplet Annihilation Upconversion

CycloParaPhenylenes ([n]CPPs) are fully conjugated macrocycles constituted by n para-linked benzene units (Figure), which exhibit size-dependent optical and electronic proprieties. Among them, they exhibit the narrowing of the HOMO-LUMO gap as the number of aromatic units decreases. Consequently, the emission spectra of CPP derivatives are red-shifted and quantum efficiency decreases as the macrocycle become smaller. CPPs, can be considered useful template for the bottom-up synthesis of single wall carbon nanotubes. Recently, many efforts have been devoted to study the triplet-triplet annihilation (TTA)-based upconversion processes. Upconversion represents a emerging wavelength-shifting technology, useful to convert low energy photons into light adequate for photovoltaic, photocatalysis and bioimaging. In TTA-based upconversion systems, the photon excitation of a triplet sensitizer, affords a triplet energy transfer toward an acceptor which give rise to upconverted fluorescence. Cycloparaphenylenes are known as excellent chromophores exhibiting high fluorescence quantum yields, however, to the best of our knowledge, no data is currently available about their abilities to act as emitter (acceptor) into upconversion schemes. Prompted by these considerations, we wish to describe here the synthesis of the new anthracene-incorporated [8]CPP macrocycle 1. In addition, details on the conformational features, optoelectronic and upconversion properties of this new derivative will be given.