Singlet Fission in Self-assembled Amphipathic Tetracene Nanoparticles: Probing the Role of Charge-transfer State

Abstract

Two tetracene derivatives with PEG group of different lengths (PhTc-PEG-1 with short PEG chain and PhTc-PEG-2 with long PEG chain) have been synthesized and fabricated into nanoparticles with re-precipitation method. Spherical nanoparticle is formed for these two compounds in water as revealed by scanning electron microscopy. Steady-state absorption and fluorescence spectra demonstrates that the interaction between the adjacent tetracene units in these two nanoparticles is relatively strong, but the interaction in PhTc-PEG-2 nanoparticle is weaker than that of PhTc-PEG-1 nanoparticle. Transient absorption experiment reveals that singlet fission (SF) can be conducted in these two nanoparticles via a real charge-transfer (CT) intermediate state resembled that in same tetracene core without PEG chain (PhTc). However, the SF yields of these nanoparticles are relatively low, suggesting that the formation of the real CT state is unfavorable for the occurrence of SF. Moreover, the weaker interaction in PhTc-PEG-2 nanoparticle leads to a relatively low SF yield compared to that of PhTc-PEG-1 nanoparticle, suggesting that the long PEG chain should be avoided when modifying SF chromophore for preparing colloidal nanoparticles with the goal of achieving efficient SF.