Zethrene

Abstract: Singlet fission offers the potential to overcome thermodynamic limits in solar cells by converting the energy of a single absorbed photon into two distinct triplet excitons. However, progress is limited by the small family of suitable materials, and new chromophore design principles are needed. Here, we experimentally vindicate the design concept of diradical stabilization in a tunable family of functionalized zethrenes. All molecules in the series exhibit rapid formation of a bound, spin-entangled triplet-pair state TT. It can be dissociated by thermally activated triplet hopping and exhibits surprisingly strong emission for an optically “dark” state, further enhanced with increasing diradical character. We find that the TT excited-state absorption spectral shape correlates with the binding energy between constituent triplets, providing a new tool to understand this unusual state. Our results reveal a versatile new family of tunable materials with excellent optical and photochemical properties for exploi...

Abstract: Higher order acenes (i.e., acenes longer than pentacene) and extended zethrenes (i.e., zethrenes longer than zethrene) are theoretically predicted to have an open-shell singlet ground state, and the radical character is supposed to increase with extension of molecular size. The increasing radical character makes the synthesis of long zethrenes and acenes very challenging, and so far, the longest reported zethrene and acene derivatives are octazethrene and nonacene, respectively. In addition, there is a lack of fundamental understanding of the differences between these two closely related open-shell singlet systems. In this work, we report the first synthesis of a challenging nonazethrene derivative, HR-NZ, and its full structural and physical characterizations including variable temperature NMR, ESR, SQUID, UV–vis–NIR absorption and electrochemical measurements. Compound HR-NZ has an open-shell singlet ground state with a moderate diradical character (y0 = 0.48 based on UCAM-B3LYP calculation) and a small...

Abstract: This paper gives a brief summary of zethrene chemistry after the pioneering works by Clar, Mitchell, Sondheimer, and Staab et al. In the past a few years, various synthetic methods and stabilizing ...