Unsymmetrical Hexafluorocyclopentene-Linked Twisted pi-Conjugated Molecules as Dual-State Emissive Luminophores

Dual-state emissive (DSE) luminophores, which can luminesce both in solution and in solid states, have recently attracted significant attention because of their broad applications. However, their development is difficult due to the difference in molecular design between solution- and solid-state luminophores. In this study, DSE luminophores based on unsymmetrical hexafluorocyclopentene-linked twisted pi-conjugated structures carrying various substituents to tune the electron-density were designed and synthesized in a single-step reaction from heptafluorocyclopentene or perfluoro-1,2-diphenylcyclopentene derivatives. The twisted pi-conjugated luminophores exhibited absorption in the UV region at approximately 330 nm, along with several signals in the high-energy region. Upon irradiating the luminophore solution (wavelength 330 nm), light-green to yellow photoluminescence (PL) was observed in the range of 422-471 nm with high PL efficiency. Theoretical calculations revealed that excitation from ground to excited states altered the structural shape of the luminophores from twisted to planar, leading to red-shifted PL and high PL efficiency (phi(PL)). The intense blue PL exhibited by the luminophores in the crystalline state was attributed to their twisted molecular structures that suppressed non-radiative deactivation via the effective blocking of pi/pi stacking interactions.