Solid-state emissions of 4H-chromenones with simple structures: mechanochromism and polymer-based doped ultralong room-temperature phosphorescence

Abstract

A series of 4H-chromenones using triphenylamine (TPA) and 9-phenyl-9H-carbazole (Cz) as electron-donating units are designed and synthesized, which have twisted molecular conformations and display dual-state emissions. Different from Cz-based derivatives with a zigzag-type crystalline structure, TPA-based derivatives have step-like arrangement with molecules arranged in the same direction, which is conducive to increasing the degree of molecular conformational distortion and thus forming tight stacking after being ground, finally resulting in significant mechanochromic (MC) properties. These results indicate that different stacking modes of crystalline structures play an important role in the formation of MC activities. Furthermore, using polyvinyl alcohol (PVA) as the host molecule and 4H-chromenones as the guest molecules, the doped materials show blue, green, and yellow-green ultralong room-temperature phosphorescence (RTP) activities with afterglow times of 5–7 s, delayed lifetimes of 636–901 ms, and phosphorescence quantum efficiencies of 10.7–25.7%. RTP emissions are demonstrated to originate from the 4H-chromenones in the rigid and compact environment provided by the formation of O–H⋯O hydrogen bonds between PVA and 4H-chromenones. This work provides an important reference for the development of novel 4H-chromenones with excellent solid-state luminescence properties and applications.