Room-temperature phosphorescence-to-phosphorescence mechanochromism of a metal-free organic 1,2-diketone

An organic 1,2-diketone, which exhibits color change of room-temperature phosphorescence (RTP) upon mechanical stimulation, is reported. Experimental and theoretical investigations revealed that this mechanochromism is based on a molecular rotational isomerization associated with a crystalline-to-amorphous transition. In general, amorphization weakens intermolecular interactions, resulting in RTP quenching. In contrast, the present diketone shows an even higher phosphorescence quantum yield after amorphization, representing the first RTP-to-RTP mechanochromism of a metal-free organic molecule. We have disclosed that a planar conformer of the diketone, which is responsible for the RTP in the amorphous state, involves intramolecular chalcogen bonding. Having this noncovalent interaction, the diketone would be a promising platform for the design of mechanochromic and RTP-active organic materials; flexible enough for a large conformational change, while rigid enough to exhibit efficient RTP in the amorphous state.