Ultralong blue room-temperature phosphorescence by cycloalkyl engineering

The development of organic room-temperature phosphorescence (RTP) materials with ultralong lifetimes is desired but remains challenging, especially those with blue RTP emission. Herein, through the cycloalkyl modification of a phenothiazine-5,5-dioxide (CsO) core, ultralong blue RTP performance with a lifetime up to 1116.10 ms has been achieved by C-6-CsO with cyclohexyl (C-6) as the substituent, which is about 1500 times that of the similar compound N-6-CsO with hexyl (N-6) as the side chain, indicating the superiority of cycloalkyl to the commonly used alkyl engineering. The crystal structure and DFT calculations revealed that the smaller steric hindrance of the cycloalkyl moieties than those of alkyl ones, together with the increased intermolecular interactions, contributing to the optimized RTP property. It provides a universal way to develop ultralong blue RTP materials, which can promote their practical applications by deeply understanding of inherent mechanism.