Highly Efficient Room-Temperature Phosphorescence Promoted via Intramolecular-Space Heavy-Atom Effect

Purely organic room-temperature phosphorescence (RTP) materials have attracted increasing attention due to their unique photophysical properties and widespread optoelectrical applications, but the pursuit of high quantum yield is still a continual struggle for RTP emission under ambient conditions. Here, a series of novel RTP molecules (26CIM, 246CIM, 24CIM, and 25CIM) are developed on the basis of indole luminophore, in which a carbonyl group bridges indole and chloro-substituted phenyl group. The structural isomerism is systematically regulated toward enhancing the intramolecular-space heavy-atom effect, thus promoting the spin-orbit coupling and intersystem crossing for high RTP efficiency. While rationally modulating the intramolecular-space heavy-atom effect, the phosphorescence efficiency is dramatically increased by 16-fold from 2.9% (24CIM) to 48.9% (26CIM). Basically, the fully occupied chlorine atoms at the positions 2 and 6 can effectively favor the stronger intramolecular (HCl)-Cl- horizontal ellipsis effect, and the tight lock coupling with anti-parallel stacking in 26CIM further boosts RTP emission synergistically. The experimental findings along with deeper theoretical insights elucidate the structure-performance relationship clearly, and further suggest a general strategy for rationally constructing high-efficiency RTP materials.