Organic Dopant Cyclization and Significantly Improved RTP Properties

Abstract

The internal rotation of triplet-generating molecules is detrimental to room temperature phosphorescence (RTP) radiation, which is always mentioned and usually mitigated by doping into rigid microenvironments. The chemical locking of internal rotation units in advance should be an effective strategy but is rarely studied in comparison. Herein, a triplet-generating molecule with two rotatable phenyls (DIA) is designed, synthesized, and then cyclized by two kinds of bonding bridge. We find that DIA/PMMA film hardly shows observable RTP afterglow despite 148 ms of lifetime, whereas carbon bridge cyclized DIA (CDIA) and oxygen bridge cyclized DIA (ODIA) emit green and blue ultralong RTP in PMMA film with lifetimes of 2146 ms and 2656 ms, respectively, demonstrating the potent role of pre-locking of internal rotation unit in promoting RTP. Benefited from the good spectral overlaps between the RTP emissions of dopants and the absorption of perylene red (PR) in PMMA film, the almost complete triplet-to-singlet Förster resonance energy transfer is achieved under trace doping (0.1%), providing red room temperature afterglow materials with lifetimes of 1567‒1800 ms. The preliminary applications of blue, green, and red afterglow materials in optical encryption and anti-counterfeiting are demonstrated. This work not only develops new triplet generating and radiating molecules but also guides an effective molecular strategy of achieving ultralong RTP polymers.