Photoirradiation‐Gated Excitation‐Dependent Room‐Temperature Phosphorescence in Through‐Space Charge Transfer Molecules

Abstract

Organic materials showing reversible changes in persistent room‐temperature phosphorescence (RTP) upon exposure to external stimuli have attracted considerable attention in recent years. One potentially groundbreaking development in this area is the introduction of the gating concept for organic persistent RTP materials. This refers to a material where a desired responsive ability only occurs when it is triggered by a specific stimulus, but it remains a formidable challenge. In this study, photoirradiation‐gated excitation‐dependent (Ex‐De) persistent RTP is achieved. A series of molecules, triphenylphosphine and carbazole derivatives connected through flexible carbon chains, are designed and prepared. Upon removal of ultraviolet (UV) irradiation, all these compounds doped polyvinyl alcohol (PVA) films exhibit obvious blue or green afterglow RTP. Among them, (2‐(9H‐[3,9′‐bicarbazol]−9‐yl)ethyl)triphenylphosphonium bromide (TPP‐2C‐Cz) doped PVA film initially exhibits blue persistent RTP after removal of 300 nm excitation but no RTP upon ceasing 365 nm irradiation. Interestingly, upon UV irradiation with a power density of 0.05 W cm−2 (UVA) for 50 min, the Ex‐De RTP behavior of TPP‐2C‐Cz doped PVA film is activated. Eventually, photoirradiation‐gated Ex‐De afterglow emission will be used for a wide range of applications, including the quantitative determination of UV irradiation dose and the permanent record of UV irradiation history, and read on‐demand.

Simultaneously enhancing organic phosphorescence quantum yields and lifetimes for triphenylphosphine salt doped polymer films

“…36,44 Alternatively, incorporating an electron donor into a triphenylphosphine salt through a non-conjugated alkyl chain not only elevates the energy level but also allows for the precise control of the energy level of CT state. 40,45,46 This regulation is achieved by adjusting the distance between the donor and acceptor through varying the lengths of the alkyl chains. Also, selecting an electron donor molecule with a suitable triplet energy level can facilitate tripletto-triplet energy transfer (TTET) from the donor group to the triphenylphosphine salts.…”

“…32,49,50 Secondly, its lowest triplet energy level is higher than that of triphenylphosphine salts. 45 The population of triplet excitons in triphenylphosphine salts might be increased due to TTET from the carbazole group (Fig. 1).…”