Mechanochromism, tunable pure organic room temperature phosphorescence, single-molecule near-white emission, digital encryption, and anti-counterfeiting

Abstract

The development of tunable pure organic room temperature phosphorescence and single-molecule white light emitters still faces a great challenge due to ineffective intersystem crossing and sensitive triplet excitons. Here, two phenothiazine based luminogens named PtzIP and PtzIPCN were designed and synthesized. PtzIP exhibits mechanochromic activity with hypsochromic shift of 25 nm, tunable room temperature phosphorescence from 613 nm to 530 nm and 560 nm, then to 540 nm and 585 nm by crushing and grinding, and single-molecule near-white light emission with the (CIE: Commission International de I'Eclairage) CIE coordinates of (0.33, 0.25), but PtzIPCN shows mechanochromism and room temperature phosphorescence inertness in crystalline state. By choosing polymethyl methacrylate (PMMA) and 4-fluorobenzophenone(F-BP) as host materials, as well PtzIP and PtzIPCN as guest materials, a series of host-guest doping systems were constructed and optimized by tuning doping ratio. PtzIP/PMMA and PtzIPCN/PMMA doping systems present concentration dependent fluorescence and phosphorescence emission, and RTP lifetime and afterglow of PtzIPCN/PMMA are up to 185.31 ms of 2.0 s. Furthermore, the lifetime of F-BP/PtzIPCN increases to 216.63 ms at doping ratio of 1:1000 for F-BP and PtzIPCN. Based on different luminescent properties of PtzIP and PtzIPCN in the doping systems, a series of high-level digital encryption and anti-counterfeiting patterns were successfully constructed. More importantly, the underlying mechanism behind luminescent properties were explored in detail by photophysical testing, crystal analysis, and theoretical calculations.