Modulating room-temperature phosphorescence of D-π-A luminogens via methyl substitution, positional isomerism, and...

Organic room-temperature phosphorescence (RTP) luminogens have showed significant potential in the fields of diagnostics, sensing, and information encryption. However, it is difficult to achieve high RTP yield (Φ_P) and long RTP lifetime simultaneously. By methyl substitution, positional isomerism, and host-guest doping, three new D-π-A type luminogens named as TBTDA, 2M-TBTDA, and 3M-TBTDA were designed and synthesized, whose RTP properties were tuned and optimized. In various solvents and glassy THF solution, similar solvatochromism and phosphorescence nature of three luminogens were revealed. In poly (methyl methacrylate) (PMMA) and polyvinyl alcohol (PVA) matrixes, the luminogens showed high-contrast RTP properties. TBTDA emitted invisible afterglow in PMMA films, but with strong RTP and long green afterglow in PVA films. More importantly, 2M-TBTDA showed RTP and afterglow lifetimes of 809.81 ms and 8 s, as well as Φ_P of up to 0.64 in PMMA at 1 % doping concentration. Taking advantage of Foerster resonant energy transfer (FRET), reddish-brown or orange afterglow were observed, with emission maxima of 593-617 nm, RTP and afterglow lifetimes of 299-566 ms and 5-6 s, Φ_P of 0.34-0.46, as well as FRET efficiency of 70-90 %. Finally, dynamic anti-counterfeiting and digital encryption were successfully constructed via different fluorescence, RTP colors, and afterglow lifetimes. This work not only obtained an efficient host-guest doping RTP system, but also can be expected to provide more theoretical guidance and experimental supports for molecular design, dynamic anti-counterfeiting and digital encryption.