Excitation wavelength-dependent room-temperature phosphorescence: unusual properties of novel phosphinoamines

Exploring pure organic single-component materials featuring room-temperature phosphorescence and excitation-dependent color-tunability has attracted great attention in recent years. Such challenging materials are highly demanded for the OLED industry and are very interesting from a photochemistry perspective. Herein, we report the synthesis of novel phenylbenzothiazole derivatives 1-3 bearing phosphine groups. The compounds demonstrate dual band emission, whose intensity depends on the excitation wavelength of ultraviolet light both in the solid state and in solution. Owing to the fact that the emission bands cover the entire visible range, manipulating the excitation wavelength allows one to achieve a white glowing of the compounds. In addition, the emission kinetics data reveal a lifetime of hundreds of microseconds, which implies a phosphorescent nature of the emission. To rationalize the unusual properties, a combination of pathways for the radiative process is suggested: 1) the transition between excited states with different molecular geometry, viz. locally excited state (LE) and a charge transfer state (TICT); 2) excited state intramolecular proton transfer (ESIPT). These mechanisms are interpreted by means of quantum chemical DFT calculations.