In situ synthesis of multicolor phosphorescent films in polyacrylamide by regulating the conjugation of guest molecules

Abstract

Long lifetime multicolor organic room-temperature phosphorescence (RTP) materials have important applications in advanced anti-counterfeiting and optical information storage. However, one-step in situ synthesis of multicolor organic RTP flexible films proved to be challenging. In this work, organic guest molecules 4-ethoxycarbonyl phenylboronic acid (4-EpBA) and 9-phenanthracenylboronic acid (9-PhBA) with different degrees of conjugation were selected to synthesize 4-Ep@PAM and 9-Ph@PAM flexible phosphorescent films in situ with polymer polyacrylamide (PAM). At high temperatures, the organic guest molecules cross-link with PAM, forming numerous effective hydrogen bonds that restrict chromophore vibrations, thereby stabilizing the triplet state and enabling room-temperature phosphorescence (RTP) emission. Besides, the gradual increase of conjugation for 4-EpBA and 9-phBA, resulting in a gradual red-shift of the RTP emission for 4-Ep@PAM and 9-Ph@PAM. Therefore, 4-Ep@PAM and 9-Ph@PAM exhibit bright blue and green RTP, respectively, after the ultraviolet (UV) light is turned off. The rationality behind RTP emission mechanism and wavelength modulation is further conformed by density functional theory (DFT) calculations. Finally, multicolor organic RTP flexible films are successfully applied for advanced anti-counterfeiting and optical information storage.