In situ synthesis of multicolor phosphorescent films of 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 is challenging. In this work, the 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), respectively. 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 in conjugation for 4-EpBA and 9-phBA resulted in a gradual red-shift in the RTP emission for 4-Ep@PAM and 9-Ph@PAM, respectively. Therefore, 4-Ep@PAM and 9-Ph@PAM exhibited bright blue and green RTP, respectively, after ultraviolet (UV) light was turned off. The rationale behind the RTP emission mechanism and wavelength modulation was further confirmed using density functional theory (DFT) calculations. Finally, multicolor organic RTP flexible films were successfully applied for advanced anti-counterfeiting and optical information storage.