Time-dependent color-tunable room temperature phosphorescence from unusual conformational transitions in phenothiazine polymers under UV irradiation

Achieving color-tunable room-temperature phosphorescence (RTP), especially including blue RTP from a single-component polymer still faces a formidable challenge. Herein, we wisely choose conformation-dependent phenothiazine with trifluoromethyl substituent as the side group of the phosphor monomer (CzPT) and then copolymerize it with N-isopropylacrylamide (NIPAM) through photopolymerization to obtain polymers PPCzPTs. Time-dependent color-tunable phosphorescence from unusual quasi-equatorial (eq) to quasi-axial (ax) conformers are obtained, and the RTP color changes from orange (550 nm) to blue (470 nm) with phosphorescence lifetime up to 0.96 s. The theoretical calculations confirm that the quasi-axial conformer is the preferred structure that facilitates the formation of intramolecular hydrogen bonds on the trifluoromethyl group. The EPR spectra illustrate that the persistent UV irradiation generates radical cations to induce the conformational transitions first, followed by photopolymerization immobilizing the ax conformation in PPCzPTs. Applications of data encryption and anti-counterfeiting are fabricated to show prompt and delayed multicolor information. This work affords a simple and feasible avenue for two-dimensional color tunable room temperature phosphorescence from a single-component polymer.