Metal coordination-induced time-dependent phosphorescence colors (TDPC) in multi-component-doped films for multifunctional applications

Abstract

Dynamic room-temperature phosphorescence (DRTP) possesses a wide variety of advantages for developing smart optical devices to satisfy specific demands. In particular, the development of time-dependent phosphorescence colors (TDPC) towards anti-Kasha emission is challenging and less reported. Herein, a flexible multi-component film with controllably regulated lifetime/efficiency and TDPC was fabricated by encapsulating (4-([2,2′:6′,2′′-terpyridin]-4′-yl)phenyl)boronic acid (TPy-BA) and ZnCl₂ into an amorphous poly(vinyl alcohol) (PVA) matrix. The coordination effects can promote ISC and restrict molecular motion. Significant improvements in phosphorescent lifetimes (from 99.13 ms to 218.75 ms) and efficiencies (from 3.90% to 6.51%) were achieved. Moreover, the triplet charge-transfer phophorescence was achieved in the TPy-BA/ZnI₂/PVA-doped film. The afterglow color was also changed to green. Specially, the TDPC phenomenon from blue to green for the TPy-BA/ZnCl₂/PVA films was observed at different delay times, which was the result of the emission from the anti-Kasha T₂ energy level with a short lifetime (72.56 ms) and T₁ emission with a long lifetime (218.75 ms), simultaneously. Based on these findings, the four-component TPy-BA/ZnCl₂/NaI/PVA films were prepared, showing blue-shifted phosphorescence emission through gradually doping NaI. This phenomenon can be explained by the stronger coupling of the high-lying energy level towards external heavy atoms, facilitating the anti-Kasha emission from the T₂ energy level. These flexible films have exhibited versatile applications in multi-level encryption, silk-screen printing, and high-definition displays.