Wide‐Range Color‐Tunable Organic Phosphorescence Materials for Printable and Writable Security Inks

Abstract

Organic materials with long‐lived, color‐tunable phosphorescence are potentially useful for optical recording, anti‐counterfeiting, and bioimaging. Herein, we develop a series of novel host–guest organic phosphors allowing dynamic color tuning from the cyan (502 nm) to orange red (608 nm). Guest materials are employed to tune the phosphorescent color, while the host materials interact with the guest to activate the phosphorescence emission. These organic phosphors have an ultra‐long lifetime of 0.7 s and a maximum phosphorescence efficiency of 18.2 %. Although color‐tunable inks have already been developed using visible dyes, solution‐processed security inks that are temperature dependent and display time‐resolved printed images are unprecedented. This strategy can provide a crucial step towards the next‐generation of security technologies for information handling.

Tunable Phosphorescence/Fluorescence Dual Emissions of Organic Isoquinoline‐Benzophenone Doped Systems by Alkoxy Engineering

“…Recently, our works have shown that the host molecule not only provides a rigid environment to restrict movement, but also contributes to the energy transfer of the guest molecule (Scheme 1). [7c, d] Herein, a new doped system with strong RTP property was developed through prediction and design, in which isoquinoline derivatives (IQL‐C n ) containing different alkoxy chains were selected as the guest molecules and cheap benzophenone (BPO) as the host molecule (Scheme 1). The guests were prepared from a simple three‐step procedure by using commercially available 2,6‐dimethyl‐4 H ‐pyran‐4‐one as the starting material according to Scheme S1 (in the Supporting Information) [8] .…”

“…To the best of our knowledge, this is the first time the effect of different alkoxy chains on the RTP properties of the doped materials has been studied. Based on the previously reported mechanism, [7c, d] BPO was chosen as the host owing to the characteristics of low melting point, good crystallinity, and phosphorescent emission. The low melting point facilitates the preparation of large quantities of the doped materials by the melt‐casting method, and the good crystallinity is conducive to providing a rigid environment for the guest molecules.…”

“…BPO is a typical phosphor with a maximum phosphorescence wavelength of 485 nm at room temperature, which is between the fluorescence wavelengths (around 440 nm) and phosphorescence wavelengths (around 550 nm) of the guests [9] . This means that the T 1 energy level of the host is between the T 1 and S 1 energy levels of the guests (Figure S9 in the Supporting Information), which is beneficial for the host to assist the energy transfer of the guests from the singlet state to the triplet state [7c, d] . Additionally, the melting point of BPO is only 48.5 °C (Figure S10 in the Supporting Information), so the guests can be uniformly dispersed in BPO by a simple melt‐casting method.…”

“…The interaction between host and guest molecules is an important factor for the RTP characteristic of the doped materials, and the reasonable contact between the host and guest molecules is the prerequisite for the intermolecular interactions [7a, c] . The longer alkoxy chain will hinder the reasonable contact between the guest molecule and the surrounding host molecules, which is not conducive to the host molecule assisting the energy transfer of the guest molecules.…”

Color‐Tunable, Excitation‐Dependent, and Time‐Dependent Afterglows from Pure Organic Amorphous Polymers

“…Therefore, further development of versatile platforms to realize distinct p ‐RTP emissions from blue to red is highly desired. [ 21 ] On the other hand, most of these p ‐RTP materials just show a single emission color, and only scattered examples demonstrating excitation‐dependent [ 4 ] or time‐dependent emissions [ 22 ] were reported. If the afterglow color can vary with time, it would empower the materials with rich encryption modes in security protection, thus promoting more reliable protection at much higher levels.…”