Pyrene-Based Polyimide Covalent Organic Framework with Temperature-Dependent Fluorescence

The synthesis of a fluorescent covalent organic framework (COF) using perylene and pyrene building blocks (PEPy-COF), via a one-pot condensation reaction is reported. PEPy-COF is crystallized into 2D nanosheets with a cubic
and prismatic crystalline morphology and demonstrates structural stability at temperatures up to 500 °C. The structural morphology is confirmed using X-ray diffraction and atomic-level simulations. These 2D porous polymer
sheets form a tetragonal framework that is found to have a high specific surface area of 772 m2 g−1. Based on the definition of porous materials, the network is mesoporous with an observed pore size of 3.03 nm, which is in good agreement with the material’s calculated pore size. The experimentally obtained HOMO-LUMO band gap is 2.62 eV, confirming the semiconducting nature of PEPy-COF. PEPy-COF emits a shiny blue luminescence under UV and visible light. This luminescence intensity is temperature-dependent in solvents with different polarities and dielectric constants demonstrating that the PEPy-COF has potential use in a wide range of temperature-sensing devices. The fluorescence intensity ratio is similar for different temperatures under ultra-sound conditions and varying solvents.

Amin Zadehnazari, Ahmadreza Khosropour, Ataf Ali Altaf, Saeed Amirjalayer, and Alireza Abbaspourrad*