Modulating Optoelectronic Properties of TBQP-Based Covalent Organic Frameworks for Chemical Sensing

Covalent organic frameworks (COFs) have emerged as promising porous organic semiconductors for chemical sensing, owing to their structurally tunable electronic properties and accessible pores. A key challenge for the rational design of these materials is establishing a clear understanding of how molecular-level functionalization dictates their optoelectronic response. Here, we address this challenge through a computational investigation of TBQP-based COFs, combining density functional theory and molecular dynamics to investigate the impact of edge functionalization on their electronic structure, optical properties, and adsorption reactivity toward Cl₂, ClF₃, and SO₂. Using representative molecular models and fragments derived from the TBQP architecture, our results demonstrate that the Frontier orbital energies and band gap of the extended framework are primarily governed by the electronic character of the constitutive building blocks. This enables systematic property modulation through targeted substituent effects. We establish quantitative correlations between experimental Hammett parameters, DFT-based reactivity indices, and analyte-induced electronic perturbations, providing descriptors that link chemical modification to optoelectronic behavior. Furthermore, we find that analyte adsorption can introduce midgap states, revealing a general electronic sensing mechanism for π-conjugated COFs. These findings not only offer practical guidelines for tailoring the electronic and reactive properties of TBQP frameworks but also underscore the critical role of molecular functionalization in governing the sensing performance of porous organic semiconductors. The identified structure-property relationships provide useful guidelines for the rational design of COF-based sensors.