Due to the key role of Fe(III) species in living organisms, real‐time detection of Fe3+ ions is an important topic for the accurate diagnosis of many diseases, such as Alzheimer's, Huntington's, and Parkinson's diseases. Here, soft long‐chain alkyl groups serving as the grippers are introduced into the rigid porous skeleton through a one‐step Suzuki‐coupling reaction. Through the ion‐induced dipole interaction of long‐chain alkyl groups with Fe3+ ions, the resulting PAF solid exhibits excellent enrichment effect for metal elements. Accordingly, an absorption competition quenching (ACQ) phenomenon is observed leading to the selectivity and sensitivity for monitoring Fe3+ ions in the presence of various interfering ions. The sensing performance with the detection limit of 5.34×10−6 M far exceeds that of other porous solids including MOFs, ZIFs, COPs, and PNTs, etc. This work pioneers an efficient strategy that introducing long‐chain alkanes as the grippers for the design of advanced sensors for practical application. [ABSTRACT FROM AUTHOR]