With the aim of considering a progressive increase of the molecular flexibility, the second selected target is the 2,7-pyrenylene polymer, which is composed by stiff PAH units (pyrene), connected by rotatable bonds. As detailed in Table , although the structure of each PAH unit can be safely handled through the harmonic term defined in equation ( ) depending on the stiff dihedrals φ , the rotation of two neighboring units around the C-C bond connecting them (see Figure .b) can undergo large amplitude oscillations and present several minima. To take such slow anharmonic motions into account, with respect to the previous test case, both the flexible dihedrals δ and their contribution, accounted for by equation ( ), are automatically added by JOYCE3.0 to the IC collection and to the set of employed model functions, respectively. A three unit chain of pyrenylene polymer has been recently parameterized by some of us, following the JOYCE procedure. The resulting trimer QMD-FF was thereafter extended to a chain of 35 units, to perform MD simulations of the polymer on a gold surface, well reproducing the molecular adhesion/detaching forces as measured by cryogenic atomic force microscopy. Given such successful validation, in the present work we build a QMD-FF (see Section S5.2 in the Supporting Information for the full list of parameters) for a four-unit polymer chain (target II) by directly transferring the JOYCE parameters previously obtained for the trimer, following the same procedure reported in Ref. [36]. Although the quality of the JOYCE tailored QMD-FF for poly(2,7-pyrenylene) chains of 35 and 10 units has been already assessed in previous work, here we specifically validate the JOYCE3.0 procedure on target II by comparing the description of the molecular structure achieved with our QMD-FF, with that obtained with a standard one. This was done to further highlight the potential shortcomings of relying on a general-purpose description and the advantages offered by a specifically tailored approach. Figure : a) Tetra(2,7-pyrenylene) IR spectra computed from the isolated molecule's Hessian matrix and optimized geometry at full QM level (top, green line) or at MM level, either with the general purpose GAFF (center, orange line) or the QMD-FF (bottom, green line); b) UV/VIS spectra computed for tetra(2,7-pyrenylene) at the geometry optimized at QM level (top, green line) or at MM level, using either GAFF (center, orange line) or QMD-FF (bottom, green line).