A recent paper from our group has identified a novel orbital structure-function relationship in donor-acceptor (D-A) materials, enabling predictions of the degree of S1 CT using ground state orbital analysis alone. For integration of such relationships into high-throughput screening procedures, metrics that quantify these relationships must be tested on new chemical systems where high-quality crystallographic and spectroscopic data are available. To this aim, we present a comparative study of the crystallographic structure, spectroscopy, and electronic structure of two D-A cocrystals: 4-(1-naphthylvinyl)pyridine (Npe) co-crystalized with 1,2,4,5tetracyanobenzene (TCNB) and Npe co-crystalized with 1,2,4,5tetracyanoquinodimethane (TCNQ), shown in Figure . We report a revised crystallographic study of Npe:TCNB, in which we find a monoclinic crystal structure, in contrast to the previously reported triclinic structure. A crystal structure of the second system studied here, Npe:TCNQ, has not been reported to date; we thus present the first studies of the structure and photophysical properties of Npe:TCNQ. Theoretically, the S0 optimized geometries of the D-A dimer models are computed using density functional theory (DFT) and compared to calculations of the extended solids via periodic boundary conditions (PBC) DFT to assess the role of the extended crystal in constraining molecular geometries of the D-A subunits. Comparisons of the experimental vs. theoretical UV-Vis spectra enable benchmarking theoretical cluster models against the experimentally studied extended solids. We report the degree of CT in the ground (S0) and first electronically excited singlet state (S1) of our theoretical dimer models to compare between the two co-crystal systems. Furthermore, we rationalize the degree of S1 CT by computing the orbital similarity between isolated and D-A complexes, using our recently developed metric. A variety of DFT methods and basis sets were benchmarked and used to identify possible minimum energy structures along the neutral Npe:TCNB and Npe:TCNQ dimer surfaces, with additional information given in ESI Tables S1-S2. Geometry optimizations and relative energies were computed and compared using functionals ωB97X-D, B3LYP, B3LYP-D3, CAM-B3LYP, CAM-B3LYP-D3, and M06-2X and basis sets 6-31G(d,p), 6-31+G(d,p), and 6-311+G(d,p), resulting in 18 combinations of functional and basis set. Here, a D3 suffix on the functional name refers to the Grimme D3 dispersion correction, needed for the calculation of non-covalent bonding interactions. We find that CAM-B3LYP-D3/6-31+G(d,p) calculations of the dimer clusters best reproduce the geometries found in the experimental crystal structures and UV-Vis spectra without the need for any long-range parameter tuning. Geometry optimization calculations were also performed with periodic boundary conditions (PBC) DFT using the hybrid functional HSE06 and 6-31G(d,p) basis using crystallographic information file (CIF) geometries from the experimental crystal structure as initial guesses. Hybrid functionals such as HSE06 combine semi local exchange and non-local Hartree-Fock exchange, which yields improved band gaps, excitation energies, and thermochemical properties over pure functionals (see Ref. 32 and references within). Structures were obtained by optimizing all coordinates and unit cell lengths using an energy convergence criterion of 10 -5 . The number of k points used for Npe:TCNB is 28 and for Npe:TCNQ, 36. Direct band gaps are reported using these PBC DFT parameters. Excited state calculations were carried out using CAM-B3LYP-D3/6-31+G(d,p) within the linear response timedependent DFT (TDDFT) formalism, with additional details given in ESI, Tables S3-S12 and Figures S14-23. Natural bond orbital (NBO) population analyses were performed to quantify the amount of CT in the ground state of the complexes, while transition density matrix analysis was used to calculate the degree of CT in the S1 excited states using Theodore. Excited state analysis was facilitated by Martin's Natural Transition Orbital (NTO) model. All calculations described in 2.1.1 were carried out using the GAUSSIAN suite of electronic structure programs, G16. Stability was tested on all converged Kohn-Sham determinants. Stationary points were verified as minima using harmonic frequency analysis, employing analytical second-derivative calculations. All relative energies of structures are zero-point energy corrected, employing the harmonic approximation for frequency analysis. See ESI Tables S1-S2 and ESI Section 2.4 for more details.