This dataset contains the computational data and source code for the manuscript “Mechanical Tuning of Singlet–Triplet Resonance for Efficient Triplet–Triplet Annihilation Upconversion.” It includes Gaussian 16 input and output files for the S₀, S₁, and T₁ electronic states, optimized geometries, frequency calculations, vertical excitation calculations, force-distorted resonance structures, and the complete optimization trajectories for anthracene, 1,4-bis(phenylethynyl)benzene (BPEB), and 9,10-diphenylanthracene (DPA). The repository also provides the Fortran implementation of the constrained minimum-force algorithm developed to identify the molecular displacement and external force required to satisfy the singlet–triplet resonance condition relevant to TTA-UC, together with example input and output files and compilation instructions.