Theoretical and spectroscopic data of the investigated Cu(I) NHC complexes with the anionic carbene An6DAC and other pyridine-derived ligands. This study provides a detailed overview of the possibilities of targeted molecular design to selectively address desirable optical properties, especially thermally activated delayed fluorescence (TADF). The theoretical data include high-level DFT/MRCI calculations. The spectroscopic data include steady-state and temperature-dependent time-resolved luminescence measurements on different time scales (ns, µs, ms). Author Contributions Conceptualization: C. M. M. and M. S.; Methodology: J. G., D. S., P. S., S. F., R. K., M. S.; Validation: J. G., D. S., P. S.; Formal analysis: J. G., D. S., P. S., S. F., R. K., M. S.; Investigation: J. G., D. S., P. S. M. S; Data curation: J. G., D. S., P. S., S. F., R. K.; Writing – original draft preparation: J. G., D. S., P. S., C. M. M., M. S.; Writing – review and editing: J. G., D. S., P. S., R. K., C. G., C. A. M. S., C. M. M., M. S.; Visualization: J. G., D. S., P. S.; Project administration: C. G., C. A. M. S., C. M. M., M. S.; Funding acquisition: C. G., C. A. M. S., C. M. M., M. S.