A multireference excited state database for correlation-aware screening of organic semiconductors in excitonic energy-materials discovery.

Organic semiconductors are attractive molecular platforms for excitonic energy materials, including light-harvesting, photon-management and energy-relevant optoelectronic technologies, but their discovery depends on reliable excited-state screening across large and chemically diverse molecular spaces. Here, we develop a multireference excited-state database for 1581 organic semiconductors to benchmark screening descriptors that control energy-relevant photophysical behaviour. For each molecule, we compute the two lowest singlet and triplet excitation energies and the oscillator strengths of the two lowest singlet transitions using the multireference methods SA-CASSCF and SC-NEVPT2, and compare these data with existing single-reference TD-DFT screening results. This comparison shows that TD-DFT provides a useful low-cost route for broad pre-screening, particularly for more robust descriptors such as triplet excitation energies, while singlet excitation energies, oscillator strengths, singlet-triplet gaps and singlet-singlet separations are more sensitive to electron correlation. The largest method-dependent deviations occur for electronically soft, heteroatom-rich, sulphur-containing and acyclic conjugated scaffolds, whereas rigid aromatic cores are more transferable across levels of theory. These differences have direct consequences for molecular candidate prioritisation. Relative to the original TD-DFT pre-screening results, SC-NEVPT2 expands the chemically diverse thermally activated delayed fluorescence candidate space, identifies optically relevant inverted singlet-triplet-gap molecules, and broadens the scaffold diversity of anti-Kasha candidates. By establishing where routine screening is transferable and where multireference reassessment reveals additional opportunities, this database provides a practical correlation-aware framework for molecular pre-screening and prioritisation of organic semiconductor candidates for excitonic energy-materials applications.