Supplementary Material

The supplementary material contains experimental details, materials, and methods; crystallographic and refinement data for compounds 1c-d, 2a, 2c-d, 3a, and 4d; angles between the planes of the central pyrimidine core and the adjacent aryl rings; energy and relative energy in the ground and first excited states calculated at the PBE0/6-31+G** level of theory; dipole moments for the ground and first excited states of compounds 1-4; energy and relative energy in the ground and first excited states calculated at the PBE0/6-31+G** level of theory; calculated vertical electronic transitions, oscillator strength, and main component of the S0Sn transition at the TD-PBE0/6-31+G** level of theory; calculated energies and relative energies for the dimer of 4d; wavenumbers, reorganization energy, and Huang-Rhys factors (compounds 1-4); NMR and MALDI-TOF MS spectra (2a, 2d, and 3a-d); absorption and emission spectra in solution and in the solid state (compounds 1-4); selected dihedral angles for the ground and excited states (compounds 1-4); calculated molecular orbitals (compounds 1-4); optimized molecular geometry for the dimer of 4d (enol and keto) in the ground and excited states; Huang-Rhys factors vs. normal mode wavenumbers of the excited state (compounds 1-4); and QM/MM model clusters for compounds 1c, 1d, 2a, 2c, 2d, and 3a.