Optical properties of 4-bromobenzaldehyde derivatives in chloroform solution.

In this work we give a deeper insight into the electronic structure of a series of purely organic molecules that were recently employed as building blocks in crystals with very efficient phosphorescent emission. With this purpose, the low-lying excited states of a series of 4-bromobenzaldehyde derivatives in chloroform solution are explored by means of time-dependent density functional theory (TDDFT) calculations, together with the absorption, fluorescence, and phosphorescence experimental spectra. The optical properties of the studied molecular models are extensively discussed, in terms of the frontier molecular orbitals involved in the relevant electronic transitions, the recorded and simulated absorption profiles, and the molecular geometries and transition energies of the emitting states. The calculations eventually help in the assignment of the character of the lowest lying singlet and triplet emitting states for these compounds.