3,4-Diamino naphthalimides and their respective imidazoles – Synthesis, spectroscopic and theoretical investigation

• Naphthalimide derivatives as precursors for photoactive NHCs are obtained.
• Their structure-media-spectra relationships are analysed.
• An unusual NHC dimer (tetraaminoethylene) with strong cyan emission was isolated.
• PBE0 and M06 functionals proved to accurately model the respective S0/S1 states.

A series of compounds containing 1,8-naphthalimide photoactive core were synthesized and studied with respect to their optical properties and applications. Combined spectral measurements and quantum chemical calculations allowed better understanding of the electronic effects in any particular substitution pattern starting from 3,4-diamino naphthalimides, through their respective imidazoles and quaternary N-heterocyclic carbene precursors, to corresponding carbene dimer (tetraaminoethylene). The absorption and fluorescence energies have been calculated with the PCM TDDFT formalism. PBE0 and M06 functionals were found to accurately model the distinctly different photophysical characteristics of the newly synthesized compounds.

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