Photophysical tuning via piperazine nitrogen torsion in a ferrocene-aminonaphthalimide derivative

Molecules respond to changes in their environment which may affect their photophysical properties. This computational study uses DFT and TD-DFT methods to investigate how the environmental changes tune photophysical properties in a ferrocene-aminonaphthalimide-piperazine derivative. Modeled in water and THF solvents, via implicit and explicit solvation, the work identifies two critical dihedral angles that influence the UV-vis absorption spectrum: piperazine N-torsion and CCNN torsion. Potential energy scans and UV-vis absorption spectra along these dihedral angles are presented. Environment affects both dihedral angles, CCNN varies with molecular substitutions, shifting the main absorption peak up to 90 nm from UV to vis area and altering its intensity, while there is also a weak peak in vis area at around 450 nm whose intensity increased with the planarity of the N atom. Overall, changes in the relative orientation of the piperazine unit to the aminonaphthalimide significantly alter the absorption spectrum. These results demonstrate that the piperazine-aminonaphthalimide geometry governs spectral behavior, illustrating how microenvironment-induced intramolecular rotations can be leveraged to tune absorption through molecular design principles.