Study of photophysical properties in bronsted acids for nitrogen atoms with different hybrid (sp, sp2, sp3) orbitals

Fluorescent tiny molecules that are resistant to acid have long been the center of interest. The nitrogen atoms on benzyl cyanide were sp hybridized, while the two nitrogen atoms at pyrimidine were sp² hybridized in the primary structure that we constructed. With the addition of a protonic acid (H₂SO₄, CH₃SO₃H, and HF), the nitrogen atoms at acridine underwent sp³ hybridization, which caused the hydrogen protons to interact with the three types of nitrogen atoms to varying degrees. This distribution of the electron cloud density led to a decrease in fluorescence emission. Furthermore, Gaussian 09 software and DFT calculations were used to model its orbital conformation, which is the highest occupied molecular orbital—lowest unoccupied molecular orbital (HOMO–LUMO). Furthermore, its crystal structure was assigned to the orthorhombic system with stronger non-homogeneity (a = 8.9160 (4) Å, b = 44.289 (3) Å, c = 9.6131 (7) Å, α = 90°, β = 90°, γ = 90°, V = 3796.0 (4) ų, z = 4, Dc = 1.244 g/cm³).

Graphical abstract