Relaxation of Optically Excited p-Nitroaniline: Semiempirical Quantum-Chemical Calculations Compared to Femtosecond Experimental Results

摘要: p-Nitroaniline (pNA) was examined with the semiempirical SAM1 Hamiltonian in vacuo and water. Geometry optimizations were performed ground lowest excited state along −NH2 wagging −NO2 twisting coordinate. The latter is shown to play a key role spectroscopy dynamics of pNA. strong charge-transfer (CT) absorption band conformationally broadened. Red-edge excitation prepares CT distribution conformations which concentrated around coplanar conformation benzene moiety. In water, C-amino C-nitro stretching vibrations are also excited. structural reorganization those modes assumed occur on same time scale as ultrafast polar solvation. this case relaxation water after ∼100 fs consists mainly an evolution twist toward deep minimum at perpendicular conformation; dipole moment change during that process has upper limit 2 D. Stimulated emission...