Die Lösungsmittelabhängigkeit der Elektronenspektren und die Änderung der Dipoleigenschaften N-substituierter Acridone bei elektronischer Anregung / The Solvent Dependence of the Electronic Spectra and the Change of the Dipole Properties of N-Substituted Acridones at Electronic Excitation

Abstract

Abstract The absorption and fluorescence spectra of acridone, N-methylacridone and N-phenylacridone are measured at 298 K for 35 solvents of different polarity. For the long wave 1La-transition, which shows a distinct positive solvatochromism, the oscillator strenght and the natural fluorescence lifetime are calculated. The change of the dipole moment (pd), determined from the Stokes’ shift as a function of solvent polarity, is nearly parallel to that of the ground state (pg). The absolute values and directions of pg and pe confirm the increasing polar character of the S1-state within the sequence N-phenylacridone, acridone and N-methylacridone. These values are used for an interpretation of the charge distribution and solvatation of the S0- and S1-states. By consideration of the solvent relaxation and the activation energy of the temperature dependent S1-T2 intersystem crossing process it is shown that in addition to the decrease of the S1-energy with increasing solvent polarity the T2-energy increases relative to S0, especially in the case of protic solvents.