Experimental and theoretical determination of transition dipole moments of ethyl 5-(4-aminophenyl)- and 5-(4-dimethylaminophenyl)-3-amino-2,4-dicyanobenzoate

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The absorption and fluorescence transition dipole moments ( $$\hat M_{ge}$$ and $$\hat M_{eg}$$ ) for ethyl 5-(4-aminophenyl)-3-amino-2, 4-dicyanobenzoate (EAADCy) and ethyl 5-(4-dimethylaminophenyl)-3-amino-2, 4-dicyanobenzoate (EDMAADCy) have been determined on the basis of the steady-state and time-resolved spectroscopic measurements and semiempirical quantum-chemical calculations. The values of the transition dipole moments of perpendicular and flattened forms of the investigated molecules were estimated as a function of the solvent polarity. Noted differences between the absorption and emission transition dipole moments (i.e., $${{\hat M_{ge} } \mathord{\left/ {\vphantom {{\hat M_{ge} } {\hat M_{eg} }}} \right. \kern-\nulldelimiterspace} {\hat M_{eg} }} \ne 1$$ ) confirm that the change of the electronic and molecular structure take place in the excited state.