Phys Chem Chem Phys 2021 Jul 28. Epub 2021 Jul 28.
Department of Chemistry, Biology and Biotechnology and Centro di Eccellenza sui Materiali Innovativi Nanostrutturati (CEMIN) University of Perugia, via Elce di Sotto 8, 06123 Perugia, Italy.
Two symmetric quadrupolar cationic push-pull compounds with a central electron-acceptor (N+-methylpyrydinium, A+) and different lateral electron-donors, (N,N-dimethylamino and N,N-diphenylamino, D) in a D-π-A+-π-D arrangement, were investigated together with their dipolar counterparts (D-π-A+) for their excited-state dynamics and NLO properties. As for the quadrupolar compounds, attention was focused on excited-state symmetry breaking (ESSB), which leads to a relaxed dipolar excited state. Both electron charge displacements and structural rearrangements were recognized in the excited-state dynamics of these molecules by resorting to femtosecond-resolved broadband fluorescence up-conversion experiments and advanced data analysis, used as a valuable alternative approach for fluorescent molecules compared to time-resolved IR spectroscopy, only suitable for compounds bearing IR markers. Read More