title: Photoinduced symmetry-breaking intramolecular charge transfer in a quadrupolar pyridinium derivative.
abstract: We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-π-acceptor-π-donor)(+) quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.
authors.affiliation: 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. benedetta.carlotti@gmail.com.
authors.forename: Benedetta
authors.initials: B
authors.lastname: Carlotti
authors.forename: Enrico
authors.initials: E
authors.lastname: Benassi
authors.forename: Anna
authors.initials: A
authors.lastname: Spalletti
authors.forename: Cosimo G
authors.initials: CG
authors.lastname: Fortuna
authors.forename: Fausto
authors.initials: F
authors.lastname: Elisei
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Barone
mesh_terms: D003198:Computer Simulation; D004579:Electron Transport / Q000528:radiation effects; D008027:Light; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation / Q000528:radiation effects; D011726:Pyridinium Compounds / Q000737:chemistry* / Q000528:radiation effects*; D011829:Radiation Dosage; D055672:Static Electricity
chemical_list: D011726:Pyridinium Compounds