Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push-Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD-DFT Computational Study.
Three (donor-π-acceptor)(+) systems with a methyl pyridinium or quinolinium as the electron-deficient group, a dimethyl amino as the electron-donor group, and an ethylene or butadiene group as the spacer have been investigated in a joint spectroscopic and TD-DFT computational study. A negative solvatochromism has been revealed in the absorption spectra, which implies a solution color change, and interpreted by considering the variation in the permanent dipole moment modulus and orientation upon photoexcitation. The fluorescence efficiency decreases upon increasing solvent polarity, in agreement with the excited-state optimized geometries (planar in low-polarity media and twisted in high-polarity media). Femtosecond transient absorption has revealed the occurrence of a fast photoinduced intramolecular charge transfer (ICT) and the molecular factors that determine an efficient ICT. Considering the crucial role of the ICT in tuning the nonlinear optical (NLO) properties, these compounds can be considered promising NLO materials.
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.
Benedetta
B
Carlotti
Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy). enrico.benassi@sns.it.
Enrico
E
Benassi
Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa (Italy).
Vincenzo
V
Barone
Department of Industrial Engineering, University of Catania viale Andrea Doria 6, 95125 Catania (Italy).
Giuseppe
G
Consiglio
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).
Fausto
F
Elisei
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).
Alessandra
A
Mazzoli
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).
Anna
A
Spalletti
charge transfer; density functional calculations; femtosecond transient absorption; nitrogen heterocycles; solvent effects