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Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push–Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD‐DFT Computational Study
Author(s) -
Carlotti Benedetta,
Benassi Enrico,
Barone Vincenzo,
Consiglio Giuseppe,
Elisei Fausto,
Mazzoli Alessandra,
Spalletti Anna
Publication year - 2015
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201402896
Subject(s) - solvatochromism , photoexcitation , chromophore , intramolecular force , ultrafast laser spectroscopy , photochemistry , chemistry , acceptor , excited state , femtosecond , photoinduced electron transfer , two photon absorption , materials science , electron transfer , spectroscopy , molecule , organic chemistry , atomic physics , optics , laser , physics , quantum mechanics , condensed matter physics
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.