Vibronic Splitting of the Electronic Origin in Two Conformers of the 3‐Tolunitrile Dimer

• Published in: Chemphyschem 2024-11, Vol.25 (22), p.e202400509-n/a
• Main Authors: Martini, Jascha, Ortlepp, Jan, Henrichs, Christian, Schmitt, Michael
• Format: Article
• Language: English
• Subjects: 3-tolunitrile dimer; Aromatic compounds; Charge transfer; Dimers; Dipoles; Emission spectra; Excitation; Excitation spectra; excitonic splitting; fluorescence emission; Franck–Condon analysis; laser induced fluorescence; Splitting; structure
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.202400509

3‐tolunitrile (3‐TN) can form three different dimers, which differ in the relative orientation of the methyl groups. We determined the geometry changes of two of these conformers of 3‐TN upon electronic excitation via a Franck–Condon fit of the vibronic intensities in the fluorescence emission spectra. Both aromatic rings expand upon electronic excitation, showing a delocalized one‐photon excitation of the cluster. The conformer with the smaller center‐of‐mass distance shows an unusual order of the split components of the electronic origin. We attribute this changed order to the stronger charge transfer contributions to the splitting and a partial breakdown of the point dipole approximation, made in the Frenkel type interaction. The geometry change of different isomers of the 3‐tolunitrile dimer is determined from Franck–Condon fits of the vibronic intensities in the respective fluorescence emission spectra and from ab initio calculations. In the inversion symmetric dimers, both aromatic rings expand upon electronic excitation, showing a delocalized one‐photon excitation of the cluster.