Solvent effects on the intramolecular charge transfer excited state of 3CzClIPN: a broadband transient absorption study

The prediction of solvent properties using molecular probes often relies on correlating steady-state absorption and fluorescence measurements, as well as determining absorption maxima and/or Stokes shifts. In this study, we employ femtosecond broadband transient absorption (fs-bb-TA) spectroscopy to investigate the spectroscopic behaviour of the intramolecular charge transfer (ICT) excited state of 3CzClIPN (2,4,6-tri(9H-carbazol-9-yl)-5-chloroisophthalonitrile), a representative ICT organic molecule, in both aromatic and non-aromatic solvents. Unlike observations in non-aromatic media, fs-bb-TA spectra of 3CzClIPN in aromatic solvents exhibit enhanced spectral broadening that strongly correlates with the solvent's polarity. We hypothesise that this spectral broadening originates from a wider configurational energy landscape experienced by the positively charged carbazole Cz+ group, owing to the larger size and, consequently, reduced solvation effectiveness of aromatic solvent molecules. Broadening of intramolecular charge-transfer excited-state absorption of 3CzClIPN in aromatic solvents: a local probe of the medium's polarity.

Automated summary

In this study, femtosecond broadband transient absorption spectroscopy was used to investigate the spectroscopic behavior of the ICT excited state of 3CzClIPN in both aromatic and non-aromatic solvents. The results showed that the absorption spectra of 3CzClIPN in aromatic solvents exhibited enhanced spectral broadening, which strongly correlated with the polarity of the solvent. This broadening is hypothesized to be caused by a wider configurational energy landscape experienced by the positively charged carbazole group in aromatic solvents.