Fluorescence quenching of indolo[3,2-b]carbazole compounds by conformational motions of attached substituents

• Fluorescence yields of ICZ compounds are higher in solids than in solutions.
• Conformational motions of substituents cause fast non-radiative relaxation.
• Radiative relaxation rates are not sensitive to the conformational states.

The influence of substituents on spectral properties and the excited state relaxation of indolo[3,2-b]carbazole derivatives has been studied by means of steady-state and time-resolved spectroscopy and quantum chemical calculations. Conformational motions of the substituents in solutions were found to cause a significant acceleration of the non-radiative excited state relaxation and concomitant fluorescence quenching of the studied compounds in comparison with their solid films, where the conformational mobility is suppressed. Although the substituents also strongly influence the radiative relaxation rates, these rates are not sensitive to the conformations of the substituents.

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