The influence of substituents of perylenediimides on their spectroscopic properties

The influence of substituents of newly synthesized perylenediimides on their spectral properties and excited state relaxation has been studied by means of steady-state and time-resolved spectroscopy and quantum chemical calculations. Substituents at the perylene core cause broadening and shift of the absorption and fluorescence bands and also reduce the fluorescence quantum yield. Organic 4-tert-butylphenoxy substituents reduce the fluorescence yield by tens of percent by slightly reducing the oscillator strength of the radiative transition and by significantly increasing the non-radiative decay rate. We attribute both changes mainly to the distortion of the planarity of the perylene core. Bromine substituents reduce the fluorescence quantum yield by up to two orders of magnitude by opening an internal conversion channel.