Emission from Charge Recombination during the Pulse Radiolysis of Bis(diarylamino)dihydro-indenoindene Derivatives

As a new series of compounds designed for organic light-emitting diodes and organic photovoltaics, dihydro-indenoindenes (DI) substituted by bis­(diarylamino) groups (R-DI) including bis­(diphenylamino)­dihydro-indenoindene, bis­(ditolylamino)­dihydro-indenoindene, and bis­(carbazolyl)­dihydro-indenoindene were studied during the pulse radiolysis in solvents to measure the transient absorptions of the corresponding radical cations (R-DI^•+), radical anions (R-DI^•–), and R-DI in the triplet excited states (³R-DI*). It was clearly indicated that the origin of the electronic transitions in the visible region of DI^•+, DI^•–, and ³DI* is mainly attributed to the <i>trans</i>-stilbene skeleton of DI. With increasing the electron-donating ability of the diarylamino substituents, the absorption peaks of R-DI^•+, R-DI^•–, and ³R-DI* showed a red shift. The observed spectra and theoretical calculations suggested that the positive charge is mainly localized on the triphenylamine moiety of R-DI^•+, whereas the negative charge is localized on the <i>trans</i>-stilbene moiety of R-DI^•–. All R-DI showed emissions during the pulse radiolysis in benzene. It was found that the fluorescence quantum yields and the difference between annihilation enthalpy changes and singlet excited-state energies are responsible for the relative emission intensity obtained during the pulse radiolysis. Moreover, on the basis of the observed spectra and thermodynamic calculations, the emissions are suggested to be originated from R-DI in the singlet excited states, which are generated from the charge recombination between the corresponding R-DI^•+ and R-DI<sup>•–