γ-Ray radiolysis and theoretical study on radical ions of star-shaped oligofluorenes having a truxene or isotruxene as a core

► Radiolysis provides absorption spectra of radical ions of star-shaped oligofluorenes. ► Absorption spectroscopic properties depend on oligomer size extensively. ► TDDFT provides reasonable assignments to the visible and near-IR absorption bands. ► Extensive charge delocalization was indicated by planarization of oligomers.