Rylene diimides are among the most studied chromophores due to their stability and ability to generate charge carriers through photoinduced electron transfer. For this, the study of photoinduced charge transfer processes on these molecules is of paramount importance for the design of molecular systems that allow the conversion of light into electrical energy. To this goal, transient absorption spectroscopy (TAS) is the tool that allow to extract both spectral and kinetic information of such molecular architectures. In this Dissertation, charge separation processes of three rylene diimide systems are discussed: a perylenediimide (PDI) monomer, a PDI oligomer, and several polymers containing napthalenediimide (NDI) as electron acceptor.

First, we studied the photoinduced charge transfer dynamics in luminescent donor-acceptor polymers and copolymers that use a single unit of naphthalene diimide (NDI) as acceptor, polystyrene chains as primary donor, and secondary stronger-donor chains. Our results show that while in solution charge separation occurs mostly intrachain and the charge recombination is ultrafast, in solid-state films charge separation occurs mostly interchain, with the participation of secondary electron donors. We also show that luminescence occurs through radiative charge recombination from highly coupled pairs, which can be photoselected upon red-edge excitation. As a competitive pathway, recombination to the triplet state of NDI is also present. We found that this pathway is almost fully suppressed with a strong secondary donor. Lastly, a direct excitation of the secondary donor leads to competitive photodynamics which do not result in the formation of charge-separated states, thus competing against radiative recombination.

Secondly, we confirmed the occurrence of symmetry-breaking charge separation in an oligomer consisting of three units of PDI which form a cage, by the detection of PDI radical anion (PDI•⁻) and radical cation PDI•⁺ in solvent mixtures of increasing polarities. We showcase a six-parameter target kinetic model which joins together the information extracted from TAS and the bi-exponential decay (due to delayed fluorescence) obtained from time-resolved fluorescence, by means of constraints resulting from calculating the eigenvalues of the k-matrix (amplitudes and lifetimes derived from the fluorescence decay). We used this approach to extract time constants from this complicated model, and to detect the occurrence of SB-CS in low-polarity solvent mixtures, by contrast a simple global analysis it is not sufficient to confirm that SB-CS is operative.

Thirdly, we presented a strategy to photogenerate and photoexcite the elusive PDI•⁻ species in acetonitrile using pump-pump-probe spectroscopy. Our approach allows for the photoexcitation of PDI with a first pump, followed by PET with the first (halogenated) electron donor, generating a geminate ion pair (GIP). This GIP is able to recombine to the triplet state of PDI, from which quenching with a second donor electron donor generates a GIP with triplet multiplicity. Hence, this GIP is unable to recombine to the ground-state due to spin-selection rules, and rather undergoes cage escape, generating free ions. We proved that the PDI radical anion generated this way can then be excited by the second pump pulse, allowing for the study of its photodynamics.