A TDDFT investigation of bay substituted perylenediimides: Absorption and intersystem crossing

Abstract

The conformational structure and electronic spectra properties of a series of bay substituted perylenediimides (PDI) derivatives have been investigated by means of density functional theory (DFT) and time‐dependent DFT. The B3LYP and PBE0 hybrid exchange‐correlation functionals were applied in conjunction with the double‐ζ quality SVP basis set. These compounds are interesting for organic materials science and as photosensitizers in cancer phototherapy (PDT), because of their intense absorption in the visible region. Results show that the substitution at the bay position of the PDI parent molecule with N‐alkyl groups shifts the absorption maxima towards the red part of the visible spectrum (around 650–700 nm) as required for the applications in PDT. The main PDT action mechanisms have been investigated by computing of electron affinities, ionization potentials, triplet energies and spin‐orbit matrix elements between singlet and triplet excited states. © 2012 Wiley Periodicals, Inc.

Radical‐Enhanced Intersystem Crossing in a Bay‐Substituted Perylene Bisimide−TEMPO Dyad and the Electron Spin Polarization Dynamics upon Photoexcitation**

“…Due to the amino‐substitution at the bay position, the PBI core is twisted by ca. 20° on one side, whereas on the other side the core it is twisted by 10° [75,97] . The distance between the nitroxide spin carrier and the centroid of PBI moiety is 9.2 Å, which is similar to the previously reported PBI−TEMPO dyad with the TEMPO moiety attached on the imide position (9.9 Å) [52] .…”

“…Therefore, in this particular case, we demonstrate that the REISC is more efficient than the heavy atom effect to induce ISC. Note that, the PBI−NH shows a negligible Φ Δ , although it was proposed that bay amino‐substituted PBI may show ISC, based on DFT computations on the spin orbit coupling effect [75] . The Φ F of PBI−NH is also low (2.9 %), as compared to the unsubstituted PBI ( Φ F =95.2 %).…”

Singlet Fission in Perylenediimide Dimers

“…This functional has been also used by Engels and co-workers. , Additional calculations with CAM-B3LYP yielded excitation energies that are very close to the ωB97X-D values; the corresponding E stt is −0.118 eV, which is close to −0.203 eV obtained by ωB97X-D. In contrast to popular functionals that might yield excitation energies in better agreement with experimental values, ωB97X-D was shown to better reproduce the character of excited-state wave functions . These reference values determine the accuracy of the absolute excitation energies of the dimers.…”

Substituent effects on the optical properties of naphthalenediimides: A frontier orbital analysis across the periodic table

“…Early theoretical work addressed the effect of substituents on the optical properties of aromatic molecules . Recent time‐dependent density functional theory (TDDFT) studies have focused on perylene diimides (PDIs), but those addressing the influence of substituents on the optical properties of NDI are limited. An important distinction between these two closely related chromophores is the fact that PDIs are mainly substituted at bay positions, resulting in sterically induced distortions of the perylene backbone, whereas NDI substituents can be subject to H‐bonding with the imide carbonyls.…”