Probing Charge Management across the π-Systems of Nanographenes in Regioisomeric Electron Donor–Acceptor Architectures

Abstract

Inspired by light-induced processes in nature to mimic the primary events in the photosynthetic reaction centers, novel functional materials combine electron donors and acceptors, i.e., (metallo)­porphyrins (ZnP) and fullerenes (C60), respectively, with emerging materials, i.e., nanographenes. We utilized hexa-peri-hexabenzocoronene (HBC) due to its versatility regarding functionalization and physicochemical properties, to construct three regioisomeric ZnP-HBC-C60 conjugates, which foster geometrical diversity by arranging ZnP and C60 in ortho-, meta-, and para-positions to each other. The corresponding hexaarylbenzene (HAB) motifs, with an interrupted π-system, were also prepared. Transient absorption measurements disclosed the fast population of charge transfer as well as singlet and triplet charge-separated states. With the help of density functional theory (DFT) calculations, we further conceive the communication across the HBCs and HABs. This work reveals the impact of both the geometrical arrangement with respect to through-space versus through-bond interactions and the structural rigidity/flexibility on the charge management across the different π-systems.

Regioisomeric Benzidine‐Fullerenes: Tuning of the Diverse Hole‐Distribution to Influence Charge Separation Patterns

“…To further discuss the effects of delocalization and localization on charge separation, global analysis is employed to study of the time‐dependent excited‐state features and kinetics. Comparing the TA of these three dyads, it is discernible that, similarly, all of them have undergone spectral narrowing process, especially the characteristic absorption peaks of radical ion pairs becoming sharper, reflecting the enhancement of ionic features, consistent with the transition of partial charge transfer to charge separation [4a] . Differently, excited state of 1 p generates and decays more rapidly, with the ESA reaching its maximum within 10 ps and decaying to the ground state within 200 ps.…”

“…Then it rapidly transforms into the second component, partial charge transfer ( p ‐TPTA δ+ ‐C 60 δ− ) within 0.9 ps. Sufficient proof lies in the overlapping features of partial singlet (520 nm) and C 60 − ⋅ (1030 nm) [4a] . The third component with larger ESA amplitudes is populated from the second within 2.5 ps, and the ESA of C 60 − ⋅ slightly blueshifts to 1020 nm and becomes sharper, which can be attributed to the conversion from partial charge transfer to charge separation.…”

“…In brief, chemical modifications in the ortho ‐, meta ‐, para ‐ sites of benzene core. This strategy bears distinct features at least the followings: [4a, 12] (i) taking structures into account, compared with ortho ‐, the steric hindrance of two chromophores connected in the counterpoint for para ‐ is minimum, providing a more comfortable space for wavefunction delocalization; (ii) aiming at electronic effects, compared with the meta ‐, the electronic conjugation is continuous in the ortho ‐ and para ‐derivatives, resulting in more unobstructed electron transfer path; (iii) in terms of the molecular design, regioisomers are prone to templates as regards preciseness, designment and processability, because ortho ‐, meta ‐, and para ‐ sites of benzene cores can be used as very simple structural templates [12a, 13] . Triphenylamine (TPA) is a popular donor [14] .…”

“…Fullerenes, especially C 60 , are prevalent acceptors, [15] benefiting from the high electron affinity, low reorganization energy, [16] which will improve the efficiency and extent of CS. Based on these advantages, fullerenes are full‐fledged to emerge as typical molecules for investigating of photocatalytic, photovoltaic and photosynthetic D‐A systems, [4a, 17] wherein the charge separation process is the key photophysical event.…”

Thioether‐Substituted Hexa‐peri‐hexabenzocoronenes

“…Additional references cited within the Supporting Information. [26,[28][29][30][31][32][33][34][35][36]…”