Multistep Electron Transfer Systems Containing [2.2]- or [3.3]Paracyclophane

Abstract

Paracyclophanes (PCPs), which exhibit interesting properties due to their transannular interactions, have been employed as a spacer in various electron transfer (ET) systems. In the present work, we investigated ET processes in dyads and triads containing [2.2]PCP or [3.3]PCP as donors to study their properties in multistep ET processes. The dyad molecules of PCP and 1,8-naphthalimide (NI) as a photosensitizing electron acceptor exhibited charge separation (CS) upon excitation of NI. In addition, triads of NI, PCP, and carbazole showed charge shift after an initial CS, thus confirming multistep ET. In this study, we demonstrated that use of [3.3]PCP in place of [2.2]PCP enhanced the initial CS rate. Lower oxidation potentials and a smaller reorganization energy for [3.3]PCP are shown to be key factors for this enhanced CS rate. Both of these properties are closely related to the strained structure of PCP; hence, the present results demonstrate the importance of strain in ET chemistry.

Protonation-Induced Sign Inversion of the Cotton Effects of Pyridinophanes. A Combined Experimental and Theoretical Study

“…The difference in transannular interaction between [2.2]-and [3.3]paracyclophanes has been recently investigated by comparing their electron transfer processes. 54 Considerably greater differences were found in CE intensity (10-fold in Δε) and also in anisotropy (g) factor (4.7fold, 0.014 vs 0.003) for the CT band of 1-H + and 2-H + . This may be better explained by the conformational diversity of dithia[3.3]cyclophane and the mutual cancellation of CEs, rather than the intrinsic reduction of CEs for [3.3]cyclophane, as judged from the calculation results for models with varying separations (Figure S5 in the Supporting Information).…”

“…As expected, the H DA value for [2.2]­paracyclophane 1-H + was markedly larger (by a factor of 2.5) than that for [3.3]­cyclophane 2-H + , as a consequence of the smaller separation between the planes. The difference in transannular interaction between [2.2]- and [3.3]­paracyclophanes has been recently investigated by comparing their electron transfer processes . Considerably greater differences were found in CE intensity (10-fold in Δε) and also in anisotropy ( g ) factor (4.7-fold, 0.014 vs 0.003) for the CT band of 1-H + and 2-H + .…”

Importance of Through-Space Interaction of [2,2′]-Paracyclophane-oligo(p-phenylenevinylene) Molecular Wires for Photovoltaic Application and Effective Wire Design by Chemical Substitution

“…One type of dye-sensitized molecule is a donor–wire (bridge)–acceptor (D–W–A) system − (see also Figure a and Figure a). Porphyrin and fullerene (C 60 ) have been widely used in combination as donor and acceptor units, respectively. − ,,, In the CS in a typical D–W–A molecule, photoexcitation occurs at a donor site, and the excited electron moves to an acceptor site through multistep electron transfer using the LUMOs of each part (Figure b).…”

“…For example, a donor–acceptor connected oligo­( p -phenylenevinylene) (oPPV) molecular wire was reported to achieve good CS properties. , In the experiment, CS between donor and acceptor was observed even when the wire had a length of 40 Å. More recently, the inclusion of [2,2′]-paracyclophane (pCp) and its derivatives in the wire part in the D–W–A system (see Figure a) has attracted much interest due to its unique effects. ,,,,, Cyclophane (Cp) has two six-membered rings locked by two alkyl chains. , Various Cp-based molecular wires have been proposed as new optical/electronic materials. − Among these, a pCp-oPPV mixed wire was proposed to change the CS and CR rate. It was experimentally observed that the inclusion of pCp increases the CS rate and reduces the CR rate .…”

“…More recently, the inclusion of [2,2′]paracyclophane (pCp) and its derivatives in the wire part in the D−W−A system (see Figure 2a) has attracted much interest due to its unique effects. 8,9,11,13,15,16 Cyclophane (Cp) has two six-membered rings locked by two alkyl chains. 18,19 Various Cp-based molecular wires have been proposed as new optical/electronic materials.…”