Charge Transfer Pathways in Three Isomers of Naphthalene-Bridged Organic Mixed Valence Compounds

Abstract

Naphthalene was substituted at different positions with two identical triarylamine moieties to result in species which are mixed-valence compounds in their one-electron oxidized forms. They were investigated by cyclic voltammetry, optical absorption, EPR spectroscopy, X-ray crystallography, and DFT calculations. When the two redox-active triarylamine moieties are connected to the 2- and 6-positions of the naphthalene bridge, their electronic communication is significantly stronger than when they are linked to the 1- and 5-positions, and this can be understood on the basis of a simple through-bond charge transfer pathway model. However, this model fails to explain why electronic communication between triarylamine moieties in the 1,5- and 1,8-isomers is similarly strong, indicating that through-space charge transfer pathways play an important role in the latter. In particular, charge transfer in the 1,8-isomer is likely to occur between the triarylamino C atoms in α-position to the naphthalene linker because the respective atoms are only about 3 Å apart from each other, and because they carry significant spin density in the one-electron oxidized forms of triarylamines. This particular through-space charge transfer pathway might be generally important in molecular structures based on the 1,8-disubstituted naphthalene pillaring motif.

Thienylvinylenethienyl and Naphthalene Core Substituted with Triphenylamines—Highly Efficient Hole Transporting Materials and Their Comparative Study for Inverted Perovskite Solar Cells

“…Since both cores, TVT and NAP, have been shown to be two of the best candidates for obtaining high hole mobility, it would be an obvious choice to use them as cores in the design of new hole transporting materials . For the naphthalene core unit, there are three possibilities to functionalize the conjugated backbone – via 1, 4‐, 1, 5‐, or 2, 6‐positions . Among these options, the 2,6‐postion of naphthalene will result in the most planar conformation to achieve highly extended π‐conjugation .…”

Through-Space Conjugation: A Thriving Alternative for Optoelectronic Materials

“…As through-space conjugation has high sensitivity to geometric and electronic structures, 16 the moieties generally need to overcome steric hindrance to form a favorable face-to-face geometry with an inter-ring separation of less than 3.5 Å. 17 Based on this general principle, many molecules with diverse optical and electronic properties have been designed by exploiting through-space conjugation, such as carbazole hexaphenylbenzene (CzHPB), 18 naphthalene-1,8∶4,5-bis (dicarboximide) dimer ((−)-2NDI), 19 o-phenylene hexamer (oP 6 (H) 6 ), 20 1,8-triarylamino naphthylene (N-1,8TAA), 21 paracyclophane analogue (CP[(NBP) 2 F]), 22 etc. Active studies on these molecules have propelled further development of through-space conjugation theory and has shown them to be highly promising for a series of optoelectronic materials and devices.…”

Mixed‐Valent Molecular Triple Deckers

“…Their unusual three‐dimensional structure likely plays an important role in mediating charge transfer between the two redox‐active PTZ centers, particularly in view of the long through‐bond distance involving 23 σ‐bonds between N‐atoms. The 1,8‐substitution pattern at the naphthalene bridging units employed here is expected to provide only weak through‐bond electronic coupling, and it seems plausible that the overall charge‐transfer pathway includes a mixture of through‐bond and through‐space interactions. Long‐range ET across oligo‐naphthalene structures is yet far less well explored than across oligo‐ p ‐phenylenes, and the insights gained here point to uncommon phenomena that deserve further attention in future studies, particularly in view of recent advances in the synthesis of oligo‐naphthalenes .…”