PAH/PAH(CF3 )n Donor/Acceptor Charge-Transfer Complexes in Solution and in Solid-State Co-Crystals.

Karlee P Castro,Xue‐Bin Wang,Igor V Kuvychko,Yu‐Sheng Chen,Steven H Strauss,Alexey A Popov,Olga V Boltalina,Eric V Bukovsky,Shihu H M Deng,Nicholas J Deweerd

doi:10.1002/chem.201902712

Abstract

A solution, solid‐state, and computational study is reported of polycyclic aromatic hydrocarbon PAH/PAH(CF3)n donor/acceptor (D/A) charge‐transfer complexes that involve six PAH(CF3)n acceptors with known gas‐phase electron affinities that range from 2.11(2) to 2.805(15) eV and four PAH donors, including seven CT co‐crystal X‐ray structures that exhibit hexagonal arrays of mixed π‐stacks with 1/1, 1/2, or 2/1 D/A stoichiometries (PAH=anthracene, azulene, coronene, perylene, pyrene, triphenylene; n=5, 6). These are the first D/A CT complexes with PAH(CF3)n acceptors to be studied in detail. The nine D/A combinations were chosen to allow several structural and electronic comparisons to be made, providing new insights about controlling D/A interactions and the structures of CT co‐crystals. The comparisons include, among others, CT complexes of the same PAH(CF3)n acceptor with four PAH donors and CT complexes of the same donor with four PAH(CF3)n acceptors. All nine CT complexes exhibit charge‐transfer bands in solution with λ max between 467 and 600 nm. A plot of E(λ max) versus [IE(donor)−EA(acceptor)] for the nine CT complexes studied is linear with a slope of 0.72±0.03 eV eV−1. This plot is the first of its kind for CT complexes with structurally related donors and acceptors for which precise experimental gas‐phase IEs and EAs are known. It demonstrates that conclusions based on the common assumption that the slope of a CT E(λ max) versus [IE−EA] plot is unity may be incorrect in at least some cases and should be reconsidered.

Highlights

Organic co-crystalline materials containing electronically- and structurally-tuneable aromatic donors and acceptors exhibit a wide range of physicochemical properties that have found, or are expected to find, use in molecular electronic applications.[1,2,3,4,5,6,7,8,9,10] Of particular interest are the ways that strong electron-withdrawing groups can affect the electronic [b] Dr Y.-S
The recently published UV spectra of ANTH and ANTH-6-1 are shown in Figure S4.[47]. The similarity in lmax values for ANTH and ANTH-6-1 shows that the HOMO– LUMO gaps for these two compounds must be similar, even though they have electron affinity (EA) that differ by nearly 2.3 eV (0.53(2) eV for ANTH[88] and 2.81(2) eV for ANTH-6-1[26])
KGaA, Weinheim es as the size of the acceptor increases, from AZUL-5-1 (À0.78 eV) to ANTH-6-1 (À0.83 eV) and PYRN-6-2 (À0.82 eV) to TRPH-6-1 (À0.91 eV), and not as a monotonic function of acceptor EA. These results indicate that the polycyclic aromatic hydrocarbons (PAHs)/PAH(CF3)n CT complexes studied in this work have negligible charge-transfer character in their electronic ground states

Summary

Introduction

Organic co-crystalline materials containing electronically- and structurally-tuneable aromatic donors and acceptors exhibit a wide range of physicochemical properties that have found, or are expected to find, use in molecular electronic applications.[1,2,3,4,5,6,7,8,9,10] Of particular interest are the ways that strong electron-withdrawing groups can affect the electronic [b] Dr Y.-S. Coupling of donors and acceptors but the degree of p–p overlap and one-dimensional stacking.[11,12,13] In particular, F atoms[14,15,16,17,18,19] and perfluoroalkyl (RF) groups[20,21,22,23] can have desirable electronic and structural effects. PAH/PAH(F)n co-crystals have been studied for many years

Results

Discussion

Conclusion