Oligotriarylamines with a Pyrene Core: A Multicenter Strategy for Enhancing Radical Cation and Dication Stability and Tuning Spin Distribution

Abstract

Monoamine 1, diamines 2-4, triamine 5, and tetraamine 6 have been synthesized by substituting dianisylamino groups at the 1-, 3-, 6-, and/or 8-positions of pyrene. Diamines 2-4 differ in the positions of the amine substituents. No pyrene-pyrene interactions are evident in the single-crystal packing of 3, 4, and 6. With increasing numbers of amine substituents, the first oxidation potential decreases progressively from the mono- to the tetraamine. These compounds show intense charge-transfer (CT) emission in CH2 Cl2 at around 530 nm with quantum yields of 48-68 %. Upon stepwise oxidation by electrolysis or chemical oxidation, these compounds were transformed into radical cations 1(⋅+) -6(⋅+) and dications 2(2+) -6(2+) , which feature strong visible and near-infrared absorptions. Time-dependent density functional theory studies suggested the presence of localized transitions from the pyrene radical cation and aminium radical cation, intervalence CT, and CT between the pyrene and amine moieties. Spectroscopic studies indicated that these radical cations and dications have good stability. Triamine 5 and tetraamine 6 formed efficient CT complexes with tetracyanoquinodimethane in solution. The results of EPR spectroscopy and density functional theory calculations suggested that the dications 2(2+) -4(2+) have a triplet ground state, whereas 5(2+) and 6(2+) have a singlet ground state. The dication of 1,3-disubstituted diamine 4 exhibits a strong EPR signal.

Pyrene Molecular Orbital Shuffle—Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals

“…We note that the oxidation potential of the D/A‐compound 11 ( E 1/2 (ox)=0.29 V), which is very similar to that of H ( E 1/2 (ox)=0.26 V), and also that of the JulPyr 8 ( E 1/2 (ox)=0.20 V) are significantly higher than that of Jul 2 Pyr 4 ( E 1/2 (ox) 1 =−0.18 V), implying that the HOMO in 4 is greatly destabilized by the second donor. This is in stark contrast to the findings of Zhong et al., who studied the influence of one to four amino substituents in the 1‐, 3‐, 6‐, and 8‐positions of pyrene on the E 1/2 (ox) 1 values . According to their experiments, E 1/2 1 of the 1‐monoamino‐substituted pyrene differs from that of the 1,3‐diamino‐substituted pyrene by only 0.11 V, and from that of the 1,3,6,8‐tetraamino‐substituted pyrene by 0.28 V. In addition, the HOMO energy difference upon going from one to four amino groups in that study is not as large as it is for our compounds 4 and 8 , which underlines the much stronger destabilizing effect on the HOMO of our donor substituents at the 2,7‐positions compared to diarylamino groups at the 1‐, 3‐, 6‐, and 8‐positions.The D‐π‐D compounds 4 and 14 , unlike the mono‐donor substituted compounds, display a second reversible one‐electron oxidation at +0.26 V and +0.11 V, respectively, and a remarkably large potential splitting Δ E (440 mV) for this type of compound (Table ) .…”

“…The difference of the HOMO energy of 1.16 eV between the bis(donor)‐ and mono(donor)‐substituted compounds 4 and 8 is relatively large compared to that of analogous compounds. Even substitution with donors at the 1‐, 3‐, 6‐, and 8‐positions does not lead to such a strong destabilizing influence on the HOMO . Consequently, the HOMO–LUMO gap of the doubly‐substituted pyrene 4 is smaller than that of the mono‐substituted pyrene 8 .…”

Studies on Pyrene and Perylene Derivatives upon Oxidation and Application to a Higher Analogue

“…47 Generation of the cationic species of 1 was carried out with NOSbF 6 , which is known as a powerful one-electron oxidation agent. 1 was subjected to stepwise oxidations with NOSbF 6 (1 or 2 equiv) in CH 2 Cl 2 /CH 3 CN.…”

Experimental and Theoretical Examination of the Radical Cations Obtained from the Chemical and Electrochemical Oxidation of 5‐Aminothiazoles

“…However, most of these compounds are unstable and/or are present only at low temperature. For example, the radical cation of 1,3,6‐tris(di‐ p ‐anisylamino)pyrene, which contains fused rings, exhibits a half‐life of 3 h . In addition, several radical cations generated from sulfur‐containing monocyclic aromatics, such as thiophenes and thiazoles, have been reported.…”

“…For example, the radicalc ation of 1,3,6-tris(di-p-anisylamino)pyrene, which contains fused rings,exhibits ah alf-life of 3h. [8] In addition, several radicalcationsgenerated from sulfur-containing monocyclica romatics,s uch as thiophenes [9] and thiazoles, [10] have been reported. Some thiazoleradical cations,such as 1-butyl-5-methylthiazolium, [9d] have been reported, butt heir photophysical properties have not been disclosed.…”