1,3,5-Triphenylbenzene and Corannulene as Electron Receptors for Lithium Solvated Electron Solutions

Summary

The authors report on conductivity studies carried out on lithium solvated electron solutions (LiSES) prepared using 1,3,5-triphenylbenzene (TPB) and corannulene as electron receptors.

Abstract

The authors report on conductivity studies carried out on lithium solvated electron solutions (LiSES) prepared using two types of polyaromatic hydrocarbons (PAH), namely 1,3,5-triphenylbenzene and corannulene, as electron receptors. The solid PAHs were first dissolved in tetrahydrofuran (THF) to form a solution. Metallic lithium was then dissolved into these PAH/THF solutions to yield either blue or greenish blue solutions, colors which are indicative of the presence of solvated electrons. Conductivity measurements at ambient temperature carried out on 1,3,5-triphenylbenzene-based LiSES, denoted by Li_xTPB(THF)_24.7 (x = 1, 2, 3, 4), showed an increase of conductivity with increase of Li:PAH ratio from x = 1 to 2. However, the conductivity gradually decreased upon further increasing the ratio. Indeed the conductivity of Li_xTPB(THF)_24.7 for x = 4 is even lower than for x = 1. Such behavior is similar to that of the previously reported LiSES prepared from biphenyl and naphthalene. Conductivity versus temperature measurements on corannulene-based LiSES, denoted by Li_xCor(THF)₂₄₇ (x = 1, 2, 3, 4, 5), showed linear relationships with negative slopes, indicating a metallic behavior similar to biphenyl and naphthalene-based LiSES.

Introduction

Lithium solvated electron solutions (LiSES) prepared using simple two-ring polyaromatic hydrocarbons (PAH) such as biphenyl and naphthalene can potentially be utilized as liquid anodes in refuelable lithium cells^1-7. In the LiSES, these simple PAH molecules served as the electron receptors for solvated electrons from dissolved metallic lithium.

Progressing from these two-ring systems, the authors have since then carried out conductivity measurement studies on LiSES which are prepared using more complex PAHs, starting with the group of cyclopenta-2,4-dienone derivatives⁸. These PAHs include larger PAHs (>two benzene rin....

Protocol

1. Preparation Procedure for 1,3,5-Triphenylbenzene (1)

1. Place a mixture of acetophenone (4.0 g, 33.3 mmol) and 100 ml of absolute ethanol into a round bottom three neck 250 ml flask equipped with magnetic stirrer, reflux condenser, nitrogen inlet, bubbler, dropping funnel and thermometer. Add silicon tetrachloride (11.9 g, 8.0 ml, 70.2 mmol, 2.1 eq.) to the mixture in one portion at 0 °C under nitrogen using the dropping funnel.
2. Observe the evolution of gaseous hydrogen chloride for 10 min. Then stir the reaction mixture at 40 °C for 20 hr.
3. Cool down the reaction mixture to 23 °C and pour in 200 g of water mixed with ice ....

Results

Reaction between various amounts of lithium and mixtures of 1,3,5-triphenylbenzene with THF gives greenish blue or deep blue colored solutions as shown in Figure 2. A light color indicates that the particular sample of LiSES has a low concentration of solvated electrons. 1,3,5-triphenylbenzene demonstrates increase of conductivity with increase of Li:PAH ratio from 1 to 2 in 0.5 M THF solution (Table 1). However, conductivity value gradually decreases upon further increasing the molar ra.......

Discussion

For the 1,3,5-triphenylbenzene-based LiSES, a sample with a light color shows that it has a low concentration of solvated electrons. Li_xTPB(THF)_24.7 (for x = 1, 2, 3, 4) demonstrates a behavior in its conductivity versus x similar to that seen for LiSES made from biphenyl and naphthalene^{1, 2}.There is an initial increase in conductivity with increase of Li:PAH ratio from 1 to 2 and a subsequent decrease in conductivity upon further increasing the molar ratio to 3 and 4, with condu.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Tetrahydrofuran Anhydrous, ≥99.9%, Inhibitor-free	Sigma Aldrich	401757-100ML
Lithium Foil	Alfa Aesar	010769.14
Cond 3310 Conductivity Meter	WTW	Not Applicable
1,3,5-triphenylbenzene			Synthesized from acetophenone according to procedure described in literature
Silicon tetrachloride	Sigma Aldrich	215120-100G
acetophenone	TCI	A0061-500g
Ethanol	Merck Millipore	1.00983.2511
Corannulene			Synthesized by literature procedure