Covalent Functionalization of Single-Walled Carbon Nanotubes by the Bingel Reaction for Building Charge-Transfer Complexes

Abstract

Functionalization of nanotubes with donor and acceptor partners by the Bingel reaction leads to formation of charge-transfer dyads, which can operate in organic photovoltaic devices. In this work, we theoretically examine the mechanism of the Bingel reaction for (6,5)-chiral, (5,5)armchair, and (9,0)-zig-zag single-walled carbon nanotubes (SWCNTs), and demonstrate that the reaction is regioselective and takes place at the perpendicular position of (6,5)-and (5,5)-SWCNTs, and oblique position of (9,0)-SWCNT. Further, we design computationally the donoracceptor complexes based on (6,5)-SWCNT coupled with partners of different electronic nature.Analysis of their excited states reveals that efficient photoinduced charge transfer can be achieved in the complexes with exTTF, ZnTPP, and TCAQ. The solvent can significantly affect the population of the charge separated states. Our calculations show that electron transfer (ET) occurs in normal Marcus regime on sub-nanosecond time scale in the complexes with exTTF and ZnTPP, and in inverted Marcus regime on picosecond time scale in the case of TCAQ derivative. The ET rate is found to be not very sensitive to the degree of functionalization of the nanotube. construct novel donor-acceptor materials with advantageous optical and electrical properties. 3,4,5,6 To date, a number of donor-acceptor SWCNT-based hybrids are known, particularly, with porphyrins, ferrocenes, perylene diimides, phthalocyanines, and polyaromatic hydrocarbons. 7,8,9,10,11,12 Photoactive molecules can be attached to the nanotube via covalent or noncovalent interactions. Noncovalent functionalization preserves π-electron conjugation of the sp 2 carbon network but it is difficult to provide environmental and long-time stability of systems.In turn, covalent binding is strong, but usually generates sp 3 carbon sites on CNTs, which disrupt the transitions of π-electrons, leading to loss of desired properties.Insolubility of nanotubes and low charge mobility between donor and acceptor parts can be overcome by functionalization of nanotubes using Bingel cycloaddition reaction. 13 Nowadays, this reaction is successfully applied to fullerenes for their chemical modification. 14,15,16,17,18,19,20 A classical Bingel reaction is a type of nucleophilic addition reaction introducing a cyclopropane on the fullerene cage. Despite a widespread use of this reaction in fullerene chemistry, 21 only a few reports have appeared for the functionalization of SWNTs 22,23 and other carbon materials, such as nanodiamond, 24 graphene 25,26 and carbon nanohorns. 27 The first example of SWCNTs functionalization via the Bingel reaction was reported in 2003 by Coleman and co-workers. 22 They confirmed the successful cyclopropanation of SWNTs by AFM in conjunction with chemical tagging techniques. Later, structures and spectroscopic properties of functionalized SWNTs were examined in detail. 23 Resonant Raman and UV-vis-NIR absorption spectroscopies revealed that the electronic properties of SWNTs are well preserved even after significan...

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