Fullerene Desymmetrization as a Means to Achieve Single‐Enantiomer Electron Acceptors with Maximized Chiroptical Responsiveness

Abstract

Parent fullerene structures have extremely challenging solubility, which limits their processability and miscibility with host materials in bulk heterojunction OPVs; an issue which has been addressed through the production of more soluble derivatives using simple cycloaddition chemistry. Bis[60]PCBM (PCBM = phenyl-C61-butyric acid methyl ester) (dimethyl 4,4′-[61,62-diphenly,3′H,3″Hdicyclopropa(C 60 I h)[5,6]fulleren-1,9:X,Ydiyl]dibutanoate) is one such derivative and one of the most utilized solubilized fullerenes, which is easy to synthesize, highly processable, and solar cells based on this material have high power conversion efficiencies. [11-18] The addition of two solubilizing addends to C 60 results in a large number of structural isomers however, each with varying energetic properties (influencing device voltage) and morphological properties (influencing device current). Despite this, bis[60]PCBM is synthesized and used as an isomeric mixture, and the role of individual isomers on morphological, spectroscopic, and device performance is very poorly understood. In a previous study, Dennis and coworkers separated the 19 structural isomers of bis[60]PCBM and characterized them using a combination of NMR, UV-vis, and retention times by HPLC. [19,20] Although the performance Solubilized fullerene derivatives have revolutionized the development of organic photovoltaic devices, acting as excellent electron acceptors. The addition of solubilizing addends to the fullerene cage results in a large number of isomers, which are generally employed as isomeric mixtures. Moreover, a significant number of these isomers are chiral, which further adds to the isomeric complexity. The opportunities presented by single-isomer, and particularly single-enantiomer, fullerenes in organic electronic materials and devices are poorly understood however. Here, ten pairs of enantiomers are separated from the 19 structural isomers of bis[60]phenyl-C61-butyric acid methyl ester, using them to elucidate important chiroptical relationships and demonstrating their application to a circularly polarized light (CPL)-detecting device. Larger chiroptical responses are found, occurring through the inherent chirality of the fullerene. When used in a single-enantiomer organic field-effect transistor, the potential to discriminate CPL with a fast light response time and with a very high photocurrent dissymmetry factor (g ph = 1.27 ± 0.06) is demonstrated. This study thus provides key strategies to design fullerenes with large chiroptical responses for use as chiral components of organic electronic devices. It is anticipated that this data will position chiral fullerenes as an exciting material class for the growing field of chiral electronic technologies.

Emerging materials for circularly polarized light detection

“…In extreme cases, g R is up to 3 orders of magnitude higher than g abs . A few explanations were provided by different studies, including (1) difference in photocurrent generation caused by the differential absorption, 8,42,47 (2) difference in spin charge transport of the photo-induced charge carriers, 9,10,42,57,59 and (3) chirality induced orbital angular momentum. 50 However, so far, we have not yet had a consensus on which has the dominate contribution on the enhanced g ph .…”

“…Shi et al separated ten pairs of enantiomers from the 19 structural isomers of bis-PC 61 BM. 42 Enantiomers of 12 and 13 were selectively used for CPL detection on bottom-gate bottom-contact phototransistors (Fig. 5a and b).…”

Highly Selective High‐Speed Circularly Polarized Photodiodes Based on π‐Conjugated Polymers

“…[16] The device architectures that demonstrate the greatest CP selectivity (i.e., approaching |g ph | ≈ 2, perfect CP selectivity) are based on the field-effect transistor (FET) structure, but these devices suffer from low EQE (≈ 10 −2 %) and cannot be scaled up. [10,17,18] Chiral hybrid organic-inorganic perovskite (HOIP) photodetectors have achieved impressive EQEs (≈57%), but unfortunately, the majority of published devices demonstrate poor CP selectivity (|g ph | ≈ 0.1). [19][20][21] More recently, a low-dimensional chiral HOIP has been reported that allows for high CP selectivity in the UV (|g ph | = 1.9).…”

Para‐C60(CF2)(CF3)R: a family of chiral electron accepting compounds accessible through a facile one‐pot synthesis

“…Very recently Shi et al. constructed a CPL discriminating phototransistor based on bis[60]PCBM enantiomer [3] – only the second CPL discriminating phototransistor based on the inherent chirality of an organic compound. While this result is exciting in terms of photocurrent dissymmetry factor and response time of the device, the electron mobility is not particularly high, and the individual isomer of bis[60]PCBM had to be isolated from a mixture of 19 structural isomers.…”