Towards a Sustainable Future: Challenges and Opportunities for Early-Career Chemists.

The concepts of sustainability and sustainable chemistry have attracted increasing attention in recent years, being of great importance to the younger generation. In this Viewpoint Article, we share how early-career chemists can contribute to the sustainable transformation of their discipline. We identify ways in which they can engage to catalyse action for change. This article does not attempt to answer questions about the most promising or pressing areas driving research and chemical innovation in the context of sustainability. Instead, we want to inspire and engage early-career chemists in pursuing sustainable actions by showcasing opportunities in education, outreach and policymaking, research culture and publishing, while highlighting existing challenges and the complexity of the topic. We want to empower early-career chemists by providing resources and ideas for engagement for a sustainable future globally. While the article focuses on students and early-career chemists, it provides insights to further stimulate the engagement of scientists from diverse backgrounds.

Intermolecular Aminocarbonylation of Alkenes using Concerted Cycloadditions of Iminoisocyanates.

The aminocarbonylation of alkenes is a powerful method for accessing the ß-amino carbonyl motif that remains underdeveloped. Herein, the development of intermolecular aminocarbonylation reactivity of iminoisocyanates with alkenes is presented. This includes the discovery of a fluorenone-derived reagent, which was effective for many alkene classes and facilitated derivatization. Electron-rich substrates were most reactive, and this indicated that the LUMO of the iminoisocyanate is reacting with the HOMO of the alkene. Computational and experimental results support a concerted asynchronous [3 + 2] cycloaddition involving an iminoisocyanate, which was observed for the first time by FTIR under the reaction conditions. The products of this reaction are complex azomethine imines, which are precursors to valuable ß-amino carbonyl compounds such as ß-amino amides and esters, pyrazolones, and bicyclic pyrazolidinones. A kinetic resolution of the azomethine imines by enantioselective reduction (s = 13-43) allows access to enantioenriched products. Overall, this work provides a new tool to convert alkenes into ß-amino carbonyl compounds.

Patchy Nanofibers from the Thin Film Self-Assembly of a Conjugated Diblock Copolymer.

An unexpected morphology comprising patchy nanofibers can be accessed from the self-assembly of an all-conjugated, polyselenophene-block-polythiophene copolymer. This morphology consists of very small (<10 nm), polythiophene- and polyselenophene-rich domains and is unprecedented for both conjugated polymers and diblock copolymers in general. We propose that the patchy morphology occurs from the enhanced miscibility of the blocks arising from the longer alkyl chains in comparison to similar block copolymers with shorter alkyl chains, which fully phase separate, as well as the difference in rigidity between the polythiophene and polyselenophene blocks. This work demonstrates a facile way to tune the self-assembly behavior of conjugated block copolymers by modification of the side chain substituents.

Programmable Assembly of π-Conjugated Polymers.

π-Conjugated polymers have numerous applications due to their advantageous optoelectronic and mechanical properties. These properties depend intrinsically on polymer ordering, including crystallinity, orientation, morphology, domain size, and π-π interactions. Programming, or deliberately controlling the composition and ordering of π-conjugated polymers by well-defined inputs, is a key facet in the development of organic electronics. Here, π-conjugated programming is described at each stage of material development, stressing the links between each programming mode. Covalent programming is performed during polymer synthesis such that complex architectures can be constructed, which direct polymer assembly by governing polymer orientation, π-π interactions, and morphological length-scales. Solution programming is performed in a solvated state as polymers dissolve, aggregate, crystallize, or react in solution. Solid-state programming occurs in the solid state and is governed by polymer crystallization, domain segregation, or gelation. Recent progress in programming across these stages is examined, highlighting order-dependent features and assembly techniques that are unique to π-conjugated polymers. This should serve as a guide for delineating the many ways of directing π-conjugated polymer assembly to control ordering, structure, and function, enabling the further development of organic electronics.

Synthesis of Macrocyclic Poly(3-hexylthiophene) and Poly(3-heptylselenophene) by Alkyne Homocoupling.

Here we report the synthesis of cyclic samples of poly(3-hexylthiophene) (P3HT, degrees of polymerization = 25, 40, and 75) and poly(3-heptylselenophene) (P37S, DP = 30). Cyclization was accomplished using a mild alkyne-alkyne homocoupling procedure. Alkyne-terminated poly(ethylene glycol) was then coupled to residual uncyclized polymers, which were subsequently removed by column chromatography, enabling isolation and characterization of pure cyclic polymers. Cyclization was confirmed by the disappearance of terminal alkyne protons, the decrease in hydrodynamic radius [measured by size exclusion chromatography (SEC)], and the observed identical molecular weight distribution [measured by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry]. The lower weight macrocyclic polymers have decreased self-assembly as measured by optical absorption and transmission electron microscopy. The highest weight macrocycles were imaged using scanning tunneling microscopy. Cyclic polymers adopted a tightly bent conformation, while their linear analogues assembled as fully extended chains. Our method of cyclization and purification is broadly applicable to conjugated polymers (CPs) and will enable the development of novel optoelectronic materials.