Regio- and Chemo-selective C-H Arylation of 3-Bromothiophene: A Synthesis Shortcut to Versatile π-Conjugated Building Blocks for Optoelectronic Materials

Unlike traditional multi-step synthetic approaches, we developed a single-step synthesis of versatile π-conjugated building blocks bearing post-functionalizable C-H and C-Br bonds. Direct C-H arylation of 3-bromothiophene with various iodo(hetero)aryls was successfully carried out with good regio- and chemo-selectivity. Under optimized reaction conditions, 20 new compounds were facilely prepared in yields up to 91 %. One of the obtained compounds was demonstrated to further extend its conjugation length using a succinct synthetic plan to create two symmetrical oligo(hetero)aryls (MLC01 and MLC02) that were fabricated as effective hole-transporting materials (HTM) for perovskite solar cells (PSC). PSC devices utilizing MLC01 as hole-transport layer displayed promising power conversion efficiencies of up to 17.01 %.

Development of Step-Saving Alternative Synthetic Pathways for Functional π-Conjugated Materials

Synthetic organic chemists endeavor to develop new reaction conditions, improve product yields, and enhance atom economy (synthetic methodologies), whereas the material scientists strive to create novel functional molecules/structures, increase device stabilities, and promote power conversion efficiencies via device engineering (organic optoelectronics). However, these two prominent research fields seem to have no intersections. Since joining national central university in 2012, our research philosophy aims to narrow, or rather to bridge the gap between synthetic methodologies and π-functional organic materials. In contrast to using multistep synthetic approaches based on Suzuki- or Stille coupling reactions, this personal account describes various step-saving and viable synthesis-shortcuts developed by our group, to access thiophene-based small molecules for optoelectronic applications. We expect these succinct and user-friendly alternative pathways designed by synthetic chemists would help material scientists to reach their target molecules in a more step-economical manner.

Combined LCA and Green Metrics Approach for the Sustainability Assessment of an Organic Dye Synthesis on Lab Scale

New generation photovoltaic devices have attracted much attention in the last decades since they can be efficiently manufactured employing abundant raw materials and with less-energy intensive processes. In this context, the use of powerful environmental assessment is pivotal to support the fine-tuning of solar cells fabrication and hit the target of manufacturing effective sustainable technological devices. In this work, a mass-based green metrics and life cycle assessment combined approach is applied to analyze the environmental performances of an innovative synthetic protocol for the preparation of organic dye TTZ5, which has been successfully proposed as sensitizer for manufacturing dye sensitized solar cells. The new synthetic strategy, which is based on the C-H activation process, has been compared with the previously reported synthesis employing classic Suzuki-Miyaura cross-coupling chemistry. Results highlight the contribution of direct energy consumption and purification operations in organic syntheses at lab scale. Furthermore, they demonstrate the usefulness of the environmental multifaceted analytic tool and the power of life cycle assessment to overcome the intrinsic less comprehensive nature of green metrics for the evaluation of organic synthetic protocols.

Pd(II)-Catalyzed Direct Dehydrogenative Mono- and Diolefination of Selenophenes

Pd(II)-catalyzed dehydrogenative Heck olefination of selenophenes with a broad olefinic substrate scope and high functional group tolerance is demonstrated. Carbonyl-substituted and phenyl-substituted olefins with electron-donating (D) and electron-accepting (A) groups can be regioselectively installed at C2 of the selenophene. The 2-olefinated selenophenes can subsequently undergo a second oxidative olefination to rapidly produce a new class of symmetrical D-π-D or unsymmetrical D-π-A 2,5-diolefinated selenophene materials.

Reactivity of bromoselenophenes in palladium-catalyzed direct arylations

The reactivity of 2-bromo- and 2,5-dibromoselenophenes in Pd-catalyzed direct heteroarylation was investigated. From 2-bromoselenophene, only the most reactive heteroarenes could be employed to prepare 2-heteroarylated selenophenes; whereas, 2,5-dibromoselenophene generally gave 2,5-di(heteroarylated) selenophenes in high yields using both thiazole and thiophene derivatives. Moreover, sequential catalytic C2 heteroarylation, bromination, catalytic C5 arylation reactions allowed the synthesis of unsymmetrical 2,5-di(hetero)arylated selenophene derivatives in three steps from selenophene.