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The ion/chemical‐based modulation feature of organic mixed ionic‐electronic conductors (OMIECs) are critical to advancing next generation bio‐integrated neuromorphic hardware. Despite achievements with polymeric OMIECs in organic electrochemical neuronal synapse (OENS). However, small molecule OMIECs based OENS has not yet been realized. Here, for the first time, we demonstrate an effective materials design concept of combining n‐type fused all‐acceptor small molecule OMIECs with subtle side chain optimization that enables robustly and flexibly modulating versatile synaptic behavior and sensing neurotransmitter in solid or aqueous electrolyte, operating in accumulation modes. By judicious tuning the ending side chains, the linear oligoether and butyl chain derivative gNR‐Bu exhibits higher recognition accuracy for a model artificial neural network (ANN) simulation, higher steady conductance states and more outstanding ambient stability, which is superior to the state‐of‐art n‐type OMIECs based OENS. These superior artificial synapse characteristics of gNR‐Bu can be attributed to its higher crystallinity with stronger ion bonding capacities. More impressively, we unprecedentedly realized n‐type small‐molecule OMIECs based OENS as a neuromorphic biosensor enabling to respond synaptic communication signals of dopamine even at sub‐μM level in aqueous electrolyte. This work may open a new path of small‐molecule ion‐electron conductors for next‐generation ANN and bioelectronics. [ABSTRACT FROM AUTHOR]

The ion/chemical‐based modulation feature of organic mixed ionic‐electronic conductors (OMIECs) are critical to advancing next generation bio‐integrated neuromorphic hardware. Despite achievements with polymeric OMIECs in organic electrochemical neuronal synapse (OENS). However, small molecule OMIECs based OENS has not yet been realized. Here, for the first time, we demonstrate an effective materials design concept of combining n‐type fused all‐acceptor small molecule OMIECs with subtle side chain optimization that enables robustly and flexibly modulating versatile synaptic behavior and sensing neurotransmitter in solid or aqueous electrolyte, operating in accumulation modes. By judicious tuning the ending side chains, the linear oligoether and butyl chain derivative gNR‐Bu exhibits higher recognition accuracy for a model artificial neural network (ANN) simulation, higher steady conductance states and more outstanding ambient stability, which is superior to the state‐of‐art n‐type OMIECs based OENS. These superior artificial synapse characteristics of gNR‐Bu can be attributed to its higher crystallinity with stronger ion bonding capacities. More impressively, we unprecedentedly realized n‐type small‐molecule OMIECs based OENS as a neuromorphic biosensor enabling to respond synaptic communication signals of dopamine even at sub‐μM level in aqueous electrolyte. This work may open a new path of small‐molecule ion‐electron conductors for next‐generation ANN and bioelectronics. [ABSTRACT FROM AUTHOR]

Aldol condensation is a cost‐effective and sustainable synthetic method, offering the advantages of low complexity, substrate universality, and high efficiency. Over the past decade, it has become popular for creating next‐generation organic functional materials, particularly rigid‐rod conjugated (semi)conductors. This review focuses on conjugated small molecules, oligomers, and polymeric (semi)conductors synthesized through aldol condensation, with emphasis on their remarkable features in advancing n‐type organic field‐effect transistors (OFETs), organic electrochemical transistors (OECTs), organic photovoltaics (OPVs), and organic thermoelectrics (OTEs) as well as NIR‐II photothermal conversion. Coherence character, optical properties, microstructure, and chain conformation are investigated to understand material‐property relationships. Future applications and challenges in this area are also discussed. [ABSTRACT FROM AUTHOR]

Aldol condensation is a cost‐effective and sustainable synthetic method, offering the advantages of low complexity, substrate universality, and high efficiency. Over the past decade, it has become popular for creating next‐generation organic functional materials, particularly rigid‐rod conjugated (semi)conductors. This review focuses on conjugated small molecules, oligomers, and polymeric (semi)conductors synthesized through aldol condensation, with emphasis on their remarkable features in advancing n‐type organic field‐effect transistors (OFETs), organic electrochemical transistors (OECTs), organic photovoltaics (OPVs), and organic thermoelectrics (OTEs) as well as NIR‐II photothermal conversion. Coherence character, optical properties, microstructure, and chain conformation are investigated to understand material‐property relationships. Future applications and challenges in this area are also discussed. [ABSTRACT FROM AUTHOR]

In the development of high‐performance organic thermoelectric devices, n‐type materials, especially with small molecule semiconductors, lags far behind p‐type materials. In this paper, three small molecules are synthesized based on electron‐deficient naphthalene bis‐isatin building blocks bearing different alkyl chains with the terminal functionalized with 3‐ethylrhodanine unit and studied their aggregation and doping mechanism in detail. It is found that crystallinity plays an essential role in tuning the doping behavior of small molecules. Molecules with too strong crystallinity tend to aggregate with each other to form large crystalline domains, which cause significant performance degradation. While molecules with weak crystallinity can tolerate more dopants, most of them exhibit low mobility. By tuning the crystallinity carefully, organic thermoelectric devices based on C12NR can maintain high mobility and realize effective doping simultaneously, and a high power factor of 1.07 µW m−1 K−2 at 100 °C is realized. This delicate molecular design by modulating crystallinity provides a new avenue for realizing high‐performance organic thermoelectric devices. [ABSTRACT FROM AUTHOR]

The primary challenge for n‐type small‐molecule organic electrochemical transistors (OECTs) is to improve their electron mobilities and thus the key figure of merit μC*. Nevertheless, few reports in OECTs have specially proposed to address this issue. Herein, we report a 10‐ring‐fused polycyclic π‐system consisting of the core of naphthalene bis‐isatin dimer and the terminal moieties of rhodanine, which features intramolecular noncovalent interactions, high π‐delocalization and strong electron‐deficient characteristics. We find that this extended π‐conjugated system using the ring fusion strategy displays improved electron mobilities up to 0.043 cm2 V−1 s−1 compared to our previously reported small molecule gNR, and thereby leads to a remarkable μC* of 10.3 F cm−1 V−1 s−1 in n‐type OECTs, which is the highest value reported to date for small‐molecule OECTs. This work highlights the importance of π‐conjugation extension in polycyclic‐fused molecules for enhancing the performance of n‐type small‐molecule OECTs. [ABSTRACT FROM AUTHOR]

The primary challenge for n‐type small‐molecule organic electrochemical transistors (OECTs) is to improve their electron mobilities and thus the key figure of merit μC*. Nevertheless, few reports in OECTs have specially proposed to address this issue. Herein, we report a 10‐ring‐fused polycyclic π‐system consisting of the core of naphthalene bis‐isatin dimer and the terminal moieties of rhodanine, which features intramolecular noncovalent interactions, high π‐delocalization and strong electron‐deficient characteristics. We find that this extended π‐conjugated system using the ring fusion strategy displays improved electron mobilities up to 0.043 cm2 V−1 s−1 compared to our previously reported small molecule gNR, and thereby leads to a remarkable μC* of 10.3 F cm−1 V−1 s−1 in n‐type OECTs, which is the highest value reported to date for small‐molecule OECTs. This work highlights the importance of π‐conjugation extension in polycyclic‐fused molecules for enhancing the performance of n‐type small‐molecule OECTs. [ABSTRACT FROM AUTHOR]

Highly efficient mixed ionic and electronic conduction is critical to developing high‐performance organic electrochemical transistors (OECTs) devices. While currently, the n‐type small molecules mixed conductors design strategy remains extremely lacking. Herein, ethylene glycol (EG) chain substituted electron‐deficient naphthalene bis‐isatin and rhodanine acceptor units with easily accessible steps are rationally fused, affording fused and planar novel semiconductors with weak intramolecular S–O 'conformation locks', where gNR with EG side chain and hgNR with hybrid alkyl‐EG side chain. The rigid, planar and highly electron‐deficient skeleton enables the resulting small molecule semiconductors to be efficient mixed ionic‐electronic conductors with very high OECT electron mobility up to 0.01 cm2 V−1 s−1. Remarkedly, gNR displays the record value of geometry‐normalized transconductance of 0.4 S cm−1 and μC* of 2.6 F V−1 cm−1 s−1, which can also be compared with the state‐of‐art n‐type semiconducting polymers in OECTs. Moreover, the effect of the alkyl spacer on the n‐type mixed ionic and electronic conduction features of the small molecule materials is investigated. The fused electron‐deficient acceptor‐acceptor (A–A) system with intramolecular conformation lock design strategy in this work provides a new avenue to realize next‐generation high‐performance small molecule mixed ionic and electronic conductors for OECT materials. [ABSTRACT FROM AUTHOR]