Enhancing the Backbone Coplanarity of n-Type Copolymers for Higher Electron Mobility and Stability in Organic Electrochemical Transistors

Electron-transporting (n-type) conjugated polymers have recently been applied in numerous electrochemical applications, where both ion and electron transport are required. Despite continuous efforts to improve their performance and stability, n-type conjugated polymers with mixed conduction still lag behind their hole-transporting (p-type) counterparts, limiting the functions of electrochemical devices. In this work, we investigate the effect of enhanced backbone coplanarity on the electrochemical activity and mixed ionic-electronic conduction properties of n-type polymers during operation in aqueous media. Through substitution of the widely employed electron-deficient naphthalene diimide (NDI) unit for the core-extended naphthodithiophene diimide (NDTI) units, the resulting polymer shows a more planar backbone with closer packing, leading to an increase in the electron mobility in organic electrochemical transistors (OECTs) by more than two orders of magnitude. The NDTI-based polymer shows a deep-lying lowest unoccupied molecular orbital level, enabling operation of the OECT closer to 0 V vs Ag/AgCl, where fewer parasitic reactions with molecular oxygen occur. Enhancing the backbone coplanarity also leads to a lower affinity toward water uptake during cycling, resulting in improved stability during continuous electrochemical charging and ON-OFF switching relative to the NDI derivative. Furthermore, the NDTI-based polymer also demonstrates near-perfect shelf-life stability over a month-long test, exhibiting a negligible decrease in both the maximum on-current and transconductance. Our results highlight the importance of polymer backbone design for developing stable, high-performing n-type materials with mixed ionic-electronic conduction in aqueous media.

Lactone Backbone Density in Rigid Electron-Deficient Semiconducting Polymers Enabling High n-type Organic Thermoelectric Performance

Three lactone-based rigid semiconducting polymers were designed to overcome major limitations in the development of n-type organic thermoelectrics, namely electrical conductivity and air stability. Experimental and theoretical investigations demonstrated that increasing the lactone group density by increasing the benzene content from 0 % benzene (P-0), to 50 % (P-50), and 75 % (P-75) resulted in progressively larger electron affinities (up to 4.37 eV), suggesting a more favorable doping process, when employing (N-DMBI) as the dopant. Larger polaron delocalization was also evident, due to the more planarized conformation, which is proposed to lead to a lower hopping energy barrier. As a consequence, the electrical conductivity increased by three orders of magnitude, to achieve values of up to 12 S cm and Power factors of 13.2 μWm^-1  K^-2 were thereby enabled. These findings present new insights into material design guidelines for the future development of air stable n-type organic thermoelectrics.

Polaron Delocalization in Donor-Acceptor Polymers and its Impact on Organic Electrochemical Transistor Performance

Donor-acceptor (D-A) polymers are promising materials for organic electrochemical transistors (OECTs), as they minimize detrimental faradaic side-reactions during OECT operation, yet their steady-state OECT performance still lags far behind their all-donor counterparts. We report three D-A polymers based on the diketopyrrolopyrrole unit that afford OECT performances similar to those of all-donor polymers, hence representing a significant improvement to the previously developed D-A copolymers. In addition to improved OECT performance, DFT simulations of the polymers and their respective hole polarons also reveal a positive correlation between hole polaron delocalization and steady-state OECT performance, providing new insights into the design of OECT materials. Importantly, we demonstrate how polaron delocalization can be tuned directly at the molecular level by selection of the building blocks comprising the polymers' conjugated backbone, thus paving the way for the development of even higher performing OECT polymers.

Acene Ring Size Optimization in Fused Lactam Polymers Enabling High n-Type Organic Thermoelectric Performance

Three n-type fused lactam semiconducting polymers were synthesized for thermoelectric and transistor applications via a cheap, highly atom-efficient, and nontoxic transition-metal free aldol polycondensation. Energy level analysis of the three polymers demonstrated that reducing the central acene core size from two anthracenes (A-A), to mixed naphthalene-anthracene (A-N), and two naphthalene cores (N-N) resulted in progressively larger electron affinities, thereby suggesting an increasingly more favorable and efficient solution doping process when employing 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI) as the dopant. Meanwhile, organic field effect transistor (OFET) mobility data showed the N-N and A-N polymers to feature the highest charge carrier mobilities, further highlighting the benefits of aryl core contraction to the electronic performance of the materials. Ultimately, the combination of these two factors resulted in N-N, A-N, and A-A to display power factors (PFs) of 3.2 μW m^-1 K^-2, 1.6 μW m^-1 K^-2, and 0.3 μW m^-1 K^-2, respectively, when doped with N-DMBI, whereby the PFs recorded for N-N and A-N are among the highest reported in the literature for n-type polymers. Importantly, the results reported in this study highlight that modulating the size of the central acene ring is a highly effective molecular design strategy to optimize the thermoelectric performance of conjugated polymers, thus also providing new insights into the molecular design guidelines for the next generation of high-performance n-type materials for thermoelectric applications.

Energetic Control of Redox-Active Polymers toward Safe Organic Bioelectronic Materials

Avoiding faradaic side reactions during the operation of electrochemical devices is important to enhance the device stability, to achieve low power consumption, and to prevent the formation of reactive side-products. This is particularly important for bioelectronic devices, which are designed to operate in biological systems. While redox-active materials based on conducting and semiconducting polymers represent an exciting class of materials for bioelectronic devices, they are susceptible to electrochemical side-reactions with molecular oxygen during device operation. Here, electrochemical side reactions with molecular oxygen are shown to occur during organic electrochemical transistor (OECT) operation using high-performance, state-of-the-art OECT materials. Depending on the choice of the active material, such reactions yield hydrogen peroxide (H₂ O₂ ), a reactive side-product, which may be harmful to the local biological environment and may also accelerate device degradation. A design strategy is reported for the development of redox-active organic semiconductors based on donor-acceptor copolymers that prevents the formation of H₂ O₂ during device operation. This study elucidates the previously overlooked side-reactions between redox-active conjugated polymers and molecular oxygen in electrochemical devices for bioelectronics, which is critical for the operation of electrolyte-gated devices in application-relevant environments.

Reporting and prediction of work-related sickness absence by general practitioners

BACKGROUND

Information on sickness absence (SA) duration in general practice is difficult to record. The duration of absence certified by general practitioners (GPs) can be viewed as a prognosis for return to work. The Health and Occupation Research network in General Practice (THOR-GP) collects SA information from GPs associated with cases of work-related ill-health. A sample of these cases is followed up 1 year retrospectively to gather information on the duration of absence.

AIMS

To examine the extent of the underestimation of SA in routinely reported data and to investigate how well GPs predict patients' return to work.

METHODS

THOR-GPs submit case and SA information using a web-based form. GPs who submitted selected cases were asked about the total number of days of SA and whether the patient had returned to work.

RESULTS

THOR-GPs' routine SA data collection underestimated absence duration by 61%. According to the retrospective data, a much larger proportion of periods of absence due to work-related mental ill-health developed into long-term SA (60%) than episodes attributed to musculoskeletal disorders (32%). In over half the reported cases, the return to work was longer than the GP initially predicted.

CONCLUSIONS

THOR-GP prospectively reported SA data underestimated the total length of absence; however, these data can examine the episodic rates of absence within different groups. More accurate longitudinal data can be collected retrospectively. GPs' ability to predict the length of time a patient will be away from work is important to enable treatment and rehabilitation planning in order to decrease the likelihood of a patient falling into long-term SA.

Patients' attitudes to sickness certification in general practice

BACKGROUND

In 2010, the sick note was replaced with the fit note, designed to enable return to work. Despite considerable research relating to general practitioners' (GPs') attitudes and practice towards the fit note, little is known regarding the patients' perspective.

AIMS

We sought to identify patients' attitudes to and feelings about the process of sickness certification.

METHODS

Patients who received fit notes were invited to participate in tape-recorded telephone interviews, which were conducted with a semi-structured approach. Participants described their reason for sickness absence and whether it had been related to work. They were then asked to provide a narrative regarding their experience of the fitness for work process and their feelings about their GP and employer's reaction to sickness absence.

RESULTS

Nine patients were interviewed. Four main themes emerged from analysis of the interviews: 'significant stigma', 'a GP who knows me', 'value of work' and 'emotional barriers'. Patients expressed preference for being seen by a familiar GP with a greater perceived understanding of the patient's attitude to sickness and work.

CONCLUSIONS

The four emergent themes of stigma, the value of work, a doctor who knows you and emotion suggest that further research should focus on the problems of stigma associated with sickness certification and patients' emotional response to asking for certification.

Recording occupation in general practice--a second cycle audit

BACKGROUND

An audit of working age patients' records in two Cornish general practices in 2012 found infrequent and inconsistent recording of patients' occupations. A concurrent survey of general practitioners (GPs) in Cornwall found that a majority of them believed it was important to do so.

AIMS

To review occupation recording in the same practices a year later and to audit a third practice, following the introduction of the electronic fit note. To repeat the survey of attitudes to recording occupation in GPs in Cornwall.

METHODS

We manually checked 300 randomly selected patient records in Practice A and electronically searched all records of working age patients (aged 16-65 years) in Practices B and C for recorded occupation. We sent an electronic survey of attitudes to recording occupation to 202 GPs in Cornwall.

RESULTS

Recording of occupation increased from 17 to 30% of records (χ(2) = 15, P < 0.001) in Practice A and from 12 to 14% (χ(2) = 16.5, P < 0.001) in Practice B. In Practice C, 1% of records had occupation recorded and coded. The proportion of GPs in Cornwall who said that it is important to records patients' occupation increased from 70 to 90% (Fisher's exact statistic 0.01, P < 0.05).

CONCLUSIONS

Recording of patients' occupation increased in both practices from 2012 to 2013, but remains infrequent and inconsistent and the very low levels in a third practice not previously audited is of concern.

Sickness certification difficulties in Ireland--a GP focus group study

BACKGROUND

Sickness certification causes problems for general practitioners (GPs). Difficulty with the assessment of capacity to work, conflict with patients and other non-medical factors have been shown to influence GPs' decision-making. Inadequate leadership and management of certification issues add to GPs' difficulties.

AIMS

To explore problems associated with sickness certification, as part of a larger mixed method research project exploring GPs' experiences and perceptions of sickness certification in Ireland.

METHODS

A qualitative study in an urban region of Ireland. A focus group of four male and four female GPs explored problems encountered by GPs in certifying sickness absence. Thematic data analysis was used.

RESULTS

Three major themes emerged: perception of the sickness certification system, organization of health care and cultural factors in sickness absence behaviour. Employment structures in public and private sectors and lack of communication with other health care providers and employers were identified as complicating sickness certification.

CONCLUSIONS

GPs encounter a complexity of issues in sick certification and are dissatisfied with their role in certifying sickness absence. Our results open the debate for policy change and development in Ireland.