Enhanced Static and Dynamic Properties of Highly Miscible Fullerene-Free Green-Selective Organic Photodetectors

Dynamic Fluorescence Sensing of Bromide Ions by Photochromic Bi(III)-Coordination Polymers Based on a Ligand Integrated by Naphthalene Diimides and Pyridinium in Solution and Films

Bismuth(III)-based complexes have garnered increasing attention in fluorescence sensing due to their environmentally friendly and sustainable characteristics. A Bismuth(III) coordination polymer (CP),1-Cl based on a naphthalene diimides(NDI)-pyridinium is synthesized by an in situ reaction method. Notable for its sensitivity to visible light, 1-Cl shows excellent photochromic properties, and the integration of NDI and pyridinium in one ligand makes photogenerated radicals more stable. Structural analysis and theoretical calculations are employed to investigate the potential pathway of photoinduced electron transfer (ET) during the photochromic process. Notably, in aqueous solutions, 1-Cl displays an extraordinary fluorescence enhancement response to bromide ion (Br-), resulting in a distinct transition from yellow to orange in color. The potential mechanism of fluorescence sensing has been revealed through single-crystal X-ray diffraction analysis. This insight highlights a continuous substitution process where the Cl- ions are successively replaced by Br- ions. Consequently, a single-crystal-to-single-crystal transformation (SCSC) occurs, yielding the intermediate species, 1-Cl-Br, which ultimately transforms into the final product, 1-Br. Finally, the photochromic film is successfully prepared and applied to practical applications such as ink-free printing, information anti-counterfeiting, and the visual detection of Br- ions. This work combines photochromism with fluorescence sensing, broadening the research field and practical application of photochromic materials.

Self-Powering Sensory Device with Multi-Spectrum Image Realization for Smart Indoor Environments

The development of organic-based optoelectronic technologies for the indoor Internet of Things market, which relies on ambient energy sources, has increased, with organic photovoltaics (OPVs) and photodetectors (OPDs) considered promising candidates for sustainable indoor electronic devices. However, the manufacturing processes of standalone OPVs and OPDs can be complex and costly, resulting in high production costs and limited scalability, thus limiting their use in a wide range of indoor applications. This study uses a multi-component photoactive structure to develop a self-powering dual-functional sensory device with effective energy harvesting and sensing capabilities. The optimized device demonstrates improved free-charge generation yield by quantifying charge carrier dynamics, with a high output power density of over 81 and 76 µW cm-2 for rigid and flexible OPVs under indoor conditions (LED 1000 lx (5200 K)). Furthermore, a single-pixel image sensor is demonstrated as a feasible prototype for practical indoor operating in commercial settings by leveraging the excellent OPD performance with a linear dynamic range of over 130 dB in photovoltaic mode (no external bias). This apparatus with high-performance OPV-OPD characteristics provides a roadmap for further exploration of the potential, which can lead to synergistic effects for practical multifunctional applications in the real world by their mutual relevance.

Development of n-Type Small-Molecule Acceptors for Low Dark Current Density and Fast Response Organic Photodetectors

Suppressing the dark current density (Jd) while maintaining sufficient charge transport is important for improving the specific detectivity (D*) and dynamic characteristics of organic photodetectors (OPDs). In this study, we synthesized three novel small-molecule acceptors (SMAs) densely surrounded by insulating alkyl side chains to minimize the Jd in OPDs. Introducing trialkylated N-annulated perylene diimide as a terminal moiety to the alkylated π-conjugated core structure was highly efficient in suppressing Jd in the devices, resulting in an extremely low Jd of 4.60 × 10-11 A cm-2 and 10-100 times improved D* values in the devices. In addition, SMAs with a geometrically aligned backbone structure exhibited better intermolecular ordering in the blended films, resulting in 3-10 times as high responsivity (R) values in the OPDs. Outstanding OPD performances with a D* of 8.09 × 1012 Jones, -3 dB cutoff frequency of 205.2 kHz, and rising response time of 16 μs were achieved under a 530 nm illumination in photoconductive mode. Geometrically aligned core-terminal SMAs densely surrounded by insulating alkyl side chains are promising for improving the static and dynamic properties of OPDs.

Highly Efficient Ternary Near-Infrared Organic Photodetectors for Biometric Monitoring

Near-infrared (NIR) small-molecule acceptors that absorb at wavelengths of up to 1000 nm are attractive for applications in organic photodetectors (OPDs) and biometrics. In this study, we incorporated IEICO-4F as the third component for PffBT4T-2OD:PC₇₁BM-based OPDs to provide an efficient NIR response while greatly suppressing the leakage current at reverse bias. By varying the blend ratio and thickness (250-600 nm), we obtained an NIR OPD displaying an ultralow dark-current density (J_D = 2.62 nA cm^-2), ultrahigh detectivity [D* = 7.2 × 10¹² Jones (850 nm)], high sensitivity, and photoresponsivity covering the region from the ultraviolet to the NIR. We used tapping-mode atomic force microscopy, optical microscopy, grazing-incidence wide-angle X-ray scattering, and contact angle measurements to investigate the effect of IEICO-4F on the performance of the ternary OPDs. The low compatibility of PffBT4T-2OD and IEICO-4F, originating from weak intermolecular interactions, allowed us to manipulate the degree of phase separation between the donor and acceptor in the ternary blends, leading to an optimized blend morphology featuring efficient charge separation, transport, and collection. To demonstrate its applicability, we integrated our OPD with two light-emitting diodes and used the system for precisely calculated transmissive pulse oximetry.

Development of Benzobisoxazole-Based Novel Conjugated Polymers for Organic Thin-Film Transistors

Benzo[1,2-d:4,5-d']bis(oxazole) (BBO) is a heterocyclic aromatic ring composed of one benzene ring and two oxazole rings, which has unique advantages on the facile synthesis without any column chromatography purification, high solubility on the common organic solvents and planar fused aromatic ring structure. However, BBO conjugated building block has rarely been used to develop conjugated polymers for organic thin film transistors (OTFTs). Three BBO-based monomers, BBO without π-spacer, BBO with non-alkylated thiophene π-spacer and BBO with alkylated thiophene π-spacer, were newly synthesized and they were copolymerized with a strong electron-donating cyclopentadithiophene conjugated building block to give three p-type BBO-based polymers. The polymer containing non-alkylated thiophene π-spacer showed the highest hole mobility of 2.2 × 10^-2 cm² V^-1 s^-1, which was 100 times higher than the other polymers. From the 2D grazing incidence X-ray diffraction data and simulated polymeric structures, we found that the intercalation of alkyl side chains on the polymer backbones was crucial to determine the intermolecular ordering in the film states, and the introduction of non-alkylated thiophene π-spacer to polymer backbone was the most effective to promote the intercalation of alkyl side chains in the film states and hole mobility in the devices.