Nanometer-scale optical waveguides are attractive due to their potential applicability in photonic integration, optoelectronic communication, and optical sensors. Nanoscale white light-emitting and/or polychromatic optical waveguides are desired for miniature white-light generators in microphotonic circuits. Here, polychromatic (i.e., blue, green, and red) optical waveguiding characteristics are presented using a novel hybrid composite of highly crystalline blue light-emitting organic nanowires (NWs) combined with blue, green, and red CdSe/ZnS quantum dots (QDs). Near white-color waveguiding is achieved for organic NWs hybridized with green and red QDs. Light, emitted from QDs, can be transferred to the organic NW and then optically waveguided through highly packed π-conjugated organic molecules in the NW with different decay characteristics. Remote biosensing using dye-attached biomaterials is presented by adapting the transportation of QD-emitted light through the organic NW.

Herein we report a rational design strategy for tailoring intermolecular interactions to enhance room-temperature phosphorescence from purely organic materials in amorphous matrices at ambient conditions. The built-in strong halogen and hydrogen bonding between the newly developed phosphor G1 and the poly(vinyl alcohol) (PVA) matrix efficiently suppresses vibrational dissipation and thus enables bright room-temperature phosphorescence (RTP) with quantum yields reaching 24 %. Furthermore, we found that modulation of the strength of halogen and hydrogen bonding in the G1–PVA system by water molecules produced unique reversible phosphorescence-to-fluorescence switching behavior. This unique system can be utilized as a ratiometric water sensor.

Herein we report a rational design strategy for tailoring intermolecular interactions to enhance room-temperature phosphorescence from purely organic materials in amorphous matrices at ambient conditions. The built-in strong halogen and hydrogen bonding between the newly developed phosphor G1 and the poly(vinyl alcohol) (PVA) matrix efficiently suppresses vibrational dissipation and thus enables bright room-temperature phosphorescence (RTP) with quantum yields reaching 24 %. Furthermore, we found that modulation of the strength of halogen and hydrogen bonding in the G1–PVA system by water molecules produced unique reversible phosphorescence-to-fluorescence switching behavior. This unique system can be utilized as a ratiometric water sensor.

To devise a reliable strategy for achieving specific HOMO and LUMO energy level modulation via alternating donor-acceptor monomer units, we investigate a series of conjugated polymers (CPs) in which the electron withdrawing power of the acceptor group is varied, while maintaining the same donor group and the same conjugated chain conformation. Through experiment and DFT calculations, good correlation is identified between the withdrawing strength of the acceptor group, the HOMO and LUMO levels, and the degree of orbital localization, which allows reliable design principles for CPs. Increasing the acceptor strength results in an enhanced charge transfer upon combination with a donor monomer and a more pronounced decrease of the LUMO level. Moreover, while HOMO states remain delocalized along the polymer chain, LUMO states are strongly localized at specific bonds within the acceptor group. The degree of LUMO localization increases with increasing polymer length, which results in a further drop of the LUMO level and converges to its final value when the number of repeat units reaches the characteristic conjugation length. Based on these insights we designed PBT8PT, which exhibits 6.78% power conversion efficiency after device optimization via the additive assisted annealing, demonstrating the effectiveness of our predictive design approach.

All-organic dyes have shown promising potential as an effective sensitizer in dye-sensitized solar cells (DSSCs). The design concept of all-organic dyes to improve light-to-electric-energy conversion is discussed based on the absorption, electron injection, dye regeneration, and recombination. How the electron-donor–acceptor-type framework can provide better light harvesting through bandgap-tuning and why proper arrangement of acceptor/anchoring groups within a conjugated dye frame is important in suppressing improper charge recombination in DSSCs are discussed. Separating the electron acceptor from the anchoring unit in the donor–acceptor-type organic dye would be a promising strategy to reduce recombination and improve photocurrent generation.

The correlation between the molecular design of a conjugated polyelectrolyte (CPE) and its aggregated structure and the emissive properties in water is systematically investigated by means of UV–vis spectrometry, fluorescence spectroscopy, and scanning/transmission electron microscopy. Five different and rationally designed CPEs having carboxylic acid side chains are synthesized. All five conjugated polyelectrolytes are seemingly completely soluble in water in visual observation. However, their quantum yields are dramatically different, changing from 0.45 to 51.4%. Morphological analysis by electron microscopy combined with fluorescence spectrophotometry reveals that the CPEs form self-assembled aggregates at the nanoscale depending on the nature of their side chains. The feature of the self-assembled aggregates directly determines the emissive property of the CPEs. The nature and the length of the spacer between the carboxylic acid group and the CPE backbone have a strong influence on the quantum yield of the CPEs. Our study demonstrates that bulky and hydrophilic side chains and spacers are required to achieve complete water-solubility and high quantum yield of CPEs in water, providing an important molecular design principle to develop functional CPEs.

Rationally designed polydiacetylene (PDA) molecules have been developed for rapid, selective, sensitive, and convenient colorimetric detection of organophosphate (OP) nerve agents, a mass destruction weapon. Oxime (OX) functionality was incorporated into diacetylene molecules to utilize its strong affinity toward organophosphates. The diacetylene molecules having an OX functional group (OX-PDA) were self-assembled to form PDA liposomes in an aqueous solution. Upon exposure to organophosphate nerve agent simulants, OX at the OX-PDA liposome surface interacts with nerve agent simulants, which results in intraliposomal repulsive stress due to steric repulsion between OP-occupied OX units at the liposome surface as well as interliposomal aggregation induced by increased hydrophobicity of the liposome surface via OP-OX complex formation. The resulting intra- and interliposomal stress causes disturbance of the conjugated backbone of OX-PDA, producing color change as a label-free and sensitive sensory signal. The effects of molecular structure on selectivity and sensitivity of OX-PDA liposome solution, OX-PDA liposome-embedded agarose gels, and OX-PDA liposome-coated cellulose acetate membranes were systematically investigated. The optimized OX-PDA liposome in the solid state showed selective and rapid optical transition upon exposure down to 160 ppb of diisopropylfluorophosphate (DFP), a nerve agent simulant. The results provide an insightful molecular design principle of PDA-based colorimetric sensor and suggest portable sensory patches for rapid, selective, sensitive, and convenient colorimetric detection of organophosphate nerve agents.

The relationship between the exciton binding energies of several pure organic dyes and their chemical structures is explored using density functional theory calculations in order to optimize the molecular design in terms of the light-to-electric energy-conversion efficiency in dye-sensitized solar cell devices. Comparing calculations with measurements reveals that the exciton binding energy and quantum yield are inversely correlated, implying that dyes with lower exciton binding energy produce electric current from the absorbed photons more efficiently. When a strong electron-accepting moiety is inserted in the middle of the dye framework, the light-to-electric energy-conversion behavior significantly deteriorates. As verified by electronic-structure calculations, this is likely due to electron localization near the electron-deficient group. The combined computational and experimental design approach provides insight into the functioning of organic photosensitizing dyes for solar-cell applications. This is exemplified by the development of a novel, all-organic dye (EB-01) exhibiting a power conversion efficiency of over 9%.

The pH chromism of polydiacetylenes (PDAs) is examined with respect to the molecular size and acidity of acid analytes, along with the alkyl spacer length of primary-amine-functionalized diacetylene (DA) lipids. pH turns out to be an important parameter to charge amine headgroups of PDA but a change in pH does not necessarily result in a PDA color change. The molecular size of acid analytes is identified as another factor that can produce a configurational change in PDA amine headgroups, followed by perturbation of the ene–yne conjugated backbone. In addition, the length of a flexible alkyl spacer between the amine headgroup and the amide group of the diacetylene lipids is found to strongly affect the degree of PDA chromatic transition. The longer alkyl spacer shows a smaller chromatic transition from blue to red phase. The alkyl spacer seems to provide a certain degree of freedom to the amine headgroup, thus decreasing the transfer of headgroup steric effects to the PDA backbone. These correlations found for PDA chromism are applied to the development of a system that colorimetrically detects diethyl phosphate (DEP), a degraded nerve agent simulant. PDA liposomes show a selective chromatic transition upon binding with DEP compared to other acid analytes.

A conjugated polymer (CP) and molecular-beacon-based solid-state DNA sensing system is developed to achieve sensitive, label-free detection. A novel conjugated poly(oxadiazole) derivative exhibiting amine and thiol functional groups (POX-SH) is developed for unique chemical and photochemical stability and convenient solid-state on-chip DNA synthesis. POX-SH is soluble in most nonpolar organic solvents and exhibits intense blue fluorescence. POX-SH is covalently immobilized onto a maleimido-functionalized glass slide by means of its thiol group. Molecular beacons having a fluorescent dye or quencher molecule as the fluorescence resonance energy transfer (FRET) acceptor are synthesized on the immobilized POX-SH layer through direct on-chip oligonucleotide synthesis using the amine side chain of POX-SH. Selective hybridization of the molecular beacon probes with the target DNA sequence opens up the molecular beacon probes and affects the FRET between POX-SH and the dye or quencher, producing a sensitive and label-free fluorescence sensory signal. Various molecular design parameters, such as the size of the stem and loop of the molecular beacon, the choice of dye, and the number of quencher molecules are systematically controlled, and their effects on the sensitivity and selectivity are investigated.