Hydrochromic materials find great utility in a wide range of applications including humidity sensing and measuring the water contents of organic solvents, as well as substrates for rewritable paper and human sweat pore mapping. Herein, an inkjet printable diacetylene (DA) is described that can be transformed by UV irradiation to a hydrochromic-conjugated polymer on conventional paper. Specifically, an amphiphilic DA that contains an ­imidazolium ion head-group is found to be compatible with a common office inkjet printer. Various computer-designed images are printed on paper using this substance. UV irradiation of the printed images results in the generation of blue-colored images associated with formation of a polydiacetylene (PDA). The resolutions of the images are almost identical to those generated using a conventional black ink. Importantly, the printed images undergo a blue-to-red color change upon exposure to water and the hydrochromism is found to be temperature dependent. The facile color change that occurs near body ­temperatures enables use of the hydrochromic PDA-coated paper for rapid and precise mapping of human sweat pores from fingers, palms, and feet.

Recently, the development of directly writable techniques for depositing functional materials on solid substrates has received great attention. These pen-on-paper approaches enable generation of diverse patterned images on solid substrates in a flexible, easy handling, and inexpensive manner. Herein, the development of a directly writable conjugated polymer is described. Mechanically, drawable colorimetric polydiacetylene (PDA)–wax composites are readily fabricated by using a simple mixing-molding method. Images are mechanically drawn on a paper substrate using the PDA–wax composites, display thermochromism, and mechanothermochromism. The thermochromic transition temperature is dependent on the melting point of the wax and, as a result, can be precisely controlled by the type of wax used. Optical microscopic analysis shows that formation of the DA–wax composite involves movement of wax molecules into a single diacetylene (DA) crystal. This process results in growth of the crystal. Importantly, the PDA crystal, obtained after UV light irradiation, undergoes significant shrinkage upon heating because of the release of monomers and the embedded wax molecules from the crystal. The release of these molecules creates void in the PDA supramolecules, allowing the PDA chains to undergo C–C bond rotation and hence the blue-to-red color transition.

“Digitalization” represents one approach to shift society's dependence on paper-based communication. However, thus far, this tactic has not had a significant impact on global paper consumption, which has risen over the past few decades. The escalating demand of paper making and consumption has resulted in an intensified negative effect on the environment. Because of this, the development of rewritable paper or erasable ink appears to be an ideal approach to alleviate the increasing demand for paper. In the investigation described herein, novel light-stimulated (UV–vis), reversible color switching, photochromic diarylethene (DE) derivatives are designed, which serve as cyan, magenta, and yellow colored ink materials for full color ink-jet printing. The structures of the DE derivatives are unique in that they contain hydrophilic ethylene glycol chains that enable them to be compatible with aqueous based, ink-jet printing systems. The results of these studies demonstrate that the new DE derivatives can be used in a printing system based on the “write–erase–write” concept that utilizes the same paper multiple times. The approach appears to be ideal for reducing the negative environmental consequences of paper production and consumption.

Exceptional challenges have confronted the rational design of colorimetric sensors for saturated aliphatic hydrocarbons (SAHCs). The main reasons for this difficulty are the extremely nonpolar nature of these targets and their lack of functional groups that can interact with probes. By taking advantage of a mechanochromic conjugated polydiacetylene (PDA) and the hydrocarbon-induced swelling properties of polydimethylsiloxane (PDMS), a sensor film that enables simple, colorimetric differentiation between a variety of C5 to C14 aliphatic hydrocarbons is fabricated. The unprecedented PDA–PDMS composite sensor undergoes a blue-to-red colorimetric transition on a timescale that is dependent on the chain length of the hydrocarbon target. In addition, the development of the red color is directly proportional to the swelling ratio of the film. This straightforward approach enables naked-eye differentiation between n-pentane and n-heptane. The versatility of the sensor system is demonstrated by using it for the colorimetric determination of kerosene in adulterated diesel oil. Finally, the observation that a PDA microcrystal in the film undergoes significant expansion and tearing in concert with a blue-to-red colorimetric transition during the swelling process provides direct evidence for the mechanism for the mechanochromic behavior of the PDA.

A microfluidic technique was employed to fabricate polydiacetylene (PDA)-embedded hydrogel microfibers. By taking advantage of calcium ion-induced insoluble hydrogel formation, supramolecularly assembled diacetylene (DA)-surfactant complexes were successfully immobilized in the calcium alginate fibers. Thus, instantaneous microfiber formation was observed when the core flow of DA supramolecules-containing alginate solution met the sheath flow of calcium ions. UV irradiation of the resulting fibers afforded blue colored PDAs, and the formation of a conjugated polymer was confirmed by heat-induced phase transition and by Raman spectroscopy. By adjusting the core and sheath flow rates, PDA-embedded hydrogel fibers of various sizes were obtained.

A micropatterning method for depositing polydiacetylene (PDA) supramolecular vesicles on glass substrates, employing a pre-patterned hydrophobic thin film, is presented. The pre-patterned hydrophobic thin film is used to define surface-exposed regions on hydrophilic glass substrates where selective immobilization of PDA vesicles takes place. The observation that fluorescent patterns are generated by heat treatment of the deposited PDAs demonstrates that the vesicles are successfully immobilized in the form of micropatterns. Finally, the possibility that this strategy may be used to design a vesicle-based sensor chip system is demonstrated by the observation that fluorescence patterns are generated when the immobilized PDA vesicles interact with cyclodextrin.

A direct method for the generation of magnetically responsive conjugated polymer supramolecules is described. By immobilizing magnetite nanoparticles (MNP) on the surface of polydiacetylene (PDA) supramolecules, an inorganic/conjugated polymer hybrid system results that enables the incorporation of an important property (magnetism) to an attractive class of colorimetric PDA sensors. Benefits of this new system include: (1) ease of preparation, (2) variability in diacetylene labeling of MNPs, (3) diversity in conjugated PDA morphologies, (4) facile isolation process, and (5) immobilization of the PDA without altering the colorimetric (sensory) properties. It is demonstrated that PDA/MNP systems offer advantages in applications including film formation, separation, and sensing.

The synthesis, characterization, and functionalization of polydiacetylene (PDA) networks on solid substrates is presented. A highly transparent and cross-linked diacetylene film of DCDDA-bis-BA on a solid substrate is prepared first by tailoring the monomers with organoboronic acid moieties as pendant side groups and consequent drop-casting and dehydration steps. Precisely controlled thermal curing plays a key role to obtain properly aligned diacetylene monomers that are closely packed between the boronic acid derived anhydride structures. A second cross-linking, which occurs by polymerization of the diacetylene monomers with UV irradiation, induces a transparent to blue color shift. Accordingly, colored image patterns are readily available by polymerization through a photomask. The color change that takes place as a response to various organic solvents can be simply detected by naked eyes. The thermofluorescence change of PDA networks is demonstrated to be an effective method by which to obtain the microscale temperature distribution of thermal systems. The ease of film formation and stress-induced blue-to-red color change with a simultaneous fluorescence generation features of the network structure should find a great utility in a wide range of chemical and thermal sensing platforms.

A combinatorial approach for the colorimetric differentiation of organic solvents is developed. A polydiacetylene (PDA)-embedded electrospun fiber mat, prepared with aminobutyric acid-derived diacetylene monomer PCDA-ABA 1, displays colorimetric stability when exposed to common organic solvents. In contrast, a fiber mat prepared with the aniline-derived diacetylene PCDA-AN 2 undergoes a solvent-sensitive color transition. Arrays of PDA-embedded microfibers are constructed by electrospinning poly(ethylene oxide) solutions containing various ratios of two diacetylene monomers. Unique color patterns are developed when the conjugated polymer-embedded electrospun fiber arrays are exposed to common organic solvents in a manner which enables direct colorimetric differentiation of the tested solvents.

Polydiacetylenes (PDAs), a family of highly π-conjugated polymers, have unique characteristics associated with their ability to self-assemble. Disruption of the extensively delocalized enyne backbones of molecularly ordered PDA sidechains induces a blue-to-red color change, which has been elegantly applied in the design of chemosensors. Recently, colorimetrically reversible PDAs have received significant attention, not only to gain a better understanding of the fundamentals of PDA chromism, but also to develop methodologies to overcome limitations associated with their colorimetrically irreversible counterparts. In this article, recent progress made in the field of colorimetrically tunable (reversible, stable, or sensitive) PDAs is described. Major emphasis is given to rational design strategies developed in our group. Relevant mechanistic investigations, a diagnostic method to test colorimetric reversibility, as well as future challenges in this area will be also discussed.

A universal colorimetric method for the detection of nucleic acids, based on ionic interactions by polydiacetylene (PDA) liposomes, is described. Primary and quaternary amine-modified diacetylene monomers were synthesized and used to generate positively charged PDA liposomes. The resulting PDA sensors showed a dramatic color change from blue to red upon the addition of nucleic acids amplified by using the polymerase chain reaction (PCR) due to the stimuli caused by ionic interactions between the positively charged PDA and negatively charged phosphate backbone of the nucleic acids. The color change that takes place can be simply detected by the naked eye. Compared with quaternary amine-functionalized PDA vesicles, the primary amine-functionalized PDA underwent a more intense color transition under optimized conditions. By using the PDA-based colorimetric sensor, nucleic acids amplified by common PCR reaction, whose typical concentration is around 100 nM, can be readily detected. Since implementation of this universal colorimetric method is simple, rapid and does not require any sophisticated instrumentation, it should have greatly enhanced applications as a technology for DNA diagnosis.