Detection and identification of VOCs in their vapor phase is essential for safety and quality assessment. In this work, a novel platform of a paper-based polydiacetylene (PDA) colorimetric sensor array is prepared from eight diacetylene monomers, six of which are amphiphilic and the other two are bolaamphiphilic. To fabricate the sensors, monomers are coated onto a filter paper surface using the drop-casting technique and converted to PDAs by UV irradiation. The PDA sensors show solvent induced irreversible color transition upon exposure to VOC vapors. When combined into a sensing array, the color change pattern as measured by RGB values and statistically analyzed by principal component analysis (PCA) is capable of distinguishing 18 distinct VOCs in the vapor phase. The PCA score and loading plots also allow the reduction of the sensing elements in the array from eight to three PDAs that are capable of classifying 18 VOCs. Utilizing an array containing only two PDAs, various types of automotive fuels including gasoline, gasohol and diesel are successfully classified.

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A series of bishydrazide compounds have been developed for selective turn-on detection of Al3+ cation, based on metal chelation-enhanced fluorescence (CHEF) effects that inhibit the nonradiative PET and ESIPT processes. In aqueous solution, Al3+ selectively induces strong fluorescence of these compounds with large Stokes shifts up to ∼133 nm and emission colors varying from blue to orange. In the solid phase, both Al3+ and Zn2+ give apparent fluorescence which is simultaneously detected based on chromatographic separation.

Mono-and diamides derivatives of 10,12-pentacosadiynoic acid (PCDA) were synthesized from condensation of PCDA with various aliphatic and aromatic diamines. Polydiacetylenes of the amido-PCDA derivatives were prepared by photopolymerization of their molecular assembly homogeneously dispersed in aqueous media. Thermochromic properties of the resulting polydiacetylene sol were studied by temperature variable UV-vis spectrometry along with photographic recording. The color transition temperatures and thermochromic reversibility of the polymers are varied depended on the number of amide groups and the structure of the aliphatic and aromatic linkers. The phenylenediamide and polymethylenediamide PCDA derivatives give polydiacetylenes with complete thermochromic reversibility, while the polydiacetylenes obtained from 1,2-cyclohexylene and glycolic chain diamide derivatives exhibited irreversible thermochromism, whereas the polymers attained from the aromatic monoamide analogues are partially reversible. The variation of the linkers also allows the color transition temperature of the polydiacetylene to be tuned in the range of 20 °C to over 90 °C. The results provide a fundamental idea about the factors affecting the thermochromic properties of polydiacetylenes toward the development of materials for universal thermal indicators.

Thermochromism, solvatochromism, and alkalinochromism of a poly-10,12-pentacosadiynoic acid (poly(PCDA)) vesicle solution are studied by electronic absorption spectroscopy. The spectroscopic profiles reveal different sequences of side-chain movement during the chromic transitions. The gradual hypsochromic shift and reversibility of the purple solution at low temperature in the thermochromic transition indicates that the transition starts with reversible conformational alteration of methylene side chains leading to metastable purple vesicles. Further heating to 80 degrees C or higher eventually causes the hydrogen bonds at the carboxylic head groups to break and turns the vesicle solution to red. The irreversibility of the red vesicles indicates that it is the most thermodynamically stable form. In the ethanolochromism and alkalinochromism, the processes are however induced at the vesicle-media interface, directly bringing about the hydrogen bond breaking. The purple solutions observed in the ethanolochromism and alkalinochromism cannot reverse back to the blue one. The absorption spectra clearly demonstrate that they are mixtures of the blue and red vesicles.

Triphenylamine-based fluorophores containing pyrene or corannulene show variable fluorescence quenching sensitivity toward nitro explosives. The most sensitive fluorophore is capable of detecting TNT on the ng cm(-2) scale; the array is useful for identifying nitro aromatics.

A series of bisdiynamide lipids containing various lengths of methylene spacer (m = 2, 3 and 4) between the diynes and the diamide headgroup and number of methylene units (n = 6 and 9) in their hydrophobic tails are synthesized. All six lipids synthesized can be dispersed in water and photopolymerized by UV irradiation to give the corresponding polydiacetylene (PDA) sols. The color transitions from blue to red during heating-cooling cycles of the PDA sols are photographically recorded and monitored by UV-vis absorption spectroscopy. The bisdiynamide PDAs exhibit excellent thermochromic reversibility and the color transition temperature can be tuned between ca. 25-55 °C by the variation of m and n values. Temperature indicators can be obtained by applying a screen printing ink formulated from the bisdiynamide monomer on plastic substrates followed by UV irradiation to generate desired patterns of thermochromically reversible PDAs.

Two series of symmetrical (Sx) and unsymmetrical (Uy) diacetylene monomers containing diamide groups with different methylene units are successfully prepared. Photopolymerization of their nanovesicles dispersed in water is carried out by irradiation at 254 nm affording blue sols of the corresponding PDAs. The degree of thermochromic reversibility (%DR) of the PDA sols are determined using UV−vis spectroscopy in order to probe effects of the number of the methylene units, x and y, within the linker and hydrophobic tail, respectively. The complete color reversibility (%DR > 89%) is observed only when x is an even number while partially reversible or irreversible thermochromism (% DR < 65%) is displayed in the case of odd x number. For the Uy series, the color recovering ability within the heating and cooling process increases along with the y number; %DR = 3, 62, and 90% for y = 0, 4, and 16, respectively. This work is the first direct demonstration of the roles of number of methylene units within the diacetylene monomers on the thermochromic reversibility of their PDAs that provide additional dimensions for rational molecular design in the development of PDA thermal sensors.