Flexible patch-type hydrochromic polydiacetylene sensor for human sweat pore mapping

The Unusual Photochromic and Hydrochromic Switching Behavior of Cellulose-Embedded 1,8-Naphthalimide-Viologen Derivatives in the Solid-State

Stimuli-responsive chromic materials such as photochromics, hydrochromics, thermochromics, and electrochromics have a long history of capturing the attention of scientists due to their potential industrial applications and novelty in popular culture. However, hybrid chromic materials that combine two or more stimuli-triggered color changing properties are not so well known. Herein, we report a design strategy that has led to a series of emissive 1,8-naphthalimide-viologen dyads which exhibit unusual dual photochromic and hydrochromic switching behavior in the solid-state when embedded in a cellulose matrix. This behavior manifests as reversible solid state fluorescence hydrochromism upon changes in atmospheric relative humidity (RH), and reversible solid state photochromism upon generation of a cellulose-stabilized viologen radical cation. In this design strategy, the bipyridinium unit serves as both a water-sensitive receptor for the hydrochromic fluorophore-receptor system, and a photochromic group, capable of eliciting its own visible colorimetric response, generating a fluorescence quenching radical cation with prolonged exposure to ultraviolet (UV) light. These dyes can be inkjet-printed onto cellulose paper or drop-cast as cellulose powder-based films and can be unidirectionally cycled between three different states which can be characteristically visualized under UV light or visible light. The material's photochromism, hydrochromism, and underlying mechanism of action was investigated using computational analysis, dynamic vapor sorption/desorption isotherms, electron paramagnetic resonance spectroscopy, and variable humidity UV-Vis adsorption and fluorescence spectroscopies.

A hybrid hydrochromic molecular crystal applicable to invisible ink with high reversibility

Highly reversible hydrochromic behavior is realized in a novel hybrid molecular crystal by controlling the gain and loss of coordinated water.

Tuning of the Topochemical Polymerization of Diacetylenes Based on an Odd/Even Effect of the Peripheral Alkyl Chain: Thermochromic Reversibility in a Thin Film and a Single-Component Ink for a Fountain Pen

The topochemical polymerization of diacetylenes (DAs) is closely related to the length of their alkyl chain. DA monomers have two types of alkyl chain side groups: the inner alkyl chain and the outer alkyl chain, that is, the peripheral alkyl chain. Herein, we designed and synthesized a series of DA monomers that possess bis-amide linkages with different peripheral alkyl chains ( n = 6-9; DA1-DA4). The peripheral alkyl chain length of these DA monomers exhibits an odd/even effect on topochemical polymerization. The polymerization of DAs was achieved only when n is an odd number, whereas no polymerization occurred when n is an even number. The odd/even effect on the topochemical polymerization was also investigated using ab initio density functional theory calculations. The thermochromic reversibility of polydiacetylenes (PDAs) was investigated using UV-vis absorption spectroscopy at temperatures ranging from 20 to 60 °C. Monomer DA2 was used as a single-component ink solution in a fountain pen that can be transformed into thermochromic letters on conventional paper. Furthermore, a PDA-embedded polyethylene oxide film was included to monitor the thermochromic reversibility and was found to exhibit excellent thermochromic reversibility between 20 and 100 °C and stability, enabling storage for a few months without deformation. Finally, a green-colored patterned polymer film is readily obtained by a subtractive color (blue and yellow) mixing method and exhibits high thermochromic reversibility at temperatures between 20 and 100 °C.