Preparation of multi-purposed paper indicators from diacetylene lipids

Abstract

Diacetylenes with β-alanine ethyl ester and di-β-alanine ethyl ester were synthesized by amide coupling method using EDC and HOBt as coupling reagents. The diacetylene were fabricated onto filter paper and polymerized by 254 nm UV light. The prepared devices were intended to be used as indicators i.e. UV-dose, temperature, solvent and humidity indicators. The color transitions of the indicators were determined from their color images using the RGB color system in which the crossing point of %B and %R curves from their plots against the independent variables such as time and temperature. The sensitivity of UV and temperatures can be tuned by converting carboxylic acid head group to -alanine ethyl ester and di--alanine ethyl ester and varing the number of aliphatic chain length. Comparing between different functional groups, the thermal sensitivity was not always in line with the UV sensitivity that demonstrated other mechanisms beyond the photo-induced thermochromism for the blue-to-red color transition induced by UV light. The attempt in constructing an indicator array from 6 PDAs for detection and classification of organic solvents gave relatively low classification accuracy of 74%. The diacetylene carboxylic acid could be used as humidity sensing materials via an alkalinochromism effect by a zone coating of the diacetylene and K2CO3. The blue PDA zone turned red at 62% RH with time dependence starting from the PDA/ K2CO3 interface at 3 h and completed within 24 h. This time dependent colorimetric transition is very attractive for real applications where the moisture-protected products are usually unintentionally exposed to the ambient humidity for an unknown period of time.