Evaluation of UV-Stability of Coumarins-Loaded Porphyrin-Type Humidity Indicator
Matsumoto, Tomoko ,
Sugano, Kento ,
Matsumoto, Jin ,
Fueda, YoshiyukiYasuda, Masahide
11 , 2017-07-31 , 宮崎大学工学部
Cobalt-free humidity detection indicator (HDI) for silica gel was developed using tetraphenylporphyrin (Tpp) which showed distinguishable color change depending on pH. The HDI was prepared by the mixing of dichloro(tetraphenylporphyrinato)phosphorus chloride (PTpp) and MgCl2 with SiO2 beads and the drying at 130 °C for 24 h. During the preparation, the PTpp was decomposed into the protonated Tpp (H2Tpp2+). The pH change arose from a proton release by the reaction of MgCl2 with silanol of the SiO2 under dry conditions and neutralization under humid conditions. The HDI showed green color due to H2Tpp2+ under dry conditions and orange color due to Tpp under humid conditions. However, the HDI took place partial decoloration on extended exposure to sunlight. Here, in order to prevent this decoloration of the HDI by sun light, UV-absorbents such as 7-methoxycoumarin (1a) and 6- methylcoumarin (1b) were loaded to the HDI. The HDIs with and without 1 were irradiated at 352 nm by black light under dry conditions. The irradiated HDI beads were analyzed by microscopic absorption spectra on a confocal laser scanning microscope. The absorbance (A) at 650 nm of the HDI was monitored. The light-protecting ability of UV-absorbent was evaluated by the slope (%R) for time-conversion plots of absorbance ratio (A/A0), where A0 denotes absorbance before irradiation. Since the %R values were minimum values at the loading of 0.100 wt% of 1a and 0.075 wt% of 1b, these were determined to be the optimized concentrations. Thus the loading of 1 was effective to prevent the color degradation.