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LCAM DTM TF TU Liberec,
Photochromism is a chemical process in which a compoundundergoes a reversible change between two states having separate absorptionspectra, i.e. different color [1]. In our previous work we have published somesolutions of problems of measurement photochromic textile sample by classicalspectrophotometer system [2]. Fig. 1 shows optical scheme of present commercial spectrophotometer and Fig. 2 shows our new experimental measuring system.
Main problem with measurement of kinetic behavior ofphotochromic pigments by classical spectrophotometer is relative long timeperiod between individual measurements (cca 15s) and impossibility ofmeasurement whole color change during exposition without interruption ofillumination of sample during measurement. That means classical commercialspectrophotometers enable off-line measurement of kinetic behavior duringexposition period and quasi on-line measurement during reversion period.
Based on this problems is possible to obtain only duringreversion decay process valid data and growth process (exposition) isaffected by high variation of data, as is shown on Fig. 3.
Following this knowledge we developed our original experimental system with short time scanning of color change of photochromic samples during growth and decay period of color change. Common period between individual measurements which we now use is 1 s (Fig. 2). Second difference between our experimental system and commercial system is in the usage continuous illumination by excitation and measuring light sources against discontinuous measuring light source discharge lamp, which is today used in commercial systems. Continuous controlled light source have smaller problems with light source drift.
Third difference between classical system and our measuring system is in decomposition of time delay between excitation illumination and measurement during exposition period. Last main difference is utilization of excitation monochromator, which allow us to select variable bandwidth of wavelengths for excitation that means we use bispectral measuring configuration. In this study we have used seven excitation bands with maxima 400, 375, 350, 325, 300, 275 and 250nm (full width at half-maximum (FWHM) 50nm). Integral intensity of illumination was modified bellow average value 900 W.cm-2.
Because we have tested pigments with different colors is necessary to recalculate absolute sensitivity to relative sensitivity for better understanding of sensitivity spectral shape. Fig.5 documents that except pigment P5 other pigments have main sensitivity at 375 nm.
Both spiroindolinonaftopyran structures with same orientation of naftopyran (P2 and P3) show narrowest bandwidth, conformable shape has also spironaftooxazins (P1 and P4). Only pigment no P5 spiroindolinonaftopyran with opposite orientation of naftopyran structure have maximum of sensitivity move to lower wavelength (350 nm) and flat shape of sensitivity curve. That means if we need sensors with low sensitivity on spectral characteristics of UV radiation we need to use pigment no. 5, if we need high sensitivity of sensors on spectral characteristics of UV radiation we need to use pigments no 2 or 3. But if we think about good selectivity of amount of UV radiation we need to use pigment no. 1 or 2.
REFERENCES
[1] Bamfield, P.: Chromic phenomena, technological applications of colour chemistry, RSC Cambridge 2001
[2] Vikov, M., Vik, M.: Molecular Crystals and Liquid Crystals Volume 431 (2005), p. 103-116
ACKNOWLEDGEMENTS
This work was supported by Czech Ministry of Education research project 1M4674788501.
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