Mechanical strain sensing in a SIS-type elastomer with single site strain probes based on carbazole

Four fluorescent strain probes with one or two carbazole units placed in the middle of an elastomeric triblock of polystyrene -polyisoprene-polystyrene (SIS) have been prepared and their fluorescence behaviors investigated under strain. The probes were dissolved in commercial SIS type rubbers at low levels of 0.1 wt %. Films cast from this blend were subjected to tensile elongation while the fluorescence spectra were obtained. A rather large change from ca. 0.7 to 1.1 in the relative intensity at two wavelengths (I-350/I-370) was observed on elongations up to 400%. The spectroscopic change is strongest for small strain levels around 0-200% and leveled out above 300-400%. This is attributed to changes in the intensities of the vibronic bands of the substituted carbazole units rather than changes in molecular overlap of carbazole dimers.