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.