Stampfl, J., Graupner, W., Leising, G., & Scherf, U. (1995). PHOTOLUMINESCENCE AND UV-VIS ABSORPTION STUDY OF POLY(PARA-PHENYLENE)-TYPE LADDER-POLYMERS. Journal of Luminescence, 63(3), 117-123. doi:10.1016/0022-2313(94)00058-K.