Excitonic quadrupole absorption in a polydiacetylene

Abstract Excitonic states in a polydiacetylene (polyTCDU) single crystal have been investigated using temperature-dependent optical absorption, Raman and polarization-dependent optical spectroscopy. The expected significance of a linear quadrupolar component in the excitonic transition has been experimentally demonstrated. Formation and detectability of such quadrupoles is a unique attribute of the symmetry, order, valence geometry and one-dimensionality of the polydiacetylene backbone.