In order to fully understand the dependence of device electroluminescence (EL) on the, chemical structure of two light-emitting materials: 1,2,3,4-tetraphenyl-1,3-cyclopentadiene (TPCP) and 1,23,4,5-pentaphenyl-1,3-cyclopentadiene (PPCP), their properties in solution and as evaporated thin films of UV-Vis absorption, geometric structures, photoluminescence (PL), electrochemistry, glass transition temperature and EL were compared. Compared with that of TPCP, the first absorption band of PPCP shifts to the shorter wavelength region both in solution and thin film state; the photoluminescence in solution exhibits lower quantum efficiency but in thin film state has a higher intensity; the electrochemical oxidation happens at a higher potential; the solid powder exhibits higher glass transition temperature; and the electroluminescent device shows higher luminescence and efficiency. Reasons responsible for the differences were analyzed. (C) 2002 Published by Elsevier Science B.V.