Charge transfer emissive singlet excited states and photoinduced electron transfer properties in the diarylideneacetone compounds (RCHCH) 2 CO; R = phenyl, 1- and 2-naphthyl, 3-( N -ethylcarbazoyl), and 4-(C 5 H 5 )Fe(C 5 H 4 C 6 H 4 CHCH(CO)CHCHC 6 H 5 )