Abstract
E-α-(2,5-dimethyl-3-furyl) ethylidene (dicyclopropyl methylene)-2,5 furadione or dicyclopropyl fulgide (DCPF) is crystalline in as-synthesized condition. It turns to amorphous structure upon thermal deposition. Annealing temperatures (333
→
393) K do not influence the amorphous structure of films. The color of films in as-deposited condition is yellow–orange indicating E-isomer formation, this color turns to red–violet (C-isomer) upon irradiation with ultra violet (UV) light of wavelength 366 nm for 15 min. The optical properties for E-, C- and Z-isomers of DCPF were investigated using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 200–2500 nm. The films are transparent for a wave length >450 nm. The presence of a sharp absorption edge in transmittance spectra of E- and C-isomers of DCPF recommends such a compound as a good optical filter material. The optical properties are independent of film thicknesses in the 550–1736 nm range. The photochromic properties of films are lost as a result of annealing. The dielectric constant, oscillator energy and dispersion energy slightly increase upon conversion from E- to C-isomer. The types of electronic transitions are direct allowed with energy gap of 3.08 eV for all isomers and indirect allowed with energy gap of 2.76 eV for E- and C-isomers and with energy gap of 2.52 eV for Z-isomer.