Synthesis, structure, and properties of 4,8,12-trioxa-12c-phospha-4,8,12,12c-tetrahydrodibenzo-[cd,mn]pyrene, a molecular pyroelectric

The title compound (4) was synthesized, and its crystalline structure was determined. The molecule has C-3v point symmetry and crystallizes in the trigonal space group R3m. Crystal data for 4: a = 16.6710(13) Angstrom, b = 16.6710(13) Angstrom, c = 4.2590(3) Angstrom, alpha = beta = 90 degrees, gamma = 120 degrees, Z = 3, R(F) = 0.0234. The material has a permanent polarization and consequent pyroelectric properties. The room temperature pyroelectric coefficient was found to be -3 +/- 2 mu C m(-2) K-1, which is in accordance with a calculated value of -3.2 mu C m(-2) K-1. The molecular dipole moment was determined to be 3.3 +/- 0.2 D, the direction of which was unambiguously assigned with respect to the molecular coordinates. The thermal expansivity was determined at temperatures in the range -93 to 200 degrees C. The relative dielectric permittivity tensor was obtained at optical frequencies (epsilon(11) and epsilon(22) = 3.16 and epsilon(33) = 2.48) and in the microwave region at 35 GKz (epsilon(11) and epsilon(22) = 5.2 +/- 0.6 and epsilon(33) = 2.9 +/- 0.2), and at low frequencies (120 Hz and 1 kHz), the isotropic permittivity was determined (epsilon(120 Hz) = 4.7 +/- 0.8 and epsilon(1 kHz) = 4.7 +/- 1.1). Finally, an estimate of the molecular heat capacity was calculated (C-p = 900 J Kg(-1) K-1) and the material was considered for potential use in infrared detection as its detectivity merit factor, M(r), was determined (M(r) = 8.8 x 10(-2) m(2) C-1).