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 3 v point symmetry and crystallizes in the trigonal space group R3m. Crystal data for 4: a = 16.6710(13) Å, b = 16.6710(13) Å, c = 4.2590(3) Å, α = β = 90°, γ = 120°, 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 μC m-2 K-1, which is in accordance with a calculated value of −3.2 μC 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 °C. The relative dielectric permittivity tensor was obtained at optical frequencies (ε11 and ε22 = 3.16 and ε33 = 2.48) and in the microwave region at 35 GHz (ε11 and ε22 = 5.2 ± 0.6 and ε33 = 2.9 ± 0.2), and at low frequencies (120 Hz and 1 kHz), the isotropic permittivity was determined (ε120 Hz = 4.7 ± 0.8 and ε1 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 × 10-2 m2 C-1).