Synthesis, Structure, and Properties of 4,8,12-Trioxa-12c-phospha-4,8,12,12c-tetrahydrodibenzo[<i>cd</i>,<i>mn</i>]pyrene, a Molecular Pyroelectric

Abstract

The title compound (4) was synthesized, and its crystalline structure was determined. The molecule has C3v 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 (Cp = 900 J Kg-1 K-1) and the material was considered for potential use in infrared detection as its detectivity merit factor, Mr, was determined (Mr = 8.8 × 10-2 m2 C-1).