Synthesis and properties of a new polydiacetylene: Poly[1,6‐di(N‐carbazolyl)‐2,4‐hexadiyne]

Abstract

The solid‐state synthesis and properties are reported for a new polydiacetylene: poly[1,6‐di(N‐carbazolyl)‐2,4‐hexadiyne]. The monomer crystals polymerize quantitatively with γ irradiation or thermal annealing. An Autocatalytic effect is observed in both γ‐ray polymerization and thermal polymerization and is attributed to an increase in chain propagation length at about 5% conversion. The activation energy for thermal polymerization is about 25 kcal/mole, independent of the degree of conversion to polymer. The exceptional thermal stability of the polymer crystals allowed a thermomechanical analysis over a large temperature range, −50 to 300°C. With increasing temperature, the polymer contracts in the chain direction linearly with temperature over the entire range, yielding a thermal expansion coefficient of (−2.32 ± 0.02) × 10−5°C−1. Photoconductivity action spectra are reported for the polymer crystals. The energies for the photoconductivity onset (ca. 2.3 eV) and for the lowest energy optical transition (1.89 eV) are the lowest reported for the polydiacetylenes. The photoconduction onset is blue‐shifted with respect to optical absorption—a result which is consistent with the excitonic assignment for the lowest energy optical transition in the polydiacetylenes.

The study of model polydiacetylene/epoxy composites

“…The substituted diacetylene derivative 1,6-di-(Ncarbazolyl)-2,4-hexadiyne (DCH) was prepared by previously described techniques [11,12]. Monomer crystals with their axial dimension much longer than their transverse dimension were prepared by slow evaporation from toluene solution.…”

Third-order nonlinear optical properties of polydiacetylene single crystal.

“…Material and thin single crystal formation 1,6-N-Carbazolyl-2,4-hexadiyne (DCH) monomer was synthesized and polymerized in the solid-state according to the literature [14]. The polymer single crystal was embedded and solidified in an epoxy resin.…”

Low-lying excitations of polydiacetylene

“…We note that these values show a great deal of variability owing to the variety of phases and the disorder present in PDA. Hence, despite the apparent success of the Su-Schrieffer-Heeger model [28]- [29] neutral excitons with large binding energies are the low-lying excitations in PDA [24], [30]- [31]. This is borne out by the Pariser-Parr-Pople calculation presented in this work, which incorporates electron-electron interactions.…”

“…First, in polymeric crystal form, the linear absorption spectrum is see to be symmetric and peaks at ∼ 1.8-1.9 eV. However, the onset of photoconduction occurs not at this value but at ∼ 2.3-3.0 eV (corresponding to uncorrelated π-π* transitions) [24]. In addition, comparison of the linear absorption with the EA spectrum shows an EA feature at ∼ 2.0 eV corresponding to the first derivative of the absorption: this is attributed to the Stark shift of the exciton.…”