Glass-Forming Carbazolyl and Phenothiazinyl Tetra Substituted Pyrene Derivatives: Photophysical, Electrochemical, and Photoelectrical Properties

Abstract

Carbazolyl and phenothiazinyl tetra substituted derivatives of pyrene, namely, 1,3,6,8-tetra(9-ethyl-9H-carbazol-3-yl) pyrene (1), 1,3,6,8-tetra(9-ethyl-9H-carbazol-2-yl) pyrene (2), 1,3,6,8-tetra(10-ethyl-10H-phenothiazin-3-yl) pyrene (3) and 1,3,6,8-tetra(9-dodecyl-9H-carbazol-3-yl) pyrene (4), were synthesized and characterized. They displayed excellent thermal stability, with the onsets of thermal degradation well exceeding 400 °C, and demonstrated glass transitions between 32 and 232 °C. Pyrene derivatives with carbazole arms were shown to be highly fluorescent in dilute solution (fluorescence quantum yields, ΦF, up to 0.84) and in rigid polymer matrix (ΦF up to 0.60). They displayed significant emission quenching and shortening of the fluorescence decay time in neat films. In contrast, the phenothiazinyl-substituted pyrene derivative showed moderate fluorescence quantum efficiency in dilute solution (ΦF = 0.21) or in polymer matrix (ΦF = 0.25) and expressed intramolecular charge transfer character, which was revealed by the studies in different polarity media. The carbazolyl-substituted pyrene derivatives exhibited dicationic behavior and subsequently underwent electropolymerization as characterized by cyclic voltametry. Ionization potentials of thin layers of these materials measured by photoelectron spectroscopy ranged from 5.2 to 5.5 eV. Compound 4 showed hole-drift mobility of 5.8 × 10–5 cm2 V–1 s–1 at an electric field of 106 V cm–1 as characterized by xerographic time-of-flight technique.