Synthesis and characterization of a novel spirocyclic aromatic derivative: unique roles of phenothiazine

Abstract

In order to investigate the explicit effects of phenothiazine on the general properties of a spirocyclic aromatic derivative with a sterically perpendicular configuration for electro-optical applications, a novel spirocyclic aromatic derivative SPIS, based on fluorene and phenothiazine, was synthesized and fully characterized by ¹H NMR, ¹³C NMR, elemental analysis and matrix assistant laser desorption/ionization time-of-flight mass, respectively. The photophysical properties, thermal stability and energy levels of compound SPIS were further compared with those of 2,7-dibromo-9,9,-diethyl fluorene. The experimental results indicated that compound SPIS displayed a high thermal stability with a decomposition temperature of 386 °C at 5% mass loss and a melting temperature of 221 °C, which was a notable improvement compared to those of 2,7-dibromo-9,9,-diethyl fluorene. Compound SPIS took on a band gap of about 2.63 eV with blue-green emission in the thin solid film. The introduction of phenothiazine into the spirocyclic aromatic derivative can lower the lowest unoccupied molecular orbital level to −3.05 eV, while increasing the highest occupied molecular orbital level to −5.68 eV relative to those of 2,7-dibromo-9,9,-diethyl fluorene. In conclusion, it is obviously illustrated that the introduction of a rigid segment of phenothiazine into the skeleton of a spirocyclic aromatic derivative can improve the thermal stability, and effectively adjust the photophysical properties and energy levels of fluorene-based monomers over a wide range.