# Silicon-Containing π-Conjugated Schiff Base Oligomers with Naphthalene or Binaphthalene Moieties in the Backbone: Synthesis and Study of Properties

## TL;DR

This paper reports the synthesis of silicon-containing Schiff base oligomers with naphthalene or binaphthalene units and explores their thermal, optical, and electronic properties.

## Contribution

The study introduces new silicon-containing π-conjugated oligomers with tailored properties for optoelectronic applications.

## Key findings

- Oligomers with TPS cores showed high solubility in non-polar solvents and higher molecular weights.
- TPS-based oligomers exhibited enhanced thermal stability with degradation temperatures exceeding 530 °C.
- The materials displayed wide bandgaps and tunable optical properties due to extended π-conjugation.

## Abstract

Four silane-containing Schiff base oligomers (o-SBNs and o-SBBs) were synthesized by high-temperature polycondensation reactions using silicon-based dialdehydes with naphthalene and 1,1’-binaphthalene diamine derivates. The samples showed a moderate solubility in common organic solvents, where the incorporation of TPS cores into o-SBN2 allows the formation of highly soluble material in non-polar solvents with higher molecular weights (11.58 kDa) and polydispersity. All oligo-SBs displayed high thermal resistance (above 450 °C), showing enhanced thermal stability for TPS-containing oligomers, with the degradation temperature exceeding 530 °C (o-SBB2) and high Tg values due to the higher aromatic content granted by TPS and 1,1’-binaphthalene moieties. Optical results of the oligo-SBs showed broad absorption and emission behavior in the visible spectrum, ranging from deep blue (o-SBN1 and o-SBB1) to blue (o-SBN2 and o-SBB2). The structure promotes a clear bathochromic shift for TPS-based oligomers, attributed to an extended π-conjugation across the backbone. In addition, the π-π overlap effect highlights larger Stokes shifts for the DMS core oligomers o-SN2 (133 nm) and o-SBB1 (195 nm). The oligo-SBs were found to be wide-bandgap materials, with Egopt values in the range of 2.60 eV to 3.67 eV. The higher molecular weight of o-SBN2, which provided an extended π-conjugation, allows the lowest value of Egopt (2.60 eV) to be achieved. In addition, DFT, TDDFT and EDDM calculations were performed on trimeric oligo-SBs, revealing that HOMOs are localized in the amine-terminal fraction, while LUMOs are localized over the terminal aldehyde groups. These findings highlight the used DMS and TPS cores in Schiff base materials, providing valuable insights into fine-tuning physicochemical properties through the use of suitable building blocks and their potential as optoelectronic materials.