Molecular design and physical properties of highly functionalized configurationally locked polyenes – an experimental and theoretical study

Abstract

This paper reports for the first time the molecular design, synthesis and a correlation study on the structure and physical properties of highly functionalized configurationally locked polyenes considered as broadband THz materials ∈ 0.3–30 THz, thus extending the ability of THz-spectroscopy to identify materials for the mid-IR region. The effects of the seven types of substituents replacing the malononitrile residue on theoretical first and second hyperpolarizabilities are discussed. The promising candidates among the 140 model designed molecules showed hyperpolarizabilities (β_tot) with magnitudes 4 to 11.5 times higher than the values of 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (OH1), described as a standard organic THz-material which has already been applied in THz-spectrometers. The 70 derivatives are successfully isolated, 21 of which at yields ∈ 17.4–99.7% (1–21) suitable for further experimental efforts towards their single crystal growth and related physical measurements. 48 other dyes are characterized with synthetic yields ∈ 1.7–16.2%, respectively. Therefore, the search for new strategies to optimize the synthesis procedure is of high importance. The isolated derivatives are characterized by electronic absorption and fluorescence spectroscopy, and an evaluation of the theoretical and experimental hyperpolarizabilities caused by the charge transfer effect (β_CT) is performed. A primary focus of the discussion at this stage of the presented promising data is on mass spectrometry, due to: (i) its instrumental flexibility, ultra high resolution and ability for accurate and precise gas- and condensed phase analysis within a wide temperature range, and the various ionization methods, making mass spectrometry an irreplaceable physical method in synthetic organic chemistry; (ii) the variety of sampling techniques for structural analysis of liquid and semiliquid homogeneous and heterogeneous systems, 1D–3D crystals, powders, solid thin films, and polymers; and (iii) imaging studies.