Abstract
In this work, two oligophenyleneimines type pentamers with terminal aldehydes, designated as DAFCHO (4,4′-((((((2,5-bis(octyloxy)-1,4-phenylene)bis(methanylylidene))bis(azanyl ylidene))bis(9H-fluorene-7,2-diyl))bis(azanylylidene))bis(methanylylidene))bis(2,5-bis(octyloxy) benzaldehyde)) and FDACHO (4,4′-((((((2,5-bis(octyloxy)-1,4-phenylene)bis(methanylylidene))bis (azanylylidene))bis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(2,5-bis(octyloxy) benzaldehyde)) were synthesized by mechanochemistry method using 2,5-bis(octyloxy) terephtal aldehyde and 2,7-diaminofluorene or 1,4-phenylenediamine. All compounds were spectroscopically characterized using 1H and 13C-NMR, FT-IR and mass spectrometry MALDITOF. The optical properties of the compounds were analyzed by UV-vis spectroscopy using different solvents. We observed that DAFCHO and FDACHO exhibit interesting photochromic properties when they are dissolved in chloroform and exposed to sunlight for 3, 5 and 10 min. The value of the energy band gap was calculated from the absorption spectra without irradiation Egap(optical). It was 2.50 eV for DAFCHO in chloroform solution, and it decreased to 2.34 eV when it is in films. For FDACHO, it was 2.41 eV in solution and 2.27 eV in film. HOMO (Highest Occupied Molecular Orbital), LUMO (Lowest Unoccupied Molecular Orbital) and Egap(electrochemical) values were obtained by electrochemical studies. The results indicate that the compounds can be considered as organic semiconductors since their values are 2.35 eV for DAFCHO and 2.06 eV for FDACHO. The structural and electronic properties of the compounds were corroborated with a DFT (Density Functional Theory) study.
Highlights
The study of organic semiconductor compounds with photochromic properties is of great significance [1] in the manufacture of devices such as antireflective systems for screens [2], optical memory systems [3], optical switches [4,5,6], OFETs (Organic Field Effect Transistor) [7,8], smartMolecules 2019, 24, 849; doi:10.3390/molecules24050849 www.mdpi.com/journal/moleculesMolecules 2019, 24, 849 windows [9] and a wide variety of sensors [10,11,12]
The synthesis of two oligophenyleneimines designated as DAFCHO and FDACHO was performed using 2,5-bis(octyloxy)terephtaldehyde and 1,4-phenylenediamine or 2,7-diamino fluorene by means from mechanosynthesis (Figure 1)
Studies, the greatest displacement was observed on FDACHO due to the fact that the rings originated studies, the greatest displacement was observed on FDACHO due to the fact that the rings originated from phenylenediamine give a greater planarity to the conjugated system, favoring the intermolecular from phenylenediamine give a greater planarity to the conjugated system, favoring the interactions that causes an increasement in absorption with decreasing optical gap
Summary
The study of organic semiconductor compounds with photochromic properties is of great significance [1] in the manufacture of devices such as antireflective systems for screens [2], optical memory systems [3], optical switches [4,5,6], OFETs (Organic Field Effect Transistor) [7,8], smart. A change in color is observed when imine type compounds were irradiated with sunlight; interestingly, the original color is recovered if the compound is placed in dark conditions. In this case, the π−π* transition undergoes a substantial change with respect to a configurational change in the molecules (trans-cis photoisomerization) [18,19]. A technique, such as mechanochemistry, that is free from solvents and catalysts and environmentally friendly would make these materials attractive for industrial production This mechanochemistry technique has been successfully employed to obtain organic compounds that exhibit attractive optoelectronic properties [22] and has been proved to be efficient for obtaining imine oligomers [15]. Density Functional Theory (DFT) was used to interpret the molecular structural change relating to optoelectronic and chemical properties
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