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. 2021 Mar 26;13(7):1043.
doi: 10.3390/polym13071043.

The Effect of Alkyl Substitution of Novel Imines on Their Supramolecular Organization, towards Photovoltaic Applications

Paweł Nitschke  1 , Bożena Jarząbek  1 , Marharyta Vasylieva  1   2 , Marcin Godzierz  1 , Henryk Janeczek  1 , Marta Musioł  1 , Adrian Domiński  1
Affiliations

The Effect of Alkyl Substitution of Novel Imines on Their Supramolecular Organization, towards Photovoltaic Applications

Paweł Nitschke et al. Polymers (Basel). .

Abstract

Three novel conjugated polyazomethines have been obtained by polycondensation of diamines consisting of the diimine system, with either 2,5-bis(octyloxy)terephthalaldehyde or 9-(2-ethylhexyl)carbazole-3,6-dicarboxaldehyde. Partial replacement of bulky solubilizing substituents with the smaller side groups has allowed to investigate the effect of supramolecular organization. All obtained compounds have been subsequently identified using the NMR and FTIR spectroscopies and characterized by the thermogravimetric analysis, differential scanning calorimetry, cyclic voltammetry, UV-Vis spectroscopy, and X-ray diffraction. Investigated polymers have shown a good thermal stability and high glass transition temperatures. X-ray measurements have proven that partial replacement of octyloxy side chains with smaller methoxy groups induced a better planarization of macromolecule. Such modification has tuned the LUMO level of this molecule and caused a bathochromic shift of the lowest energy absorption band. On the contrary, imines consisting of N-ethylhexyl substituted carbazole units have not been so clearly affected by alkyl chain length modification. Photovoltaic activity of imines (acting as a donor) in bulk-heterojunction systems has been observed for almost all studied compounds, blended with the fullerene derivative (PCBM) in various weight ratios.

Keywords: azomethines; organic photovoltaics; organic thin films; polymer:fullerene blends; supramolecular organization.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Synthesis procedure and chemical structures of investigated polyazomethines.
Figure 2
Figure 2
Chemical structures of synthesized compounds, together with polyazomethine obtained during previous studies (PAz-BOO-Oct) [22].
Figure 3
Figure 3
(a) Voltammograms, recorded during oxidation and reduction processes (v = 0.1 V/s; 0.1 M Bu4NPF6/ACN) of studied oligo- and polyazomethine thin films, deposited on the glass with ITO together with voltammogram obtain for PAz-BOO-Oct, presented previously in [11]; (b) the energy levels of HOMO and LUMO orbitals, designated based on the results of cyclic voltammetry measurements.
Figure 4
Figure 4
(a) Normalized absorbance of investigated oligo- and polyazomethines solutions in chloroform and (b) their thin films, deposited on quartz substrates.
Figure 5
Figure 5
Normalized (solid line) and deconvoluted (dashed line) spectra of PAz-BOO (a) and Paz-Carb (b) imine thin films.
Figure 6
Figure 6
Absorption edge parameters of investigated imines: (a) Urbach energies and (b) energy gaps.
Figure 7
Figure 7
XRD patterns of imine thin films with possible assignment of Miller indexes.
Figure 8
Figure 8
Current density–voltage (J-V) characteristics of bulk-heterojunction (BHJ) systems, consisting investigated oligo- and polyazomethines. Donor:acceptor ratios 1:2 for all, except for PAz-BOO-OMe, where the ratio D:A is 1:1.
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