“Small in size but mighty in force” – the first principle study of the impact of A/D units in A/D-phenyl-π-phenothiazine-π-dicyanovinyl systems on photophysical and optoelectronic properties

Abstract A set of N-octylphenothiazine malononitriles (P1-P4) containing (p-methoxyphenyl, p-trifluoromethylphenyl, 3,5-bis(trifluoromethyl)phenyl, or p-cyanophenyl) substituents connected via acetylene linker were designed and synthesized. The obtained structures, which exhibit A/D-π-D-A architecture, were characterized by NMR and mass spectroscopy, and elemental analyses. Photophysical, thermal, and electrical properties of these novel dyes P1-P4 were comprehensively studied and confronted with theoretical calculations. They exhibit high thermal stability of up to 306-369°C. Compounds showed an intramolecular charge transfer (ICT) absorption band at about 480 nm and emission band at around 620 nm with quantum yields between 31-50% in chloroform solution. Comparison of the solution and thin film photoluminescence (PL) spectra of P1-P4 exhibit a significant red-shift of 40-70 nm in the thin film PL spectrum. Furthermore, the impact of the end-capped groups in P1-P4 on optical and electrochemical properties was investigated in detail with the support of TD/DFT calculations. The diodes based on P1-P4 with configuration ITO/PDOT:PSS/PBK:PBD:compound/Al were constructed and their electroluminescence (EL) spectra were registered. Considering the preliminary EL investigations, the beneficial effect of the presence of p-cyanophenyl as a substituent (P4) was demonstrated.