Synthesis, Trans-Cis Photoisomerization, Fluorescence Decay Studies of Methoxy Ester Functionalized Alkoxy Side Chain Azobenzene Compounds and Their Photoluminescence Dynamics

In this study, a series of new methoxy ester functionalized core fluorinated, chloro-fluorinated azobenzene derivatives were synthesized. The molecular structures of the azobenzene derivatives (3a-3c and 4a-4c) were confirmed through various analytical methods, with variations in the alkoxy chain length on one end of the aromatic ring. Optical absorption studies of 3a, 3b revealed π-π* transitions around 368-392 nm. Further, polarizing optical microscope (POM) studies of 3a, 3b revealed birefringent textures, and their phase transitions were investigated using differential scanning colorimetry (DSC) studies. The trans-to-cis photoisomerization of 3a, 3b transpired over 3600s whereas, thermal back relaxation (cis-to-trans) isomerization took 0.75 h. Room temperature photoluminescence (RTPL) studies of 3a-3c and 4a-4c unveiled weak emission intensity peak at ~ 450 nm (blue region) when excited at 400 nm. Steady-state photoluminescence (SSPL) studies of 3a-3c, 4a-4c revealed a broad emission band in the violet region of the visible spectrum with significantly large Stokes shifts, indicating the presence of highly energized excited states and formation of additional energy levels during photoexcitation. Fluorescence decay (FLD) studies of 3a-3c, 4a-4c unveiled average lifetime (τ) dwells between 8.2 ps and 70.4 ps. The average lifetime (τ) was found to increase with the increase in the length of the alkoxy chain. Phosphorescence decay (PD) profiles of 3a-3c, 4a-4c showed average lifetime (τ) fluctuate around 373 ns to 463 ns. The obtained core fluorinated, chloro-fluorinated azobenzene derivatives having different lengths of the alkoxy side chain can find potential applications in optical storage and display technologies.