Perylene-3,4,9,10-tetracarboxylic dianhydride dye intercalated liquid crystal molecules: Synthesis, spectroscopic characterizations and photoluminescence dynamics

Abstract

The present research explores the interaction between perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA)-dye (PD) and 3b {(E)-1-[3-fluoro-4-(pentyloxy)phenyl]-2-(4-methylphenyl)diazene} liquid crystal (LC) mesophase, 3c{(E)-1-[3-fluoro-4-(hexyloxy)phenyl]-2-(4-methylphenyl)diazene} nematic liquid crystal (NLC) molecule. Spectroscopic characterizations of 3b@PD LC mesophase and 3c@PD NLC molecule were carried out using scanning electron microscopy (SEM), polarizing optical microscope (POM), Raman, Fourier transform infrared spectroscopy (FT-IR), and UV–visible analytical methods. The UV–visible studies revealed a red shift in absorption bands (348.0 nm to 374 nm) with a decrease in optical band gap from 2.43 eV to 2.25 eV. Room temperature photoluminescence (RTPL) spectra of 3b@PD LC mesophase exhibited blue light emission characteristics centred at 453.1 nm and 3c @PD NLC molecule showed broad emission peaks located at 400.7 nm and 324.8 nm. Steady-state photoluminescence (SSPL) spectra showcased indigo-purple emission bands corresponding to the wavelengths 303–353 nm, 420.5 nm, 418 nm, 418.3 nm, and 347.0 nm, however, for the 3c@PD NLC molecule, emission intensity peaks appeared at 429.6 nm, 418.0 nm and 329.0 nm. The stoke’s shift for 3b@PD LC mesophase varied between 0.01 eV to 0.613 eV while for 3c@PD NLC molecule it was found in between 0.317 eV to 0.453 eV. POM analysis unveiled distinct fan-like textures with varied colour interfaces. Time-resolved photoluminescence (TRPL) decay studies unveiled average lifetime of 3b@PD LC mesophase was 1.80 ns, 0.98 ns, 0.308 ns and for 3c@PD NLC molecule, the average lifetime was found to be 0.98 ns, 0.82 ns, and 0.306 ns at various excitation wavelengths. However, phosphorescence decay studies showed faster decay characteristics for 3c@PD NLC molecule (1.40 ns to 4.00 ns) compared with 3b@PD LC mesophase (1.65 to 5.42 ns) when excited at various wavelengths. The interaction between LC molecules and PTCDA demonstrated a significant enhancement in RTPL, TRPL, and SSPL properties, suggesting promising applications in photonics and optoelectronics.