Investigation of non-linear optical and photophysical properties of fullerene decorated photochromic liquid crystals

Abstract

In the present research work, a new series of core fluorinated photochromic liquid crystals (LCs) 3b and 3c decorated with Fullerene C60 (FC60) have been synthesized. Morphology of 3b, 3c@FC60 LCs displayed flat grains with wrinkled shapes. Room temperature photoluminescence (RTPL) studies of photochromic 3b@FC60 LC exhibited a broad and strong emission peak located at near edge band of the ultraviolet (UV) region (∼396.6 nm) at λ_excitation = 250 nm, However, photochromic 3c@FC60 LC showed sharp emission bands appeared at UV (336.0 nm, 328.7 nm) and visible region of the spectrum unveiling indigo (443.6 nm), blue (476.2 nm), and red (643.7 nm) colours. Further, time-resolved photoluminescence (TRPL) studies of 3b@FC60 LC at λ_excitation = 260 nm–387 nm and 320 nm–520 nm revealed faster decay characteristics (average lifetime of 0.82ns and 0.98ns). However, 3c@FC60 LC at λ_excitation = 260 nm–383 nm and 320 nm–532 nm exhibited slow decay characteristics (average lifetime of 2.11ns – 2.90ns). Steady-state photoluminescence (SSPL) spectra of photochromic 3b, 3c@FC60 exhibited sharp emission peaks located at near UV region (∼113 nm, ∼114 nm) with reduced Stoke's shift and full-width half maximum (FWHM). Phosphorescence decay studies of 3b@FC60 LC showed an average lifetime of photoexcited species is in between 110ns and 128ns and for 3c@FC60 LC the average lifetime dwells between 69ns and 110ns. However, cis-trans photoisomerization studies demonstrated (E-Z) isomerization occurs ∼1200s and thermal back relaxation (Z-E) takes place within 6300s. The photoconversion efficiency of 3b@FC60, and 3c@FC60 LC was found to be 80.9 % and 81.4 %, respectively. The synthesized core fluorinated photochromic 3b, 3c@FC60 composites may hold potential applications in display devices and the construction of modern LEDs.