ESIPT-active columnar liquid crystal: organic dyes and quantum dots-assisted fluorescence modulation

Abstract

Tailoring, fine-tuning, and controlling the luminescent behavior and the associated photo-physical properties of fluorophores have been the subject of contemporary research. Over the years, many strategies have been explored to address concerns such as short electronic absorption/luminescence wavelengths, small Stokes shift, low brightness, inapt permeability, poor stability, and low solubility. Among these, approaches involving binary/multi-component systems comprising different functional materials appear to be promising and everlasting. Working on this theme, we report the results of elaborative studies on the fluorescence (photoluminescence, PL) characteristics of several organic/hybrid composites realized by dispersing organic dyes and quantum dots (QDs) in the host columnar liquid crystal (Col LC) exhibiting excited-state intra-molecular proton-transfer (ESIPT) phenomenon. Precisely, the binary mixtures were realized by doping organic dyes such as methyl red/rubrene and carbon QDs/perovskite (CsPbBr₃) QDs in fluorescent (ESIPT) Col LC, namely, phasmidic bis(N-salicylideneaniline) (PBSAN-14). The investigations were carried out in three condensed states, viz., solid, LC, and liquid states, and their solutions. The composites derived from organic dyes and Col LC refrain from light emission, implying that the PL of the host is quenched; the Stern–Volmer profiles revealed the combined dynamic and static quenching mechanism. The Col LC-QD composites exhibit intense emission that covers almost the entire visible wavelength region. The CIE chromaticity diagram shows a wide range of color tuning achieved by varying the nature of additives. Thus, this investigation provides a clear insight into the effect of organic dyes and QDs on the condensed states of fluorophores.