Luminous composite ultrathin films of the DCM dye assembled with layered double hydroxides and its fluorescence solvatochromism properties for polarity sensors

Abstract

In this work, neutral dye 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) incorporated by a block copolymer micelle (BCM), poly(styrene)-b-acrylic acid (PS-b-PAA), was assembled with layered double hydroxide (LDH) nanosheets to fabricate luminous ultrathin films by the layer-by-layer method. The UV-vis absorption spectra, SEM and AFM characterization results confirmed that composite ultrathin films (UTFs) were homogenous with long-range ordered stacking vertical to the quartz substrate. The UTFs maintained the photoluminescence (PL) properties of DCM with well-defined orange fluorescence, which originate from the locally excited state of DCM without molecule aggregation. Meanwhile, these ultrathin films demonstrated a typical solvatochromism fluorescence feature of DCM molecules, with the PL peak strongly dependent on solvent polarity. The fluorescence of the UTFs can be adjusted from orange to red upon exposure to different volatile organic compound (VOC) vapours, based on the DCM twisted intramolecular charge transfer character excited state. These DCM-loaded UTFs showed fast, sensitive and reversible fluorescence solvatochromism in response to common VOCs. This work opens up the avenue for potential applications of DCM in the VOC polarity sensors.