Thiazolo thiazole based cross-linker to prepare highly fluorescent smart films with tunable emission wavelength and their multi-responsive usage

Abstract

We report novel smart films with superior optical properties. Orthoester structure formation in the films cause recyclable acid-base interactions resulting with emission wavelength shift. They are also useful material in the production of AuNP and PbO crystals. • Novel usage of HPhTT dye as highly fluorescent cross-linker to prepare PVA films. • Tunable emission wavelength depending acid, base and dye concentraion resulting from orthoester backbone formation. • Highly sensitive recyclable fluorescent and colorimetric sensor films against acid, base (0.2 µM) and gold in solution. • Additive free AuNP and PbO crystal formation in/on films. • AuNP decorated PVA film usage as SERS substrate. 2,5-Bis(4-hydroxyphenyl)thiazolo[5,4- d ]thiazole (HPhTT) molecule was synthesized and used as cross-linker in nanotubular self-assembled film preparation. Highly fluorescent, insoluble, PVA based smart films were obtained via orthoester backbone formation at basic media. Both the emission wavelength (λ em ) and photoluminescence (PL) intensity of the films were observed as strongly dependent on dye and base concentrations. These fluorescent films were highly sensitive against acid and base resulting from halochromic property of the cross-linker. These films reversibly changed their colors and λ em when treated with TFA and NH 3 solutions as a result of dynamic covalent chemistry of orthoester groups. λ em and PL intensity of these talented films also changed when they were treated with Au, Pt, Ag, Pb, Cd, Co metal cations. Gold, TFA and NH 3 sensitivities of the films make them suitable and promising candidates as chemosensors. The films also selectively reduced gold ions and caused formation of AuNPs on the surface with simultaneous color change, blue shift in λ em and fluorescent quenching. Green synthesis of hexagonal PbO crystals are also achived inside the films simultaneously. AuNPs on the film and PbO crystal-PVA composite film are characterized with XRD and SEM analysis. These films also exhibited elastic hydrogel property after treatment of acid, base and water. The change in mechanical tensile properties of the films before and after treatment were investigated with stress-strain analysis. Photoluminescence quantum yield (PLQY) of the films were measured as to be between 14% and 39%. Increasing NaOH and dye concentration lead to red shift at λ em and higher PLQY.