Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers

Abstract

We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains.Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore.

Plasma dye coating as straightforward and widely applicable procedure for dye immobilization on polymeric materials

“…In order to maintain the halochromic properties originating from the acidic phenol group, bromocresol purple (BCP) and bromothymol blue (BTB) were selected to be functionalized with styryl moieties through Stille and Suzuki-Miyaura coupling procedures onto their aryl-bromide substituents, respectively. A final dye that was synthesized especially for this project is the solvatochromic fluorescent dye 4- N , N ′-dimethylamino-1,8-acrylamidoethylnaphthilimide (DMAAENI) based on a reported synthesis of a similar dye by Inal et al 70 . While DR1-A and DMAAENI are well soluble in THF at room temperature, BCP-vinyl 2 , BTB-Sty, and RB-Sty required the use of ethanol in both the dip-coating step and the soxhlet extraction.…”

A water soluble fluorescent polymer as a dual colour sensor for temperature and a specific protein

“…This dependence of the dye's uorescence response to the chemical structure of the polymer was observed for another solvatochromic uorophore, a naphthalimide derivative, incorporated into NIPAm-or OEGMA-based copolymers analogous to P1 and P2, respectively. 21 Certain peculiarities about the Scheme 1 Dual responsiveness of P1 to the presence of antibody and to increasing the solution temperature above the cloud point. In the absence of antibody and/or at low temperatures, the emission from the DEAC label is weak.…”

“…The covalent incorporation of solvatochromic dyes, which are sensitive to the hydration state of polymer chains, is the key methodology to obtain a uorescent output of this adaptive behaviour, and thereby to develop schemes that exploit the LCST transition for optical sensing. 9 The uorophore senses the changes in its micro-environment generated as a result of the polymer phase transition, and transforms these into a marked uorescence read-out, [11][12][13][14][15][16][17][18][19][20][21] e.g., typically a hypsochromic (blue) shi and enhanced uorescence intensity. 22 Taking advantage of the delicate solubility of amphiphilic polymer chains in water, changes in the dye microenvironment can as well be induced by stimuli other than temperature.…”

Responsive Boronic Acid-Decorated (Co)polymers: From Glucose Sensors to Autonomous Drug Delivery

“…The inverse situation in which the first excited state is stabilized more thus leads to a smaller energy gap and a bathochromic (red) shift or positive solvatochromism [81,82]. This translational mechanism has mostly been used for the creation of polymeric thermometers with examples including a 1,8-naphthalimide-decorated thermoresponsive copolymer like poly( N -isopropylacrylamide) showing fluorescent enhancement upon precipitation [83] or Disperse Red 1 (DR1)-oligoethyleneglycol acrylate copolymers showing a bathochromic shift [84,85]. The possibility of using a solvatochromic dye for the creation of polymeric sensors for glucose was published by our group in 2012 where the pH-induced polymer precipitation of a P(4-VBA) was translated into a color change by incorporating DR1 [86].…”