Full Citation: Fluorescence Analysis of Thermoresponsive Polymers. A.G. Ryder and C. Morris, Reviews in Fluorescence 2015 ,
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 10 of 31
probe structure. Changing the chemical structure at the fluorophore core can be used to adjust the
sensitivity to a specific range of solvent polarity, to modulate hydrogen bonding, or to electric fields.
4’-Diethylamino-3-hydroxyflavone (FE), 5, 6-benzo-4’-diethylamino-3- hydroxyflavone (BFE), and
4´-diethylamino-3- hydroxy-7-methoxyflavone (MFE) are examples of 3-HF fluorophores, which are
sensitive to the properties of solvent environment. An increase in solvent polarity and hydrogen
bonding ability of the solvent leads to an increase in the population of the N* form relative to T* form,
which is due to a greater dielectric stabilization of the N* form [74]. It has been possible to correlate
the ratio of the emission intensities of these two forms with changes in polarity and hydrogen bonding
in various classes of solvents [74,84]. BFE, unlike FE and MFE, is nearly insensitive to the H-bond
donor ability of protic solvents because of the interference from the additional benzene ring [84].
MFE shows more solvent-dependent dual emission in more polar solvents when compared to FE [77].
For these three 3-HF probes (FE, MFE, and BFE) it was observed that the relative emission from
the N* and T* bands (as measured by the increase in log(IN*/IT*)) varied very significantly with water
ingress (Figure 5). The N* band was also significantly red shifted whereas the T* band maximum
decreased only slightly with increasing humidity. Analysis of the fluorescence data indicated that
water adsorption in the PNIPAm films followed a two-step process: First, at low relative humidity
the incoming water molecules disrupted the specific polymer-fluorophore H-bond interaction giving
rise to small changes in log(IN*/IT*) ratios and the overall fluorescence intensity. Then at higher
relative humidity (>50%), as the amount of adsorbed water increases, these intensity parameters
change dramatically indicating a larger change in the local polarity of the probe environment [61].
Figure 5: (a) Plot of the log(I N* /I T* ) ratio vs. increasing relative humidity at 25 °C for PNIPAm films doped
with BFE (), MFE (), and FE (). (b) Plot of the I N* /I T* ratio normalized to the value recorded at 90%
RH. Plots show the two-phase water adsorption process. Taken from ref [61] and reproduced with permission.
Copyright © 2010 American Chemical Society, all rights reserved.
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 10 of 31
probe structure. Changing the chemical structure at the fluorophore core can be used to adjust the
sensitivity to a specific range of solvent polarity, to modulate hydrogen bonding, or to electric fields.
4’-Diethylamino-3-hydroxyflavone (FE), 5, 6-benzo-4’-diethylamino-3- hydroxyflavone (BFE), and
4´-diethylamino-3- hydroxy-7-methoxyflavone (MFE) are examples of 3-HF fluorophores, which are
sensitive to the properties of solvent environment. An increase in solvent polarity and hydrogen
bonding ability of the solvent leads to an increase in the population of the N* form relative to T* form,
which is due to a greater dielectric stabilization of the N* form [74]. It has been possible to correlate
the ratio of the emission intensities of these two forms with changes in polarity and hydrogen bonding
in various classes of solvents [74,84]. BFE, unlike FE and MFE, is nearly insensitive to the H-bond
donor ability of protic solvents because of the interference from the additional benzene ring [84].
MFE shows more solvent-dependent dual emission in more polar solvents when compared to FE [77].
For these three 3-HF probes (FE, MFE, and BFE) it was observed that the relative emission from
the N* and T* bands (as measured by the increase in log(IN*/IT*)) varied very significantly with water
ingress (Figure 5). The N* band was also significantly red shifted whereas the T* band maximum
decreased only slightly with increasing humidity. Analysis of the fluorescence data indicated that
water adsorption in the PNIPAm films followed a two-step process: First, at low relative humidity
the incoming water molecules disrupted the specific polymer-fluorophore H-bond interaction giving
rise to small changes in log(IN*/IT*) ratios and the overall fluorescence intensity. Then at higher
relative humidity (>50%), as the amount of adsorbed water increases, these intensity parameters
change dramatically indicating a larger change in the local polarity of the probe environment [61].
Figure 5: (a) Plot of the log(I N* /I T* ) ratio vs. increasing relative humidity at 25 °C for PNIPAm films doped
with BFE (), MFE (), and FE (). (b) Plot of the I N* /I T* ratio normalized to the value recorded at 90%
RH. Plots show the two-phase water adsorption process. Taken from ref [61] and reproduced with permission.
Copyright © 2010 American Chemical Society, all rights reserved.