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 14 of 31
[100]. They reported a decrease in the I1/I3 ratio of pyrene with increasing NtBA fraction indicating
a reduction in polarity with increasing NtBA content (Figure 7), which is in agreement with previous
results obtained in a solvatochromic study involving the same polymers [19,100].
Figure 7: Plot of pyrene emission ratio I 1 /I 3 ratio vs. NtBA content for a series of copolymer films measured
at 20C. Taken from ref [100] and reproduced with permission. Copyright © 2010 Journal of Fluorescence
Spectroscopy.
The pyrene I1/I3 ratio displayed poor correlation with measured solvatochromic polarity
parameters [19], which was attributed to the fact that the polarity component sensed by pyrene is only
related to dipole-induced dipole interactions. This ignores the very significant H-bonding effects,
which are also present in these polymers. Furthermore, it was noted that the physiochemical changes
that occur at the LCST of these copolymers did not greatly affect pyrene fluorescence. This was
revealed by the small and linear decrease in the I1/I3 ratio (1.345 to 1.285) observed for these thin films
as the temperature changed from 20 to 40 °C. This contrasts strongly with the situation reported for
aqueous solutions of PNIPAm where the ratio changes decreases from 1.79 to 1.38 [105]. We also
note that this magnitude of change is almost identical to that observed for solutions of pyrene in ethanol
and 1-propanol [60]. The reason why the change is small originates from the lack of a distinct
aqueous phase, so the pyrene probe remains dispersed throughout the solid polymer where there is
much less change in probe environment and thus in emission properties. It should be noted that these
measurements were made without rigorous humidity control [100], and so these films probably
contained a significant amount of adsorbed water. The hydrogen-bonding effects inherent in the
PNIPAm thin films also produces problems for the use of 3-HF derivatives for polarity assessment of
thermoresponsive hydrophilic polymers in thin films, using simple emission parameters. This arises
from the heterogeneity of the ground-state H-bonding and an ESIPT process that is not in equilibrium,
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 14 of 31
[100]. They reported a decrease in the I1/I3 ratio of pyrene with increasing NtBA fraction indicating
a reduction in polarity with increasing NtBA content (Figure 7), which is in agreement with previous
results obtained in a solvatochromic study involving the same polymers [19,100].
Figure 7: Plot of pyrene emission ratio I 1 /I 3 ratio vs. NtBA content for a series of copolymer films measured
at 20C. Taken from ref [100] and reproduced with permission. Copyright © 2010 Journal of Fluorescence
Spectroscopy.
The pyrene I1/I3 ratio displayed poor correlation with measured solvatochromic polarity
parameters [19], which was attributed to the fact that the polarity component sensed by pyrene is only
related to dipole-induced dipole interactions. This ignores the very significant H-bonding effects,
which are also present in these polymers. Furthermore, it was noted that the physiochemical changes
that occur at the LCST of these copolymers did not greatly affect pyrene fluorescence. This was
revealed by the small and linear decrease in the I1/I3 ratio (1.345 to 1.285) observed for these thin films
as the temperature changed from 20 to 40 °C. This contrasts strongly with the situation reported for
aqueous solutions of PNIPAm where the ratio changes decreases from 1.79 to 1.38 [105]. We also
note that this magnitude of change is almost identical to that observed for solutions of pyrene in ethanol
and 1-propanol [60]. The reason why the change is small originates from the lack of a distinct
aqueous phase, so the pyrene probe remains dispersed throughout the solid polymer where there is
much less change in probe environment and thus in emission properties. It should be noted that these
measurements were made without rigorous humidity control [100], and so these films probably
contained a significant amount of adsorbed water. The hydrogen-bonding effects inherent in the
PNIPAm thin films also produces problems for the use of 3-HF derivatives for polarity assessment of
thermoresponsive hydrophilic polymers in thin films, using simple emission parameters. This arises
from the heterogeneity of the ground-state H-bonding and an ESIPT process that is not in equilibrium,