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 12 of 31
of relatively high probe concentrations compared to fluorophore indicators [88]. The most common
solvatochromic solvent polarity scales are the: ET(30) scale of Dimroth and Reichardt [85], and
scales of Kamlet and Taft [89,90], * scale of Kamlet, Abboud, and Taft [91], and the pyrene (Py)
scale of Dong and Winnik [92]. These solvatochromic methods are typically used to characterize
solvent systems but they have also been extended to study polymers.
The ET(30) scale uses the 2, 6-diphenyl- 4- (2,4,6- triphenyl- 1-pyridino)- phenolate betaine dye
(also known as Reichardt’s dye) [85,93]. The ET(30) polarity parameter is based on the transition
energy for the longest wavelength absorption band measured in the relevant environment and
expressed in Kcalmol
–1
[85]. A normalized scale (
N
T
E ) was defined from 0 to 1 using
tetramethylsilane and water as the extreme nonpolar and polar solvents respectively [85,93]. The
and scales provide a measurement of solvent hydrogen-bond donor (HBD) or a hydrogen-bond
acceptor (HBA) ability. These scales are based on a solvatochromic comparison method (SCM)
which involves the comparison of solvent induced shifts of the longest wavelength absorption band of
two similar compounds. For the determination of values one compound is capable of acting as a
HBA towards HBD solvents (e.g. Reichardt’s dye) whereas the other cannot (e.g. 4-nitroanisole)
[89,90,93]. To determine values, one compound will be capable of acting as a HBD towards
solvents (e.g. 4-nitroaniline) whereas the other cannot (e.g. 4-nitro-N,N-dimethylaniline) [93]. The
solvent dipolarity/polarizability * scale provides a quantitative measure of the non-specific part of
van der Waals interactions between solvents and solutes [91,94,95]. The original scale was based on
the spectral properties of carefully selected aromatic molecules which contain both electron-acceptor
and electron-donor groups [94,95]. Dimethyl sulfoxide (DMSO) and cyclohexane (c-C6H12) were
used as reference solvents by taking *(c-C6H12) = 0 and * (DMSO) = 1 [94,95]. More recently,
the scale has been updated/revised and is now based on the averaging of data from several
solvatochromic indicators [96]. Laurence et al. re-determined * values for 229 solvents using only
two solvatochromic indicators, 4-nitroanisole and N,N-dimethylamino-4-nitroaniline [85,96].
For the physicochemical characterization of polymers by optical spectroscopy, one generally uses
either vibrational or electronic spectroscopies. One of the key advantages of electronic spectroscopy
(either absorption or fluorescence) is the potential sensitivity, enabling the observation of subtle effects
in condensed media. One of the simplest approaches is to pursue a solvatochromic approach and
measure the UV-visible spectra of the appropriate indicators doped into the polymers [97-99]. For
example, Matsuguchi et al. employed solvatochromic methods to characterize the water sorption
behavior in polymer films [99].
They found that indicator band positions (and thus the
solvatochromic parameters) were dependent on the polymer type, molecular weight, and the amount
of absorbed water. On increasing relative water vapor pressures, all the solvatochromic parameters
(, , *) were seen to increase except for EC, PEO, PVP where the values were lower at the higher
water vapor pressures. The authors also examined the relationship between the ET(30) scale and the
*, and parameters and a linear correlation was observed indicating that the microenvironments
experienced by the probe molecules in both wet and dry films was similar to that observed in liquid
Annual Volumes, Vol. 8, pp. 97-126, (2015). ISBN: 978-3-319-24607-9 (Hardcover), 978-3-319-24609-3 (ebook) Springer.
Page 12 of 31
of relatively high probe concentrations compared to fluorophore indicators [88]. The most common
solvatochromic solvent polarity scales are the: ET(30) scale of Dimroth and Reichardt [85], and
scales of Kamlet and Taft [89,90], * scale of Kamlet, Abboud, and Taft [91], and the pyrene (Py)
scale of Dong and Winnik [92]. These solvatochromic methods are typically used to characterize
solvent systems but they have also been extended to study polymers.
The ET(30) scale uses the 2, 6-diphenyl- 4- (2,4,6- triphenyl- 1-pyridino)- phenolate betaine dye
(also known as Reichardt’s dye) [85,93]. The ET(30) polarity parameter is based on the transition
energy for the longest wavelength absorption band measured in the relevant environment and
expressed in Kcalmol
–1
[85]. A normalized scale (
N
T
E ) was defined from 0 to 1 using
tetramethylsilane and water as the extreme nonpolar and polar solvents respectively [85,93]. The
and scales provide a measurement of solvent hydrogen-bond donor (HBD) or a hydrogen-bond
acceptor (HBA) ability. These scales are based on a solvatochromic comparison method (SCM)
which involves the comparison of solvent induced shifts of the longest wavelength absorption band of
two similar compounds. For the determination of values one compound is capable of acting as a
HBA towards HBD solvents (e.g. Reichardt’s dye) whereas the other cannot (e.g. 4-nitroanisole)
[89,90,93]. To determine values, one compound will be capable of acting as a HBD towards
solvents (e.g. 4-nitroaniline) whereas the other cannot (e.g. 4-nitro-N,N-dimethylaniline) [93]. The
solvent dipolarity/polarizability * scale provides a quantitative measure of the non-specific part of
van der Waals interactions between solvents and solutes [91,94,95]. The original scale was based on
the spectral properties of carefully selected aromatic molecules which contain both electron-acceptor
and electron-donor groups [94,95]. Dimethyl sulfoxide (DMSO) and cyclohexane (c-C6H12) were
used as reference solvents by taking *(c-C6H12) = 0 and * (DMSO) = 1 [94,95]. More recently,
the scale has been updated/revised and is now based on the averaging of data from several
solvatochromic indicators [96]. Laurence et al. re-determined * values for 229 solvents using only
two solvatochromic indicators, 4-nitroanisole and N,N-dimethylamino-4-nitroaniline [85,96].
For the physicochemical characterization of polymers by optical spectroscopy, one generally uses
either vibrational or electronic spectroscopies. One of the key advantages of electronic spectroscopy
(either absorption or fluorescence) is the potential sensitivity, enabling the observation of subtle effects
in condensed media. One of the simplest approaches is to pursue a solvatochromic approach and
measure the UV-visible spectra of the appropriate indicators doped into the polymers [97-99]. For
example, Matsuguchi et al. employed solvatochromic methods to characterize the water sorption
behavior in polymer films [99].
They found that indicator band positions (and thus the
solvatochromic parameters) were dependent on the polymer type, molecular weight, and the amount
of absorbed water. On increasing relative water vapor pressures, all the solvatochromic parameters
(, , *) were seen to increase except for EC, PEO, PVP where the values were lower at the higher
water vapor pressures. The authors also examined the relationship between the ET(30) scale and the
*, and parameters and a linear correlation was observed indicating that the microenvironments
experienced by the probe molecules in both wet and dry films was similar to that observed in liquid