Spectroscopic Investigation of Fluorescence Quenching Agents: Effect of Nitromethane on the Fluorescence Emission Behavior of Select Cyclopenta-PAH, Aceanthrylene, and Fluorene Derivatives Page: 1,158
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0 I I
350 400 450 350 400 450
WAVELENGTH (nm)
FIG. 4. Fluorescence emission spectra of 4H-cyclopenta[pqr]picene
dissolved in [A (-4)] n-hexadecane; [B (- )] butyl acetate; [C
(-)] dichloromethane; and [D (-4-)] dimethyl sulfoxide. In dimethyl
sulfoxide major emission bands occur at about 377, 397, 421, and 448
nm.
(DBAA-2), 300 nm (DBgF), 290 nm (BIPh), and 320 nm
(BdCyCh) in a 1-cm2 quartz cuvette. All fluorescence data
were accumulated at 19C, ambient room temperature,
with excitation and emission slit width settings of 15 nm
and 3 nm, respectively. The fluorescence spectra, de-
picted in Figs. 3-5, represent a single scan which was
then solvent blank corrected and verified by repetitive
measurements.
RESULTS AND DISCUSSION
Representative fluorescence emission spectra of 11H-
benz[bc]aceanthrylene, 4H-cyclopenta[pqr]picene, and
4H-cyclopenta[def]phenanthrene dissolved in n-hexa-
decane, butyl acetate, dichloromethane, and dimethyl
sulfoxide are depicted in Figs. 3-5. These four nonelec-
trolyte solvents were judiciously selected so as to encom-
pass the entire range of solvent polarity, from the non-
polar n-hexadecane hydrocarbon to the moderately polar
butyl acetate and dichloromethane solvents to the very
polar dimethyl sulfoxide, which is the most polar solvent
considered in the present investigation. Examination of
the spectral data reveals that 4H-benzo[b]cyclopenta
[jkl]triphenylene, 4H-cyclopenta[def]phenanthrene, 4H-
benzo[def] cyclopenta[mno]chrysene, 13H-dibenz[bc,k]-
aceanthrylene, 11H-benz[bc]aceanthrylene, 4H-benzo-
[b]cyclopenta[mno]chrysene, 4H-cyclopenta[pqr]picene,
13H-dibenz[bc,l]aceanthrylene, and 4H-cyclopenta-
[def]chrysene do exhibit two-, three- and/or four-band
emission fine structure similar to that observed for many
of the PAH6 benzenoids studied previously. Of the nine
solutes named, only the latter five showed modest probe
character, as evidenced by systematic variation of emis-
sion intensity ratios with solvent polarity. Calculated
emission band ratios for 11H-benz[bc]aceanthrylene
(BAA; I/II) and 4H-benzo[b]cyclopenta[mno]chrysene
(BbCyCh; I/II) ranged from ~BAA = 1.80 and BbCyCh
= 1.48 in cyclohexane to BAA = 1.33 and BbCyCh = 1.00 -
330 380 430 330 380 430
WAVELENGTH (nm)
FIG. 5. Fluorescence emission spectra of 4H-cyclopenta[def]phenan-
threne dissolved in [A (-) n-hexadecane; [B (-4-)] dichlorome-
thane; [C (--)] butyl acetate; and [D (- )] dimethyl sulfoxide. In
dimethyl sulfoxide major emission bands occur at about 347, 355, 364,
and 383 nm.
in dimethyl sulfoxide. Actual numerical values for the
five PAHs that exhibited any signs of probe behavior are
tabulated in Table I. Estimated uncertainties in the mea-
sured intensity ratios are believed to be on the order of
+0.04 (or less) on the basis of replicate determinations.
The remaining compounds studied possessed one broad,
fairly unsymmetrical emission band (likely two or more
unresolvable bands) in the 350-600 nm spectral region.
Although BAA, BbCyCh, CyPi, DBAA-2, and CyCh do
show modest probe character, their dynamic ranges are
significantly smaller than those of pyrene (1.37), ben-
zo[ghi]perylene (0.98), and ovalene (2.08)." Better sol-
vent discrimination is permitted by the three PAH6 ben-
zenoids. Furthermore, benzo[ghi]perylene and ovalene
have excitation wavelengths into the visible region, and
are thus less prone to inner-filtering artifacts arising from
solvent absorption of excitation radiation. Presently there
appears to be no compelling reason for us to ever rec-
ommend using the five cyclopenta-PAH derivatives in
place of pyrene, benzo[ghi]perylene, and ovalene in sol-
vent polarity determinations.
From an analytical perspective, identification and
quantification of unknown PAH/PANH mixtures re-
quire accurate fluorescence emission intensity mea-
surements and availability of a large spectral data file
for comparing the unknown's spectrum against PAH/
PANH standards. Mixtures of environmental/industrial
importance rarely contain a single component. The ma-
jority of mixtures commonly encountered contain several
isomeric pairs or structurally similar PAHs/PANHs,
which emit in approximately the same spectral regions.
Kalman filtering and Gaussian or other curve-fitting
techniques theoretically allow uncoupling of overlapped
spectra. Such methods become less reliable, however, as
the number of mixture components increases. High-per-
formance liquid chromatographic (HPLC) separation
prior to fluorimetric analysis affords a viable alternative,
but again the method is extremely time-consuming1158 Volume 46, Number 7, 1992
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Amszi, Vicki L.; Cordero, Yvonne; Smith, Bradley; Tucker, Sheryl A. (Sheryl Ann); Acree, William E. (William Eugene); Yang, Chengxi et al. Spectroscopic Investigation of Fluorescence Quenching Agents: Effect of Nitromethane on the Fluorescence Emission Behavior of Select Cyclopenta-PAH, Aceanthrylene, and Fluorene Derivatives, article, July 1, 1992; [Frederick, Maryland]. (https://digital.library.unt.edu/ark:/67531/metadc284568/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.