Polycyclic Aromatic Hydrocarbon Solute Probes. Part VIII: Evaluation of Additional Naphthacene and Perylene Derivatives as Possible Solvent Polarity Probe Molecules Page: 186
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Polycyclic Aromatic Hydrocarbon Solute Probes.
Part VIII: Evaluation of Additional Naphthacene and
Perylene Derivatives as Possible Solvent
Polarity Probe Molecules
SHERYL A. TUCKER, I.-LIH TENG, WILLIAM E. ACREE, JR.,* and JOHN C. FETZER
Department of Chemistry, University of North Texas, Denton, Texas 76203-5068 (S.A.T., I.-L.T., W.E.A.); and Chevron Research
Company, Richmond, California 94802-0627 (J.C.F.)Fluorescence emission spectra are reported for phenan-
thro[5,4,3,2efghi]perylene, dibenzo[cd,k]naphtho[8,1,2fghi]perylene,
benzo[b]perylene, dibenzole,ghi]perylene, and benzo[a]naphtho[8,1,2cde]-
naphthacene dissolved in various organic solvents. Results of these mea-
surements are used to screen PAHs for potential solvent polarity be-
havior. Of the five PAHs studied, only phenanthro[5,4,3,2efghi]perylene
exhibited probe behavior, as evidenced by selective emission intensity
enhancement of band I with increasing solvent polarity.
Index Headings: Fluorescence; Molecular structure.
INTRODUCTION
Fluorescence probe techniques are becoming increas-
ingly popular for studying the surface micro-environ-
ment of chromatographic materials, surfactant micelliza-
tion/adsorption, polymer-surfactant interactions,
microemulsions, liquid crystals, and other molecularly
ordered media. The method involves the use of a probe
molecule (e.g., pyrene) that exhibits different fluores-
cence characteristics, depending upon the properties of
the solubilizing media. The probe molecule selectively
binds to a specific surface site or preferentially partitions
into an organized structure. Appearance of new spectral
bands, shifts in the emission wavelengths, or changes in
the emission intensities provide an indication of the en-
vironment immediately surrounding the probe. When
combined with lifetime measurements, probe techniques
can provide additional information regarding diffusion
coefficients in probe excimer formation, fluidity in lipid
vesicles, and rates of intermolecular collisions in quench-
ing experiments.
Earlier reports1-7 have been primarily concerned with
determining the photophysical properties of dissolved
polycyclic aromatic hydrocarbon (PAH), polycyclic ar-
omatic sulfur heterocycle (PASH), and polycyclic aro-
matic nitrogen heterocycle (PANH) solutes in order to
identify probe molecules for future applications. The
emission spectrum of the PAH monomer consists of sev-
eral major vibronic bands labeled I, II, etc., in progressive
order, starting with the 0-0 vibronic band. Previous mea-
surements revealed that pyrene, benzo[ghi]perylene,
ovalene, coronene, benzo[a]coronene, naphtho-
[2,3a]coronene, dibenzo[a,j]coronene, dinaphtho-
[8,1,2abc;2',1',8'klm]coronene, naphtho[8,1,2abc] coro-
Received 24 August 1989.
* Author to whom correspondence should be sent.nene, benzo[e]pyrene, dibenzo[def,p] chrysene, and ben-
zo[rst]pentaphene exhibit selective emission intensity
enhancement of vibronic band I relative to band III (or
band II or IV) in polar solvents. Ratios of emission in-
tensities serve as a measure of solvent polarity and struc-
ture.
Surprisingly, not all PAH, PASH, and PANH mole-
cules behave in a similar fashion. Approximately one-
half of the molecules studied thus far showed an en-
hancement effect. Various emission intensity ratios of
perylene, dibenzo [bc,ef] coronene, benzo[a]pyrene, ben-
zo[pqr]naphtho [8,1,2bcd]perylene, dibenzo[a,e]pyrene,
anthranthrene, and several other PAHs remained essen-
tially constant, irrespective of solvent polarity. For two
additional pentaphene derivatives studied, dinaph-
tho[2,1,8,7defg;2',1',8',7'ijkl]pentaphene and benz-
[rst]anthra[9,1,2cde]pentaphene, the number of clearly
resolvable bands varied from one solvent to another,
thereby preventing assignment of a common set of emis-
sion bands. Fluorescence spectra of 1-azapyrene, 2-aza-
pyrene, and 4-azapyrene contained many of the "pyrene-
like" spectral features; however, emission intensity ratios
failed to vary with solvent polarity.7 Our measurements
further revealed that PASH molecules also behave dif-
ferently than their PAH counterparts, perhaps because
of either the reduced "double bond conjugation" or rr*
- n transitions arising from the divalent sulfur atoms.
Emission spectra of thianthrene, 1,6-dithiapyrene, 1,7-
dithiaperylene, and 3,10-dithiaperylene contained rela-
tively few bands of low emission intensity. Significant
band broadening and very poor spectral resolution were
noted in many of the more polar solvents examined.5
Thus far the enhancement phenomenon has not been
satisfactorily explained. We have put forth several pre-
liminary ideas based upon the number of Kekule struc-
tures,5 point groups and symmetry elements,4 dissimi-
larities between a given molecule's excitation and emission
spectra,4 and the relative length of the center aromatic
row in the case of the coronene derivatives.45 The ob-
servations were far from definitive, as the spectral da-
tabase included only 28 PAH molecules, and many of
the molecular formulas were represented by only a single
family member. To expand our spectral data file, we have
measured the fluorescence emission behavior of diben-
zo[e,ghi]perylene (DBP), benzo[b]perylene (BP), ben-
zo[a] naphtho[8,1,2cde]naphthacene (BNN), diben-
zo [cd,k]naphtho[8,1,2fghi]perylene (DBNP), and
phenanthro[5,4,3,2efghi]perylene (PP; also called diben-186 Volume 45, Number 2, 1991
0003-7028/91/4502-0186$2.00/0
(C 1991 Society for Applied SpectroscopyAPPLIED SPECTROSCOPY
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Tucker, Sheryl A. (Sheryl Ann); Teng, I.-Lih; Acree, William E. (William Eugene) & Fetzer, John Charles, 1953-. Polycyclic Aromatic Hydrocarbon Solute Probes. Part VIII: Evaluation of Additional Naphthacene and Perylene Derivatives as Possible Solvent Polarity Probe Molecules, article, February 1, 1991; [Frederick, Maryland]. (https://digital.library.unt.edu/ark:/67531/metadc282646/m1/1/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.