Optical properties of spiroconjugated charge-transfer dyes

Article abstract of DOI:10.1021/ja9533003

A new type of intramolecular charge-transfer dye has been prepared. The LUMO of the acceptor part (1,3-indandione) in these compounds is spiroconjugated with the HOMO of the donor part (aromatic diamine or amino thiol). The interaction between the donor and acceptor is controlled by the energy and symmetry of the frontier orbitals. The ground state dipole moments of these compounds are aligned along the long molecular axes. In the solid state, distortions of structures are observed that are consistent with partial electron shift from the donor to the acceptor. Much more pronounced electron density shifts accompany the electronic transition that is observed in the visible region of the spectrum. These transitions are of the charge-transfer (CT) type, as shown by solvatochromic and electrooptical studies. The excited state dipole moments are in the direction opposite to that of the ground state. These observations are consistent with the excited state having radical ion pair character. The new dyes are modeled using a simple Mulliken charge-transfer theory. The mixing coefficient of neutral and ionic wave functions describing these systems is used as a measure of spiroconjugation between the subchromophores. The electrooptical data provide an estimate of the contribution of the CT transitions to the hyperpolarizabilities (β) within the two-state model. The measured values of β indicate, however, that spiro dyes have two opposing contributions to their hyperpolarizabilities, one from the CT transition and one due to the acceptor subchromophore.

Full text of DOI:10.1021/ja9533003

J. Am. Chem. Soc. 1996, 118, 1471-1481
1471
Optical Properties of Spiroconjugated Charge-Transfer Dyes
Przemyslaw Maslak,*,† Anu Chopra,† Christopher R. Moylan,‡
Ru1diger Wortmann,§ Sonja Lebus,§ Arnold L. Rheingold, and Glenn P. A. Yap
Contribution from the Department of Chemistry, The PennsylVania State UniVersity,
UniVersity Park, PennsylVania 16802, IBM Almaden Research Center, 650 Harry Road,
San Jose, California 95120, Institut fu¨r Physikalische Chemie, Johannes Gutenberg-UniVersita¨t,
Jakob Welder-Weg 11, 55099 Mainz, Germany, and Department of Chemistry, UniVersity of
Delaware, Newark, Delaware 19716
ReceiVed September 27, 1995X
Abstract: A new type of intramolecular charge-transfer dye has been prepared. The LUMO of the acceptor part
(1,3-indandione) in these compounds is spiroconjugated with the HOMO of the donor part (aromatic diamine or
amino thiol). The interaction between the donor and acceptor is controlled by the energy and symmetry of the
frontier orbitals. The ground state dipole moments of these compounds are aligned along the long molecular axes.
In the solid state, distortions of structures are observed that are consistent with partial electron shift from the donor
to the acceptor. Much more pronounced electron density shifts accompany the electronic transition that is observed
in the visible region of the spectrum. These transitions are of the charge-transfer (CT) type, as shown by solvatochromic
and electrooptical studies. The excited state dipole moments are in the direction opposite to that of the ground state.
These observations are consistent with the excited state having radical ion pair character. The new dyes are modeled
using a simple Mulliken charge-transfer theory. The mixing coefficient of neutral and ionic wave functions describing
these systems is used as a measure of spiroconjugation between the subchromophores. The electrooptical data provide
an estimate of the contribution of the CT transitions to the hyperpolarizabilities (â) within the two-state model. The
measured values of â indicate, however, that spiro dyes have two opposing contributions to their hyperpolarizabilities,
one from the CT transition and one due to the acceptor subchromophore.
Introduction
Chart 1
Charge-transfer (CT) interactions play an important role in
the area of organic materials with unusual electric, magnetic,
or optical properties.1-3 The donor and acceptor components
of such materials have been largely limited to planar conjugated
π-systems. As a consequence, the materials obtained are quasi-
one-dimensional. We have initiated a project to explore charge-
transfer interactions in systems with increased dimensionality.4,5
Our design is based on spiroconjugation,6,7 an interaction that
allows for electronic coupling between two mutually perpen-
dicular π-subsystems.
In a general case, two π-networks (A and D) are joined by a
spiro atom (Chart 1). Only the molecular orbitals of the two
π-subsystems that have the same symmetry may interact, leading
to molecular orbitals spanning the entire system. In an idealized
reference frame, the crucial symmetry elements are the two
perpendicular bisecting planes (Chart 1). As shown in the
Fischer projection of the four atomic orbitals on atoms directly
attached to the spiro atom, only those orbitals of the subsystems
that are antisymmetric with respect to the two planes lead to a
nonzero overlap required for intramolecular interactions.
† The Pennsylvania State University.
‡ IBM Almaden Research Center.
§ Johannes Gutenberg-Universita¨t.
University of Delaware.
The main contribution to charge-transfer interactions is
provided by the frontier orbitals. Thus, in our design the
HOMOs and LUMOs of the π-subsystems should satisfy the
X Abstract published in AdVance ACS Abstracts, January 15, 1996.
(1) (a) Carter, F. L., Ed. Molecular Electronic DeVices; Marcel Dekker:
New York, 1982; Vol. I; 1987; Vol. II. (b) Wudl, F. Acc. Chem. Res. 1984,
17, 227. (c) Wudl, F. In The Physics and Chemistry of Low Dimensional
Solids; Alcacer, L., Ed.; D. Reidel Publishing Co.: Dordrecht, The
Netherlands, 1980; p 265. (d) Cowan, D. O.; Wiyguli, F. M. Chem. Eng.
News 1986, 64, 28. (e) Miller, J. S.; Epstein, A. J. Angew. Chem., Int. Ed.
Engl. 1987, 26. 287. (f) Torrance, J. B. Mol. Cryst. Liq. Cryst. 1985, 126,
55. (g) Bechgaard, K.; Je´rome, D. Sci. Am. 1982, 52. (h) Gompper, R.;
Wagner, H.-U. Angew. Chem., Int. Ed. Engl. 1988, 27, 1437. (i) Bloor, D.
Mol. Cryst. Liq. Cryst. 1993, 234, 1. (j) Aviram A. Mol. Cryst. Liq. Cryst.
1993, 234, 13.
(3) (a) Prasad, P. N.; Williams, D. J. Introduction to Nonlinear Optical
Effects in Molecules and Polymers; Wiley-Interscience: New York, 1991.
(b) Khanarian, G., Ed. Molecular and Optoelectronic Materials: Funda-
mentals and Applications; SPIE: San Diego, 1986. (c) Eaton, D. F. Science
1991, 253, 281. (d) Glass, A. M. Science 1987, 235, 1003. (e) Williams D.
J. Angew. Chem., Int. Ed. Engl. 1984, 23, 690. (f) Chemla, D. S., Zyss, J.,
Eds. Nonlinear Optical Properties of Organic Molecules and Crystals;
Academic Press: New York, 1987; Vols. 1 and 2. (g) Lyons, M. H., Ed.
Materials for Nonlinear and Electro-optics; Institute of Physics Conference
Series Number 103; Institute of Physics: Bristol, New York, Cambridge,
1989. (h) Prasad, P. N.; Reinhardt, B. A. Chem. Mater. 1990, 2, 660. (i)
Eaton, D. F. CHEMTECH 1992, 308. (j) Marder, S. R. In Materials
Chemistry: An Emerging Discipline; Interrante, L. V., Casper, L. A., Ellis,
A. B., Eds.; American Chemical Society: Washington, DC, 1995; p 189.
(2) (a) Miller, J. S.; Epstein, A. J.; Reiff, W. M. Chem. ReV. 1988, 88,
201. (b) Miller, J. S.; Epstein, A. J.; Reiff, W. M. Acc. Chem. Res. 1988,
21, 114. (c) Miller, J. S.; Epstein, A. J. Mol. Cryst. Liq. Cryst. 1993, 234,
133. (d) Dougherty, D. A Acc. Chem. Res. 1991, 24, 88. (e) Iwamura, H.;
Koga, N. Acc. Chem. Res. 1993, 26, 346. (f) Rajca, A. Chem ReV. 1994,
94, 871.
0002-7863/96/1518-1471$12.00/0 © 1996 American Chemical Society

1472 J. Am. Chem. Soc., Vol. 118, No. 6, 1996
Maslak et al.
symmetry requirements. Specifically, for optical applications3
we have selected acceptors (A) that have antisymmetric LUMOs
and donors (D) that possess antisymmetric HOMOs. The
interactions between these orbitals of the two subsystems give
rise to two new spiroconjugated orbitals spanning the entire
molecule. The lower-energy one, the new HOMO, corresponds
to the bonding combination of the subsystem orbitals, and the
higher-energy antibonding combination becomes a new LUMO.
This mixing of spiroconjugated subsystem orbitals results in a
HOMO that has some electron density on the acceptor part,
and a LUMO that has nonzero orbital coefficients on the donor
part. The electronic transition between these frontier orbitals
is formally allowed, and should correspond to a charge-transfer
transition8 (Chart 1).
In practice, the strict symmetry requirements may be relaxed.9
As long as the coefficients of the frontier orbitals change signs
versus the bisecting planes, the overlap depicted in Chart 1 will
provide for the mechanism of coupling between the two
subsystems. Thus, a variety of substitution patterns are possible,
increasing flexibility in the design of these spiroconjugated
dyes.5
Figure 1. X-ray structure of 2. Selected bond lengths (Å) illustrating
the distortions in the structure are shown in normal typeface. The
calculated bond lengths (PM3) are shown in italics. Hydrogen atoms
have been omitted for clarity. The estimated standard deviations for
the indicated bonds are in the 0.005-0.008 Å range.
In the spiro dyes presented here the role of the acceptor is
played by the 1,3-indandione moiety.10,11 This π-subsystem has
an antisymmetric LUMO.12 The donor parts are based on
aromatic diamines or amino thiols.13 The HOMO symmetry
in these donors depends on the selection of the aromatic
residue.12 The 1,2-phenyl derivatives possess symmetrical
HOMOs and, therefore, are not expected to spiroconjugate with
the acceptor’s LUMO. The 1,8-naphthyl and 2,2′-biphenyl
subsystems, on the other hand, offer antisymmetric12 HOMOs
that have the potential to spiroconjugate with the indandione’s
LUMO. The new dyes can be easily constructed by a simple
condensation reaction between the ninhydrin (or its derivatives)
and the corresponding N-methylated diamines or amino thiols.
Figure 2. X-ray structure of 4. Legend is as in Figure 1.
(4) Maslak, P. AdV. Mater. 1994, 6, 405. (b) Maslak, P.; Augustine, M.
P.; Burkey, J. D. J. Am. Chem. Soc. 1990, 112, 5359. Compare also the
following: (c) Tour, J. M.; Wu, R.; Schumm, J. S. J. Am. Chem. Soc. 1990,
112, 6662; 1991, 113, 7064. (d) Aviram, A. Mol. Cryst. Liq. Cryst. 1993,
234, 13. (e) Hush, N. S.; Wong, A. T.; Bacskay, G. B.; Reimers, J. R. J.
Am. Chem. Soc. 1990, 112, 4192.
(5) Maslak, P.; Chopra, A. J. Am. Chem. Soc. 1993, 115, 9332.
(6) (a) Simmons, H. E.; Fukunaga, T. J. Am. Chem. Soc. 1967, 89, 5208.
(b) Hoffmann, R. Imamura, A.; Zeiss, G. D. J. Am. Chem. Soc. 1967, 89,
5215.
(7) For a review see: Durr, H.; Gleiter, R. Angew. Chem., Int. Ed. Engl.
1978, 17, 559.
(8) (a) Mulliken, R. S.; Pearson, W. B. Molecular Complexes: A Lecture
and Reprint Volume; Wiley-Interscience: New York, 1969. (b) Foster, R.
Organic Charge-Transfer Complexes; Academic Press: New York, 1969.
(c) Nagakura, S. Excited States; Academic Press: New York, 1975; Vol.
2, p 321.
(9) The symmetry is used here in a conceptual (i.e., approximate) way,
and does not strictly reflect the symmetry of the components or spiro
compounds.
(10) Ethylenediamine analogs of spiro dyes have been prepared: (a)
Scho¨nberg, A.; Singer, E.; Osch, M.; Hoyer, G.-A. Tetrahedron Lett. 1975,
3217. (b) Scho¨nberg, A.; Singer, E.; Eschenhof, B.; Hoyer, G.-A. Chem.
Ber. 1978, 111, 3058. (c) Scho¨nberg, A.; Singer, E. Tetrahedron 1978, 34,
1285. (d) Scho¨nberg, A.; Singer, E.; Eckert, P. Chem. Ber. 1980, 113, 3094.
(e) Sheldrick, W. S.; Scho¨nberg, A.; Singer, E. Acta Crystallogr. 1982,
B38, 1355.
(11) Spiro donor-acceptors with oxygen and sulfur atoms on the donor
moiety have recently been reported: Gleiter, R.; Hoffmann, H.; Irngartinger,
H.; Nixdorf, M. Chem. Ber. 1994, 127, 2215.
(12) The symmetry of the subchromophores (ref 9) was established using
the semiempirical MNDO-PM3 calculations (ref 15) using Spartan 3.1
(Wavefunction Inc.).
Figure 3. X-ray structure of 5. Legend is as in Figure 1.
Results and Discussion
The spiro compounds 1-6 were obtained by an acid-catalyzed
condensation of ninhydrin (or 5,6-dimethoxyninhydrin in the
case of 6) with the N-methylated diamines or amino thiols with
azeotropic removal of water. All the desired products were
highly colored, and were easily separated from side products.
Four of the compounds gave single crystals suitable for X-ray
analysis14 (Figures 1-4).
The X-ray crystal structures have significantly lower sym-
metry than one would predict on the basis of simple geometrical
arguments. Not only are nitrogen atoms pyramidalized (as
expected), but the whole donor moiety is slightly twisted
sideways from the acceptor plane. The lengths of “sym-
metrically” disposed bonds are not equal. The bond distortions
can be accounted for by an electron density shift from the amine
donor to the indandione acceptor as shown in Scheme 1. For
example, in chromophore 2 (which illustrates the general trend)
(13) Compare the following: (a) Gleiter, R.; Uschmann; J. J. Org. Chem.
1986, 51, 370. (b) Gleiter, R.; Haider R.; Quast, H. J. Chem Res., Synop.
1978, 138. (c) Spanget-Larsen, J.; Uschmann, J.; Gleiter, R. J. Phys. Chem.
1990, 94, 2334.
(14) Further details of X-ray structures, including crystal packing
arrangements, will be discussed elsewhere.

Optical Properties of Charge-Transfer Dyes
J. Am. Chem. Soc., Vol. 118, No. 6, 1996 1473
Figure 5. Calculated (PM3) structure of 1. Selected bond lengths (Å)
are shown in italics. Hydrogen atoms have been omitted for clarity.
Figure 4. X-ray structure of 6. Legend is as in Figure 1.
Figure 6. Calculated (PM3) structure of 3. Legend is as in Figure 5.
Scheme 1
one of the nitrogens serves as the electron source. It becomes
less pyramidal than the other, and its bond with the spiro carbon
is shorter than that of the other nitrogen. In turn, the bond
between one of the carbonyl carbons and the spiro carbon
becomes longer than the corresponding bond of the other
carbonyl carbon. Ultimately, this second carbonyl group
becomes the acceptor of electron density, the C-O bond
lengthens, and the carbonyl carbon pyramidalizes slightly.
as the donor (rather than sulfur), and in 6 (Figure 4) the
distortions are smaller than in other compounds, as expected
on the basis of the diminished electron demand of the carbonyls
due to the presence of the methoxy groups on the acceptor
moiety.
The semiempirical calculations15 (PM3) yield structures that
are almost devoid of these distortions. The small differences
in calculated bond lengths (on the order of thousandths of an
angstrom) do nevertheless follow the trend observed in solid
state structures. Crystal packing14 (intermolecular interactions)
might be responsible for accentuating the diminished symmetry.
In general, the calculated and observed bond lengths and angles
are comparable, and it can be assumed that the calculated
structures for 1 and 3 represent the shapes of these molecules
quite well (Figures 5 and 6).
The origin of these distortions can be traced to the pyrami-
dalization of the nitrogen atoms. In the solid state the nitrogen
inversion (requiring movement of the aryl moieties) is blocked.
The N-aryl moiety is bent toward one of the carbonyl groups,
and the nitrogen lone pairs point up (Scheme 1). As the result
of increased orbital overlap with one of these lone pairs, the
upper carbonyl carbon-spiro carbon bond is elongated. The
nitrogen serving as the donor forms a shorter bond with the
spiro carbon than the other nitrogen, thus twisting the donor
moiety away from the acceptor plane. According to the electron
flow (Scheme 1), the lower carbonyl serves as the acceptor,
and the N-aryl moiety is always bent toward it.
In solution the nitrogen inversion is rapid on the 1H and 13
C
NMR time scale. The distortions associated with the inversion
should average out under these conditions. Indeed, only one
set of signals consistent with the presence of symmetry planes
for the acceptor and the donor (where appropriate) is observed
for the spiro compounds. Even at -70 °C there is no evidence
of any signal broadening.
These bond distortions result in chiral structures. Indeed the
crystal unit cells contain both enantiomers14 that correspond to
the selection of one or the other nitrogen as the donor atom.
The stereoelectronic factors associated with the electron density
shift are rather poor (the two π-systems are nearly perpendicular)
and the distortions are quite small (sometimes within the
estimated standard deviations), but consistent for all the
compounds examined. On the basis of the bond lengths, in 4
and 5 (Figures 2 and 3) apparently only the nitrogen atom serves
All spiro dyes showed an absorption band in the visible region
(Figures 7-11). No such bands would be expected from the
(15) Stewart, J. J. P. J. Comput.-Aided Mol. Des. 1990, 4, 1.

1474 J. Am. Chem. Soc., Vol. 118, No. 6, 1996
Maslak et al.
Figure 7. Absorption (ꢀ/ν) and electrooptical absorption (Lꢀ/ν) spectra
of 2 in 1,4-dioxane. Experimental data points for parallel (hollow
circles) and perpendicular (filled circles) polarization of the incident
light relative to the applied electric field are connected by lines obtained
from regression analysis.
Figure 10. Absorption (ꢀ/ν) and electrooptical absorption (Lꢀ/ν) spectra
of 5 in 1,4-dioxane. Legend is as in Figure 7.
Figure 11. Absorption (ꢀ/ν) and electrooptical absorption (Lꢀ/ν) spectra
of 6 in 1,4-dioxane. Legend is as in Figure 7.
significant absorbance above 370 nm. The intramolecular nature
of the charge-transfer transition was confirmed using model
donor and acceptor compounds. Concentrated solutions of 1,4-
diethyl-1,2,3,4-tetrahydroquinoxaline and 2,2-dimethylindan-1,3-
dione in methylene chloride, as well as neat mixtures of these
model compounds, did not show any absorption bands in the
visible region. Similarly, no visible absorptions were detected
for 2,2-dichloroindan-1,3-dione, 1,2,2,3-tetramethylperimidine,
or their mixture in methylene chloride.
Figure 8. Absorption (ꢀ/ν) and electrooptical absorption (Lꢀ/ν) spectra
of 3 in 1,4-dioxane. Legend is as in Figure 7.
In contrast, 1 and 2 have pronounced absorptions bands in
the visible region (λmax ) 552 and 414 nm, respectively, in
methylene chloride). Apparently in the model systems the
orbital overlap is too small, or the HOMO-LUMO energy gap
is too large. For 1 and 2 the intensity of the charge-transfer
bands followed the Beer-Lambert law over more than a 1000-
fold change in concentration, confirming the intramolecular
nature of the transition. The fact that both the extinction
coefficients and λmax values remained constant over the dilution
range (5 × 10-6 to 5 × 10-3 M) also excludes complexation
between the dye molecules.
In 1 and 4 the symmetry of the donor is mismatched with
that of the acceptor. The interaction between the components
is weak, and mainly of inductive nature. As a result, the
HOMO-LUMO transition is forbidden. The observed charge-
transfer bands clearly show low probability of these transitions
(ꢀ536 ) 140 M-1 cm-1 for 1 and ꢀ464 ) 170 M-1 cm-1 for 4 in
Figure 9. Absorption (ꢀ/ν) and electrooptical absorption (Lꢀ/ν) spectra
of 4 in 1,4-dioxane. Legend is as in Figure 7.
presence of either of the two subchromophores, since both the
electron acceptors (indan-1,3-diones) and the electron donors
(such as diaminobenzene or diaminonaphthalene) have no

Optical Properties of Charge-Transfer Dyes
J. Am. Chem. Soc., Vol. 118, No. 6, 1996 1475
Table 1. Optical Propertiesa of Spiro Dyes
1
2
3
4
5
6
λmaxb (nm)
σc (×10-3 cm-1
µgd (D)
560
5.88
0.6
421
6.53
2.9
4.8(1)
4.65(4)
4.09
-5.6(5)
-5.6
-10.4(5)
11.9(4)
0.26(1)
<2.0
-15.5(8)
17.5
427
4.91
1.7
3.5(1)
3.4(1)
2.05
-1.9(7)
-4.2(1)
-5.4(6)
6.4(5)
0.29(3)
4.4(8)
-3.7(8)
8.1
427
5.91
0.7
390
391
6.69
3.3
)
2.9
µge (D)
3.2(1)
3.1(1)
2.68
-2.6(2)
-3.7(1)
-5.8(2)
5.9(2)
0.11(1)
8(1)
2.3(2)
2.7(1)
2.98
5.4(1)
4.2(1)
3.66
-5.8(7)
-5.7(1)
-11.2(6)
13.0(5)
0.27(1)
23(6)
µgf (D)
µgg (D)
3.20
µee (D)
-8(2)
µeh (D)
-4(1)
-7(1)h
7.5(9)
0.08(8)
∆µi (D)
∆ j (D)
-10(2)
12(1)
0.26(4)
2(2)
-13(2)
15.6
c j
âk (1.907 µm)
â(CT)l
-0.2(1)
-0.62(8)
9.1
-17.5(8)
39.5
Ɖm
a The estimated errors are shown in parentheses as standard deviations of the least significant digits. b In 1,4-dioxane. c Widths of CT bands at
half-height in acetonitrile. d From eq 4, in 1,4-dioxane (1 D ) 3.336 × 10-30 C m). e From EOAM in 1,4-dioxane. f From the Guggenheim expression
(ref 23), in chloroform. g Calculated (PM3). h From solvatochromic studies. The dipole of 2 was scaled to the EOAM result (see text). i ∆µ ) µe
- µg. j From the Mulliken model (eqs 5-10). k EFISH measurements in chloroform. All â values are ×1030 esu (10-30 esu ) 0.3711 × 10-50
m3 V-2). l Calculated from eq 11. m The difference between the observed and calculated â values, ∆â ) â - â(CT).
C
acetonitrile). The transitions occur most likely due to symmetry
breaking analogous to that observed in the solid state structures
(see above). The difference in the position of the charge-transfer
bands is directly related to the donor strength. As judged by
the oxidation potentials of 1 (Eox ) 0.48 V vs SCE) and 4 (Eox
) 0.95 V) the diamino compound has significantly higher
HOMO energy than the amino thiol derivative.
In contrast, the naphthyl-based donors in 2, 5, and 6 have an
antisymmetric HOMO (vs the plane of the dione). These
orbitals spiroconjugate with the LUMO of the acceptor part.
As a result of this orbital mixing, the CT transition is allowed
(ꢀ g 3800 M-1 cm-1 for all these compounds). In all the cases
the absorption band is significantly shifted to higher energies
(when compared to 1 or 4), reflecting both the differences in
the donor or acceptor strengths and the effects of spiroconju-
gation.5
In 3, the HOMO of the donor has correct symmetry, but it is
of lower energy than that in 2 (Eox ) 1.21 V for 3, Eox ) 0.72
V for 2). Additionally, the seven-membered ring formed may
not allow for optimum overlap between the nitrogen orbitals
and the corresponding carbonyl carbon orbitals (Figure 6). As
a result, the probability of transition is diminished (ꢀ428 ) 1.35
× 103 M-1 cm-1).
refractive index of the solvent, ꢀ is the dielectric constant of
the solvent, ꢀ0 is the permeability of the vacuum, A and B are
constants characteristic of the molecule, µg is the dipole moment
of the ground state of the molecule, µe is the dipole moment of
the excited state of the molecule, Φ is the angle between the
direction of µg and the direction of µe, and a is the solvent cavity
radius. This last quantity is not well defined, and different
approaches to its estimation can be found in the literature.18 As
in a previous paper,19 we avoid any arbitrariness in choosing
this parameter by scaling the solvatochromic results for µe to
the results of electrooptical absorption measurements (EOAM),
which are more accurate in general. Compound 2 was selected
as a typical representative of the present class of chromophores.
Agreement of solvatochromic and EOAM results was obtained
by setting a equal to 0.71L/2 (where L is the diameter of the
smallest sphere enclosing the molecule). This choice of the
cavity radius was then equally applied to the other spiro CT
dyes.
A linear regression of the solvatochromic data yields B values
for the dyes (see the Experimental Section). Using measured
values of the ground state dipole moments (from electrooptical
studies, or from calculations in the case of 1) and geometrical
data from X-ray structures (or calculated structures in the case
of 1 and 3), and assuming in all cases that Φ ) 180° (see
below), excited state dipole moments were estimated for the
compounds (Table 1). The values are in reasonably good
agreement with the values obtained from electrooptical experi-
ments.
In all these spiro compounds, the fluorescence intensity was
extremely low, only slightly higher than the background.
Variations in the excitation wavelengths (from UV to visible)
or polarity of the solvent (acetonitrile, dichloromethane, benzene,
formamide, dimethyl sulfoxide, and hexane) did not affect the
results. The shape of very weak emission bands was similar to
the shape of the charge-transfer absorption bands, and the
emission occurred at a longer wavelength, as expected.
The charge-transfer bands of the dyes showed pronounced
negative solvatochromism;16 i.e., a hypsochromic shift of the
charge-transfer band occurred on increasing the solvent polarity.
Following the McRae formalism,17 the expression for the
solvatochromic shifts in absorption frequency of a molecule can
be written as
In electrooptical absorption (EOA) experiments the effect of
an external electric field (E0) on the absorption of linearly
polarized light by a dilute solution of an organic compound is
given by20
(ꢀE/ν) - (ꢀ/ν)
Lꢀ/ν )
(3)
2
E0
where ꢀ ) ꢀ(ν) and ꢀE ) ꢀ(æ,ν) represent the molar extinction
coefficients in the absence and presence of the applied electric
n2 - 1
2n + 1
ꢀ - 1 n2 - 1
ωsolvent - ωvacuum ) A
+ B
-
(1)
(16) Reichardt, C. SolVents and SolVent Effects in Organic Chemistry;
VCH: Weinheim, 1990.
(17) (a) McRae, E. G. J. Phys. Chem. 1957, 61, 562. (b) Paley, M. S.;
Harris, J. M.; Looser, H.; Baumert, J. C.; Bjorklund, G. C.; Jundt, D.; Twieg,
R. J. J. Org. Chem. 1989, 54, 3774.
(18) Bakhshiev, N. G; Knyazhanskii, M. I; Minkin, V. I.; Osipov, O.
A.; Seidov, G. V. Russ. Chem. ReV. 1969, 3, 740.
(19) Wu¨rthner, F.; Effenberger, F.; Wortmann, R.; Kra¨mer, P. Chem.
Phys. 1993, 173, 305.
2
2
[
]
[
]
ꢀ + 2
n + 2
2
B )
µg(µg - µe cos Φ)
(2)
4ꢀ0πpa3
where ωsolvent is the frequency of transition (s-1) in a solvent,
ωvacuum is the frequency of transition in a vacuum, n is the

1476 J. Am. Chem. Soc., Vol. 118, No. 6, 1996
Maslak et al.
field E0, æ is the angle between the direction of E0 and the
electric field vector of the incident light, and ν is the wave-
number (cm-1) associated with the transition. The measure-
ments are made for two field directions, æ ) 0° (parallel) and
90° (perpendicular), and several wavenumbers within the charge-
transfer band. Figures 7-11 show the electrooptical absorption
spectra (Lꢀ/ν) for 2-6, together with their unperturbed analogs
(ꢀ/ν).
With the exception of 5, the charge-transfer bands are well
separated from other transitions, and in all cases the electroop-
tical spectra can be fitted numerically,20 yielding the ground
state and excited state dipole moments as well as the direction
of the transition dipole moment (µge) in the fixed molecular
frame. The UV-vis spectrum of the molecule is utilized21 to
determine µge from the integrated absorption according to
electronically couple with a significant strength. The biphenyl
donor 3, because of geometrical constraints, has diminished
overlap between the crucial p orbitals of the carbonyl carbons
and the lone pair orbitals on the nitrogens (Figure 6). In addition
to the extinction coefficient being lower (see above) the CT
band is significantly narrower in this case, leading to a transition
dipole that is only 1.7 D. The band widths at half-height (σ in
Table 1) follow a trend that might be associated with the
vibronic structure of the spiro dyes. The bands are broadest
for the naphthyl derivatives (σ is ca. 6.6 × 103 cm-1), slightly
narrower for the compounds with phenyl-based donors (σ is
ca. 5.9 × 103 cm-1), and narrowest for the biphenyl compound
(σ ) 4.9 × 103 cm-1). Perhaps the seven-membered ring in 3
adds extra rigidity to the structure. For comparison, under the
same conditions (acetonitrile), the band width of PNA is 5.2 ×
103 cm-1 and that of TCE-HMB is 5.5 × 103 cm-1
.
The excited state dipole moments are in the direction opposite
to that of the ground state dipole moments, exactly as expected
if the electron density is transferred from the HOMO localized
mainly on the donor moiety to the LUMO limited mostly to
the acceptor subchromophore. To a first approximation, the
excited state should resemble a radical cation/radical anion pair.8
The magnitudes of the excited state dipoles are, however,
relatively small (see below).
ꢀ(ν) dν ) 2π2N µ 2/(6 ln 10hcꢀ0)
(4)
∫
A
ge
where NA is Avogadro’s number, h Planck’s constant, and c
the speed of light (the integration is carried out over the entire
band). The results of EOA experiments are summarized in
Table 1, and the details are provided in the Experimental
Section.
Compounds 2-6 were also studied by electric field induced
second harmonic (EFISH) generation at 1907 nm in chloroform
solution as described previously.22 The measured molecular
hyperpolarizabilities (â) are presented in Table 1.
Using Mulliken theory,8,26 we can describe the ground state
wave function |g and the excited state wave function |e as a
linear combination of neutral (|n ) and fully ionic (|i ) wave
functions with a mixing coefficient c:
The ground state dipole moments of the spiro compounds
(as shown by PM3 calculations12) point from the dicarbonyl
moiety (positive end) to the heteroatoms of the donor moiety
(negative end) and are aligned mainly along the long molecular
axis. This polarization is reflected in distortions observed in
the solid state (see above). The independently determined
ground state dipole moments23 agree very well with those
measured by EOA. Also, the calculated values are in reasonable
agreement with experimental values. The spiro dyes show
moderate polarity in their ground states; the observed µg values
for all the compounds span a narrow range from 2.3 to 5.5 D
(Table 1).
The transition dipole moments (µge) are in the direction of
the ground state dipole moments, and their magnitudes reflect
the symmetries of the donor components. As discussed above,
the HOMOs of the phenyl-based donors 1 and 4 have incorrect
symmetry for interaction with the LUMO of the dione moiety.
The values of µge are less than 1 D. For correct-symmetry
naphthyl-based donors, the interaction between the frontier
orbitals is stronger, yielding µge values around 3 D. For
comparison, p-nitroaniline24 (PNA), which has directly conju-
gated donor and acceptor groups of strength similar to that of
our spiro components, has a transition dipole of 4.4 D for its
CT band, and the bimolecular CT complex25 of tetracyano-
ethylene with hexamethylbenzene (TCE-HMB) has µge ) 3.5
D. Thus, the perpendicular π-systems of correct symmetry can
|g ) (|n + c|i )/(1 + c2)0.5
(5)
|e ) (c|n - |i )/(1 + c2)0.5
(6)
These functions are orthonormal if n|i ) 0. Since the overlap
of molecular orbitals of the subchromophores is rather small,
we can assume n|i ≈ 0, and accordingly that n|µ|i ≈ 0, where
µ is the dipole moment operator. With these approximations
one obtains expectation values for the ground state ( g|µ|g )
µg) and excited state ( e|µ|e ) µe) dipole moments, as well as
expressions for the transition dipole ( e|µ|g ) µge) and the
change of dipole moment upon excitation (∆µ):
g|µ|g ) ( n|µ|n + c2 i|µ|i )/(1 + c2)
e|µ|e ) (c2 n|µ|n + i|µ|i )/(1 + c2)
(7)
(8)
e|µ|g ) -c∆/(1 + c2)
∆µ ) (1 - c2)∆/(1 + c2)
(9)
(10)
where ∆ is the maximum possible change of the dipole moment
(∆ ) i|µ|i - n|µ|n ).
Using the data of Table 1, the mixing coefficients and ∆
values can be estimated for all spiro dyes. The mixing
coefficient can be used as a measure of spiroconjugation
between the donor and acceptor moieties. For compounds with
donors of correct symmetry (2, 3, 5, and 6), the ionic structure
contributes just above 6% (c2/(1 + c2)) to the description of
the molecule, while in the phenyl-based compounds of incorrect
symmetry that contribution is close to 1% (Table 1). For
comparison, PNA24 (where the approximation that n|i ) 0 is
probably not valid) has c ) 0.73 (35%), and in the TCE-HMB
(20) (a) Liptay, W. In Excited States; Lim, C., Ed.; Academic Press:
New York, 1974; Vol. I, p 129. (b) Wortmann, R.; Elich, K.; Lebus, S.;
Liptay, W.; Borowicz, P, Grabowska, A. J. Phys. Chem. 1992, 96, 9724.
(21) Liptay, W. Angew. Chem., Int. Ed. Engl. 1969, 8, 177.
(22) (a) Levine, B. F.; Bethea, C. G. J. Chem. Phys. 1975, 63, 2666. (b)
Oudar, J. L. Chem. Phys. 1977, 67, 466. (c) Moylan, C. R.; Miller, R. D.;
Twieg, R. J.; Betterton, V. Y.; Matray, T. J.; Ngyuyen, C. Chem. Mater.
1993, 5, 1499.
(23) The ground state dipole moments were determined from dielectric
and refractive index measurements according to the Guggenheim expres-
sion: Guggenheim, E. A. Trans. Faraday Soc. 1949, 45, 714.
(24) Wortmann, R.; Kra¨mer, P.; Glania, C.; Lebus, S.; Detzer, N. Chem.
Phys. 1993, 173, 305.
(26) For a similar approach to intermolecular CT complexes see: Di
Bella, S.; Fragala´, I. L.; Ratner, M. A.; Marks, T. J. J. Am. Chem. Soc.
1993, 115, 682.
(25) Liptay, W.; Rehm, T.; Wehning, D.; Schanne, L.; Baumann, W.;
Lang, W. Z. Naturforsch. 1982, 37a, 1427.

Optical Properties of Charge-Transfer Dyes
J. Am. Chem. Soc., Vol. 118, No. 6, 1996 1477
complex (µg ) 1.9 D, µe ) 6.6 D, µge ) 3.5 D)25 the
contribution of the ionic structure is 18% (c ) 0.47, ∆ ) 8.5
D).
would bring the frontier orbitals of the subchromophores closer
in energy, increase their overlap, separate charges over larger
distances, and properly align the transitions within subchro-
mophores to avoid the cancellation of various contributions.
Preparation of such dyes is in progress.
Incidentally, the data for the TCE-HMB complex also allow
for a straightforward test of the CT model. The result for the
matrix element n|µ|n which can be calculated from eqs 7-10
is zero within experimental error. This is exactly the prediction
of the CT model since n|µ|n represents the total dipole moment
of the two noninteracting subchromophores and both TCE and
HMB are nonpolar. The ground state dipole of the sandwich
complex is, therefore, entirely due to admixtures of the ionic
wave function |i to the neutral wave function |n .
Experimental Section
Unless otherwise noted, all materials were obtained from Aldrich
Chemical Co., Inc., and used without purification. Reagent grade
diethyl ether and tetrahydrofuran were distilled from potassium/
benzophenone under argon immediately before use under anhydrous
conditions. Reagent grade methylene chloride and spectrophotometric
grade benzene were distilled from calcium hydride under argon
immediately before use under anhydrous conditions. Aldrich anhydrous
grade (Sure-Seal) acetonitrile, dimethyl sulfoxide, dimethylformamide
and dimethylacetamide were used for preparative work when needed
in anhydrous form. The solvents used for UV/vis and fluorescence
spectroscopies were spectrophotometric grade and used without further
purification. Pyridine was dried overnight over solid sodium hydroxide
and then distilled under argon from the hydroxide onto 4 Å molecular
sieves for storage.
Within that simple CT model the excited states of the spiro
compounds are indeed well described as the radical anion/radical
cation pair. The degree of electron transfer accompanying the
transitions ((1 - c2)/(1 + c2)) is more than 90% in all the
compounds. The moderate magnitudes of the excited state
dipole moments (µe from -2 to -8 D) can thus be traced to
the small distances between the separated charges, rather than
to a small degree of the charge transfer. This conclusion has
important implications for the design of the next generation of
spiro dyes (see below).
1
All H and 13C spectra were obtained using one of the following
Bruker spectrometers: a AC-200 or WP-200 (200 MHz for proton),
an AM-300 (300 MHz for proton), or a WP-360 (360 MHz for proton).
1H and 13C chemical shifts are reported in parts per million with respect
to tetramethylsilane (0.00 ppm). CDCl3 was used as the solvent for
1H and 13C NMR, unless otherwise noted. All of the 13C spectra were
recorded with high-power, broad-band decoupling.
Mass spectra were recorded using one of the following Kratos in-
struments: a MS-950 double-focusing mass spectrometer in the
electron-impact mode (reported as EI-MS) or a MS-25 double-focusing
mass spectrometer for chemical ionization using isobutylene as the
ionization gas (reported as CI-MS). Mass spectral data are expressed
as m/z (intensity as the percent of the most abundant ion peak). All
observed peaks with masses above m/z 80 and more intense than 10%
of the most abundant ion peak as well as peaks judged to be of particular
significance are reported.
Using the two-state model27 and the data obtained from EOA
measurements we can estimate the CT contribution to the
molecular hyperpolarizability, â(CT), for the spiro dyes:
4
3µge2∆µ
ωmax
â(CT) )
(11)
h2c2ωmax2 (ωmax2 - ω2)(ωmax2 - 4ω2)
where ω is the laser frequency and ωmax the frequency
corresponding to the maximum of the CT transition. The
absolute magnitudes of calculated values are the largest for the
naphthyl derivatives 2 and 5 (Table 1), and the smallest for the
phenyl analogs 1 and 4. In general the calculated values do
not agree with the measured data. The EFISH data represent
the total molecular hyperpolarizability;22,28 i.e., all transitions
contribute to the molecular response. The calculated values are
based explicitly and exclusively on CT band contributions. The
differences between the observed values and the calculated CT
contributions (∆â) are relatively constant for 2-5 (12.6 × 10-30
esu on the average), indicating that there is a dominant second
transition that contributes to the molecular hyperpolarizability.
This transition is common to these dyes, and it provides a
contribution that is in the direction opposite to that from the
CT transition. It is very likely that the acceptor subchromophore
is responsible for this “destructive” interference. EFISH
measurements on 1,3-indandione gave â(1.907 µm) ) 11.6(7)
× 10-30 esu in support of this conclusion. Additional support
is provided by 6, where the methoxy substituents act as the
second internal donor, and the acceptor’s contribution becomes
quite strong (∆â ) 39.5 × 10-30 esu).
All UV/vis absorbance spectra were obtained using a Hewlett-
Packard 8452A diode array spectrometer at ambient temperatures.
Fluorescence measurements were made using a Spex Fluorometer.
Infrared spectra were obtained using a Perkin-Elmer 1600 series FTIR
spectrometer (reported as FTIR).
The solvatochromic data for the spiro compounds were obtained in
benzene, dioxane, toluene, CH2Cl2, THF, pyridine, acetone, acetonitrile,
and dimethyl sulfoxide. The physical data for the solvents were
obtained from the Handbook of Organic Photochemistry.29 The
observed wavelengths for the maxima of charge transfer bands are listed
below (according to the solvent list above), followed by a values (Å,
taken as 0.71L/2, where L is the largest atom-to-atom distance in the
molecule) and B values (×10-13 s-1) obtained from the regression
analysis. 1: 580, 560, 582, 552, 558, -, 540, 536, 546; 4.0; 5.1(5). 2:
428, 420, 424, 414, 414, 412, 404, 400, 410; 4.2; 4.1(5). 3: 428, -,
428, 420, -, -, 418, 414, 418; 4.2; 2.6(4). 4: 480, -, -, 472, 472,
-, 468, 466, 470; 4.1; 2.0(1). 6: 392, -, -, 382, 374, -, 368, 370,
-; 4.9; -1.8(6).
Preparative flash column chromatography30 was performed using
Merck silica gel 60 (230-400 mesh). TLC was done on Merck
precoated plates (60F-254) with a layer thickness of 0.25 mm. All
solvents used for thin-layer and flash column chromatographies were
reagent grade.
Crystal, data collection, and refinement parameters are given in
Table 2. Suitable crystals were selected and mounted on glass fibers
with epoxy cement. The unit-cell parameters were obtained by the
least-squares refinement of the angular settings of 24 reflections (20°
e 2θ e 24°).
The compounds presented here provide examples of a new
class of organic dyes that are based on intramolecular interac-
tions between nearly orthogonal subchromophores. The spiro-
conjugation used to couple the two π-subsystems electronically
provides a reasonably strong mode of interaction and leads to
CT transitions with modest probabilities. The inversion of the
dipole moments upon transition leads to significant changes of
the dipole moments, providing a starting point for the design
of compounds with large molecular hyperpolarizibilities. The
next generation of spiro dyes should have subchromophores that
The systematic absences in the diffraction data are uniquely
consistent for the reported space groups. The structures were solved
using direct methods, completed by subsequent difference Fourier
(27) (a) Oudar, J. L.; Chemla, D. S. J. Chem. Phys. 1977, 66, 2664. (b)
Oudar, J. L. J. Chem. Phys. 1977, 67, 446.
(28) (a) Zyss, J.; Oudar, J. L. Phys. ReV. A 1982, 26, 2016. (b) Moylan,
C. R. J. Chem. Phys. 1993, 99, 1436.
(29) Scaiano, J. C., Ed. Handbook of Organic Photochemistry; CRC
Press: Boca Raton, FL, 1989; Vol. II, p 344.
(30) Still, W. G.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923.

1478 J. Am. Chem. Soc., Vol. 118, No. 6, 1996
Maslak et al.
Table 2. Crystallographic Data for 2, 4, 5, and 6
2
4
5
6
(a) Crystal Parameters
C16H11NO2S
281.3
formula
C21H16N2O2
328.4
orthorhombic
Pbca
22.413(8)
16.696(6)
8.512(2)
C20H13NO2S
331.4
orthorhombic
Pbca
23.017(16)
16.109(3)
8.273(2)
C23H20N2O4
388.4
monoclinic
P21/n
9.519(2)
12.642(2)
15.950(5)
100.95(2)
1884.4(7)
4
formula weight
crystal system
space group
a (Å)
b (Å)
c (Å)
orthorhombic
Pbca
22.086(7)
15.888(7)
7.553(3)
â (deg)
V (Å3)
3185(2)
8
2651(2)
8
3068(1)
8
Z
cryst dimens (mm)
cryst color
D(calc) (g cm3)
0.1 × 0.4 × 0.4
0.4 × 0.4 × 0.4
red-orange
1.410
2.44
293
0.2 × 0.2 × 0.4
orange
1.435
2.23
242
0.2 × 0.2 × 0.3
red
orange
1.369
0.89
295
1.370
0.94
250
µ(Mo KR) (cm-1
)
temp (K)
(b) Data Collection
diffractometer
monochromator
radiation
2θ scan range (deg)
data collected (h,k,l)
rflns collected
Siemens P4
graphite
Mo KR (λ ) 0.710 73 Å)
4.0-48.0
+25, +19, +9
2521
4.0-50.0
+26, +18, +8
2444
4.0-48.0
+26, +18, +9
2554
4.0-42.0
(9, +12, +16
2110
indpt rflns
2313
2323
2426
2023
indpt obsvd rflns [Fo g 4σ(Fo)]
1236
1539
1552
1449
(c) Refinementa
R(F) (%)
5.41
6.32
0.04
0.3
4.91
6.41
0.03
0.4
4.25
6.98
0.00
0.2
7.23
9.58
0.00
0.5
R(wF) (%)
∆/σ (max)
∆(F) (eÅ-3
No/Nv
)
5.5
8.5
7.2
9.9
GOF
1.2
1.2
1.6
1.5
a Quantity minimized ) ∑w∆2; R ) ∑∆/∑(Fo); R(w) ) ∑∆w1/2/∑(Fow1/2), ∆ ) |(Fo - Fc)|.
syntheses and refined by full-matrix least-squares procedures. Ab-
sorbtion corrections were ignored because of <10% variation of the
integrated ψ-scan intensities. Carbon atoms in 6 were refined isotro-
pically. All remaining non-hydrogen atoms were refined with aniso-
tropic displacement coefficients. Hydrogen atoms were treated as
idealized contributions. All software and sources of scattering factors
are contained in the SHELXTL Plus (4.2) program library (G. Sheldrick,
Siemens XRD, Madison, WI).
The electrooptical absorption measurements (EOAM) were
performed as described previously.19,20 All measurements were made
in dioxane which was carefully purified and dried by distillation from
sodium/potassium alloy prior to use. Accurate UV/vis spectra which
are required for the numerical analysis of the EOAM data were recorded
on a Perkin-Elmer 340 spectrophotometer.
The EFISH measurements were performed as previously de-
scribed.22 Solutions at three different concentrations of each compound
were prepared, and second harmonic generation was detected with an
applied electric field of 2 × 104 V/cm. The fundamental wavelength
was 1907 nm, obtained by Raman shifting of the 1064 nm YAG
fundamental in hydrogen. The EFISH results were referenced to a
quartz standard, whose second harmonic coefficient d11 at 1907 nm is
6.7 × 10-10 esu. The B convention for â of Willets et al. was used.39
As part of the determination of the product µâ for each chromophore,
the concentration dependence of the dielectric constant was determined.
That concentration dependence was also used to determine the dipole
moment independently. From the µâ product derived from the EFISH
measurements, and the value of µ obtained from the dielectric
measurements, â at 1907 nm was determined. UV/vis spectra were
recorded on a diode array spectrophotometer ((2 nm) in dilute
chloroform solution.
mixture was heated at reflux, and the reaction was followed by TLC
and NMR. After 90 min of refluxing, there was no starting material
left and NMR showed 5,6-dimethoxy-3,3-dibromoindan-1-one as the
only product (Rf ) 0.52, 30% ethyl acetate in hexane). 1H NMR
(CDCl3, 200 MHz): δ 7.32 (s, 1 H), 7.09 (s, 1 H), 4.11 (s, 3 H), 3.98
(s, 3 H), 3.94 (s, 2 H). The reaction mixture was cooled to room
temperature, and then a solution of bromine (3.5 g, 0.022 mol) in 20
mL of carbon tetrachloride was added dropwise over a 30 min period
with vigorous stirring. After the addition was complete, the mixture
was brought to reflux and the reaction was followed by NMR. After
2-3 h of refluxing, NMR showed the desired tetrabromide as the only
product. The mixture was cooled to room temperature and filtered,
and the filtered solids were washed with carbon tetrachloride. The
combined organic layers were then washed with water (3 × 100 mL)
and saturated sodium chloride solution (100 mL), dried over sodium
sulfate, and filtered. The filtrate was removed under reduced pressure
to yield the tetrabromide (5.07 g, 96%) as a yellow solid (Rf ) 0.52,
30% ethyl acetate in hexane) which was used for the next reaction
without further purification. 1H NMR (CDCl3, 200 MHz): δ 7.25 (s,
1 H), 7.18 (s, 1 H), 4.09 (s, 3 H), 3.97 (s, 3 H).
5,6-Dimethoxy-2,2-dibromoindan-1,3-dione was prepared by the
silver nitrate hydrolysis of 5,6-dimethoxy-2,2,3,3-tetrabromoindan-1-
one. A solution of AgNO3 (4.25 g, 0.025 mol) in 4 mL of water was
added to a solution of the bromide (5.08 g, 0.01 mol) in 50 mL of
acetonitrile, and the mixture was heated at reflux. A yellow-white
precipitate fell out of solution immediately, and refluxing was continued
for 1 h. After cooling to room temperature, the mixture was filtered
and the filtered solids were washed well with acetonitrile. The
combined filtrates were removed by rotary evaporation, and the white
solid thus obtained was suspended in 100 mL of methylene chloride.
This solution was filtered to remove any remaining silver salts, and
the filtrate was evaporated to yield the dione (3.41 g, 94%) as a white
solid (Rf ) 0.37, 30% ethyl acetate in hexane) which was used in the
next reaction without further purification. 1H NMR (CDCl3, 300
MHz): δ 7.41 (s, 2 H), 4.10 (s, 6 H). 13C NMR (CDCl3, 75 MHz):
δ 186.4, 157.8, 130.6, 105.0, 57.0, 51.8. EI-MS: m/z 366 (M+ + 4,
5,6-Dimethoxy-2,2,3,3-tetrabromoindan-1-one was prepared by
benzylic bromination followed by enolic bromination of 5,6-dimethoxy-
indan-1-one (Rf ) 0.17, 30% ethyl acetate in hexane). N-Bromosuc-
cinimide (4.0 g, 22 mmol) and 20 mg of azobisisobutyronitrile were
added to a solution of 5,6-dimethoxyindan-1-one (2.0 g, 10 mmol) in
100 mL of carbon tetrachloride under an argon atmosphere. The

Optical Properties of Charge-Transfer Dyes
J. Am. Chem. Soc., Vol. 118, No. 6, 1996 1479
49), 364 (M+ + 2, 100), 362 (M+, 51), 285 (M+ + 2 - Br, 32), 283
(M+ - Br, 30), 255 (M+ - Br - CO, 23).
acetate in hexane). 1H NMR (acetone-d6, 360 MHz): δ 7.21 (m, 2
H), 6.93 (m, 2 H), 6.68 (m, 2 H), 4.0 (s, 2 H, D2O exchangeable), 2.76
(s, 6 H). EI-MS: m/z 212 (M+, 47), 211 (M+ - H, 32), 210 (M+
2H, 24), 197 (M+ - CH3, 13), 196 (M+ - CH3 - H, 34), 195 (M+
-
-
5,6-Dimethoxyninhydrin31 was prepared by the dimethyl sulfoxide
hydrolysis of 5,6-dimethoxy-2,2-dibromoindan-1,3-dione. A solution
of the dione (2.0 g, 5.5 mmol) in 20 mL of anhydrous dimethyl
sulfoxide was heated at 90-95 °C for a period of 2 days under an
argon atmosphere. The reaction was followed by TLC and stopped
upon disappearance of starting material. After cooling to room
temperature, the mixture was poured into 200 mL of water and then
extracted with ethyl acetate (5 × 100 mL). The combined organic
layers were dried over sodium sulfate, filtered, and evaporated under
reduced pressure to yield a yellow oil. The oil was purified by column
chromatography using a mixture of 4% methanol in methylene chloride
as the eluant to yield the ninhydrin (0.78 g, 59%) as a light yellow oil
(Rf ) 0.41, 5% methanol in methylene chloride). 1H NMR (acetone-
d6, 300 MHz): δ 7.37 (s, 2 H), 6.30 (s, 2 H, D2O exchangeable), 4.06
CH3 - 2H, 26), 182 (M+ - 2CH3, 40), 181 (M+ - 2CH3 - H, 96),
180 (M+ - 2CH3 - 2H, 100), 167 (M+ - 2CH3 - NH, 41), 166 (M+
- 2CH3 - NH - H, 14), 152 (M+ - 2CH3 - 2NH, 16).
1,2-Dimethylperimidine was prepared by a modified procedure of
Pozharskii.34 Iodomethane (46.88 g, 0.33 mol) was added dropwise
over a period of 10 min to a solution of 2-methylperimidine35 (30.0 g,
0.165 mol) in 60 mL of dimethylformamide at 100 °C (Baker
spectrophotometric grade), containing finely powdered potassium
carbonate (22.75 g, 0.165 mol). The mixture was heated for 30 min,
giving a yellow precipitate. After cooling, the yellow solid was filtered
and suspended in 1500 mL of water. Aqueous ammonium hydroxide
was added slowly with vigorous stirring till the solution was slightly
basic to litmus. During the course of addition, a yellow-green solid
appeared. The solid was filtered, washed with water, and dried under
vacuum to give the desired product (20.8 g, 65%). The dimethylfor-
mamide filtrate from the first filtration was added to 1200 mL of water,
and the solution was made alkaline with aqueous ammonium hydroxide
to yield a yellow-green solid. The solid was filtered, washed with water,
and dried under vacuum to give an additional 7.8 g (24%) of product.
The product was used in the next reaction without purification. 1H
NMR (CDCl3, 200 MHz): δ 7.20 (m, 4 H), 6.85 (dd, J ) 7, 1 Hz, 1
H), 6.24 (dd, J ) 6, 2 Hz, 1 H), 3.21 (s, 3 H), 2.35 (s, 3 H).
1,2-Dimethylperimidinyl methiodide was prepared in a manner
similar to that of Pozharskii.34 Iodomethane (30.2 g, 0.21 mol) was
added in one portion to a solution of 1,2-dimethylperimidine (20.8 g,
0.106 mol) in dimethylformamide (80 mL) at 100 °C. The mixture
was heated for 20 min, giving a yellow solid. After cooling, the solid
was filtered and dried under vacuum to give the desired salt (29.5 g,
82%) which was used in the next reaction without purification. 1H
NMR (dimethyl sulfoxide-d6, 200 MHz): δ 7.66 (dd, J ) 8, 1 Hz, 2
H), 7.54 (t, J ) 8 Hz, 2 H), 7.24 (dd, J ) 8, 1 Hz, 2 H), 3.61 (s, 6 H),
2.78 (s, 3 H).
(s, 6 H). EI-MS: m/z 238 (M+, 2), 220 (M+ - H2O, 16), 192 (M+
-
H2O - CO, 30), 164 (M+ - H2O - 2CO, 100), 136 (M+ - H2O -
3CO, 79).
N,N′-Dimethyl-1,2-phenylenediamine was prepared by the method
of Cheeseman.32
N,N′-Bis(p-tolylsulfonyl)-2,2′-diaminobiphenyl was obtained by
tosylation of 2,2′-diaminobiphenyl.33 A solution of p-toluenesulfonyl
chloride (19 g, 0.1 mol) in 50 mL of anhydrous pyridine was added
slowly to a solution of 2,2′-diaminobiphenyl (9.2 g, 0.05 mol) in 25
mL of anhydrous pyridine under an argon atmosphere so that the
temperature of the reaction mixture did not exceed 60 °C. After stirring
overnight, the reaction mixture was poured slowly into 500 mL of 15%
hydrochloric acid with vigorous stirring to give a gray solid. After
stirring for 1 h the solid was filtered, washed well with water, and
dried under vacuum. Upon recrystallization from acetic acid, white
crystals of the desired tosyl amide (21.9 g, 89%) were obtained. 1H
NMR (CDCl3, 200 MHz): δ 7.66 (dd, J ) 8, 1 Hz, 2 H), 7.50 (d, J )
8 Hz, 4 H), 7.33 (m, 2 H), 7.24 (d, J ) 8 Hz, 4 H), 7.05 (m, 2 H), 6.48
(dd, J ) 8, 1 Hz, 2 H), 5.90 (s, 2 H), 2.42 (s, 6 H).
N,N′-Dimethyl-N,N′-bis(p-tolylsulfonyl)-2,2′-diaminobiphenyl. The
above diamide (12.25 g, 0.025 mol) was refluxed with 4 N aqueous
NaOH (12.5 mL, 0.05 mol) for 5 min. The mixture was cooled in an
ice bath (0-5 °C), and then dimethyl sulfate (4.5 mL, 0.05 mol) was
added dropwise. After the initial reaction had subsided, the mixture
was gently boiled for 5 min. After cooling, the suspended solid was
crushed and 12.5 mL of 4 N aqueous NaOH and 4.5 mL of dimethyl
sulfate were added. The mixture was boiled again for 5 min. After
two further similar treatments, the solid was filtered from the hot
mixture and then boiled with 200 mL of 0.75 N aqueous NaOH solution.
The insoluble material was filtered and recrystallized from 95% ethanol
to yield N,N′-dimethyl-N,N′-bis(p-tolylsulfonyl)-2,2′-diaminobiphenyl
(10.87 g, 84%) as colorless needles (Rf ) 0.41, methylene chloride).
1H NMR (CDCl3, 200 MHz): δ 7.32 (m, 14 H), 6.78 (dd, J ) 8, 1 Hz,
2 H), 3.05 (s, 6 H), 2.43 (s, 6 H).
N,N′-Dimethyl-2,2′-diaminobiphenyl was prepared by the hydroly-
sis of the corresponding tosyl amide. The dimethyl diamide (5.6 g,
0.011 mol) was heated at 120 °C in a mixture of glacial acetic acid (3
mL) and concentrated sulfuric acid (3 mL) under an argon atmosphere
for 2 h. The reaction was followed by TLC (aliquots were worked up
as mentioned later and extracted with ether, and the ether extract was
used as the sample for TLC) and stopped upon disappearance of starting
material. After cooling to room temperature, the reaction mixture was
poured into 50 mL of ice-water. Slow addition of 10 N aqueous NaOH
solution was carried out till the solution was slightly basic, and the
mixture was immediately diluted to a final volume of 300 mL. The
mixture was extracted with ether (4 × 100 mL). The combined organic
layers were dried over sodium sulfate and then evaporated under
reduced pressure to yield the desired amine (1.83 g, 81%) as a light
yellow solid (Rf ) 0.74, methylene chloride; Rf ) 0.85, 40% ethyl
1,8-Bis(methylamino)naphthalene was prepared according to the
method of Pozharskii.36 Argon was bubbled through a solution of
potassium hydroxide (76.5 g) in 95% ethanol (425 mL) for 5 min. The
methiodide salt (17 g, 0.05 mol) was added in one portion to the alkaline
ethanol and refluxed under an argon atmosphere. After 2 h, the reaction
mixture was cooled and diluted with water to yield a final volume of
2 L. The obtained solution was neutralized with glacial acetic acid till
it was weakly basic to litmus. A brown solid precipitated out during
this time. This solid was filtered, washed with water, and dried under
vacuum to yield the desired amine (7.23 g, 78%). Light yellow prisms
of the product were obtained upon recrystallization from 95% ethanol;
mp 100 °C (lit.37 mp 101 °C); Rf ) 0.42, 10% ethyl acetate in hexane.
1H NMR (CDCl3, 200 MHz): δ 7.27 (dd, J ) 8, 7 Hz, 2 H), 7.18 (dd,
J ) 8, 1 Hz, 2 H), 6.57 (dd, J ) 7, 1 Hz, 2 H), 5.45 (s, 2 H, D2O
exchangeable), 2.87 (s, 3 H). EI-MS: m/z 186 (M+, 100), 185 (M+
H, 6), 171 (M+ - CH3, 15), 170 (M+ - CH3 - H, 18), 169 (M+
-
-
CH3 - 2H, 41), 156 (M+ - 2CH3, 14), 155 (M+ - 2CH3 - H, 15),
154 (M+ - 2CH3 - 2H, 53), 141 (M+ - 2CH3 - NH, 4), 140 (M+
2CH3 - NH - H, 8), 126 (M+ - 2CH3 - 2NH, 9).
-
2-(Methylamino)benzenethiol was prepared using an approach
similar to that of Kiprianov.37 Argon was bubbled through a solution
of N-methylbenzothiazole-2-thione (Janssen Chimica; 0.534 g, 3 mmol)
in hot (60 °C) 95% ethanol (1.55 mL) for 5 min. A solution of
potassium hydroxide (0.504 g, 9 mmol) in 95% ethanol (1.55 mL) was
added in one portion and the mixture was heated at reflux under an
argon atmosphere. After 2 h, the reaction mixture was cooled to room
temperature even though TLC showed the presence of starting material.
The mixture was diluted with water to yield a final volume of 30 mL.
The obtained solution was neutralized with concentrated hydrochloric
acid till it was weakly basic to litmus and then extracted with benzene
(31) (a) Lennard, C. J.; Margot, P. A.; Stoilovic, M.; Warrener, R. N. J.
Forensic Sci. 1986, 26, 323. (b) Lennard, C. J.; Margot, P. A.; Stoilovic,
M.; Warrener, R. N. Forensic Sci. Soc. 1988, 28, 3. (c) Kametani, T.; Hibino,
S.; Takano, S. J. Chem. Soc., Perkin Trans. 1 1972, 391. (d) Almog, J.;
Hirshfeld, A. J. Forensic Sci. 1988, 33, 1027.
(32) Cheeseman, G. W. H. J. Chem. Soc. 1955, 3308.
(33) Moore, R. E.; Furst, A. J. Org. Chem. 1958, 23, 1504.
(34) Sokolov, V. I.; Ardashev, B. I.; Kashparov, I. S.; Pozharskii, A. F.
Khim. Geterosikl. Soedin. 1973, 849
(35) Whitehurst, J. S. J. Chem. Soc. 1951, 226.
(36) Pozharskii, A. F.; Suslov, A. N.; Starshikov, N. M.; Popova, L. L.;
Klyuev, N. A.; Adanin,V. A. Zh. Org. Khim. 1980, 16, 2216.
(37) Kiprianov, A. I.; Pazenko, Z. N. Zh. Obshch. Khim. 1949, 19, 1523.

1480 J. Am. Chem. Soc., Vol. 118, No. 6, 1996
Maslak et al.
(3 × 25 mL). The benzene extracts were used for the next reaction
without further purification. An aliquot of the benzene layer was
concentrated by rotary evaporation and dried under vacuum to yield a
light yellow oil. NMR of this oil showed a 1:1 mixture of the desired
amino thiol (Rf ) 0.84, 20% ethyl acetate in hexane) and the starting
material (Rf ) 0.63, 20% ethyl acetate in hexane).
Synthesis of 1. The reaction was carried out using 1.00 g of N,N′-
dimethyl-1,2-phenylenediamine and an equimolar amount of ninhydrin.
The pure compound was isolated after column chromatography (Rf )
0.42, 40% ethyl acetate in hexane) in 60% yield. Upon recrystallization
from benzene, deep purple needles were obtained, mp 142 °C. 1H NMR
(CDCl3, 200 MHz): δ 8.10-7.98 (m, 4 H), 6.68-6.65 (m, 2 H), 6.33-
6.30 (m, 2 H), 2.61 (s, 6 H). 13C NMR (CDCl3, 50 MHz): δ 198.2,
140.6, 140.5. 137.4, 123.5, 119.3, 104.4, 87.6, 30.7. EI-MS: m/z 278
(M+, 27), 249 (M+ - NCH3, 23), 221 (M+ - NCH3 - CO, 100). FTIR
(KBr): 3070 (w), 2878 (w), 2813 (w), 1747 (m), 1717 (s), 1598 (m),
1503 (s), 1403 (w), 1324 (m), 1268 (w), 1238 (m), 1218 (m), 1115
(m), 1015 (m), 932 (s), 878 (w), 774 (m), 741 (s), 711 (m), 676 (w),
N-Methyl-1,8-naphthosultam was prepared by the alkylation of 1,8-
naphthosultam (Rf ) 0.38, 30% ethyl acetate in hexane; Rf ) 0.11,
60% methylene chloride in hexane) with iodomethane. A solution of
sodium hydroxide (0.42 g, 10.5 mmol) in 10 mL of water was added,
with stirring, to a solution of 1,8-naphthosultam (2.05 g, 10 mmol) in
10 mL of dimethylacetamide under an argon atmosphere. The mixture
became warm upon addition of base and was allowed to cool to room
temperature. Iodomethane (0.65 mL, 10.5 mmol) was then added to
the mixture, and the resulting solution was stirred for 2 h. Reaction
progress was followed by TLC, and the reaction was stopped upon
complete disappearance of the starting material. The reaction mixture
was poured slowly into 150 mL of water, with vigorous stirring, yielding
a gray-white solid. After stirring for 30 min, the solid was filtered,
washed with water, and dried under vacuum. Upon recrystallization
from 20% ethyl acetate in hexane, white crystals of N-methyl-1,8-
naphthosultam (1.56 g, 71%) were obtained (Rf ) 0.55, 30% ethyl
607 (w), 561 (w) cm-1
.
Synthesis of 2. The reaction was carried out using 1.00 g of 1,8-
bis(methylamino)naphthalene and an equimolar amount of ninhydrin.
The pure compound was isolated in 64% yield after column chroma-
tography (Rf ) 0.51, 40% ethyl acetate in hexane). Recrystallization
from 95% ethanol gave red-brown needles, mp 293 °C. 1H NMR
(CDCl3, 360 MHz): δ 8.06-7.97 (m, 4 H), 7.35 (dd, J ) 8, 7 Hz, 2
H), 7.31 (dd, J ) 8, 1 Hz, 2 H), 6.64 (dd, J ) 7, 1 Hz, 2 H), 2.80 (s,
6 H). 13C NMR (CDCl3, 50 MHz): δ 199.4, 140.9, 140.3, 137.2, 133.3,
126.7, 123.3, 119.2, 113.2, 105.1, 76.9, 34.5. EI-MS: m/z 328 (M+,
36), 299 (M+ - NCH3, 5), 271 (M+ - NCH3 - CO, 100). CI-MS:
1
acetate in hexane; Rf ) 0.36, 60% methylene chloride in hexane). H
m/z 329 (M+ + 1, 84), 328 (M+, 100), 300 (M+ - CO, 5), 271 (M+
-
NMR (CDCl3, 300 MHz): δ 8.07 (dd, J ) 8, 1 Hz, 1 H), 7.97 (dd, J
) 7, 1 Hz, 1 H), 7.75 (dd, J ) 8, 7 Hz, 1 H), 7.55 (t, J ) 8 Hz, 1 H),
7.46 (dd, J ) 8, 1 Hz, 1 H), 6.72 (dd, J ) 7, 1 Hz, 1 H), 3.38 (s, 3 H).
EI-MS: m/z 219 (M+, 10), 155 (M+ - SO2, 5), 126 (M+ - NMe -
SO2, 3), 64 (SO2+, 17).
NCH3 - CO, 29). FTIR (KBr): 2880 (w), 2810 (w), 1745 (m), 1702
(s), 1582 (s), 1478 (m), 1422 (m), 1390 (w), 1335 (w), 1264 (m), 1220
(w), 1172 (w), 986 (w), 804 (m), 752 (m), 715 (w), 640 (w) cm-1
.
Synthesis of 3. The reaction was carried out using 1.00 g of N,N′-
dimethyl-2,2′-diaminobiphenyl and an equimolar amount of ninhydrin.
After column chromatography, the product was isolated in a 76% yield
(Rf ) 0.50, 40% ethyl acetate in hexane). Orange-yellow leaflets were
obtained upon recrystallization from 95% ethanol, mp 202 °C. 1H NMR
(CDCl3, 300 MHz): δ 8.05-7.95 (m, 4 H), 7.42-7.35 (m, 4 H), 7.30-
7.25 (m, 2 H), 7.14 (dd, J ) 8 Hz, 1 Hz, 2 H), 2.56 (s, 6000 H). 13C
NMR (CDCl3, 90 MHz): δ 200.8, 145.3, 139.2, 137.0, 136.3, 128.2,
128.0, 124.8, 122.8, 121.3, 90.7, 36.7. EI-MS: m/z 354 (M+, 100),
339 (M+ - CH3, 5), 325 (M+ - NCH3, 13), 297 (M+ - NCH3 - CO,
27). FTIR (KBr): 2980 (w), 2860 (w), 1743 (m), 1709 (s), 1590 (w),
1554 (w), 1500 (w), 1442 (m), 1315 (w), 1254 (m), 1190 (w), 1110
8-(Methylamino)-1-naphthalenethiol was prepared by the LiAlH4
reduction of the sultam from the previous step. A solid addition funnel
was used to deliver the sultam (0.15 g, 0.68 mmol) slowly, over a 10
min period, to a stirred solution of LiAlH4 (0.026 g, 6.8 mmol) in 20
mL of dry ether under an argon atmosphere. The resulting solution
was refluxed overnight and then cooled to room temperature. Ethyl
acetate (ca. 10 mL) was added dropwise, with vigorous stirring, to the
reaction mixture till no more gas was evolved. A solution of 3 M
sulfuric acid (10 mL) was added slowly to the reaction mixture, and
after stirring for 15 min, the ether layer was removed. The aqueous
layer was extracted with benzene (3 × 20 mL) while it was still under
the argon atmosphere. The combined organic extracts were used
immediately for the next reaction due to the ease with which the product
is oxidized upon exposure to air. An aliquot of the benzene layer was
evaporated under reduced pressure to give the product (Rf ) 0.36, 30%
ethyl acetate in hexane) as a light yellow oil. 1H NMR (CDCl3, 200
MHz): δ 7.63 (dd, J ) 8, 1 Hz, 1 H), 7.34 (m, 2 H), 7.18 (m, 2 H),
6.63 (dd, J ) 8, 1 Hz, 1 H), 5.74 (s, 1 H, D2O exchangeable), 3.41 (s,
1 H, D2O exchangeable), 2.91 (s, 3 H). EI-MS: m/z 189 (M+, 15),
188 (M+ - H, 10), 187 (M+ - 2H, 54), 174 (M+ - CH3, 15), 173
(M+ - H - CH3, 17), 172 (M+ - 2H - CH3, 100).
(w), 931 (m), 760 (m), 694 (w), 626 (w) cm-1
.
Synthesis of 4. The reaction was carried out using 0.21 g of
2-(methylamino)benzenethiol and an equimolar amount of ninhydrin.
The pure compound was isolated in 65% yield after column chroma-
tography (Rf ) 0.35, 20% ethyl acetate in hexane). Recrystallization
from 20% ethyl acetate in hexane gave red-brown needles, mp 206
°C. 1H NMR (CDCl3, 300 MHz): δ 8.09 (m, 2 H), 7.96 (m, 2 H),
7.10 (dt, J ) 8, 1 Hz, 1 H), 6.95 (dd, J ) 8, 1 Hz, 1 H), 6.73 (dt, J )
8, 1 Hz, 1 H), 6.45 (d, J ) 8 Hz, 1 H), 2.78 (s, 3 H). 13C NMR (CDCl3,
90 MHz): δ 192.4, 147.5, 140.1, 136.9, 127.0, 124.6, 121.9, 121.1,
119.5, 107.4, 78.9, 31.7. EI-MS: m/z 281 (M+, 57), 252 (M+ - NCH3,
7), 224 (M+ - NCH3 - CO, 100). FTIR (CHCl3): 3072 (w), 3016
(m), 1758 (m), 1720 (s), 1600 (m), 1476 (m), 1349 (w), 1266 (w),
1237 (m), 1200 (w), 1161 (w), 1127 (w), 1025 (w), 949 (m), 782 (w),
General Procedure for Preparation of Spiro Compounds.
A
donor compound was condensed with an equimolar amount of an
acceptor compound using benzene (spectrophotometric grade, dried over
4 Å sieves for at least 1 day before use) as solvent and p-toluenesulfonic
acid as catalyst. The reaction vessel was equipped with a Dean-Stark
trap for azeotropic removal of water as it is formed during the reaction.
Typically, the donor compound was added to a solution of the acceptor
compound and catalyst (ca. 5-10 mg) under an argon atmosphere.
The scale of this reaction varied from as little as 10 mg to as much as
1 g each of donor and acceptor compounds. The solution was brought
to reflux and the reaction followed by TLC using an appropriate amount
of ethyl acetate in hexane as the eluant. The reaction was usually
complete (marked by disappearance of starting materials on TLC) after
2-5 h of refluxing. The solvent was removed under reduced pressure,
and the products38 were isolated as highly colored solids using flash
column chromatography on silica gel with an appropriate amount of
ethyl acetate in hexane as the eluant.
761 (m), 737 (m), 674 (s), 627 (w) cm-1
.
Synthesis of 5. The reaction was carried out using 0.47 g of
8-(methylamino)-1-naphthalenethiol and an equimolar amount of nin-
hydrin. The pure compound (Rf ) 0.72, 40% ethyl acetate in hexane)
was isolated in 53% yield after column chromatography, using 20%
ethyl acetate in hexane as the eluant. Upon recrystallization from 20%
ethyl acetate in hexane, orange needles were obtained, mp 204 °C. 1H
NMR (CDCl3, 300 MHz): δ 8.01-7.98 (m, 2 H), 7.92-7.89 (m, 2
H), 7.72 (dd, J ) 8, 1 Hz, 1 H), 7.51 (t, J ) 8 Hz, 1 H), 7.44 (dd, J
) 8, 1 Hz, 1 H), 7.35 (t, J ) 7 Hz, 1 H), 7.19 (dd, J ) 7, 1 Hz, 1 H),
7.01 (dd, J ) 8, 1 Hz, 1 H), 3.09 (s, 3 H). 13C NMR (CDCl3, 50
MHz): δ 192.4, 142.5, 138.7, 136.6, 133.9, 127.9, 127.1, 125.2, 124.4,
123.8, 123.5, 120.6, 120.3, 110.6, 68.1, 37.1. EI-MS: m/z 331 (M+,
100), 316 (M+ - CH3, 6), 302 (M+ - NCH3, 6), 274 (M+ - NCH3 -
CO, 92), 271 (M+ - CO - S, 7), 256 (M+ - CO - S - CH3, 3).
FTIR (CHCl3): 3071 (w), 3026 (w), 1745 (w), 1713 (s), 1600 (w),
1568 (m), 1481 (w), 1458 (w), 1384 (w), 1349 (w), 1326 (w), 1261
(s), 1237 (w), 1190 (s), 1068 (w), 1021 (w), 972 (w), 820 (w), 809
(38) In some instances, in addition to condensation on C2 of the ninhydrin
moiety, products of condensation on C1 were formed. The details on these
spiro dyes will be published separately.
(39) Willets, A.; Rice, J. E.; Burland, D. M.; Shelton, D. P. J. Chem.
Phys. 1992, 97, 7590.
(m), 786 (s), 756 (w), 730 (m), 676 (m), 662 (w), 629 (w) cm-1
.

Optical Properties of Charge-Transfer Dyes
J. Am. Chem. Soc., Vol. 118, No. 6, 1996 1481
Synthesis of 6. The reaction was carried out using 0.36 g of 1,8-
bis(methylamino)naphthalene and an equimolar amount of 5,6-
dimethoxyninhydrin. The pure compound (Rf ) 0.60, 50% ethyl acetate
in hexane) was isolated after column chromatography, using 40% ethyl
acetate in hexane as the eluant, in 55% yield. Upon recrystallization
from acetone, orange needles were obtained, mp 284 °C. 1H NMR
(CDCl3, 300 MHz): δ 7.37 (s, 2 H), 7.35-7.27 (m, 4 H), 6.60 (dd, J
) 7, 1 Hz, 2 H), 4.04 (s, 6 H), 2.80 (s, 6 H). 13C NMR (CDCl3, 50
MHz): δ 198.2, 157.1, 141.1, 135.9, 133.4, 126.7, 118.8, 113.2, 104.6,
103.1, 77.2, 56.9, 34.2. EI-MS: m/z 388 (M+, 72), 373 (M+ - CH3,
3), 360 (M+ - CO, 2), 359 (M+ - NCH3, 4), 331 (M+ - NCH3 -
CO, 100), 316 (M+ - NCH3 - CO - CH3, 9), 301 (M+ - NCH3 -
CO - 2CH3, 10). FTIR (CHCl3): 3073 (w), 3002 (w), 2826 (w), 1739
(s), 1701 (s), 1627 (w), 1579 (s), 1504 (s), 1462 (m), 1418 (m), 1308
(s), 1148 (w), 1113 (s), 1000 (m), 919 (w), 876 (w), 834 (w), 793 (s),
Acknowledgment is made to the donors of the Petroleum
Research Fund, administered by the American Chemical Society,
for support of this research.
Supporting Information Available: Tables giving X-ray
determined atomic coordinates, bond lengths, bond angles, and
anisotropic displacement coefficients for 2, 4, 5, and 6 (24
pages). This material is contained in many libraries on
microfiche, immediately follows this article in the microfilm
version of the journal, can be ordered from ACS, and can be
downloaded from the Internet; see any current masthead page
for ordering information and Internet access instructions.
784 (s), 738 (m), 650 (w) cm-1
.
JA9533003