Spectrokinetic studies on new bi-photochromic molecules containing two naphthopyran entities

Article abstract of DOI:10.1016/j.tet.2005.09.035

A range of new bi-photochromic molecules containing two identical (3a-d) or two distinct naphthopyran units (6a-d), linked through the phenyl substituents located on the sp³ hybridised pyran ring carbon atom, using conjugated and non-conjugated

Full text of DOI:10.1016/j.tet.2005.09.035

Tetrahedron 61 (2005) 11730–11743
Spectrokinetic studies on new bi-photochromic molecules
containing two naphthopyran entities
a
b
a
Paulo J. Coelho,a, Maria A. Salvador, B. Mark Heron and Luis M. Carvalho
*
a
´
´
Centro de Quımica-Vila Real, Universidade de Tras-os-Montes e Alto Douro, 5001-911 Vila Real, Portugal
bDepartment of Colour Chemistry, The University of Leeds, Leeds LS2 9JT, UK
Received 13 July 2005; revised 8 September 2005; accepted 12 September 2005
Available online 10 October 2005
Abstract—A range of new bi-photochromic molecules containing two identical (3a–d) or two distinct naphthopyran units (6a–d), linked
through the phenyl substituents located on the sp3 hybridised pyran ring carbon atom, using conjugated and non-conjugated spacers, have
been synthesised from bis-propynols and (substituted)naphthols. Study of the spectrokinetic properties of these compounds under near
UV–vis continuous irradiation conditions revealed that the two naphthopyran units are stimulated independently leading to open forms with
higher colourabilities but without affecting the individual bleaching kinetics. Compared to the individual photochromic components and to
model mono-photochromes it was observed that the nature of the bridge has a small effect on the photochromic properties of each system.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
of coloured stereoisomers, with similar absorption charac-
teristics but with diverse thermal stabilities.2 Under
continuous near-UV irradiation a photostationary equi-
librium is attained between the uncoloured ‘closed form’
(CF) and the OF leading to a colour change of the system.
When the light source is removed the equilibrium shifts and
the system returns to the original colourless state, either via
a thermal or a photoinduced process, with light of different
wavelength from the first, unveiling the reversible colour
behaviour that is characteristic of this photochromic system.
UV and NMR studies revealed that at room temperature the
main photoproducts are the TC and TT isomers (Scheme 1),
the latter being the most thermally stable.3
The photochromic properties of naphthopyrans have been
extensively studied in the last decade due to the wide range
of applications with prominence in the manufacture of
ophthalmic plastic lenses and solar protection glasses.1
Under near-UV light irradiation these uncoloured or faintly
coloured molecules, either in solution or incorporated in
polymeric matrices, undergo an electrocyclic pyran-ring
opening with cleavage of the C(sp3)–O bond and a
subsequent structural reorganisation allowing the photo-
generated species to adopt more planar structures (the so-
called ‘open form’, OF) with greater conjugation, which is
responsible for the increased absorption in the visible part
of the spectrum (Scheme 1). The OF is constituted by a set
A great number of substitutions and/or annelations have
been studied in the naphthopyran family in order to increase
the ability to produce intense coloured forms (colourability),
to tailor chromatic properties or to change fading rates of
these systems.4–6 Consequently, there has been a significant
increase in patenting of new molecules and systems,
although many exaggerated claims were made about their
performances. Nevertheless, significant improvements were
attained and many commercially interesting photochromic
systems were discovered. An important advancement is
related to the colour range achievable with naphthopyrans
that, initially, was limited to orange/yellow colours and
nowadays is extended to virtually any colour.
Scheme 1.
Keywords: Naphthopyrans; Photochromism; bi-Photochromic; bi-
Naphthopyrans.
This feature is particularly important for photochromic lens
manufacturers because the optical lens market is dominated
by neutral colours (browns and greys). In principle, neutral
*
Corresponding author. Tel.:C351 259 350284; fax: C351 259 350480;
e-mail: pcoelho@utad.pt
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.09.035

P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
11731
Scheme 2.
colours can be produced by mixing two or more
photochromic dyes that allow a constant coverage of an
extended range of the visible spectrum (usually 420–620 nm
is acceptable). This approach meets the goal, although it
opens a set of serious problems, beyond the position of the
absorption maxima and the shape of the absorption bands in
the visible and UV (activating) spectral range. To prevent
photochromic lenses from displaying different colours
under varying exposure conditions the photochromic dyes
should have similar (within some tolerance limits)
photochromic properties. These include the colouring and
fading kinetics, temperature dependence, solvatochromic
effects and fatigue resistance. The mixture of the lesser
possible number of photochromes belonging to the same
family seems to be recommended. Several interesting
formulations were developed and can be found in the patent
literature.7
naphthopyran units, linked through their naphthalene
units, revealed that although the kind of molecular spacer
nature is critical and fading rates are sometimes affected, the
simultaneous activation of both photochromic systems is
possible. Alkyl (ethane), ester (Scheme 2), or acetylenic
bridges did not substantially change the photochromic
behaviour exhibited by the components taken individually
and an additive effect was observed.15–16
On the other hand, ethylenic spacers lead to supermolecules,
which exhibit a complex and contradictory behaviour
(Scheme 3).2,17–21 Some compounds with (Z)-ethylenic
bonds exhibited thermally irreversible photochromic
properties, and upon UV irradiation thermally stable
coloured forms that persist from days to several weeks in
the dark were formed, while others exhibited a thermally
reversible behaviour, which can be considered as the super-
position of the properties of the individual systems taken
separately. With some bi-naphthopyrans it was observed
that only one pyran unit was opened under UV irradiation,
indicating a possible de-activation of one photochrome due
to the presence of the other in the same framework.
A second and highly desired approach to obtain neutral-
colouring articles, because all the matching problems are
overcome and the formulation processes would obviously
be simpler, involves the use of a single photochromic dye
with the desired absorption properties: at least two
absorption bands conveniently spaced (Dlw100–130 nm)
in the visible spectrum, of approximately equal intensity.
Such molecules can be, in principle, obtained through
appropriate substitution/annelation of the naphthopyran
moieties, but in the literature few examples are
described.8–10
Another approach involves the linkage of the two
naphthopyrans thought one of the geminal aryl aromatic
substituents. Recently, some interesting results have been
obtained on bi-photochromic supermolecules with two
naphthopyrans sharing a bi-thiophene unit linked through
the two pyran ring sp3 C atoms (Scheme 3). These
molecules showed a very significant bathochromic shift of
the maximum wavelength of absorption of the OF and high
colourabilities due to the extension of p-conjugation and the
opening of both photochromic systems.22–23
Recently, molecular structures involving the coupling of
conveniently selected photochromes (e.g., naphthopyran–
diarylethene,11 naphthacene–diarylethene,12–13 diaryl-
ethene–dihydroazulene,14 naphthopyran–naphthopyran,15–18
spirooxazine–spirooxazine,17,19–20 naphthopyran–spiro-
oxazine15,17,21) through a covalent linkage have received
some attention.
In the present paper, we report our results on the study of
new bi-photochromic molecules obtained through the
linkage of the naphthopyran sp3 phenyl substituents, using
conjugated and non-conjugated spacers, including a shared
aromatic ring (Scheme 4).
Studies on bi-photochromic supermolecules including
Scheme 3.

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P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
Scheme 4.
2. Results and discussion
four steps starting from aromatic diketones 1a–c, which
were commercially available (1b) or readily prepared by
Friedel-Crafts benzoylation of diphenyl ether or dibenzyl
(Scheme 5).24 Treatment of diketones 1a–c with lithium
trimethylsilylacetylide in THF followed by basic hydrolysis
2.1. Synthesis
The bi-photochromic compounds 6a–d were prepared in
Scheme 5.

P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
11733
Scheme 6.
(KOH/MeOH) gave almost pure propargylic diols 2a–c in
excellent yields (91–97%).
40 W mK2, quartz cells, 1 cm light path, 3.5 ml of solution).
Three spectrokinetic parameters, normally quoted when
describing the properties of photochromic compounds, were
evaluated: maximum wavelength of absorption of the open
form (lmax), thermal bleaching rates (kD) and colourability
(Aeq), estimated by the absorbance of the solution after
reaching a photostationary equilibrium under the exper-
imental conditions. The bleaching kinetics were studied in
the dark, under thermal conditions. The data are summarised
in Tables 1–4 where three reference compounds were
included for comparison: Ref1 (Z3,3-diphenyl-3H-
naphtho[2,1-b]pyran), Ref2 (Z3,3-diphenyl-13-methyl-
13-hydroxy-3H-indeno[2,1-f]naphtho[1,2-b]pyran) and
Ref3 (Z2,2-diphenyl-2H-naphtho[1,2-b]pyran).
Heating these diols with 0.8 equiv of 2-naphthol in 1,2-di-
chloroethane in the presence of an acid catalyst (pyridinium
p-toluenesulphonate) and 2 equiv of trimethyl orthoformate,
added as a dehydrating agent,25 gave a mixture of
symmetrical bi-naphthopyrans 3a–c (minor) and mono
naphthopyrans 4a–c (major), with one reactive propargylic
alcohol function still present, which were easily separated
by column chromatography. Both compounds exhibit
photochromic properties in solution at room temperature.
Treating the mono naphthopyrans 4a–c with 1.1 equiv of
5-hydroxy-7H-benzo[c]fluoren-7-one, under the same
reaction conditions, gave the naphthopyrans 5a–c. These
compounds are highly coloured and possess two different
covalently linked naphthopyrans entities, however, they
show very weak photochromic properties due to the
presence of the carbonyl function in the indene ring.4
Treatment of these compounds with a CH3MgI solution
gave, after hydrolysis, the new photochromic bi-naphtho-
pyrans 6a–c in good yield (70–79%).
2.2.1. Compounds 4a–d. Compounds 4a–c are 3,3-
diphenylnaphtho[2,1-b]pyran derivatives substituted at the
para position of one of the 3-phenyl groups by an aryl
substituted alkyl chain, 4b–c, or a conjugative electron
donating group (OAr), 4a. The observed photochromic
behaviours are characteristic of coloured forms of this
family of compounds and, thus, similar to Ref1 (Table 1,
Fig. 1): under continuous irradiation conditions, compounds
4a–c exhibit a single wide absorption band centered
between 434–446 nm and weak colourabilities (0.2–0.3).
After the removal of the UV irradiation source these
compounds exhibit a bi-exponential colour decay with two
very different fading rates: one fast (0.07–0.09 sK1) and
another very slow (2!10K5–6!10K5 sK1). As already
referred these rate constants can be attributed, respectively,
to the TC and TT open form isomers.3 Considering similar
molar absorptivities for these isomers,2 from the amplitudes
The same methodology was used to prepare the bi-naph-
thopyran 6d from diol 2b except that 1-naphthol was used
instead of 2-naphthol (Scheme 6).
2.2. Photochromic properties
The photochromic behaviour of compounds 3–6 was studied
in 10K4 M toluene solutions at 20 8C under continuous near
UV–vis irradiation (150 W ozone free Xe lamp, light flux of

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P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
Table 1. Spectrokinetic properties under continuous irradiation: maxima wavelengths of the coloured form (lmax), colourability (Aeq), thermal bleaching rate
(kD) of compounds 3a–c, 4a–c, 5a–c and Ref1 in toluene solutions
Compounds
lmax (nm)
Aeq
Residual coloura
kD (sK1
)
6!10K2 (73)
7!10K6 (27)
Ref1
432
0.27
0.06
9!10K2 (74)
1!10K5 (26)
4a
4b
4c
LZPhOPh
LZPh
446
434
438
0.19
0.25
0.25
0.03
0.06
0.05
7!10K2 (72)
2!10K5 (28)
7!10K2 (73)
6!10K5 (27)
LZPhCH2CH2Ph
9!10K2 (72)
3!10K5 (28)
3a
3b
3c
LZPhOPh
LZPh
446
433
438
0.30
0.33
0.42
0.06
0.08
0.09
6!10K2 (72)
4!10K5 (28)
8!10K2 (78)
4!10K5 (22)
LZPhCH2CH2Ph
6!10K2 (74)
8!10K4 (14)
2!10K4 (12)
5a
5b
5c
LZPhOPh
LZPh
438b
430b
436b
0.14
0.21
0.17
0.02
0.05
0.03
5!10K2 (55)
2!10K2 (16)
8!10K6 (29)
8!10K2 (66)
2!10K2 (14)
4!10K5 (20)
LZPhCH2CH2Ph
a Absorbance after 2000 s in the dark.
b Shoulder. These measurements were not made at the lmax because these solutions of compounds were already orange/red coloured before irradiation.
of the fading kinetics it can be deduced that the coloured OF
is a mixture constituted mainly by the short lived TC isomer
(72–73%), responsible for the initial fast colour decay, and
by the more stable TT isomer (26–27%), which is
responsible for the persistence of colour for a long time
(Fig. 1). As expected, due to the presence of the
p-substituent at the 3-phenyl group, the open forms are
slightly less thermally stable than Ref1 and the observed
lower colourabilities can be related to the faster ring closure
kinetics, as these two parameters are inversely related.26
Considering Ref1, compound 4a exhibit the more pro-
nounced bathochromic shift to the lmax (C14 nm), although
smaller that the one observed when the p-substituent is a
methoxy group (C36 nm), reflecting the weaker electron
donating character of the OAr group.27
Similar results were obtained for compound 4d. This
compound is a 2,2-diphenylnaphtho[1,2-b]pyran substituted
at the para position of a 2-phenyl group and, as expected, its
photochromic properties are very similar to Ref3 (Table 2).
It exhibits a maximum wavelength of absorption, lmax, at
471 nm and two slow fading rates (7!10K4 and2!10K6 sK1
)
that are responsible for a very slow colour decay and
therefore a high colourability (AeqZ1.1) (Fig. 2). The
maximum absorbance obtained under UV exposition (AeqZ
1.0) was, however, considerably lower than the one obtained
with Ref3 (AeqZ1.5).
2.2.2. Compounds 3a–d. Compounds 3a–c are bi-photo-
chromic supermolecules with two naphtho[2,1-b]pyrans
linked through conjugated (Ph) or non-conjugated chains
Figure 1. Colour forming and colour bleaching at lmax of Ref1, 3c and 4c.

P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
11735
Table 2. Spectrokinetic properties under continuous irradiation: maxima wavelengths of the coloured form (lmax), colourability (Aeq), thermal bleaching rate
(kD) of compounds 3d, 4d, 5d, and Ref3 in toluene solutions
Compounds
lmax (nm)
Aeq
Residual coloura
kD (sK1
)
6!10K4 (76)
1!10K6 (24)
Ref3
470
1.5
0.36
7!10K4 (75)
2!10K6 (25)
4d
471
1.1
0.26
5!10K4 (65)
7!10K7 (35)
3d
480
2.7
0.94
6!10K4 (75)
2!10K6 (25)
5db
479
1.0
0.25
a After 10000 s in the dark.
b Solutions of this compound were already orange/red coloured before irradiation.
(PhOPh, PhCH2CH2Ph). Since the two sp3 aryl substituents
are not equivalent many different coloured photoisomers
can be expected to form. Relative to the lmax and fading
kinetics, it was observed a behaviour very similar to that
recorded for the mono-photochromic molecules 4a–c
(Table 1, Figs. 1 and 3).
not linearly related to concentration (Fig. 4) one can infer
that probably both pyran units were opened under exposure
to UV. The increase of the residual absorbance at the end of
the experiments corroborates this inference. Regarding the
absorption wavelength of coloured forms of the model
compounds 4a–c we can conclude that no additional
extension of conjugation was achieved in the open forms
of the bi-photochromic molecules, even considering 3b
where a phenyl group is shared by the two parts. This may
indicate that, upon UV irradiation, both photochromic
moieties are opened and the molecule adopts a confor-
mation where each ‘planar’ open form is completely out of
However, the maximum absorbances attained at the
photostationary state (colourability) are significantly higher
(Fig. 1) and as under our experimental conditions the
colourability of 3,3-diphenyl-naphtho[2,1-b]pyran, Ref1, is
Figure 2. Colour bleaching at lmax of Ref3, 3d and 4d.
Figure 3. Normalized colour bleachings of Ref1, 3c, 4c and 5c.

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P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
Table 3. Spectrokinetic properties under continuous irradiation: maxima wavelengths of the coloured form (lmax), colourability (Aeq) thermal bleaching rate
(kD) of compounds 6a–c, Ref1, Ref2 and a equimolar mixture of Ref1 and Ref2
Compounds
lmax (nm)
Aeq
Residual coloura kD (sK1
)
6!10K2 (73)
7!10K6 (27)
Ref1
Ref2
432
0.27
0.06
0.21
533
419
1.3
0.71
3!10K3 (82)
5!10K6 (18)
7!10K2 (4)
5!10K3 (83)
1!10K5 (13)
425
536
0.85
1.4
0.10
0.19
6a
6b
6c
LZPhOPh
5!10K3 (86)
1!10K5 (14)
4!10K2 (6)
3!10K3 (78)
2!10K5 (16)
423
0.76
0.12
LZPh
3!10K3 (82)
8!10K6 (18)
533
1.3
0.22
0.07
3!10K3 (87)
4!10K5 (13)
600b
0.62
6!10K2 (6)
4!10K3 (78)
2!10K5 (16)
423
533
0.84
1.3
0.13
0.20
LZPhCH2CH2Ph
4!10K3 (83)
2!10K5 (17)
6!10K2 (11)
3!10K3 (70)
2!10K6 (19)
420
528
0.85
1.2
0.15
0.22
Ref1CRef2
5!10K2 (2)
3!10K3 (80)
5!10K6 (18)
a Absorbance after 2000 s in the dark.
b Wavelengths that do not correspond to lmax
.
plane of the other. The nature of the assayed bridges linking
the two photochromic parts seems to have a negligible
influence in the photochromic behaviour of these
compounds.
phenyl (conjugative) bridge allows some extension of
conjugation in the open form of this compound. The
analysis of the bleaching kinetics revealed a bi-exponential
behaviour, with close values for kinetic constants although
with slightly different amplitudes (Table 2, Fig. 2). Relative
to Ref3 and 4d, for compound 3d the amplitude of the
slower fading rate increased from 24 to 35% that points to
an increase in the concentration of the TT species at the
photostationary equilibrium. The colourability attained by
this compound is nearly twice the one achieved by Ref3
(AeqZ1.5) and the residual colour (0.94) is much higher
than those observed for Ref3 (0.36) and 4c (0.26) (Fig. 2).
This additive behaviour unambiguously suggests the
Compound 3d has two naphtho[1,2-b]pyran units linked by
a common phenyl group. Exposure of this compound to UV
light produced a band with a lmax initially at 470 nm that
gradually shifts to 480 nm until the photostationary state is
attained (an inverse behaviour was observed during the
bleaching). Compared to Ref3 and the model compound 4d,
it can be observed a bathochromic shift (C10 nm) of the
maximum wavelength of absorption that suggests that a

P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
11737
Table 4. Spectrokinetic properties under continuous irradiation: maxima wavelengths of the coloured form (lmax), colourability (Aeq) thermal bleaching rate
(kD) of compounds 6d, Ref2, Ref3 and a equimolar mixture of Ref2 and Ref3
Compounds
lmax (nm)
Aeq
Residual coloura
kD (sK1
)
533
419
1.3
0.71
3!10K3 (82)
5!10K6 (18)
0.21
Ref2
Ref3
6!10K4 (76)
1!10K6 (24)
470
1.5
0.36
0.47
3!10K3 (23)
6!10K4 (49)
4!10K6 (28)
472a
530
1.7
3!10K3 (48)
6!10K4 (31)
7!10K6 (21)
6d
2.0
0.39
0.06
3!10K3 (78)
6!10K4 (14)
1!10K5 (8)
620a
0.91
4!10K3 (27)
6!10K4 (50)
1!10K6 (23)
470a
494
2.1
2.2
2.1
0.48
0.47
0.50
4!10K3 (35)
6!10K4 (44)
2!10K6 (21)
Ref2CRef3
4!10K3 (27)
6!10K4 (50)
1!10K6 (23)
530a
a Wavelengths that do not correspond to lmax
.
independent opening of the two pyran rings in this molecule
and the displacement of the lmax with the irradiation time
points to a consecutive opening of the pyran rings.
and concentration over a more extended concentration range
(until 2!10K4 M) than for Ref1 (Fig. 4). Obviously, at
these concentrations, deviations from direct proportionality
are strongly dependent upon discolouration kinetics values.
No measurements could be performed at higher concen-
trations due to instrumental limitations related to the very
high absorbances attained (O4 absorbance units).
Considering Ref3 a study of the effect of the concentration
on the observed colourability, under our experimental
conditions, displayed a linear relationship between Aeq
2.2.3. Compounds 5a–d. Compounds 5a–d have a
naphtho[1,2-b]pyran or a naphtho[2,1-b]pyran linked to a
non-photochromic 13-oxoindeno[2,1-f]naphtho[1,2-b]-
pyran.4 Before UV irradiation they all show a small
absorption band with a maximum between 489–503 nm
(Abs: 0.20–0.23; 3Z2000–2300 molK1 L cmK1), which is
responsible for their orange/red colourations. Upon
irradiation of compounds 5a–c with UV light a new band
appears as a shoulder between 430–438 nm that can be
assigned to the opening of the naphtho[2,1-b]pyran ring
(Table 1). From the position of these bands it is apparent
that no enhancement in the extension of conjugation is
achieved even with a conjugative bridge. The observed Aeq
for these compounds (0.14–0.21) are lower than the
colourabilities observed for the mono-photochromic 4a–c
(0.19–0.25) and for Ref1 (0.27) (Fig. 3), although there is
no apparent increase in the bleaching kinetics. The
analysis of the fading kinetics of 5a–c shows a good fit to
Figure 4. Colourability versus concentration for Ref1 and Ref3.

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P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
a tri-exponential model indicating that upon UV irradiation
a more complex mixture is obtained.
Ref2. In what it concerns the visible spectra of the open
forms of bi-photochromic compounds 6a–c only subtle
differences are observed even when compared with a
solution of the same concentration of an equimolar mixture
of Ref1 and Ref2 (see Fig. 5).
Compound 5d, also already orange/red (lmaxZ489 nm)
coloured before UV-irradiation, associates a 2,2-diphenyl-
naphtho[1,2-b]pyran and the non-photochromic 2,2-diphenyl-
13-oxoindeno[2,1-f]naphtho[1,2-b]pyran through a para
substituted phenyl group. Upon irradiation with UV light
this compound develops a stronger and wider band with a
lmax at 479 nm indicating the opening of the non-fused
naphtho[1,2-b]pyran ring (Table 2). This bathochromic
shift, relative to Ref3 and the model compound 4d, points to
an increase of the p-conjugation. The usual dual kinetic of
thermal bleaching of naphthopyrans, indicating the presence
of TT and TC isomers, was observed. The similarity of the
kinetic constants and amplitudes with the mono-photo-
chromic model compound 4d and Ref3 indicates that the
presence of the non-photochromic moiety has a negligible
effect on the thermal stability of 5d.
However, colourabilities obtained at the lower lmax (where
the maximum contribution of the Ref1 residue is expected)
are higher than for Ref2 alone and kinetic curves constants
and amplitudes at this lmax, show a good fit to a tri-
exponential model with values in a range that may indicate
that both pyran units are opened. The faster kinetic constant
(4!10K2–7!10K2 sK1), representing 4–6% of the absorb-
ance decay can be attributed to the TC isomer resulting from
the opening of the naphtho[2,1-b]pyran (Ref1) while the
second slower kinetic constant (3!10K3–5!10K3 sK1
)
representing 78–83% is probably due to the fading of the TC
isomer resulting from the opening of the indeno[2,1-f]-
naphtho[1,2-b]pyran moiety.
2.2.4. Compounds 6a–d. Compounds 6a–c have two
different photochromic units, a naphtho[2,1-b]pyran and a
13-methyl-13-hydroxy-indeno[2,1-f]naphtho[1,2-b]pyran,
linked through PhOPh, Ph, and PhCH2CH2Ph bridges,
respectively. Taken independently, upon irradiation with
UV light, one residue (Ref1), generates an open form with a
lmax centered at 432 nm (AeqZ0.27) while the other (Ref2)
generates an open form with two absorption maxima in the
visible region: one at 530 nm (AeqZ1.3) and the other near
419 nm (AeqZ0.72) (Fig. 5). Moreover, the two photo-
chromic units exhibit biexponential bleaching kinetics,
although with quite different values in the initial fading
rate: Ref1 (6!10K2 sK1, 73%) fades initially about 20
times faster than Ref2 (3!10K3 sK1, 82%).
Although the diphenyl ether bridge of series a (LZPh–O–
Ph) induced an expected small bathochromic shift in the
visible spectra and some thermal instability of the open
forms, it is apparent that the nature of the covalent bridge
has no significant effect on the photochromic performances
of the bi-naphthopyrans 6a–c.
Compound 6d is a bi-photochromic molecule associating
two different naphthopyrans (Ref2 and Ref3) with similar
absorbances at the lmax of the open forms (Table 4), linked
through a shared p-phenyl substituted ring. Taken inde-
pendently the two photochromes exhibit quite different
fading kinetics although with similar amplitudes: the first
fading rate of Ref2 (3!10K3 sK1, 82%), is about five times
faster than the first fading rate of Ref3 (6!10K4 sK1, 76%).
When solutions of each compound were submitted to UV
irradiation, under identical experimental conditions, similar
absorbance values were attained at the photostationary state:
Ref3: AeqZ1.5 (470 nm); Ref2: AeqZ1.3 (533 nm).
Compound 6d led to the formation of a single wide
absorption band with a maximum centred at 530 nm and
higher colourability (AeqZ2.0), suggesting the opening of
both photochromic entities (Fig. 6).
The covalent linkage of these two units yielded molecules
that exhibit thermally reversible photochromic properties.
As expected, due to the very different colourabilities of the
associated units, the photochromic properties of the indeno-
fused naphtho[1,2-b]pyran unit practically overlap those
observed for the other naphtho[2,1-b]pyran and conse-
quently, for the bi-photochromic compounds 6a–c, it is very
difficult to distinguish between their behaviour and those of
Figure 5. Absorption spectra of Ref1, Ref2, mixture Ref1CRef2 and 6a
after UV irradiation.
Figure 6. Absorption spectra of Ref2, Ref3, mixture Ref2CRef3 and 6d
after UV irradiation.

P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
11739
Figure 7. Time evolution of the absorption spectrum of the opened form of
compound 6d.
Figure 8. Colour bleaching of a mixture of Ref2CRef3 and 6d.
For this compound, fading kinetics were measured at
472 nm (major contribution of the naphtho[1,2-b]pyran
residue), 530 nm (major contribution of the indeno-fused
naphtho[1,2-b]pyran residue) and 620 nm (sole absorption
contribution from the indeno-fused naphtho[1,2-b]pyran
residue) and although the same values for the constants were
found (Table 4), amplitudes varied in an expected way:
the amplitude of the kinetic increased along with the
increase of the contribution of the naphthopyran residue that
is responsible for it.
p-PhCH2CH2Ph–. All compounds exhibited photochromic
behaviour in toluene solutions at room temperature.
Compared to the individual photochromic components and
to model monophotochromes it was observed that the nature
of the bridge has a small effect on the photochromic
properties of each system.
Under continuous near UV–vis irradiation the two
naphthopyran units of the bi-photochromic molecules
3a–d and 6a–d, were stimulated independently leading to
open forms with higher colourabilities but without affecting
the individual bleaching kinetics.
Spectral evolution of the UV–vis spectrum of compound 6d
was also recorded during the thermal bleaching of solutions
(Fig. 7). Clearly, it can be observed a gradual displacement
with time, of the lmax toward shorter wavelengths until lmax
of Ref3 (the slower photochromic entity) was attained.
Indeed, photochromic properties of 6d can be considered as
the superposition of the properties of the two naphthopyran
residues taken separately.
Considering the absorbance spectra of the open forms of the
bi-photochromic molecules no additional extension of the
p-conjugation was observed for 3,3-diphenylnaphtho-
[2,1-b]pyran derivatives while for 2,2-diphenylnaphtho-
[1,2-b]naphthopyran derivatives (3d and 6d) it was evident
a bathochromic shift of the lmax, suggesting that for these
last derivatives, under UV irradiation, structures with a
better global planarity are obtained.
A final comparison was made between compound 6d and an
equimolar mixture of Ref2 and Ref3 of the same
concentration (1!10K4 M). The absorption spectrum of
the open form of 6d shows a lmaxZ530 nm while the
mixture exhibits a lmaxZ494 nm. This difference in the
lmax (C36 nm) suggests that the phenyl spacer allows some
conjugation between the OF of the two photochromic
entities, although a completely planar structure is probably
not obtained.
4. Experimental
4.1. Spectrokinetic studies under continuous irradiation
For measurements of lmax, Aeq and kD under continuous
UV–vis irradiation, 1!10K4 M toluene solutions were
used. Irradiation experiments were made using a CARY 50
Varian spectrometer coupled to a 150 W Ozone free Xenon
lamp (6255 Oriel Instruments). The light from the UV–vis
lamp was filtered using a water filter (61945 Oriel
Instruments) and then carried to the spectrophotometer
holder at the right angle to the monitoring beam using a
fiber-optic system (77654 Oriel Instruments). A 40 W mK2
light flux, measured with a Goldilux Photometer with a
UV-A probe, was used. A thermostated (20 8C) 10 mm
quartz cell, containing the sample solution (3.5 ml),
equipped with magnetic stirring was used. In a preliminary
experiment, the visible absorption spectrum of the closed
form and the lmax of the open form were determined. In a
second experiment, the absorbance at photostationary
Comparison of the fading kinetics observed for compound
6d and an equimolar mixture of Ref2 and Ref3 (Fig. 8)
revealed that 6d constitutes a system that bleaches faster.
This suggests that the opened naphthopyran may act as an
electron donor substituent.
3. Conclusion
New bi-photochromic molecules, containing two identical
or two distinct diphenylnaphthopyran units, were obtained
by generally applicable methods. The strategy involved the
linkage of one of the geminal aryl aromatic substituents,
using covalent bridges, namely p-Ph–, p-PhOPh– and

11740
P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
equilibrium, Aeq, was measured at lmax and then the
decrease in the absorbance with the time was monitored.
The thermal bleaching rate constants, kD, were calculated
fitting the absorbance curve obtained in the dark, at 20 8C, to
a multi exponential model.
4.4. General procedure for the reaction of 2-naphthol
with diols 2a–c
A solution of diol 2a–c (4.0 mmol), 2-naphthol (0.504 g,
3.5 mmol), PPTS (10 mg), CH(OMe)3 (0.8 ml, 8 mmol) and
1,2-dichloroethane (50 ml) was refluxed for 2 h under
nitrogen. Solvent evaporation gave a brown oil, which
was purified by CC (3–15% ethyl acetate/hexane). Two
compounds were obtained: bi-naphthopyrans 3a–c (fraction
1 minor product) and naphthopyrans 4a–c (fraction 2, major
product). The following compounds were obtained using
this protocol.
4.2. General remarks
1H and 13C spectra were recorded for CDCl3 solutions on a
Bruker Avance 400 MHz instrument. IR spectra were
obtained on a Perkin-Elmer FTIR 1600 spectrometer using
KBr disks (wavenumbers in cmK1). Electronic impact mass
spectra were measured on a AutoSpecE spectrometer.
Melting points (8C) measured at a Bu¨chi 535 apparatus
are uncorrected. The melting points of photochromic
naphthopyrans 6a–d were not determined because thermo-
chromism was observed at high temperatures. Column
chromatography (CC) was performed on silica gel 60
(70–230 mesh). THF was pre-dried under sodium/benzo-
phenone and distilled before use. All new compounds were
4.4.1. From 2-naphthol and diol 2a: 4,40-bis[3-phenyl-
3H-naphtho[2,1-b]pyran-3-yl]diphenyl ether 3a. White
solid. Yield 16%. Mp 99–101. IR: 3056, 2923, 1590, 1496,
1240; 1H NMR: 7.94 (d, JZ8.4 Hz, 2H), 7.70 (d, JZ8.4 Hz,
2H), 7.64 (d, JZ8.8 Hz, 2H), 7.45 (m, 6H), 7.39 (m, 4H),
7.33–7.27 (m, 8H), 7.26–7.22 (m, 2H), 7.17 (d, JZ8.8 Hz,
2H), 6.90 (m, 4H), 6.22 (d, JZ10 Hz, 2H); 13C NMR:
156.3, 150.4, 144.8, 139.7, 129.8, 129.3, 128.9, 128.6,
128.5, 128.3, 128.1, 127.6, 126.9, 126.6, 125.9, 123.6,
121.3, 119.5, 118.3, 113.9, 82.2; MS: m/z (%): 682 (5), 608
(4), 570 (5), 460 (5), 391 (7), 307 (35), 154 (100), 137 (68). 4-
[3-Phenyl-3H-naphtho[2,1-b]pyran-3-yl]-40-(1-hydroxy-
1-phenyl-prop-2-yn-1-yl)diphenyl ether 4a. Yellow oil.
1
determined to be O95% pure by H NMR spectroscopy.
4.3. General procedure for the synthesis of diols 2a–c
n-Buthyllithium in hexanes (7.5 ml, 12 mmol) was added
slowly with a syringe to a cold (K10 8C) stirred solution of
trimethylsilylacetylene (1.7 ml, 12 mmol) in anhydrous
THF (50 ml). The cold solution was stirred 1 h and then a
solution of the diketone 1a–c (4 mmol) in anhydrous THF
was added and the mixture stirred at room temperature for
12 h. The reaction mixture was then cooled to 0 8C and a
solution of KOH (0.84 g) in MeOH (10 ml) was added in a
single portion. After stirring at room temperature for
30 min, the reaction mixture was poured into 50 ml of
water and acidified to pHw7 with glacial acetic acid. The
organic layer was separated and the aqueous layer extracted
with ethyl acetate (3!50 ml). The combined organic phases
were washed with water (2!50 ml) and dried (Na2SO4).
Removal of the solvent gave diols 2a–c, which were
sufficiently pure for subsequent use.
1
Yield 42%. IR: 3444, 3280, 3058, 1590, 1494, 1238; H
NMR: 7.95 (d, JZ8.4 Hz, 1H), 7.71 (d, JZ8.0 Hz, 1H),
7.66 (d, JZ8.8 Hz, 1H), 7.59 (m, 2H), 7.55–7.40 (m, 7H),
7.37–7.22 (m, 8H), 7.18 (d, JZ9.0 Hz, 1H), 6.92 (m, 4H),
6.24 (d, JZ10 Hz, 1H), 2.87 (s, 1H), 2.77 (s, 1H); 13C
NMR: 156.6, 156.4, 150.4, 144.8, 144.3, 139.8, 139.4, 129.9
(two signals), 128.6, 128.5, 128.3, 128.1, 127.9, 127.62,
127.58, 127.54, 126.9, 126.6, 125.9, 123.6, 121.3, 119.5,
118.6, 118.3, 113.9, 86.3, 82.2, 75.5, 73.9; MS: m/z (%): 556
(100), 530 (5), 479 (40), 257 (40).
4.4.2. From 2-naphthol and diol 2b: 1,4-bis[3-phenyl-3H-
naphtho[2,1-b]pyran-3-yl]benzene 3b. White solid. Yield
1
20%. Mp O250. IR: 3060, 2921, 1627, 1583, 1213; H
NMR: 7.97 (d, JZ8.4 Hz, 2H), 7.72 (d, JZ8.4 Hz, 2H),
7.66 (d, JZ8.8 Hz, 2H), 7.58–7.40 (m, 10H), 7.38–7.22 (m,
10H), 7.20 (d, JZ8.8 Hz, 2H), 6.26 (d, JZ10 Hz, 2H); 13C
NMR: 150.5, 144.6, 144.2, 129.81, 129.77, 129.31, 128.5,
128.2, 128.0, 127.5, 127.0, 126.8, 126.6, 123.6, 121.3,
119.4, 118.3, 113.9, 82.4; MS: m/z (%): 590 (35), 478 (70),
447 (50), 391 (60), 257 (100), 154 (95), 136 (80). 3-Phenyl-
3-[p-(1-hydroxy-1-phenyl-prop-2-yn-1-yl)phenyl]-3H-
naphtho[2,1-b]pyran 4b. White solid. Yield 43%. Mp 173–
174. IR: 3548, 3438, 3272, 3056, 1631, 1587, 1444, 1216;
1H NMR: 7.94 (d, JZ8.4 Hz, 1H), 7.71 (d, JZ8 Hz, 1H),
7.65 (d, JZ8.8 Hz, 1H), 7.59 (m, 2H), 7.55 (d, JZ8.0 Hz,
2H), 7.50–7.40 (m, 5H), 7.37–7.20 (m, 8H), 7.18 (d, JZ
8.8 Hz, 1H), 6.24 (d, JZ10 Hz, 1H), 2.86 (s, 1H), 2.77 (s,
1H); 13C NMR: 150.4, 144.54 (two signals), 144.0, 143.5,
129.9, 129.7, 129.3, 128.5, 128.3, 128.1, 127.9, 127.6,
127.4, 127.0, 126.9, 126.6, 125.9, 125.8, 123.6, 121.3,
119.5, 118.3, 113.9, 86.3, 82.3, 75.5, 74.1; MS: m/z (%): 464
(100), 387 (45), 333 (20), 257 (70), 131 (12), 105 (16), 77
(13).
4.3.1. 4,40-Bis(1-hydroxy-1-phenyl-prop-2-yn-1-yl)
diphenyl ether 2a. Light yellow oil. Yield 93%. IR:
1
3428, 3284, 2113, 1596, 1498, 1240; H NMR: 7.61 (m,
4H), 7.54 (m, 4H), 7.40–7.22 (m, 6H), 6.93 (m, 4H), 2.97
(large s, 2H), 2.87 (s, 2H); MS: m/z (%): 430 (100), 413 (15),
353 (50), 207 (24), 131 (12), 105 (17), 77 (17).
4.3.2. 1,4-Bis(1-hydroxy-1-phenyl-prop-2-yn-1-yl)ben-
zene 2b. Light yellow solid. Yield: 91%. Mp 143–145.
IR: 3426, 3286, 2115, 1486, 1448, 1166; 1H NMR: 7.59 (m,
4H), 7.57 (s, 4H), 7.32 (m, 4H), 7.27 (m, 2H), 2.90 (large s,
2H), 2.86 (s, 2H); MS: m/z (%): 338 (100), 321 (32), 261
(70), 207 (24), 131 (55), 105 (60), 77 (17).
4.3.3. 40,400-Bis(1-hydroxy-1-phenyl-prop-2-yn-1-yl)-1,2-
diphenylethane 2c. Light yellow oil. Yield: 97%. IR: 3421,
3288, 2956, 2115, 1448, 1178; 1H NMR: 7.59 (d, JZ7.2 Hz,
4H), 7.49 (d, JZ8.2 Hz, 4H), 7.33 (dd, JZ7.2 Hz, 4H), 7.27
(dd, JZ7.2 Hz, 2H), 7.14 (d, JZ8.2 Hz, 4H), 2.86 (m, 8H);
MS: m/z (%): 442 (30), 424 (7), 297 (20), 221 (60), 204 (55),
105 (100).
4.4.3. From 2-naphthol and diol 2c: 40,400-bis[3-phenyl-
3H-naphtho[2,1-b]pyran-3-yl]-1,2-diphenylethane 3c.

P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
11741
White solid. Yield 22%. Mp 204–205. IR: 3056, 3023, 2921,
1629, 1587, 1511, 1446, 1222; 1H NMR: 7.95 (d, JZ8.4 Hz,
2H), 7.70 (d, JZ8.0 Hz, 2H), 7.65 (d, JZ8.8 Hz, 2H), 7.5–
7.4 (m, 6H), 7.36 (d, JZ7.8 Hz, 4H), 7.30 (m, 8H), 7.25 (m,
2H), 7.19 (d, JZ8.8 Hz, 2H), 7.11 (m, 4H), 6.24 (dd, JZ
1.2 Hz, 9.9 Hz, 2H), 2.84 (s, 4H); 13C NMR: 150.5, 144.9,
142.4, 141.1, 129.8, 129.3, 128.5, 128.1, 127.8, 127.5, 127.1
(two signals), 126.9 (two signals), 126.6, 123.5, 121.3,
119.4, 118.4, 114.0, 82.4, 37.3; MS: m/z (%): 694 (5), 582
(20), 505 (10), 446 (15), 318 (35), 257 (22), 227 (55), 131
(34), 119 (50), 91 (100). 40-[3-Phenyl-3H-naphtho[2,1-
b]pyran-3-yl]-400-(1-hydroxy-1-phenyl-prop-2-yn-1-yl)-
1,2-diphenylethane 4c. Yellow oil. Yield 38%. IR: 3419,
3284, 3056, 1648, 1589, 1446, 1243; 1H NMR: 7.93 (d, JZ
8.5 Hz, 1H), 7.68 (d, JZ8.0 Hz, 1H), 7.63 (d, JZ8.0 Hz,
1H), 7.58 (m, 2H), 7.50–7.40 (m, 5H), 7.37 (d, JZ8.3 Hz,
2H), 7.32–7.15 (m, 9H), 7.12 (m, 4H), 6.24 (d, JZ10 Hz,
1H), 2.86 (large s, 1H), 2.82 (m, 5H); 13C NMR: 150.5,
144.9, 144.4, 142.5, 142.1, 141.4, 141.0, 129.7, 129.2,
128.5, 128.3, 128.1, 127.8, 127.4, 127.1, 126.9, 126.6,
126.0, 125.9, 123.5, 121.3, 119.4, 118.3, 114.0, 86.4, 82.5,
75.5, 74.0, 37.3, 37.2; MS: m/z (%): 568 (50), 551 (10), 542
(17), 491 (20), 345 (25), 257 (50), 105 (32), 91 (100).
4.5.1. 4-[3-Phenyl-3H-naphtho[2,1-b]pyran-3-yl]-40-[13-
oxo-3-phenyl-indeno[2,1-f]naphtho[1,2-b]pyran-3-yl]
diphenyl ether 5a. Red crystals. Yield 77%. Mp 150 d. IR:
1
3058, 2954, 1702, 1598, 1496, 1240, 1170; H NMR: 8.35
(m, 2H), 7.94 (d, JZ8.4 Hz, 1H), 7.89 (d, JZ9.9 Hz, 1H),
7.86 (d, JZ7.6 Hz, 1H), 7.70 (d, JZ8.1 Hz, 1H), 7.64 (d,
JZ8.8 Hz, 1H), 7.55 (m, 3H), 7.50–7.35 (m, 10H), 7.32–
7.18 (m, 9H), 7.17 (d, JZ8.8 Hz, 1H), 6.90 (m, 4H), 6.32 (d,
JZ9.9 Hz, 1H), 6.22 (d, JZ9.9 Hz, 1H); 13C NMR: 195.9,
156.5, 156.2, 150.4, 149.1, 144.9, 144.8, 144.6, 139.8,
139.4, 135.5, 134.5, 134.4, 129.84, 129.8, 129.7, 129.32,
129.29, 128.6, 128.5, 128.2, 128.1, 128.0, 127.9, 127.8,
127.7, 127.6, 127.5, 126.9, 126.8, 126.6, 126.2, 124.7,
123.7, 123.6, 123.5, 122.3, 121.3, 119.6, 119.5, 118.44,
118.38, 118.3, 113.9, 113.3, 105.7, 83.3, 82.2; MS (FAB):
m/z (%): 785 ([MC1]C, 7), 784 (MC, 6), 707 (2), 659 (2),
391 (14), 338 (25), 154 (100), 136 (74); HRMS:
[C57H36O4]C, found 784.2628, requires 784.2614.
4.5.2. 13-Oxo-3-phenyl-3-[p-(3-phenyl-3H-naphtho[2,1-
b]pyran-3-yl)]phenyl-indeno[2,1-f]naphtho[1,2-b]pyran
5b. Red crystals. Yield 67%. Mp 135–138 d. IR: 3058,
2923, 1702, 1602, 1461, 1369; 1H NMR: 8.36 (m, 2H), 7.93
(d, JZ8.4 Hz, 1H), 7.87 (d, JZ10 Hz, 1H), 7.86 (d, JZ
7.6 Hz, 1H), 7.69 (d, JZ7.9 Hz, 1H), 7.63 (d, JZ8.8 Hz,
1H), 7.55 (m, 3H), 7.50–7.40 (m, 10H), 7.30–7.18 (m, 9H),
7.16 (d, JZ8.7 Hz, 1H), 6.32 (d, JZ9.9 Hz, 1H), 6.23 (d,
JZ9.9 Hz, 1H); 13C NMR: 195.7 (two signals), 150.4,
149.1, 144.8 (two signals), 144.5 (two signals), 144.4 (two
signals), 144.0, 135.5, 134.5 (two signals), 134.3 (two
signals), 129.8 (two signals), 129.7 (two signals), 129.3,
128.5, 128.4, 128.2, 128.1, 127.8 (two signals), 127.7,
127.6, 127.5, 127.4, 126.94, 126.9 (two signals), 126.64,
126.6 (two signals), 126.2 (two signals), 124.7, 123.6, (two
signals), 123.5 (two signals), 122.3 (two signals), 121.24,
122.19, 119.6 (two signals), 119.5, 118.3 (two signals),
113.8, 113.3 (two signals), 83.4 (two signals), 82.3; MS: m/z
(%): 692 (5), 583 (6), 555 (12), 527 (5), 391 (90), 149 (100);
HRMS: [C51H32O3]C, found 692.2363, requires 692.2351.
4.4.4. Procedure for the reaction of 1-naphthol with diol
2b. A solution of diol 2b (4.0 mmol), 1-naphthol (0.504 g,
3.5 mmol), PPTS (10 mg), CH(OMe)3 (0.8 mL, 8 mmol)
and 1,2-dichloroethane (50 ml) was refluxed for 2 h under
nitrogen. Solvent evaporation gave a brown oil, which was
purified by CC (3–15% ethyl acetate/hexane). Two
compounds were isolated. 1,4-Bis[2-phenyl-2H-
naphtho[1,2-b]pyran-2-yl]benzene 3d. Pale pink solid.
Yield 8%. IR: 3052, 1644, 1617, 1446, 1394, 1371, 1267,
1097; 1H NMR: 8.31 (dd, JZ7.5, 1.8 Hz, 2H), 7.70 (dd, JZ
7.2, 1.8 Hz, 2H), 7.50–7.38 (m, 12H), 7.35–18 (m, 8H), 7.13
(d, JZ8.3 Hz, 2H), 6.68 (d, JZ9.7 Hz, 2H), 6.12 (d, JZ
9.7 Hz, 2H); 13C NMR: 147.7, 144.9, 144.4, 134.6, 128.1,
127.6, 127.5, 127.1, 126.8, 126.64, 126.59, 126.3, 125.5,
124.6, 123.7, 122.0, 120.4, 115.3, 83.0; MS: m/z (%): 590
(100), 513 (10), 447 (10), 436 (10), 322 (16), 257 (41), 185
(40), 105 (24), 77 (27). 2-Phenyl-2-[p-(1-hydroxy-1-
phenyl-prop-2-yn-1-yl)]phenyl-2H-naphtho[1,2-b]pyran
4d. Yellow oil. Yield 32%. IR: 3415, 3282, 3027, 2923,
1446, 1371; 1H NMR: 8.31 (d, JZ8.1 Hz, 1H), 7.73 (d, JZ
8.6 Hz, 1H), 7.60–7.38 (m, 12H), 7.30–7.18 (m, 5H), 7.11
(d, JZ8.3 Hz, 1H), 6.68 (d, JZ9.7 Hz, 1H), 6.12 (d, JZ
10 Hz, 1H), 2.85 (large s, 1H), 2.80 (m, 1H); 13C NMR:
147.6, 144.9, 144.8, 144.0, 143.5, 134.6, 128.3, 128.2,
128.1, 127.8, 127.6, 127.5, 126.8, 126.3, 125.90, 125.88,
125.84, 125.82, 125.6, 124.5, 123.8, 121.9, 120.5, 115.3,
86.3, 82.8, 75.5, 74.1; MS: m/z (%): 464 (100), 446 (70), 387
(37), 333 (27), 257 (52), 105 (24), 77 (19).
4.5.3. 40-[3-Phenyl-3H-naphtho[2,1-b]pyran-3-yl]-400-
[13-oxo-3-phenyl-indeno[2,1-f]naphtho[1,2-b]pyran-3-
yl]-1,2-diphenylethane 5c. Red crystals. Yield 60%. Mp
1
108–111 d. IR: 3054, 2921, 1702, 1600, 1455, 1367; H
NMR: 8.38 (m, 2H), 7.94 (d, JZ8.4 Hz, 1H), 7.87 (m, 2H),
7.70 (d, JZ8.2 Hz, 1H), 7.64 (d, JZ8.8 Hz, 1H), 7.60–7.14
(m, 27H), 6.33 (m, 1H), 6.24 (d, JZ9.9 Hz, 1H), 2.84 (s,
4H); 13C NMR: 195.9, 158.6, 150.5, 149.2, 144.9 (two
signals), 144.7, 142.5, 142.2, 141.3, 141.0, 135.4, 134.5,
134.4, 130.0, 129.7, 129.3 (two signals), 128.5, 128.2 (three
signals), 128.0, 127.9 (two signals), 127.8, 127.6, 127.5,
127.4, 127.1, 127.0, 126.9 (two signals), 126.8, 126.6,
126.5, 126.0, 124.7, 123.6, 123.5, 122.3, 121.3, 119.5,
119.4, 118.3, 114.0, 113.4, 83.5, 82.4, 37.30, 37.26; MS
(FAB) m/z (%): 797 ([MC1]C, 35), 796 (MC, 33), 663 (35),
641 (65), 608 (45), 580 (72), 555 (100), 527 (44), 419 (53);
HRMS: [C59H40O3]C, found 796.3011, requires 796.2977.
4.5. General procedure for the synthesis of bi-naphtho-
pyrans 5a–d
A solution of compounds 4a–d (1.0 mmol), 5-hydroxy-7H-
benzo[c]fluoren-7-one (0.246 g, 1.1 mmol), PPTS (10 mg),
CH(OMe)3 (0.2 mL, 2 mmol) and 1,2-dichloroethane
(50 ml) was refluxed for 2 h under nitrogen. Solvent
evaporation gave a red oil, which was purified by CC (3–
10% ethyl acetate/hexane). Recrystallization from hexane/
CHCl3 gave crystalline materials.
4.5.4. 13-Oxo-3-phenyl-3-[p-(2-phenyl-2H-naphtho[1,2-
b]pyran-2-yl)]phenyl-indeno[2,1-f]naphtho[1,2-b]pyran
5d. Red crystals. Yield 69%. Mp 138–143 d. IR: 3052,
1
2921, 1702, 1579, 1461, 1400, 1367; H NMR: 8.36–8.29
(m, 4H), 7.86 (m, 1H), 7.80 (m, 2H), 7.68 (m, 1H), 7.60–7.32

11742
P. J. Coelho et al. / Tetrahedron 61 (2005) 11730–11743
(m, 15H), 7.32–7.10 (m, 6H), 6.68 (m, 1H), 6.32 (d, JZ10 Hz,
1H), 6.14 (d, JZ9.8 Hz, 1H); 13C NMR: 195.8, 149.1,
147.6, 144.9, 144.7, 144.3, 143.9, 135.5, 134.6, 134.5,
134.4, 129.7, 129.3, 128.2, 128.1, 128.0, 127.81, 127.75,
127.61, 127.56, 127.5, 127.0, 126.9, 126.8, 126.70, 126.66,
126.5, 126.4, 126.3, 126.2, 125.6, 124.7, 124.6, 124.5,
123.8, 123.6, 123.5, 122.3, 122.0, 120.5, 115.3, 113.2, 83.4,
83.0; HRMS: [C51H32O3]C, found 692.2367, requires
692.2351.
2-b]pyran-3-yl]-1,2-diphenylethane 6c. Pale red crystals.
Yield 70%. IR: 3330, 3023, 2924, 1633, 1366; H NMR:
1
8.51 (d, JZ8.3 Hz, 1H), 8.44 (d, JZ8.3 Hz, 1H), 8.06 (d,
JZ7.7 Hz, 1H), 7.92 (m, 1H), 7.69 (d, JZ8.1 Hz, 1H), 7.63
(d, JZ7.5 Hz, 1H), 7.60–7.00 (m, 28H), 6.27–6.18 (m, 2H),
2.8 (m, 4H), 2.05 (s, OH), 1.78 (m, 3H, CH3); 13C NMR:
151.0, 150.5, 148.7, 145.5, 144.9, 144.7, 143.9, 143.0,
142.5, 141.2, 141.1, 139.6, 129.8, 129.3, 128.9, 128.5,
128.2, 128.11, 128.05, 128.0, 127.8, 127.6, 127.44, 127.36,
127.3, 127.04, 127.01, 126.8, 126.7, 126.6, 126.12, 126.06,
125.43, 125.36, 123.9, 123.6, 123.3, 122.4, 122.1, 121.3,
120.6, 119.4, 118.4, 114.0, 113.0, 82.9, 82.4, 80.7, 37.32,
37.31, 26.4; HRMS: [C60H44O3]C, found 812.3273,
requires 812.3290.
4.6. General procedure for the synthesis of photo-
chromic naphthopyrans 6a–d
A solution of CH3MgI in dry Et2O (1 ml, 1 mmol) was
added slowly to a cold solution (0 8C) of naphthopyrans
5a–d (0.25 mmol) in THF (10 ml). After stirring at room
temperature for 1 h, the solution was quenched in aqueous
satd NH4Cl, extracted with Et2O (3!40 ml), dried
(Na2SO4) and concentrated in vacuo. The residue was
purified by CC (3–10% ethyl acetate/light petroleum).
Recrystallization from hexane/CHCl3 gave a crystalline
material.
4.6.4. 13-Hydroxy-13-methyl-3-phenyl-3-[p-(2-phenyl-
2H-naphtho[1,2-b]pyran-2-yl)]phenyl-indeno[2,1-f]
naphtho[1,2-b]pyran 6d. Pale red crystals. Yield 73%. IR:
1
3371, 3286, 3053, 2923, 1642, 1393, 1367; H NMR: 8.51
(m, 1H), 8.42 (m, JZ8.4 Hz, 1H), 8.31 (m, 1H), 8.05 (m,
1H), 7.68 (m, 1H), 7.60–7.32 (m, 15H), 7.32–7.18 (m, 8H),
7.12 (m, 1H), 6.68 (m, 1H), 6.23 (m, 1H), 6.16 (d, JZ9.7,
0.5 Hz), 6.13 (d, JZ9.7, 0.5 Hz), 2.03 (s, 1H, OH), 1.80 (m,
3H, CH3); 13C NMR: 151.01, 150.95, 148.6, 147.65, 147.63,
145.05, 144.96, 144.9, 144.8, 144.6, 144.5, 144.3, 143.9,
143.8, 139.5, 134.6, 129.8, 128.9, 128.2, 128.1, 128.0,
127.7, 127.6, 127.50, 127.47, 127.3, 127.1, 127.0, 126.8,
126.74, 126.71, 126.64, 126.60, 126.57, 126.3, 126.1, 125.8
(two signals) 125.40, 125.36, 124.5 (two signals), 123.9,
123.3, 123.1, 123.0, 122.4, 122.1, 122.0, 120.6, 120.4 (two
signals), 115.3, 115.2, 113.0, 112.9, 112.8 (two signals),
83.0 (two signals), 80.6 (two signals), 26.4, 26.3; HRMS:
[C52H36O3]C, found 708.2652, requires 708.2664.
4.6.1. 4-[3-Phenyl-3H-naphtho[2,1-b]pyran-3-yl]-40-[13-
hydroxy-13-methyl-3-phenyl-indeno[2,1-f]naphtho[1,2-
b]pyran-3-yl]diphenyl ether 6a. Pale red crystals. Yield
1
79%. IR: 3355, 3055, 2956, 1596, 1495, 1235; H NMR:
8.51 (d, JZ8.5 Hz, 1H), 8.42 (d, JZ8.3 Hz, 1H), 8.05 (d,
JZ7.7 Hz, 1H), 7.93 (d, JZ8.4 Hz, 1H), 7.70 (d, JZ
8.1 Hz, 1H), 7.64 (d, JZ8.5 Hz, 1H), 7.60–7.15 (m, 24H),
6.93–6.86 (m, 4H), 6.25–6.18 (m, 2H), 2.04 (s, OH), 1.78
(m, 3H, CH3); 13C NMR: 158.3, 156.6, 156.3, 156.1, 151.0,
150.4, 148.6, 145.3, 144.8, 144.6, 143.8, 140.2, 139.82,
139.75, 139.5, 139.3, 129.84, 129.79, 129.3, 128.9, 128.6,
128.5, 128.4, 128.22, 128.16, 128.1, 127.8, 127.7, 127.6,
127.5, 127.3, 126.9, 126.65, 126.63, 126.2, 125.4, 123.9,
123.6, 123.2, 122.4, 122.1, 121.3, 120.6, 119.5, 118.5,
118.4, 118.3, 118.2, 113.9, 113.0, 82.74, 82.69, 82.2, 80.67,
80.64, 26.6; HRMS: [C58H40O4]C, found 800.2938,
requires 800.2927.
Acknowledgements
To FCT (Portugal’s Foundation for Science and Tech-
nology) and FEDER for financial support to the research
´
unit Centro de Quımica-Vila Real (POCTI-SFA-3-616).
4.6.2. 13-Hydroxy-13-methyl-3-phenyl-3-[p-(3-phenyl-
3H-naphtho[2,1-b]pyran-3-yl)]phenyl-indeno[2,1-f]
naphtho[1,2-b]pyran 6b. Pale red crystals. Yield 75%. IR:
3388, 3264, 2923, 1633, 1365; 1H NMR: 8.52 (m, 1H), 8.42
(d, JZ8.4 Hz, 1H), 8.06 (m, 1H), 7.92 (m, 1H), 7.72–7.10
(m, 26H), 6.24 (d, JZ9.9 Hz, 1H), 6.23 (m, 1H), 2.00 (s,
1H, OH), 1.7 (m, 3H, CH3); 13C NMR: 151.0 (two signals),
150.4 (two signals), 148.6, 145.6, 144.6, 144.4 (two
signals), 144.3 (two signals), 144.1, 144.0 (two signals),
143.9, 143.8, 139.5, 129.8 (two signals), 129.3, 128.9,
128.5, 128.2, 128.1, 128.05, 128.01, 127.7, 127.5 (two
signals), 127.3, 127.0 (two signals), 126.9 (two signals),
126.8 (two signals), 126.7, 126.6, 126.5, 126.1, 125.4, 123.9,
123.6, 123.3, 122.4, 122.0, 121.3, 120.6, 120.5, 119.4, 119.3
(twosignals), 118.31, 118.27, 113.9, 113.8, 113.0, 112.8, 82.8,
82.4 (two signals), 80.6 (two signals), 26.4 (two signals); MS
(FAB): m/z (%): 708 (1), 691 (1), 663 (1), 53 (2), 555 (4), 460
(5), 307 (35), 154 (100), 137 (67); HRMS: [C52H36O3]C,
found 708.2684, requires 708.2664.
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