Temhe&on Vol. 43, No. 7. pp. 1393 to 1408. 1987 Britain.
oo4o-m0/87 s3.00+ .oo Rrgunon Joumds Lid.
Printedin Great
ORSANIC RRACTIONSIN LIQUID CRYSTALLINESOLVRMS. 5. INTRAMJLBCULAR PHENOLICQURNCHItfUOF ARORATICKETONETRIPLETS AS A PROBEOF SOLUTE CONPORRA’fIONAL MOBILITY IN LIQUID CRYSTALS. WILLIAR J. LBIOI+*and STBPRANUSJAKOBS2 Department of Chemlatry McRaster Univemity Haailton. Ontario, Canada L8S 4Hl
(Received in UK 16 February 1987) The effects of liquid crystalline order on the confomational motions ABSTRACT: Jnvolved in end-to-end, Intramolecular triplet quenching of aromatic ketones by a Triplet state quenching suitably situated phenolic moiety have been investigated. Norrish II fragmentation quantur has been monitored using two Jndependent probes: and direct lifetime leaaureaents in yields of valeryl-aubstituted derivatives using the corresponding anlsyl-substituted ketones as methyl-substituted ketones. models for triplet state behaviour in the absence of phenolic quenching. Quantum yields for Norrish II fragmentation in the liquid crystalline solvents have been estimated using 4-¤ethoxyvalerophenone (HP) as the actlnometer. The ability of liquid crystalline solvents to inhibit Intramolecular phenolic quenching is deIn one case. intramolecular pendent on both phase type and solute length. Indicating that the conforquenching Is coapletely suppressed in smectic phasea. mational notlons inyolved in achieving the quenching geometry are slowed by a factor of at least 10 relative to their rates in non-viscous. isotropic solvents. ratios from photolyslo of IWP in the liquid crystalline The Norrish II product solvents are also affected dramatically by liquid crystalline order. IRTRUDUCTION Liquid
crystals
intermediate liquid
crystalline
are
oriented
the
only
type
of liquid
(or
nearly
hexagonal, the
talline
the
order
on the
solutes to
have
is
crystal similar
environment changes
In the
extremely ordered
solute’s
media.
variety fluorescent
has, of
ordered
further
and perpendicular of smectic
of packing
rlthin
and the preferred
to orient 3.5
the
appear8 effects
types
the angle
and restrict the
the
effects
layers of
tilt
diffusive
of liquid
that
crys-
of interest state
is
excimer used
1393
ketone
when
solute’s
the solute’s
involvea
local
substantial
ketones
mobility formation
to inveatlgate excited
of
aromatic
exciplex
Aromatic
“intrinsic’
largest
when the
approached.‘-’
in
conformational
or
by a number of the
phases).
disruption
processes the
be governed potentially
smectic
process
transition
to are
(e.g. (so
monitoring
been widely 7,lO 8ystena.
since
the
quenching
of course,
organized
type
as the
Intramolecular
probes
are
Is
fluid
mobility
the lesogen
for
This
the most
p1anea.l
crystals
this
triplet probes
molecules
moleculea
are a variety
type
etc.)
and when the
shape
are
In
(and asaoclated chemical reactivity) e-9 been demonstrated. The ability of liquid crya-
highly of
There
propertlea solJds.3
on average.
to one another
to the layer
and
constituent
which
constituent
well-recognized.
general,
minimJzed).
useful
rolecules
la is
Intramolecular
is
of
to that
Jr,
liquid
recently
motions
layers.
and the
conformational
factors.
liquid
shape
of
the
nematic.
solutes
only
affect
interrelated
the
phases,
parallel
according
axes
ability
dissolved
of
of
orthorhombic,
of
tals
plane
classified
the
to one another,
in nematic
axes
structure6 and crystalline
“mesogena”.
parallel phases,
long
uJth liquids
by rod-like axes
present
theJr
to the are
fluids.
18otropic
In smectlc
with
long molecular
Nhile mobility
the
of ordering
so)
(e.g. between
long
crystal.
and these
of
formed
their
in layers
known,
ordered
thoae
phase8 with
degree
arranged
are
between
molecular lifetime
in
in fIuorescent mobility
photochemlstry
state
provide
of solutes
in
complements is
much longer
a
W. J. IXIOH and S.
1394
(allowlng
the
usually the
investigation
smaller
medium).
by
direct
in
such
methods
We wish and
as
rhlch
liquid
from a suitably
state
triplet-triplet depend the
absorption
initial
results
moiety
f_
direct
hydrogen
In
has
the
1.
indicator
been measured
process, abstraction
1).
f b.
and 1ndirc:c:l
employed. dlagnoatic
or
of s~octlc
cyclizatlon
by remote
bH Both
decay,
of the effects
&.-
(I)
of either
photochemlstry.lI
on an end-to-end (Eq.
are
disruptive
or phosphorescence
triplet
ketone
and ketones less
can be monitored
of carbonyl of a study
solvents
phenollc
aotlons)
(and hence
behavlour
on some aspect
of an aromatic
sltuated
conformational
fluorophores
excited
crystalline
quenching
slower
typical
ketone
to report
nematlc
involving
than
Furthermore.
methods
by lndlrect
of such
size
JAKOLB
methods
for
erflclency
of phenollc directly
monilorinC
1 r~plr!l
OC the Norrlsh quenching.
by nanosecond
while laser
state!
quenching.
Type II reaction in 3.
flash
the
have
serves
triplet
state
hf!c:n
as
the
llfotlme
photolysis:
0
(2)
8 R R-H
1
3
R-Clo
4
6
There
is
intramolecular Ylrst,
the
formed 4
products
in detectable
exhibits
in
the
Norrlsh same
presence
of
to the
formation
from Norrlsh upon photolysls
II reactivity Thus,
ol
the
at
of the
the
1,13-phenoxy/ketyl
II reactlon
the other addition
that
in
with
high
end
blradical
3 and 3) are
solution,
of & is
even
carbonyl of
the
provlded
mechauisas
triplet molecule
behavlour direct
3 from the
triplet
state are
not
though (NVPI
due primarily
quenching
spectroscopic has
soluLlon. 12,13
efflclency.
of &methoxyvalerophenone
and other reactive
fluid
of _1 (a.
In acetonltrlle to that
transient
and in
indicate
and a occurs
non-reactivity
hydrogen,
between
group I4
same concluslonr.
slwllar the
phenollc
Comparison
unimportant.
1
amounts
solvent.
aryl
to
in
expected
interactions
electron-rich
evidence
quenching
the remote
donor-acceptor
lead
considerable triplet
to the such
as
and the
relatively
of 8 and 6 has evidence
Par the
state
ol p.12
1395
Organic reactions in liquid crystalline solvents-V The short rapid
triplet
llfetime
phenollc
obrerved
for
hydrogen-abstractlon.
1 in non-viscous
yielding
solvent8
biradlcal
is
the
rerult
of
7_:
7
The cates
rubstantial
that
hydrogen the
process: quenching this.
geoeetry
formation
transfer
motions
fores
In
are
increased
and
1
triplet
of
saectic
on
considerably
state
that
enormous
these
molecules.
less
liquid severe
solute
order
conforaational
on triplet
lifetiee
than
in phenolic
magnitude
quen-
and hence
of the
observed
effects
previously
ebOc it
appeared
eight
be obtained
and reactlvlty
in
exciter
lifetime.
we have
motions.
scale
intraeoiecuiar
involved the
sandwich-like
time
of 1-3 nanoseconds
in triplet
which
of 0 Indl-
in the quenching the
shorter of
motions
Considering
in 1.
step
scale
studies
in an increase
crystalline
likely with
Propertles The
liquid
crystals
(##I)
and
enantiotropic
seectic
and nematic
exist
between
teaperature seectic
phases
of these
has been assigned
temperature
the
smectic
whose
x-ray
order
in
within
are
layers,
(17.5&I,
(3lA
with to the
for
consistent
and
of the
have
4’-propyl
were
such
that
the
long
molecular
layer the
slmllar
(rCa)
interdigitated
diffraction reported.
axes
are
oriented
less bllayer
data
17
(hQ31)
parallel
structure
for
Seectic
hexagonally
twice
phases
corresponding the MaI
homologs
and Leadbetter.
distance
than
form
high
and 4’-pentyl
by Brownsey
4-
both
and neaatic
BCCN the
to the
The repeating
somewhat
for
X-ray
the molecules
plane. is
18
coepounds
seectic
while
been recently
reported
O’~hutylbicyclohexylThese
the
44-4Q°C.
is
BCClf’) with
for m.
Sa-B structure,
data
phases
perpendicular
thickness
phases
work are (ECU).
respectively,
two compounds
diffraction these
the
25-44°C
bllayer
this
homolog
phases;
29-54OC and 54-79%. ranges
in
employed the II-ethyl
carbonitrlle
and
on a time
conforaational
llfetlae
achieving
on a soeewhat
to occur
result
reactivity
effects
in
of reported 15 derivatives.
down the
tl lplet
determining
basis
should
and nematic
rate
occur
expected
on the
slowing
&
the
on the
involved
therefore
in 1.3-dlphenylpropane
Clearly.
effect
motions
must
solventa.
non-viscous
Solvent
atoa
isotope
conformational
These
ching
deuteriua
la
The
close-packed to one another
defining
the
the molecular proposed
layer length
previously
W. J. LEIGH and S. JAKOBS
1396
for
PCQ
and to
nllghtly
more ordered
that
Smectlc order
that
is
of PCCH’8,
has
phase
rulectfc
in mixtures
where
oP
like)
and
liquid
Solubllfty
of
1-4
the solute’s of
the
Lures a
of
If@ as
measured
considering
the
the
of
saectic
formation
tures
than
upon
of
the
Dosalc tic
phase
The siderably BCUI
in the
MJCII
at
of
is
as
and
mixtures,
of
Is
of
18 clear
that
case
of p.
phase
tenpere-
the mixture
in Table
1.
or nematic
phase8
the Sm-N and N-I retrrrlt
one
atoms shorter
than
rapidly
they disrupt
suectic
foraatlon
the rosaic
of
range.
different
batonnets
teapera-
to a greater
srectic
fashion
texture
to the Wp
The cooJfng
from this:
of
and its
and uniformly.
order
In a similar
temperature
in this
texture
the pure mesogen,
proceeds
of
transition
1s the expected
carbon
of
through
of NVP and
and from the transition
proceed8
within
measure
the transftion of
the
between
1 ~01% mixtures
three
phase
to BCU,
fundamentally
the
sore
behavfour
for8atlon
of
the
casf! than in the others,
the swec-
which gradually
to
the transition
ranges
licroscoplc
is
thus appear8
coalesce
range,
form a
the coexistence
are
of
of
(QO-96%)
the reletive
& and 4 are largely
rnectic
phase.
mixtures
ruch
in a ketone-rich While
not known. the suggestion
and nematic smectlc.
soluble
of
con
the a_35%)
phaseu,
but a8 the of
nematic
in SReCtfc
nematlc
the precise that
of
(2 day8 at
proportion less
are
to that
annealed
both emectic
predoalnantly
that
and &-Scar
is anaiogous
Inepectlon
(2-10%).
and reside
m-rich
phases
are
increased
the a-
behaviour
the presence
the samples
the bulk
of
pronounced. reveals
concentration It
an
COBpIete.
di8tinctly
the two coexistent
(IICU-
and is
The mosaic microscopic
nematlc
temperature
oniy
with
fby weight)
saectlc
In disruption
the saecttc
from that
aiailar
SSFrated
than IfVF, 8, and 4 are.
equilibrium
the
neeatfc
Proa
This
it
indistlnguiahable
fn the
apparently
Increase8.
a 2:l
respectively,
collected
Iowerfm
solute:
a somewhat broader
transition
1aolX
ketone
of
results
for
either
and flexibility.
At temperatures
30*
that
inspectJon
are
of
slight
OF this
it
mixture
broader.
crystal
temperatures
prOCeed8 more gradually
mixture.
samples
phase
is
in
BCCII
the pure material.
lengths
the
appearing
monOdOMaIn
bulk
from
texture.
Is
and 25-S7°C,
mIcroscopy.
fron
of
NWP dOi?8.
texture
mosaic
is
cooling
@-BACH
of
breadth
though over
mixture.
phaS88,
at hJgherteRperetllres
forms enantlotropic
and by visual
disruption
structure
mixtures,
cooling
atudy
can be obtained
Transition
those
and 4 are the
occur8
by the only
mixture
3 of
extent
this
little
similar
upon
Ketones
lo-25OC
in a lfquid
by thereal
very
from
BCCII and is
IICCII and occurs
mixture
and Nematic
mesogen.
indfcated
temperatures
This
between
microscope.
Ix
the DCUI/BCIYI
the two saectlc
which depend8 primarily on the si~ilnritlos 8e,Tc.8,9.20 and that oP the wesogen. A qualitative
to which
causes
to be a higher-
for
a degree
the solute-doped
1_4 In BCQ.
thought
is
forma a
exfst.‘*
a solute
structure
extent
polarizing
WCQI,
of to
smectlc
of
structure
the former
S7°C.19
In Smactfc
matrix,
phase
that
and is
ordering
in the present
(BB).
phase8
incorporation cloivent
wfth
srectlc
indicate
The phase diagram
relative
phase-types
above
IcQ’s
structure
of ##(.l’
this
and ilcQl
nematlc
isotropic
that
phase enployed
ECCU
that
studies I9 than PCQ.
rhoabohedral
inmfsclbla
both
The nematic rlxture
a
with
BCCII is
18 clear
phase
then
consistent
it
miscibility
smectlc
m
smectic
system
While
?oCU.~~
almilar
phase
in
compositions
the ketone8
reside
1397
Organic reactions in liquid ctystslline solvcuts-V predominantly cal
In nematlc
behavlour
uniformly
(vlde
soluble order
smstic
phaees
at 30%
Infra).
On
in smcctic
Lo a degree
m
is
the
further
other
(at 30%,
which correlates
Transitloa
temperatures
for
--_-_-..-...--..-_
_.
and cause
dlaruptlon
wJth their
molecular
lengths.
_.
g
51.5.52.5O
7H.M-790
r
46 520
__
.- __..
cycles
by thermal
o? 2 _and
llfetlmes were
followed on
the
Ir_dc_4l_9w!_._C‘rx5l_G~.!x
_scllvente. phases
mcasuretl by nanosecond af 1c:r Laser
bdsls
excitatJon flash
time)
320
their
similar
overlap.
At 30°C.
JndJcatJng this
magnl tude
that
similar
(bimolecular)
temperature
(triplet
temperatures). acetonJtrJle12
Tr Lplet are collected
The Photochemlstry The sini l.lr
W
of 1. 4.
absorption
to
lhose
shifted
to
longer
Slallar
features
recorded
absorptlon
1 from g could with
hohaviour at
g
absorption
is rLrongest)
of
1 and blradical
the degree
results
were
I Jfetimes
for
in Tablr and DP spectra
ln Liquid of 1, 4.
from
comparatively and
g
of
These because
In
state
of L In D,
IS negliglblr
shorter these
of
the two species
1 ~1% solutions
the triplet
Cryatalllne
only
at
al hiKht:r
solvents
and Isotropic
and JID (not solution,
compared to thetr
have been observed
of 275ns
respectively.
aud
i II
2.
in acetonltrtle
wavelengths
g
Analysis
1lmit.s (r(:s)~rtJv(:lyJ.
were obtained of
p.
Is strongcut)
to esllnates
7,
at ca.
(Jn trolh poai
ahsorptlon led
solvent
JO.2 molt:
of overlap
to which the spectra
self-quenching llfctlmes
in either D
whose
lo the* triplet 11.12.22 No
g and blradlcal
(where trIpJet
39Onm
triplet
I lol% aolu-
spectra.
neaatic
;IS I result
tran-
to transients
he found in
to trlplltl
to ho upper and lower and
deoxyt:nnatc:d.
and whJch were assIgned
characteristic
and ln
lonliorlng
10~1s. 86a.7) from a
at 36°C gave rise
asslgnable
lhts Ilfetlmes
I \WY must be considered
of annealed.
kinetics.
drcny proflles
for
J337.lnm.
solvents
to mor(: complex
35Onm (where biradical ns
Ihr pulses
cxperlmants
of absorptlons
the flrst.order
photolysln.
with
hiradlcal
of #x31 and DD
laster flash
photolysls
their
Slml la1
O.OOSMJ Kavo rJsc and
of
fornlat ion of
temperature.
----
for 3 and g In the smectlc
cJc*an l’trst -order
fo1
microscopy.
-----_-----
of g and g in the two smectlc
at
76-T7.5P 7L(.2-78.5”
_. ______ --
nbsorptJous 21 laser. ni troKen
i(lonc.6~
600
50.5-52“
sient
and
_
76-76O
D
and
_---_------.._
1 _.
nematic
this
- .--_- --__--.
10.0-70.2~
Trlplet
states
N->I
.-..--..
46.51 o
T_r!~_letMU+ j m.e
decay
m1xtures.a
51.5-52.5“
__-_____
tions
ketone/m
IID
_ ._
--__
1 ~01% aroaatlc
53.8-540
a Measured in heatiny
“a
to be
of local
none
_a
of
photocheml
and S_ appear
Sm->N -.
I Ion
1.
--1:
Ketone
cv
by their
DP,
anyway).
----___ Table
..
indicated
hand,
by us previously
Solvents
shown) in nomatic
the 77.77. abstrrptlons
posltions
D
are being
in methylcyclohexane.
in the W absorption
spectra
1398
W. J. Lmon and S. JAKOLIS
Table 2: solvents
Triplet lifetimes at 30°C.a
for
1 and g in
isotropic
and liquid
crywtalline
Ketone MeCNb EB(nen)” __________________________________~~~~___________--____~~~~~~___________--~~~ 275
15
n
!!
ERXJI(~mld 3HlJO
5600
2300
J 1000
._--__________--____.----_--_ - .- ..__.-- __..-- ----... --. . _--_. ..-._-.__ -- __.__._.--___ aReanured by nanosecond Jnaer flash photolysie; bllfetines given In nanoseconds. Brror 1s approxlaately Yrom Ref. 12. 3.2 loJ% solutjons. 3mm cells. 1 aoJ% solutions, 0.7mm cell*.
of
other
BcQl.
and
to
those
proxygennted.
compared
1
0.02M
HCUI a
Dara_.alkoxyphanyl
solutions
(1:s
by wt:
perl od
of
photolyaates former
solveuts values
studied.
from
anulyels.
cyclobutanols severe with
GC the
Prom
4 so
injected.
4,
by
ED,
(IW)
conversion
data
are
are the
used
listed
of
In
these
Table
ketones
unstable
calculated
P/C
of
also
for
‘Thus,
4.
but
the
3.
the
F/C
each
The
for
ratios
the
both
not
undrr
deconposltlon for
4 are
does
._. ._.__.
more
not
vary
meaningful.
----_-Table 3: Kragmentatlon/cyclizatlon (F/yand trans/cls cyclobutanol nud Llquitl fro8 the Norris b1 11 roncl Jons of JWP and 4 in iclutropic Solvents ut 30°C. H&NC
The the
----
.--- -_.--_---~----
Ketone
four
newswry
quantitative.
deconposo
reported
ketonos the
corresponding 12 The solution.
gc conditions
are
partially
case].
lhe
ln acetonltrlle under
a
Tho
from JIVP in with
In for
JIVP samplc.
ratios
along
percentage
ralios
cyclohcxane:
(In
cyclobutanols
l.hermally
WP
the
and by hplc
of
(312+10un)
was continued
of
IF/C)
(t/c)
phases
KXZJ and BCQI.
Irradiated
photolysls
(NVP and 6)
dlastereomerlo
amectlc
(isotropic)
were
solvent,
10-30X
vpc
and NVP in
in nematic
each
to
photolysls
condltlons
.tmount
Por
photolysis
frum
1,
ketones
fra~entatIur~/cyc:iizatlon
oP the Thnsc
obtained
the
saae
and methylcyclohexane
yJeJded
cyclobutanoJ(e) for
the
analysed
yields
macro- and isotropic
and methylcyclohexane.’
eolutions
corresponding
analyses
and relative
the
of
oi
were
In
In acetonltrlle
apparatus.
time
ketones
aoJ%
“EC”).
merry-go-round
alkyl
_tlO%.
r4CJld
Bc(isot
I
BB(IWB)
Bccll(s=)
______-__-_--_._ -..---__-_ .__..._ - __._-._ -. - ..__.
(t/c) rallos Crystal I inf:
Bcca(sa) . _-___._._
.._
F/C
4.4TO.3
4.2~0.4
4.4tO.2
6.1+0.2
3.2.1_0.3
4.710.3
t/c
2.29.1
4.420.2
2.2TO.2
2.69.2
5.2+0.3
3.0+0.3
*VP
F/C I .._-__..-..-
6.420.5 .._.__ _- ____ -
1522 -_._
.-..
J 622 ---_ - .._-_.-..-...
2023 ..___.--.-..-__
I!?+;!
iRatios calculutctl using the t.ol.al (1 ,I:) cyclobutanol yield. triplicate analyseo from at least two photolycrls Average of response Pactors were not determined. “The data for 4 In lhis solvent are from ref. 12. dMethyJcycJoh~ane.
17+2
-..--. runs.
_--__
.._.
Relative
vpc
Organic reactions in liquid crystalline solvents--V
so
long
as we conelne
solvents
the
studled.
We
dIscussJon
have
peak
corresponding
to
(see
kxperimental)
represents
the
various
Table
4
mentation
of
an attempt
to
for
cyclobutanal
lists
cfrcurvent
the
(IsotropIcI
solution
phase
sqatterlng/rePlectlon oosity
effect)
completely (:50X1. the
nsinw of
irs
solubility tlrthi is
J in
the
phase of
n
in
in
same solvent.
stmi Jar
TahJe
rates
acetonltrfJeJ.
the
smectlc
lit ies
JragmentatJon
al1
whl le
four those
solvents of
1
(and
and r
quantum Crystalltne
yields f’oi Solventu.a
large
bcQ
are
the
In
-3
and the
in more
similar.
$
series
oC
last to
and dif-
nenatlc
be discussed
of IBP
order
~1s’ been
opaque,
with
thus,
of
the
Nurrlsh
II
O.tSto.04
O.OSfo.02
?
I*OitO.l
1.elu.2
<.OOJ
0.03*0.02
%12flOnn
Pal lowed
RBB(nemJd --..-___ . . _.
e.001
-..- . . .
factor
Palrly
dffferencrs
from 3 relative
ECI isot I” ___-_-----_
f
- ..-.---
are
the
era~entatio1~
a
bulk
has not
those
from 4
proceeded
Paster
at
than
gB>MU>IIc>>n
in and
resptrctjvrlv.
HrJat ivc and Liquid
*l/+4
II
Is
it
light
to be further
amectic 1s:
errploy
sample
co~pleiety
and will
*pP
yields
Norrlsh
which
rates
appear
frag-
represents
determinations
results
from
4 and 4 in
1 than ._
yfeld
comparison
result phases.
of
for
QualJtaClvely.
Ketone HeCN’ __...I.._^ _-------------__--__--_-_
-_
the
rendri
These
actlnometer
4 lists
In
EB”EC>SCCN-kCCN.
‘fable 4: Isotropic
4 .unJ ? In
better
that
aamp1os
There
II
procedure
solvents.
are
1. and + fe
Norrlsh
irreproducible
phase
much lower).
for
the
quenching
single
gc conditions
solvents
samples
different the
two.
yields
urlng
JSOtrOpJc
saeclfc
the
our
the
quantum
impurity
fo the
difftcult.
under
Thfs
ulth
InnanneaIefJ is
Ilec:n~~st~ that ~rllihl
ehlxlcs the
errors
case
vix.
to
for
whether
of
orystalllno
different
samples
smecttc
NVP.
1~19 J ow Pact
the
resuJts
liquid
compared
reproduclbilfty
with
isot ropfc
as
eiutes
standard.
actlnometers:3a’d vastly
annealed
the
associated
In
crystals
successful,
degree
ficult
and 1x1 liquid
even
problems
reactions
results
a mixture
each
In
as
solvent
or
of
determining
II fragmentation
calculated
HVp fn_Sh~__sane
in which
fsomer
Norrlsh
relative
studied,
photochemical
a comparison
producttat
a single
the
solvents
to
been unsuccessful
I399
_.---. ._“I ..-.._...
fragmentat
_-.
2.3itJ.3
irradlwticm. 3O*C. Calculated reJative acetophenone Prom JIWP in the same solvent. blJata from Heference 12. :5:1 8CCH:cycJohexane (by wt.). 2:J IIcQ:#xI (by wt.).
_... .,. tn the
8 and 4 in
MiYIIsmJ .-_-- .._--.
ECCWISRJ --_...._.,_ ___..
0.12fo.04
o.or1to.oo5
J.Oti.1
0.08&0*02
. .
ion of
o.afo.2
0.121t.04
__ yield
0.01b&r.J.005
_ of
4-nethoxy.
W. J. LEIGHand S. JAKOBS
1400
DISCUSSION
Norrish
II
Reactivity
Wf?iSS Norrlsh
II
phases
to
lntcrpreted
as
ref’lectlng
the
ciaold-
of Lo
yield
involves
solvent
wilt1
in
counted
for
product
ratios.
effects
A
of the
JY storlcally
order
that
are on
effects
ratio
of
the
trans-
polarity
also
affects
solvent
polnrlty the of the
probe
thorough
In
smect
have
features.
is
the
solute
ic
yl~anc~s
been The
structure
of
ordered
and
the
(In of
polurity
nedlw
more demanding
the
the
of
behavinur
Norrlsh
contrlbutiun
of
workers
have
structure
of.
the
formed
II 8.23
be-
by the
clsoJd.bJradJcal it/c)
P/C and t/c
formed,
product
must
rfgitli
used Norrish
Jon.
ordered
as medium rigidity
and this
medlu~
been
kinetic
blradlcal
cyclobutanols
being
llyuld
has
t.hau fragmentat
aPPected
Isomer
III
on the
more strongly
decreases,
degree of
ratios.
iaIwicvs tk* a(’
1(I t Iw ~~t~s~~mwd
ty II
product
and solutc/medJum
rntlos
In
interacttons
in.
ecCH.2
Ttlr-
varytng
drnmetlcally
r,thr*r
observc:tl
smectlc
stale
st t‘~~rl~~r’a
ivi ly
that
and t/c:
of
rallos
with
sintldr
phases
behavlnur
to
the
shape
change
,ee.Rd.ga.b
panies
the
solvents
Jve to these
and t/c solvent
All
phase those
the
else
solute beJng
more
Isotropic
solute
of 6--phenyl
ratios (Tuble
which
8
mesogcn. extremely
in
length
sousii
Ivf: to
only
one or
of
betwec:n
solute
R-KH,)$i,
length
moblllty
(4.~alkoxyproptoyhenont?sl lmrtinrtnnl
k(*toru!‘s
Varlatious
conformational
in
i@l
in
*a: thf* mnI:nitudf!
n-l-8
Rhf. olkyl
undergo
In
the
course
the
shape
equal.
the
larger
strongly
it
Is
Jnhlbited
somewhat
surprised
we were
from 31.
have
rust
structural
I tw
whru
01
thy
proM:s!;
of
accom-
change
that
in
liquid
crystalline
to
find
ones.
conslderntions.
product
arc
I f‘avtor whir-h :~pp~k+~‘.: 10 hr
the
process.
relal Clven
which
the
changes
,&)%&, Jnterest
oblkin
relationahlps
rostrlct
t/c producl rat icss
irnd
solute/mesogen
rencl
and breadth) on g/C
to which
relative
on hlradlc~il
length
We have
11~: t.riplct
with
thr! cffcct
often
atoms.
studies
parallel
ratios
bulk
1ntermedtates:g
diastereomeric
correlate effects
largest
slallar
length, carbon
Of
(F/C)
t hc. subst ill11ial ~*fCc~:lson F/C
,
observed
naynltutlr
two
F/C
of
media.
that
of
Solsve
investigations
siaiihr
1.4-biradlcal
the
number
to
of
transold-
determining
fashion 24
ordered
In
a8
several
Crystalline
and aroma1 ic8a*b’d ketones in the solId. 8a-c, e 8d stearate and m. The observation
solvents
motions
in
Solvent
Increasing
similar
and
proportlona
increases. both
the
Sol vent
manifested
and Llauld
fragmentatJon/cycJJzatJon
cyclobutanuls
matrix.
higher
reported 8b,c.e
isotropic
conformatlonal
also
are
Iaotronic
n-butyl
in
relative
and
of
increases
crystalline
coup1 ing
have
OP aliphatlc
isotropic
substantial
haviour
and 4 In
coworkers
reactivity
and
meso-. 0e
and
of M
photolysio The variations
been
observed
of
#VP vary
dramatically
in
ratios
these
by Weiss
both
the
as a function
qr!sophasc*
wlth
and coworkers
that
In
other
type
systeas
Organic reactions in liquid crystalline solvents-v
such
as
sary
for
bonds
0 and I_o.
0d
product
The conformational
(Equation
3).
motions
of the
biradlcal
‘d’e’25
involve
rotation
about
The present
results
Indicate
either
fornation
1401
that
are
neces.
the
C ketyl-% and Ca?P that these motions are
af Feel cd
-
WVP: R-W, X-OMo 9: R- tCy,f~ X-H 10: R-cyclohoxyl. X-H by
liquid
are
in
CrystallIne those
depending of
the
in
derived
on the
ratios
It seems
most
size.
nematic Hence,
tlonal
the
moblllty. occur
must possible the
in
thrt
than
though
the
biradicals
is
in
EaI.
studies greater
the
solvent
tions
vary
the
four
Y/C
clearly F/C
The
factor
obtained
vironnants expected
its
aore
in saectic
highly
group
solvent,
changes
than
BCCN. It
is
is
situuted
although
in
we have
UCCJI indicate
ordered
no
That this
(and hence
on biradlcai
WCM because defined
the
“cavity”,
from photolysis phase.
more rigid)
dynamics
higher
beyond
that
crystalllnity
In which
to both
This
would shell
the
order
in
of
minters ?iolute
for .J is
listed similar
in isotropic
4
these
four
each
suggest phase,
Fragmentation
the
that
solvents this
identical of
case
Is
in Table
the
RO
with
4 for
for m
EC and nemalic
+reJ
values
MVP proceeds
of
local That 6
of bw
is
Comparison
those
in llrQl
ln these
of
and ICB
phaaes.
II fragmentation
in t’he smectjc
phases
EB.
P/C ratios
as we11 as the residee
causes
phaees
Norrish
H
in each
phases.
the mixture.
non-polar
do not
experiences
ketone
and nematic of
solvents
solute
soJve”ts
and ncmatic
largely
to that
four
biradlcal
if
smectic
smectic
lesogenic
the
higher
in
the
the
and mlcroviscosity)
temperatures
2--2.5
both
be
environment
quantum ylalds 4rr
that
polarity
In the
in
transition
biradical’s
of + in the
indicating
nolvation
obtained the
that
since
shape
smaller conforma.
results have been obtalned previously 9b-d and ECal. Perhaps solutes in this phase cx
respect
solvent
relative
in
solvated its
Similar
a better
solvent
from
ratios
for
m
obtained
types.
disrupts
&BCCM mixture
of
In smectic
of NW III smectjc is
or no 1nPluence
than
(with
of
of
in
with
phase
4 indicate
.8d
valeroyl
the
3).
to its
much saaller
the
of
basis
(Table
unrestricted.
environment
that
a way that
it
phase.
crontcs
ratios
evident
i”dJCate8
involve
val~ieo
on the
more tightly
at; a ror;ult
restrictlons
From 0 and H
region
little
g
matrix
“Isotropization” severt?ly
in such
nematic
oP
appreciably
simi Jar
motlons derived
polarity out
and Icp
eimply
@ and @ are
to comparable
From photolysir
muhllity
can proceed The
these
Fac:t that
exerts
Jn the
our
NVP is
that
than
as they
this.
ol‘ the
occurs
solvent
to suggest
between-layer
in spite sncctic
local
blradical
can be ruled
of MVP in lcQl
phases
solvated
or that
poS8JbiJity
from photolysis
lo subject
even
to support
perience
a
smectic
ratfos
which
of
reasonable
The product phase,
the
obtained
interdigitatcd,
evidence
The latter
biradical
m
and M.ed
9
type.
and
as much in the NW-derived
almost
from
phase
product
the
order
F
SJnce
microscopic
in virtually
In the
the
four
at a similar
study
rate
of the
identical
rolvents
en--
should
in each
and
be
phase.
W. J. LEIGHand S. JAKOBS
1402
Perhaps
It
4
those
and
la the difference
efficiency. those In
While
containing the
that
f simply
viscous
amectic
4 consisted
its
Isotropic
less
excitation
apparently
EB
(relative
to is
that
presumably
as
tional
mobility.
Thls
slight
quenching
the
renote,
shorter conditions: tlvity
are
triplet
such
n.ll*
identical.
thus possible
is
in the saectic
usJ2
that.
phases.
in nrmat ic or
state
yl+
conforma there
1Jfetine
sinct:
lhls
!,s
with of 6 in
is somewhat
compounds which do not have the under
It does not appt~rr lo derive energy. (heucc: allowing
from a
n wc
aspect
of
rc?ac: rflr!c:1
Iluenc
sllbst
l’nci le
as the p)losptlorc:8c:trl1(:~ emission
Hlrnl Iar
inl rinsic:
lht’ appirrcr~l ly hi&:r
this
its
interactions
4-acthoxvncetophenone
I’O~HI~I 1‘w
We ’ are investigating
lo
solvents.
The triplet
wJth this.
oP
than #VP in VISCOIIS
through-.space
of analogous
by 4 in EC
The implication
restrictions
ring.
I(!.&?. (
The
exhibited
in non-viscous
I is consistent
lifetimes
the lT.ll* slats! stats 22b.26 l2
of solvent-induced triplet
yield
in acetonitrile.
&~t_r:!!!s!c rc~cllvity
Indicate
intrractlons
> 10 US).
TT
raises
Jnterspersed
it
compared to that
~ragaonlation
Ecz!-alkoxyphcnyl (2.3
4 Is not. clear:
of
reactive
result would
the reactive
the
for
the higher Is of higher
electron-rich
than
which
of
6 a
solulfon
potential
droplets
conditions,
than NVP does
NVP) compared to that
media,
acetonltrile
light
in quantum
In appearance.
solvents.
results
these
glassy
to be nematic
rorlucc!d reactivity
ones containing
dJffr:ronce
IfUP samples YCIV unlfornly
Under our photolysis
We do not yet understand and
the apparent
of what appeared
phase.
receives
for
between the saectic
IIVP which Js causing
the
bulk saectlc
accounting
in sample quality
containing
populution
of the
spc!c:tre of‘ 9 and MP
lhcs photochenlstry
c~f’ 4 and
5 in more delail. Intramolecular --~---_----
Phenolic
enchinp.
r~~_C_a~hot~~y__! ._.~_!J?~~_~~~_..___._ 1n !,.iA\G!!..!:!:rs !_aNj 12:
Solvents --
1Ilcorp6ratJ “1, of virl.uaJJy This
oonplete
sandwich-like emcctic tion
from
be
transltlon
lncorporeted
in
molecules. solute
The is
extended
then
effects
the on
inr:reasing
reactlon
transition the
outweighs
rates
ePPect
state
in
is
oP snectic
of over
sulvcnls.
With
1 that 2 is unlPoraiy
its
It is expected fully
extended
parallel
lowering
geometry.
of
enthalpy
and entropy
the c?nerRy of
t.he
the enCropy to bt! galnrd
on the
activation
in the process.
enthalpy
crystalline effect An
of
in
involved
that
1nc:rrSr:;l*cl
the process.
In the actlvalion
the increased disorder which is imparted 5e.Qd.Q In the present case, approached. order
solvent thr
1I y . liquid
values)
in
of
restriction
to mure posltlvc!
soluble
that ? will
lobility
has on tho rn(t?.
of solvent-induced (1 .e.
103 In lhe
couforn.tlion
to the notions Genera
the
t.ht* lndica
to nelghbourlny
on the conformational restriction
I Is I II 2 I.
(Table
ln achieving
are aasked somewhat owing to the opposing
Increase of
by a factor
of a relative
quenching
involved
slightly,
aligned
order
result
is the result
the result
phases
a very pronounced
sandwich-like
acconpanying
is
as the
and
enthalpy
thr
entropy
conbined
the
only
long axis
smectic
oP
hoth the activation
activation while
Its
in Table
order
smectic
with
effect
conformer
achieving
solvent
the
and
motions
in non-viscous
temperatures
BCCQ and disrupts
(preferentially)
that
to the value
BCCH ~11‘ECUI rcsu
phenol Jc quenching
have been slowed
conpiex
relative
the
IntramoiecuJar
of
OP the conforaational
quenching
phases.
snectlc
in the smect ic phase of either
the rate
that
means
3
suppression
for
on the ~o.ly+J it
is
apparent
cyclizatlon
far
Organic reactions in liquid crystalline solvents--V In lesser
the
nematlc
extent
pronounced effect results
in viscous
simple
microviecoaity that in
changes state
the
rates
of
since
triplet
peded enough
decay.
et..a_l.
and
temperature
I fragmentation results conclusion
amectic
solvent.
yields
listed
problems 1
and
the
Aa
4.
reactivity
in
the
triplets self
bulk
quenching on
solution21b),
phases.
*’
at
solvent, occur
10%
of
according
bimolecular
upper lower
to
-10%)
limit
of 1.5 of 0.21
trlplets published
the are
in aromatic
for
the
rate
(the
effective
of diffusion
quenched
determinations
s-l
from
with the
the
(hulk)
because
of wlth
of 4 as the ac-
the
in
similarily
of m.
bulk
smectic
reactivity
in the ketone
x 10’
the
dct ived
solvent,
relative
to
phenollc quenching of ketone 13 Our results indicate that
muet prevail.
abstraction
limit
we calculate the
rate.
of 1. that
the
npparunt
cro88-
(to WP) quantum
fragmentation
within
its
of
biradical
were encountered
phaae
im
to explain
correlatable
demonstrate
smectic
phase
(more than
of v-hydrogen
an
“sub-phase”, if
(bulk)
to reduce since
the
clearly
for
consistrut
relative
not
on
are
the rate
phascq within
problems
to use
nematic
the
are
similar
the diffusion-controlled not
a
for 4,
two solvents
together
intersystem etep
EB are
?.I*
effect
motions
blradlcals
in a nematlc
These
sites
isotope
of
In
of biradical
arguments
BcQl and nematic
II) and the
coucentratlon
rate
end
nematic
reasonable.
the
of
(via
Intersystem
EB that
rate
by
conformer.
rate-determining remote 26
Since
solvent.
the
phase.
controlled
Iv&
in nematic to)
in
of the
quenching
conformational
similar
more meanlngful
nematic
hlgh
assuming
less,
samplea.
is
two radical
presented
previously
self..quenching
does
of the
solvents
the
out
dependence
deuterium
decay
resides
& In the
in a ketone--rich
expect
however,
or
is
proceeds
in splte
4 for
of 1 In nematic
one might
that
solute
pointed
1 in a given
Jf ,a resides then
thle
smectlc
it
for
recently
dependent
those
triplet
the
these
the
than
the decay
by the
similar
becomes
& in smectic
that
thr
to bring
microviscosity
least
the
8evere
sandwich-like
of 2-phenylcycloalkanones.
in Table
with
tino8eter
have
for
earlier
(or at
oyclization
Doubleday
Our
both
than
and/or
but
decay
a
evidenced
Presumably.
order
oncl- to end
viscusltyNorriah
lifetlael*).
Is alower
and
ing,
(as
the
of 2,’
species
Both
controls
required
scale
for
decay
in the nematic
of both
to
crossing
accounts
pre-
work.
similar
biradlcal
cyclization
motions time
by solvent
cyclizatlon
the decay motions.
intersystem
conformational
15ns
that
of future
The
analogous
We have
entirely
temperature
1 are
the
to what extent
result.
triplet
to a
types.
but without
are much leas
subject
and
end-to..end
on a much faster
the
fact
conformational
solution.
the
occur
the
abstraction)
cros*ing*‘)require acetonitrile
of
for
but
considering
two phase
overall
almoat
g and blradical
impeded.
to ancertain
the
the complete
of g and _S la the
similar
phenolic-hydrogen
to
quenching of
the
ordering.
parameters
in B-phenyl
of triplet
as a result
between
microviscosity
Arrhenlus
alma
lo expected
18 difficult
contribute
solvent
behaviour
The lifetlnes preauaably
It
solventa.
is
This
and rigidity
Determination
case.
quenching
phase.
may be due to rolvent
the
involved
present
triplet
phase effects
increases
shape
smectic order
laotropic
concluded
slight the
in
ncmatlc
intramolecular
the
in
differences
in the
viously
phase.
than
1403
rich
nematic
The effects ketones value
phase,
of nematic 1s not known;
for
llllp fn fluid
concentration
of 1, In -1 -1 to be 107..108 H 8
bimolecularly. of diffusion
Thla ratea
value
la
in nematic
W. J. LUGH and S. JAKOBS
1404 The relatively tlonal
higher
1 4 OJJ/+JJ
higher
vlacoslty
motlona
not
be
a
the
case
rates
in
than those that
that
greater phases
are
that
mesogen.
Ketone
solvent olecular
Is
about
and
ICQ.
obtalned
a
in the case
In
these
oP e,
present
these
the
fact
the
solutes
that
excimer
separation
phase
i‘luoresconce bulk
must contact
saectlc
with
a
shortened
very
to its inducing
may
(if
nromatlc Prom Its
high
order
phases).
the highly-ordered
in smectic
lntrnmolecular
are
solvents.
exclmer
formn-
involves
complexes
slmllar
as those
shorter
in the
time scale
Kxclmer formation
BCCII. although
does
at somewhat reduced
Conslderlng
our results
in the pyrene systems
In the smectic
phase,
concentrations simJlar
for
local
as a result
rates
1 and 1,
solute of
that
discrete
employed
solute
presumably
(300Indeed
Indicates
although
The isotropized
bulk environment.
MXII
results
be compured to the behavlour
one would expect
mJcrovJscosity.
we have found that 30 Ketone 1 ex-
in particular1
at the low solute did,
in sm~!c:tII:
HCCNand cholestcrlc
a conslderably
Is observed
the
lntram-
in m.
Analogous 9b.c: than go.
quenching
solvents.
of
at fcctod
mobility
longer
in BCCII of smectJc
reElecting
separation.
fluorophore).
local
and nematic
over
la
uY the
Yur smectl I: gCCN to
ketones, length
conlormational phsse
which are
smectic
it
phases
In the course
simi Iarly 9b
for 1 and 3 should
must occur
not occur
in fact
to that
The ef’Eect
solvent.
liquid
Pormation
respect
phase.
1 js
sandwich-like
disrupt
is
in the smectic
with
oE g Is even greater,
in B-phenyl
in
phase
as 6--pherlyl.-4-mc?thoxyprol,lophenonc!
oP &k In this
the isolated
rcasurementa
have
mobility
and isotropic
severely
molecules
(1.3-bis(pyrenyl)propanc
systems
interest--
of 1 and g in the Iwo snectlc
solute
the
crystalline 7c,d by Welss and coworkers.
of
to nematlc
relative
these
of
Por solutes
and
in which
It is
smectic
moJec:uJ~ must undergo
results
they
lifetime
in
proceed
the
but
case. the
ordered
detectable,
environment
the trlplet state behaviour of g as a 9 and corroborate the conclusion
Interestingly,
in
motions
of 1 is scarcely
the bulk snectic
this
oP Its
coapounds
conformational 400”s)
that
qoblllty
has been studled
tion
ot‘ tnn
stern found to be impeded substantially
range of
the present
Finally,
than a factor
such as PC.
the same length
to be Purther
a..w-bis(pyrenyJJalkanes
which
oP
motions
result
In
1enKth
minor restrictions
as
should
two solvents.
to the behavlour
needs only
are less
In the behaviour
quenching.
conlormational
periences
solvents
on the conformational
contrast
solute
Self-quenching
low viscosity
very highly
mobility the
3
trlplet
lnhlbit the
oE
and to
shape changes
in
gccn.
to the
on the conforma-
with only minor restriction.
in these
the temperature order
in 1.
solvent,
a Cairly
isotropic
whose conformatlonal
more severe
attributable
efPect
phase.
fragmentation
to the variations
solubility sensitive
throughout
11
oP 3. in this
substituent
extremely
t-J.
quenching
vfscuus
dilferences
analogous
of’
the
of
experiences
in vlncous
pronounced
Punotion
and Its
since it does not occur in 12 .003M In acetonltrile; it Is unlikely that
a fairly
solute
mobility
than that The
IIC,
is probably
9
In the isotropic
quenchJnK can proceed
the
phase,
to intramolecular Cactor
BCCII, Norrlsh
the
intramolecular
compared toU:
in acetonjtrile.
smectic
showing
BB
the nematic
0e 8 at a concentration
In
ing
leading
contrlbutlng
diffusion slower
in of
in the
behaviour
In
environment its
Intimate
Organic reactions in liquid crystalline
We are llquld relative
continuing
crystalline
to
investigate
solvents
solute/nesophase
on
structural
the solute
delicate mobility
1405
Solvents-V
balance
between
and associated
the
effects
reactivity
of and
features. EXPERIMENTAL
Melting points and transition temperatures were measured on a Bausch & Lomb fitted with a brass hot-stage and polarixfng filters (Spindler & 10x microscope. HI’C corrected. Temperatures were measured ustng a Cole-Pnrmer Model Hoyer 1 and 8110-10 Theraocouple Thermometer, the probe of which was embedded in the hot stage wlthln 2mm of the viewing wfndow. were recorded on a Hewlett Packard HP-8451 UltravIolet absorption spectra Perkln-Elmer Lambda-Q spectrometer equlpped with a PE Model spectrometer. or a Phosphorescence emlsslon spectra were recorded on a Perkin3600 Oata Station. I.95 spectrofluortreter equipped with the associated phosphorescenct! Klrnrr attachment .tnd Data Station. usiug 3-ma cylindrical quartz tubes. Laser flash phatotysis experiments employed the pulses (337.1 nm. 3.10 m.1. ca. 8 nsI Prom a Molectron IN-24 rtltrogen laser for excitation. and the CONpttte~i controlled detectlon lbat has been described In detail elsewhere. system Samples were contained in 0.3 x 7 rn~ rectangular ceJls built with Pyrex tubing IVitto Dynamics} Samples were prepared by adding an ailquot of a standard sotulion of the ketone in lIich~ox,om~,thant, to a cell by alcrolftre syringe. evaporating the solvent under a stream of nItroR!en followed by haklng in a 50* oven for a few hout~s ;1nrl tlw?n welghlng the npproprlate amount of the mesogcn into the cell. wits hubbled N i f rogen through the melted samples to ensure soIuLion hvmogrnc~ilyq were finally deoxygonatad wlth three freeze-.pump-melt cyclas I to 10 and they tllrr) srillf!d. Smect ic phase samples wer$’ then annealed in a 4O*C oveIl for 7 iind clnys The optical densltles of the soIutIons at 337 nm were in the range 0 150.20. Decay of laser-generat cd transic%t s was munitored by uv abnorpt ion, and tfdnslent Iffetines were caIr:ul.ltrd from traces obtalned by averaging IO-50 shots, r%r.h cnrrot~ted for haekKrouud scat taring of the excitat Ion pulse. Gas chroma tograph I c: separations employed 3700 gas a Varian Model chromatn~:raph equipped ~4th a flame ionlxntion detector. 2mX1/8” stainless steel Ov I7 Ion 801100 SctpeIcoportI or 30mX0.75mm 1 ‘urn SPkI Microbore columns (Supelco. a Hewlett-Packard Model 3393A and/or Varian CDS 111 Integrator. Inc I. dnd High Iw~rformancr I iquid ChronatoKraphic: anaiysas wore performed nsfng a 6r lson isoc:rat 1%: hplc system, consisting of a Model 302 pump ffltted with a 5 ml, head). Mndf*1 RO2B qanometrlc module. Holochrome variabJr wavt:Iant:th detector, a Hheodynt: Model 7125 loop injection valve. and a 0.46 cm Merck Hibar S160 I10 urn) analytIca column. Ethyl acctdte/hexnne mixtures were used as elunnts (0.51 OmL/minI. nnd ;,n analytical wnveJength of 2ROnn was used throughout. The detector wes interv i a an Adalnb data acyuisition/contt~ol f.tceii t $3 d U0 1 t 1’013 microcomputer cord I fnleractivt~ Microwarf~, Inc.}. after amplificnt ion of the 0- fOmV signal to 6 lv WItit an Adaanp analog amp1 If ier. Chromatogram acquisition. storage. and tntegration was performed using the Chromatochart finteract1ve Microware. Inc.) software package. Acetonitrilr ffaledon BI’LCI. dichloronrthane ICaledon IIPLCJ, ethyl acetate (BDH Reagent). hexane (Calrdorr HPJCI , meLhylrycIoIw?xane iBDH Omnlsolv). nnd cyclohexane (Baker Phot rex) were usrd as received. 4’.Butylblcyclohaxyl.4 carbonf triie IBCCN: EM Lfcristal ZLff938) and 4~ethyibfcyclohexyl-~4-carbo~~Itrfle EX Llrrfstal ZLII537I were used as reccivod from E. Merck Co. IBCCW: Cyr I nhexyl hcnzenf! was used as received from Aldrich Chemical Co., and dlmethyl isophtholate (Aldrich) was recrystallized from methanol Im.p. R7-6R°CI 1. 4-Methoxyvalerophenone (NVPI wds prepared by Frledrl .Crafts acyIatIon& anisole with valeroyl chloride and vacuum-dlstllled twice (b.p. IIS°C. 2mn lit. ’ 1434. RmmI. Kt:tonfj ?_. 3% 9, and S were prepared and purified according tu our published procedure. Solutions for the transition temperature study were prepared by dissolving BCCR In appropriate altquots of dichloroaethane solutions of the ketones. and off evaporating the solvent under high vacuum. Smmplcs were prepared on covered glass slides. Solutions for quantitative phutolyses ware prepared fin the dark) by adding att dltquot of a standard dichloromettlane solution of the ketone to a Jmm quartz tube, stripping the solvent under a stream of nitrogen, and adding the required amount of the nesogan. In some of the runs, the llvp samples also contalned 0.251101% (.006MI cyclohexylbenzene as an internal standard for vpc analysis. The tubes were sealed with rubber septa. deoxygenated by bubbling nitrogen through the isotropic phase (formed by heating, where necessary], and sealed with Parafila. Smectic phase samples were then annealed at 40°C for 2-3 days. Irradiations were conducted in a merrygo-round apparatus immersed in a thermostatted (30+10) water bath. with d 45OW medlur pressure Ranovia mercury laap. The latter was suspended
1406
W. J. L~IQH and S. JAKOB~ in a quartz f CrO (O.S4g/l J immersion well. surrounded by an aqueoys /Na CO (2.Og/l) solution filter (1 cm pathlength) In a Pyrex ves el (312+10nm). The2 ostical densities of the eolutlone (estimated from the UV absorption spectra) were -1 at 312 nm. and varied between 0.8-2.5 throughout the bandwidth of the aolution filter. Solutiona of NVP. 1. and 4 in emectic IcQl and ICQ (1.0~01%) and in RB. gCc. and acetonitrile (0.021) were prepared ae above and irradiated together for a The period of time correrpondlng to 10-30X conversion of the IIIIP/mesogen samples. tubes were then opened and dichloromethane (200 ul) wae added. Solutions containing HVP and 4 were analysed by vpc to determine t/c and P/C ratios. These ratios (Table 3) are the averages of triplicate analyses of two runa. The relative detector response for the fragmentation and cyclobutanol products wae not determined. Aliquots of a standard dlchloromethane solution oP dimethylieophthalate were added to the aolutlone of & and 4. and these were then analyeed by hplc. Relative quantum yielda were determined from the yields of p and e from a and 4. respecto dlmethylisophthalate; relative detector tlvely (measured by hplc relative responses calibrated) and from that of 4-methoxyacetophenone from NVP (measured by detector response calibrated). In one run, relative to cyclohexylbenzene: vpc reaction nixturee was carried out by hplc, using analysis of all three dlmethylisophthalate as internal standard. Identical results were obtained, within experimental error. The results (Table 4) were obtained from the averaKe of no fewer than triplicate analyses of three runs. We wish to thank E. Merck. Darmetadt for generous auppllcs of Acknowledgementa. Scaiano and NRC (Canada) for allowing us the use of the bed and ICQI. J.C. nanosecond laser flash photolysis facility. and R.G. Weisa (Georgetown University) S.J. is grateful to the Deutsche Akademlsche for preprints of reperencee 8d.e. We acknowledge the Natural Sciences and Auetanechdienst for a scholarship. Engineering Research Council of Canada Car Its generous financial support of this work. HEWHENCBS 1. Natural Sciences Research Fellow, 1983-88. 2.
On leave
and
Engineering
Prom Univereitat
Uuisburg.
Research
Duieburg,
Council
Ped.
(Canada)
Rep.
University
Germany.
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Bdftfon.
Edited
by We;tot.
R.c.:
CRC