Organic reactions in liquid crystalline solvents. 5.

Organic reactions in liquid crystalline solvents. 5.

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 CRYST...

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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.

3. For comprehensive deecriptlons of the structure and propertles oP liquid “Liquid crystals and leading references. see : (a) Sanva. Y.D. (editor). Warcel Dekker Inc.. New York, 1979. The Fourth State OC Watter”. Crystals. (b) Kelker, H.: Hatz. R.; “Handbook of Liquid Crystals”. Verlag Chemie. Welnheim. Deerfield. 1980. 4.

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21.

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Bdftfon.

Edited

by We;tot.

R.c.:

CRC