Substituent and solvent effects on the UV-absorption spectra of 2-phenylindan-1,3-dion-2-yl free radicals

283

.JourmlofMolecularSbucture,114(1984)283-286 Ekevier Science Publishers B.V., Amsterdam -

SUBSTITUENT

AND

SOLVENT

EFFECTS

2-PHENYLINDAN-1,3-DION-2-YL

ON THE

FREE

WBhringerstrasse Institute Sofia 3

38, A-1090

of Organic

1113,

_

University

F.FRATEV* und

Wien,

Chemistry,

UV-ASSORPTION

SPECTRA

OF

RADICALS

N.GETOFF1,1.TIMTCHEVA2, J.ZECHNERl, 1 Institut fijr Theoretische Chemie 2

printed in The Netherlands

and

ST.MINCHEV3

Strahlenchmie

der

Universitat

Wien,

Austria

Bulgarian

Academy

of Sciences,

Bulgaria of Shun-ten, Shumen,

Bulgaria

ABSTRACT 2-Phenylindan-1,3-dion-2-yl free radicals substituted in the 4'-position were produced by flash photolysis of the corresponding indandiones. Their UV-absorption spectra exhibit a pronounced solvent shift indicating a higher dipole moment in the excited state than in the ground state. Substituent effects were analyzed by means of a linear free energy relationship. The effects of substitution on the energy gap between the grcund and excited states of the free radicals and on the curvature of the excited state's energy hypersurface are discussed.

INTRODUCTION Derivatives ding a

on the

ijfl- band

the enole and

visible

Two

of P-phenylindandione

nature

of

at&e220

and

primary

forms

media

photoprocesses

OOZZ-2860/84/$03.00

0 1984

been

at approx.

300

in the most

for

these

formation

likely

Elsevier Science Publishers B.V.

after

forms

depen-

is responsible nm

absorption

acetonitrile;

observed

resulting

tautomeric

diketoform

to additional

(alcohols,

methylene-1-(3H)-isobenzofuranones,

the

snY-band

rise

have

process

in several

(refs.l,Z);

a weak give

in polar

(1) A photoisomerization

exist

solvent

nm and

enolate

range

the

for

in cyclohexane, bands

alkaline

compounds

in the

UV

water):

(ref.3):

of 3-phenylbond

splitting

due

to

28.4..

I’Norrish type I” mechanism. This is the predominant photoreaction

a

diketo

(2) A.spl.itting of the H-atom in &-position

to both keto groups from the diketo-

form or from the OH-group of the enol form or photoejection electron

from the enolabeform

the corresponding As has been pointed portance

for

several

ning substituent

respectively,

in all

Z-phenylindtin-1.3-dion-2-yl

free

out earlier

processes

effects

vent effects gy relationship

states

a:ld solvent

series analysis

(refs.8,9)

on the electronic

the relevant

these

for

cases

radicals

effects

of. a solvated under formation

radicals

of

(ref.3).

are of significant

interest.

It was now of interest

using a larger

and to perform a detailed

(ref.5)

of. -:echnol ogical

(ref.6)

have al ready been reported.

effects

from the

form (ref;4)

Some results

(ref.7)

im-

concer-

on their

spectra

to study substituent

and sol-

of derivatives

substituted

in the 4’-position

of the results

by appliing

a linear

the substituent

transitions

effects

free

and to interprete

in terms of electrostatic

ener-

solvent

influences

on

(refs.lO,ll).

METHODS The free responding

radicals

were generated

2-phenylindandione

of the experimental tus “Northern cribed

setups

Precision”)

by conventional

derivatives (applied

as well

flash

photolysis

in argon saturated

of the cor-

solutions.

Details

Photophysics, London, and a modified as of the synthesis of the indandiones

apparaare des-

elsewhere(refs.3,12).

RESULTSANDDISCUSSION UV-absorption

spectra

of transient

The UV-absorption ten 4’-substituted ethanol

absorption

(740 nm), alkaline The absorption

spectra

radicals

12).

by flash

were taken

of this

transi.ent

is furthermore

of

cyclohexane,

tu-

(735 nm), methanol

(670 nm) and n-heptane

(665 nm).

are in good agreement with those of the

(refs.13-15)

of the observed

photolysis in

For the 4’-dimethylamino-substi

maxima were measured in ethanol

produced by photo&is free

(ref.

assignment

obtained

of 2-phenylindandione

water (750 nm), cyclohexane

dimer. The assignment -Z-y1

and their

of the transients

derivatives

and al kal ine water (pH=lZ)

ted derivative

species

spectra

species

or thermolysis

transient

spectra

backed by the fact

(refs.6,13-15)

of the

to 2-arylindan-1,3-dionthat the decay of the radi-

cals leads back to the dimar. This dimer can also be prepared by radical-mediated one-electron oxidation (e.9. with HNO3, K3CFe(CN)6] or 12/0H- (ref.5). Sol vent effects A marked solvent of the absorption was observed.

dependence

(25 solvents

were examined,

this work and ref.-/)

maximumof the 2-(4’-aminophenyl)indandion-2-yl

Al though as a rule neither

fluorescence

.free radical

data nor ground state

285

dipole to

morremts or polarizabilities

correlate

the solvent

lations

(refs.lO,ll):

Despite

rather

terpretation in solutions

poles

tained These

the results

all

by fitting values

The ground

(2)

The excited

(3)

Effects Because

should

of

state

the

with

last

with

solute

first

cm-l)

following

are

the

term in eq.(3) and induced

agreed

in-

the absorptions which

solvent

di-

With this

cm-l_

interactions) well

in polar

with

that

solvents

ob-

(P72D).

interpretation:

higher

dipoles

re-

equations

term (dipole-dipole

has a permanent

in this

was attempted

following

(A+C)=-22500

the absorptions

the

radical

both

dipoles

yielding

(D=-1050

has a considerably

induced

dipole

dipole of

monent.

moment.

minor

importance.

treatmen t quantitative

conclusions

care.

effects

The UV-absorption bathochromically relation

term with

the approximations

be taken

Substi tuent

last

of

it the

Therefore

to the

solute

dipoles, to the

radicals

doubtful.

fitted

The result

in agreement

state

due to of

fitted

data.

the

are

(1)

were

free

by means of

by fitting

rather

permanent

induced

were

25 solvent

radical

obtained

between

as mutually

known for

this

remains

momentsp(lD

dipole

as well

using

the results

interactions

constant

of

good correlations of

represents

are

shifts

diagrams

spectra

of

the arylindandionyl

upon substitution according

to

(ref .12).

free

From the

the Hammett equations

are

radicals spectra

(4)

shifted

in ethanol

and (5)

cor-

were con-

s tructed. (4) (5)

As found consists Similar alkaline

of

for

vari,ous

two branches. shifts

water.

of

closed

she!1

organic

The reaction

the absorption

compounds

constants”3

spectra

are

(ref.9). given

were obtained

each

diagram

in table

in cyclohexane

1. and

in

Ham& (

correlation

9 A)

and

wavelenght

coefficients

O-O transitions edge

of

the

for. (soo;

absorption

estimated band)

aminophenyl)indan-1,3-dion-2-yl difference

absorption

free

maxima from

of

radicals

the

long

2-(4’-dimethyland

their

xl 7

.eoo

TA

I

%

Ccm-1]

GP

0

612

103

.-1.74

103

6.6 103 -1.5

103

-3.0 2.2

lo2 102 A

Similar shifts of the absorption spectra are obtained in cyclohexane and water. For the arylindandionyl free radicals both geometry changes and changes of the force constants upon substitution are obviously small.

REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

S.V.Kalinin (ed.),Structure.and Tautomerization Rearrangements of !3-Dicarbonylic Compounds, Zinatne, Riga, 1977 (in Russian) L.Linaberg;O.Nej,land, A.Veiss,G.Vanag, Cokl.Akad.Nauk S.S.S.R., 154, ( 1964) 1388 mechner, G.I.Grabner, G.Kijhler, N.Getoff, I.Timtcheva, F.Fratev, St.Minchev, J.Photochem., in print d.Rigaudy and P.Derible, Bull.Soc.Chim.France, (1965) 3047,3055,3061 V.V. Moiseev, I.T.Poluektov, Usp.Khim., 42, (1973) 471 A.I.Yasmenko, A.A.Kuznetsov, I.V.Khudyakov, Zh.Fiz.Khim., 54 (1980) 1776 A.I.Yasmanko, A.P.Wardin, I.V.Khudyakov, V.A.Kuzmin, Izv.Akad.Nauk S.S.S.R.,Ser.Khim., (1980) 2014 O.E.Polansky, F.Fratev, P.Nikolov, Z.Naturforsch., e, (1981) 197 F.Fratev, P.Nikolov, O.E.Polansky, Z.Naturforsch,. z, (1982) 1341 N.G.Eakshiev, Opt. i Spektros. 10 (1961) 717 M.F.Nicol, Appl.Spectros.Rev., 8(1974) 183 J .Zechner, N.Getoff, I .Timtcheva, F.Fratev, St.Minchev, Z.Naturforsch., in print I.V.Khudyakov, A.I.Yasmenko, V.A.Kuzmin, Int.J.Chem.Kinet., 11 (1979) 621 A.I.Yasmenko, I.V.Khudyakov, A.P.Darmanjan, V.A.Kuzmin and Sxlaesson, Chem.Scripta, 18 (1981) 49 I.V.Khudyakov,T.I.Yasmenko, A.P.Khardin, A.I.Prokovev and V.A.Kuzmin, Izv.Akad.Nauk S.S.S.R.,Ser.Khim., (1978) 1499