Intramolecular electronic energy transfer in 1,8(6′, 7′-dioxododecamethylene)phenanthrene

Volume 61, number 1

CHEMICAL

PHYSICS

LETTERS

1 February

iNTRAbfOLECULAR ELECI-RONIC ENERGY TRANSFER IN I,8(6’, i’-DIOXODODECAMETHYLENE) PHENANTHRENE Shammai SPEISER, Departntenr

Reuven KATRARO,

of Chemistry.

Recetxed Z Norember

Techion-Israel

Samuel WELNER

Imtirure

of TechnoIog>

1979

=

and Mordecai B_ RUBIN Haifa. IsraeL

1978

The absorption spectrum of 1.8 (6’.7’-dioxododccameth~ lene) phenanthrene (I) is composed of a superposition of the phensnthrene and btacetyl chromophores. The band at 340 nm corresponds to the phenanthrene absorptton and that at 450 nm can be asstged to the bixetyl chromophore_ Cvzitation at 337.1 nm results in emission from both chromophores. The Metime of the phenanthrene moiety in I is 10 ns compared to 60 11sin phmanthrcne. This IS indxatire of trn mtnmolecular energ> tansfer process_ T~ko-photon excitation of the biacrtyl chromophore results in emission from the phenanthrew mart). The mechxusm for these energy transfer processes IS probably of the Dexter type

1_ Introduction Intramolecular eiectronic energy transfer (intra-ET) between nonconjugated chromophores in a single molecule has been the subject of many studies [ 1] since it allows control of the spatial relationship between the two chromophores without the r,mdomness characteristic of intermolecular processes and has signifxcant implications in biological systems [2] _The first examples were studied in the pioneering works of Weber [3--5] and of Schnepp and Levy [6] _The necessary condition for inrra-ET is the presence of two moieties which satisfy the usual spectral overlap requirements for an energy transfer of the type D**A-+A*+D.

(I)

Both flexlble chains and rigid hydrocarbon skeletons have been employed to link the light absorbing donor and the acceptor. The experimental observation in the

past has been comp!ete

quenching

of donor fluores-

cence, even for donor moieties with high fluorescence quantum yield, with concomitant emission solely from

acceptor moiety. However, the observed transferyields have been less than 100%. This means that a fraction ’ Based in part on a thesis submitted by S.W_ (May 1978) to the Senate of the Technion. in partial fulfdment of the requirements for the DSc_ degree.

I

I

CH3C0 COCH3 a 1-g 1. I.&(6’.7’-dio\ododeameth)lene) phenanthrene I; 1.8-bls-(5’clrbometho~~pentyl) phemmthrme II; blacet\l III.

of the excited species decay nonradiatively directly to the ground state. We report preliminary results of emission studies on 1 ,S-(6’,7’-diosododecamethylene) phenanthrene (I). The spectroscopic properties of I and the model compounds 1 S-bis-(5’-carbomethosypentyl) phenanthrene (II) and biacetyl (III) (see fig. I) are shown in fig-2 where it can be seen that I is a good candidate for study of intra-ET between the phenanthrene and a-diketone moieties_

2. Experimental Syntheses

of i and II will be described separately I99

CHEMICAL

Volume 61. number I

I’ig

1.

Xbsorptton

[7] _ Fktorcscence

PHYSICS

LEXTERS

1 February

1979

speLtr.i of 1. II and bi.wzt> I (in acctottitrde).

spectra

were

t&en

using a laser flu-

oritttcter

[Sf_A tir) 15 spectrophotometer was used for absorption measurements. Lifetime studies were performed using nttrogen Idser and dye laser excitation (MoIectron UV -100 and DL 200) and a PAR 162 boxcar, the det.nIs \vilI be given elsewhere [9f _

fig_

her

3. Durtl fluorcsccnce spectra at 337 nm (in 231eTIiIQ).

of

I

exited

by a nitrogen

. zF!z CO$“3

,

\ ,

CO,CH,

XE==_ 337

nm

3_ Reruits and disct&on Fig_ 3 shows the fluorescence spectra of I and assorted liferimes obtained b?; escitation with a nitrosen Iasa (337 nm) at 193 K and at 77 K. These can be compared with the nitrogen Iaser cxctted Ihtorescence spectra of If at these temperatures