Received: January 2, 1989 [Z 31 10 IE] German version: Angew. Chem. 101 (1989) 618

N . Schnell, K.-D. Entian, U. Schneider, F. Gotz, H. ZBhner, R. Kellner, G. Jung. Nurure (London) 333 (1988) 276. E. Gross. J. L. Morell, J. Am. Chem. Soc. 93 (1971) 4634. A. Hurst. Adv. Appl. Microbiol. 27 (1981) 85. E. Gross, H. Kiltz, E. Nebelin, Hoppe-Seyler's Z. Physiol. Chem. 354 (1973) 810. E. Gross, Adv. Exp. Med. Biol. 886 (1977) 131 T. Wakamiyd, Y. Ueki, T. Shiba, Y Kido, Y. Motoki, Tetrahedron Lett. 26 (1985) 665. a) H. Allgdier, G. Jung, R. G. Werner, U. Schneider, H. Zlhner, Angew. Chem. 97(1985) 1052; Angew. Chem. Int. Ed. Engl. 24 (1985) 1051 ; b) Eur. L Biochem. 160 (1986) 9. a) H. Kessler. S. Steuernagel, D. Gillessen. T. Kamiydma, Helv. Chim. Acru 79 (1987) 726; b) H. Kessler, S. Steuernagel, M. Will, G. Jung, R. Kellner, D. Gillessen, T. Kamiyama, ibid. 71 (1988) 1924. R. Kellner, G. Jung, T. Homer, H. Zihner, N. Schnell, K. D. Entian, F. Gotz, Eur. J . Biochrm. 177 (1988) 53. a) L. C. Ingram, Eiochim. Biophys. Acru 224 (1970) 263; b) C. Nishio, S . Komura. K. Kurahashi, Biochem. Biophys. Res. Commun. 116 (1983) 751. S. Banerjee. J. N. Hansen, J. Biol. Chem. 263 (1988) 9508. G. W. Buchmdn, S. Banerjee, J. N. Hansen, J. Biol. Chrm. 263 (1988) 16260. C. Kaletta, K.-D. Entian, J Eucreriol. 171 (1989) 1597. N. Schnell, K. D. Entian, F. Gotz, T. Homer, R. Kellner, G. Jung, FEMS Microhiol. Lett. 58 (1989) 263. a) H.-G. Sahl, H. Brandis, J. Gen. Microbiol. 127 (1981) 377; b) H.-G. Sahl. M. Grossgarten, W. R. Widger, W. A. Cramer, H. Brandis, Antimi- croh. Agents Chemorher. 27(1985) 836; c) M. Kordel, R. Benz, H.-G. Sahl, J Bucteriol. 170 (1988) 84. C. Kalettd, K.-D. Entian, R. Kellner, G. Jung, M. Reis, H.-G. Sahl, Arch. Microhiol., in press. E. Kusters, H. Allgaier, G. Jung, E. Bayer, Chromurogruphiu 18 (1984) 287. For automated Edman degradation, a pulsed liquid-phase sequencer Model 477 A with an on-line Model 120 PTH-analyzer (Applied Biosys- tems) was used. Sequencing reagents and solvents were from Applied Biosystems. The acidic total hydrolysates were analyzed by gas chroma- tographic enantiomer analysis on the chiral phase ChirasilLVal[171, using a Sichromat Autoderivat 100 (Siemens). FAB-Mass spectra were recorded with a VG 70/250/SEQ and the samples were applied in a matrix of 3-ni- trobenzylalcohol/methanoL a) E. Nebelin, E. Gross, Hoppe-Seyier's Z . Physiol. Chem. 354 (1973) 807; b) E. Gross, J. L. Morell, J. Am. Chem. Soc. 92 (1970) 2919.

Synthesis of a Rigid Electron-Donor/Acceptor Compound- Evidence for Intramolecular Charge Separation ** By Hans Heitele,* Peter Finckh, and Maria Elisabeth Michel-Beyerle

Particularly suitable for investigating the factors which determine the rate of electron transfer are compounds in which an electron donor and an electron ac- ceptor are rigidly bound together.[3 - The mutual diffusion of the reaction partners and possible changes of conforma- tion during the reaction are thereby excluded. Our investiga- tions on electron transfer processes1' O- ''I have now led to the compound 5, in which a (electronically excited) naph- thylene residue acts as electron donor and a dicyanoethyli- dene residue as electron acceptor. Compound 8 served as reference standard for fluorescence measurements.

Essentially all the steps of the synthesis of 5 and 8 can be taken from Ref. [3]. (Scheme 1). Upon fusion, acenaph-

I*] Dr. H. Heitele, Dr. P. Finckh, Prof. Dr. M. E. Michel-Beyerle Institut fur Physikalische und Theoretische Chemie der Technischen UniversitPt Munchen LichtenbergstraDe 4, D-8046 Garching (FRG)

the Volkswagenstiftung. I"] This work was supported by the Deutsche Forschungsgemeinschaft and

thalene reacts with polychlorocyclopentadienes at 110 "C in a Diels-Alder reaction to give the endo products 1 and 6 in 70-75 % yield. By reduction with a large excess of sodium in boiling ethanol/THF and rearomatization by heating with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in benzene all the chlorine atoms can be replaced by hydrogen atoms (2, 7; 63 and 32 % yield respectively). The double bond is hydro- genated at normal pressure in ethyl acetate on 10% PdjC (3 and 8). The ketal3 is then cleaved in a mixture of THF and 40% H'SO, (1 : 1) to give the ketone 4 (yield 78%), which upon Knoevenagel condensation with malonodinitrile in a Dean and Stark condenser (for removal of H,O) affords the desired product 5 (yield 79 YO). All compounds form color- less crystals.

X

x = O M , , CI x=ocH, 1 u 6

1. Na/EtOH/M 2. DDO

X + X

x = ow, 3 H 8

0

x = O M , 2 H 7

4 5

Scheme 1. Synthesis of the donor/acceptor compound 5 and the reference com- pound 8.

The structures of the products are confirmed by 'H NMR and mass spectra (Table 1). The large upfield shift (6 = 0.6- 0.9) of two of the four protons of the ethylene bridge in 3,4, 5 and 8 in the endo isomers can be explained, in particular, by a ring current effect on the H atoms lying directly above the naphthalene system. The larger extinction coefficient in 5 at ca. 290 nm compared to that in 8 indicates a direct charge transfer absorption[31 in 5 below 300 nm.

A comparison of the fluorescence spectra['31 (not correct- ed) of the compounds 5 and 8 in methanol and n-hexane affords the first evidence for their electron transfer proper- ties (Fig. 1). The shapes of the spectra of 5 and 8 in methanol are almost identical, the relative quantum yield q5 in the case of 5 is, however, only 1 YO of the yield for 8. The strong quenching is probably attributable to an intramolecular elec- tron transfer from the excited naphthylene residue to the dicyanoethylidene residue, which competes with the fluores- cence of the naphthylene residue. Intermolecular quenching processes can be ruled out because of the low concentration of the sample. From the ratio of the quantum yields q5J& 5 0.01 and the fluorescence lifetime za z 40 ns, a low- er limit of ca. 2.5 x lo9 s-l can be given for the electron transfer rate in 5.[L41 The free enthalpy of this reaction in

Angen. C'hem. lnr. Ed. Engl. 28 (1989) No. 5 0 VCH Verlagsgesellscht$t mbH. 0-6940 Wrinheim, 1989 0870-0833/89/0S08-0619 $02.80/0 619

Table 1. Spectroscopic data of the compounds 1-8 [a] methanol is estimated to be ca. -0.9 eV.['51 The emission spectrum of 5 in hexane shows, besides a small donor fluo- rescence with similar quantum yields as in methanol, a broad fluorescence band with a maximum at ca. 41 5 nm. The fluo- rescence excitation spectra in n-hexane (not shown) do not change upon variation of the wavelength of the observed fluorescence light between 330 and 470 nm and agree with the excitation spectrum of 8, i.e. the initial state of the red- shifted emission is populated via the excitation of the napthylene residue. The strong quenching of the donor fluo- rescence shows that the intramolecular electron transfer in 5 is also thermodynamically possible in apolar solvents. The emission at 415 nm is presumably due to a recombination fluorescence (transition from the charge transfer state into the ground state of the In polar solvents this emission is shifted into the infrared and its intensity decreas- es This explains the absence of a red shifted fluorescence band of 5 in methanol. A confirmation of this preliminary interpretation, however, requires further time resolved measurements.

The advantages of compound 5 are its simple synthesis, its completely rigid structure, the fact that electron transfer is possible in arbitrary solvents, and the long fluorescence life- time of the unquenched donor, which makes changes in the rate-by decreasing the temperature-of three orders of magnitude measureable.

l:m.p. 165.5-166"C(fromethanoI) 'H NMR:6 = 3.6(s,3H;OCH3),3.75(s. 3 H ; OCH,), 4.5 (s, 2 H ; Aryl-CH). 7.2-7.7 (m, 6 H ; Aryl-H). MS: mi; 414 ( M e , 19%), 381 (97), 379(100), 343(37), 152(62) 2: m.p. 120.5-122.5"C (from hexane). ' H N M R : 6 =3.1-3.4 (m, 2 H ; C=C-CH);overlapping with 3 .2(~,3H;OCH,)and3.37(~, 3H;OCH3),4.2 (br., 2 H ; Aryl-CH), 5.45 (m, 2H: HC=CH). 7.0-7.6 (m. 6 H ; Aryl-H). MS: miz 278 (Me, 100%). 263(45), 250(34). 203(86), 152(50) 3: m.p. 118-120°C (from hexane). 'H NMR: 6 = 0.6.- 0.8 (m. 2 H ; endo-H of CH,),1.3-1.6(m,2H;exo-HofCH2),2.5(br.,2H;CH),3.3(s,3H:OCH,), 3.4(s, 3H;OCH,),4.1 (br.,2H;Aryl-CH),6.9-7.6(m,6H;Aryl-H). M S : m / i 280 (Me, 97%), 265(100), 205(36) 4: m.p. 106.5-107.5"C (sublimed at lo-' mbar) 'H N M R : 6 = 0.8-1.7 (m, 4 H ; CH,), 2.45 (br., 2 H ; CH), 4.1 (br.. 2 H ; Aryl-CH), 7.0-7.6 (m, 6 H ; Aryl- H). MS: m / z 234 (Me, 67%), 179(100) 5:m.p. 198-199°C (fromethanol). 'H N M R : 6 = 0.9-1.6(m.4H; CH,), 3.4 (br.,2H;CH),4.1 (br.,2H;Aryl-CH), 7.1-7.7(m, 6 H ; Aryl-H). MS:m/z282 ( M e , 29%), 153(100), UV (MeOH): i.,,,[nm](lg E ) = 321 (3.06), 289(3.96) 6: m.p. 189-190°C from ethyl acetate). 'H NMR: 6 = 4.7 (s, 2 H ; Aryl-CH). 7.1-7.7 (m, 6 H ; Aryl-H). MS: mji 422 ( M e , Soh), 152(100) 7: m.p. 54-55°C (sublimed at lO-'mbar). ' H NMR: 6 = 1.65 (m. 2 H ; CH,). 3.23(br.,2H;CH),4.03(br.,2H;Aryl-CH),5.35(m,2H;HC = CH),7.0-7.6 (m, 6 H ; Aryl-H). MS: miz 218 ( M e , 18%), 152(100) 8: m.p. 84-85°C (sublimed at los3 mbar). 'H NMR: 6 = 0.7-2.0 (m, 6 H ; CH,), 2.6 (br., 2 H ; CHI, 3.9 (br., 2 H ; Aryl-CH), 6.8-7.7 (m. 6 H ; Aryl-H). MS: miz 220 ( M e . 511, 179(36), 153(100). UV (MeOH): E.,,,[nrn](lg E ) = 321 (3.12), 291 (3.84)

[a] The 'H NMR spectra were recorded at 60 MHz in CDCI, and the mass spectra at 70 eV.

ti \\ x 100

0 310 L10 510

2 x

1 I

:loS-"

I I

h l n m l -

, , I

I /

I I ,

\

\\ 5 \ \ \ \ ! \ \ \

klnrnl - Fig. 1. Fluorescence spectra of the compounds 5 and 8 in methanol (a) and n-hexane (b). Spectra of 5 ; 100 x and 10 x , respectively.

Received: December 27, 1988 [Z 3107 IE] German version' Angeu. Chem. 101 (1989) 629

CAS Registry numbers: 1, 119945-29-8; 2,119909-42-1 ; 3,119909-43-2: 4. 120010-45-6; 5, 119924-07-1 ; 6, 63784-80-5; 7, 26159-42-2; 8. 119945-30-1 ; CH,(CN),, 109-77-3; acenaph- thylene, 208-96-8; 5,5-dimethoxytentachlorocyclopentadiene, 2207-27-4; per- chlorocyclopentadiene, 77-47-4.

111 M. D. Newton, N. Sutin, Annu. Rev. P h w Chem. 35 (1984) 437, and references cited therein.

I21 R. A. Marcus, N. Sutin, Eiochim. Eiophys. Acta811(1985) 265, and refer- ences cited therein.

[3] H. Oevering. M. N. Paddon-Row, M. Heppener, A. M. Oliver. E. Cot- saris, J. W. Verhoeven. N. s. Hush, J . Am. Chem. Soc. 109 (1987) 3258.

[4] J. M. Warman, M. P. de Haas, M. N. Paddon-Row, E. Cotsaris, N. S. Hush, H. Oevering, J. W. Verhoeven, Nature (London) 320 (1986) 615.

[5] M. R. Wasielewski, M. D. Niemczyk, W. A. Svec, E. B. Pewitt, J. Am. Chem. Sor. 107 (1985) 1080.

161 D. Haler, G. McLendon, P. Rogalsky, J Am. Chem. SOC. 109 (1987) 604. 171 G. L. Closs, L. T. Calcaterra, N. J. Green, K. W Penfield, J. R. Miller, J

[S] A. D. Joran, B. A. Leland, G. G. Geller, J. J. Hopfield. P. B. Dervan, J

[9] R. J. Harrison. B. Pearce, G. S. Beddard, J. A. Cowan, J. K. Sanders,

Phw. Chem. 90 (1986) 3673.

Am. Chem. Soc. 106 (1984) 6090.

Chem. Phys. 116 (1987) 429. 1101 H. Heitele. M. E. Michel-Beyerle, J. Am. Chem. Soc. 107 (1985) 8068. [I I ] H. Heitele, M. E. Michel-Beyerle, P. Finckh, Chem. Ph.w Lett. 134 (1987)

273. [12] P. Finckh. H. Heitele, M. Volk, M. E. Michel-Beyerle, J Phys. Chem. 92

(1988) 6584. [13] Sample concentration 1 0 - 5 ~ , excitation wavelength 295 nm. The spectra

are independent of the excitation wavelength between 290 and 320 nm. All samples were prepared shortly before the measurement and carefully freed of oxygen.

[14] Electron transfer rate k = l/r, (&/b5-l). Fluorescing impurities (e.g. residues of 4) of < 1 % in 5 cannot, as yet, be excluded. The actual transfer rate could therefore be significantly greater than 2.5 x lo9 sCI.

1151 The free enthalpy of the electron transfer AGO is glven by AGO = E,, - ErCd -e2/cd - AE,,,, with the oxidation potential of the donor (acenaphthene) E,. % 1.35 V [16], the reduction potential of the acceptor Eled % -1.70 V [3] , the excitation energy of the acceptor A€,," = 3.85 eV (from the absorp- tion spectrum). and the coulomb energy of the ion pair with the ionic distance d = 6 A and the dielectric constant of the solvent (methanol) i: = 32. This gives AG" = -0.9 eV in methanol.

[I61 A. J. Bard, L. Lund: Encyrlopediu (q Electrochemistr>, of the Elements. Val. X I . Marcel Dekker, New York 1978.

620 0 VCH Veriugsgeselkchaft mbH, 0-6940 Weinheim. 1989 0570-0833/89lOS0S-0620 $02.S0/0 Angeu. Chem. h i . Ed. Engl. 28 (1989) No. 5