By means of fluorescence spectroscopy and nonlinear absorption experiments, excited-state processes of the modified pigments [3-acetyl]-chlorophyll a, [31-OH]-bacteriochlorophyll a and [3-vinyl]-bacteriochlorophyll a were investigated and compared with those of chlorophyll a and bacteriochlorophyll a

Katheder, Ingrid

Leupold, D.

Scheer, Hugo

Stiel, H.

Teuchner, K.

English

Universität München: Elektronischen Publikationen

JOURNAL OFLUMINESCENCE
ELSEVIER Journalof Luminescence60&61 (1994) 520-522
From chlorophyll a towardsbacteriochiorophyll a: excited-state
processesof modified pigments
K. Teuchner*,H. Stiel, D. Leupold,1. Katheder’,H. Scheer’
A4ax—Born—lnstitulfur iVichilineare Optik and Kur::eit.spcktro.ckopic. Rudower (haussec6. D—12474Berlin, (Jcr,nanv
Abstract
By meansof fluorescencespectroscopyand nonlinearabsorptionexperiments,excited-stateprocessesof the modified
pigments[3-acetyl]-chlorophylla,[31-OH]-bacteriochlorophyl!a and [3-vinyl]-bacteriochlorophylla wereinvestigated
and comparedwith thoseof chlorophyll a and bacteriochlorophylla.
I. Introduction becausethe structuraldifferencesbetweenChIaand
BChla involve the degreeof unsaturation(chlorin
Excited-statepropertiesof pigmentsof higher versus bacteriochlorin)as well as a changedsub-
plant and bacterial photosynthesisand of related stituentat C-3 (vinyl versusacetyl),thesemodified
modifiedpigmentsare of multifariousinterest,e.g., pigmentscharacterizetwo waysof this transit.Also
as basic information for molecular(excited-state) investigatedwasthe [3’-OH]-BChla, in which the
engineering,also with respectto the photophysical C-3 substituenthas no double bonds capableof
processesof photosynthesisandtheir alterationin conjugationwith the macrocycle.
caseof pigmentexchange,aswell as with respectto
photochemistryin view of photodynamictherapy.
Somewerepublishedrecently,especiallythose of
2. Experimentalchlorophyll a, bacteriochlorophyll a, chlorophyll
b and 20-chloro-chlorophyll a [1,2]. For a more
detailed characterization of the effect of the The pigmentsinvestigatedwerepreparedasde-
scribed in [3]. The solvent diethylether was of
transit chlorophyll a (ChIa) —+ bacteriochlorophyll
UVASOL grade. Fluorescencespectra,emissiona (BChla) on the excitedstateproperties,further
cross-sections,quantum yields, decay times and
fluorescencespectroscopyand nonlinearabsorp- ISC rates were determinedaccording to Ref. [4]
tion studieswere carried out with the modified
and literature cited therein. For determinationof
pigments [3-acetyl]-Chla and [3-vinyl]-BChla. thefluorescencequantumyields of [3-vinyl]-BChla
and[3’-OH]-BChla, the referencecompoundwas
BChla(i~F = 0.19, [5]), whereasthe quantumyield
of [3-acetyl]-Chla was calibrated against ChIa
* Correspondingauthor.
BotanischesInstitut der UniversitätMOnchen.MenzingerSir. (~. = 0.32, [1]). The nonlinear absorption appar-
67, D-80638 München,Germany. atus and the data processingwere describedin
0022-2313’94/$07.00~ 1994-——ElsevierScienceB.V. All rights reserved
.S~SDI0022-2313(93(E0452-4
K. Teuchnerci a!. / Journalof Luminescence60&61 (1994)520—522 521
Ref [6]. Excitation wasperformed by a dye laser larged by a factor of about two. Probably,this
pumpedby a nitrogenlaser(pulseduration:1.4 ns, couldbeexplainedby thelossof conjugationof the
pulseenergy:6—12 j.
1J). For further details cf. [1]. C-3 substituentwith the macrocycleleadingto an
additionalenergydissipationby therotationof this
group.
3. Resultsand discussion
3.2. Excited-stateabsorptions
3.1. Fluorescence,internal conversionand intersys-
tern crossing The values for the excited-singlet-stateabsorp-
tion cross-sections(cf. bargraphsin Figs. 1 and2)
In Table 1 the excitedstatedeactivationpara- were calculatedby curve simulation of intensity-
metersaresummarized.Theradiativelifetime (i/kR) dependenttransmissioncurves measuredfor dis-
of all pigmentsinvestigatedis approximatelythe tinct excitation wavelengths.For this an energy
same.Thedifferencesin thefluorescencelifetime (t) level scheme with two absorption steps in the
are mainly causedby intersystemcrossing (ISC). singlet and one in the triplet system (cf. inset of
Changeto a C7—C8 single bond gives increased Fig. 1) was utilized consideringthe rate constants
ISC in both cases(Chla—~[3-vinyl]-BChla; [3- of Table 1. The Franck—Condon relaxation
acetyl]-ChIa—~ BChla), whereas in cases of a (FC) and the triplet parameterswere generally
vinyl —+ acetyltransitionthe ISCchangewithin the set to kFc = 1 x 10
12s’, k~h= 1 x 104s’,
samemacrocycleconjugationsystemin minor.Our aT <5 x 10-17 cm2, kTfl = lx 1012 51 Further-
resultsfor BChla differ from that of Connollyet a!. more, it proves necessaryto considerthe cross-
[5], who discussedsmaller ISC yields (4jS. ~0.4) sectionsfor stimulatedemissionacm at leastfor the
obtainedfrom theoreticalcalculations,andcorre- long-wavelengthside of the S
1 absorptionband
latewith earlierexperimentalresultsof Gurinovich ~.(nm)/aemx 1016(cm
2): Chla — 666/2.6, 669/2.5;
eta!.[7]. Therateconstantsfor internalconversion [3-acetyl]-Chla — 677/2.3,686/3.4; [3’-OH]-BChla
(k~~)are aboutone order of magnitudelower than —. 730/2.3,734/3, 738/3.3,740/3.3; [3-vinyl]-BChla
for intersystemcrossinganddo notdiffer markedly. — 750/2.5,755/2.9,760/3,770/2.2;BChla —. 775/3.8,
An exceptionis [3’-OH]-BChla where k
1~is en- 780/4.3,785/4.4,790/3.6).
Table I
Excited-state deactivation channels of Chla, [3-acetyl]-Chla, [3’-OH]-BChla, [3-vinyl]-BChla and BChla in diethylether
Compound t (ns)
4~sc 4ic Ts~(ps)
kR(s’) k,,~(s”’)
ChIa 6.0 ±0.2 0.32 0.60 0.08
5.310~ iiO~ l.310~
[3-acetyl]-Chla 5.9 ±0.2 0.41 0.49 0.10 ~50
6.910~ 8.310~ 1.710~
[3’-OH]-BChla 2.9 ±0.2 0.23 0.67 0.10 ~50
7I0~ 210~ 3.410~
[3-vinyl]-BChla 3.1 ±0.2 0.20 0.75 0.05
6.510~ 2.410~ 1.610~
BChla 3.0 ±0.2 0.19 0.76 0.05 10
6.310~ 2.510~ I.7l0~
522 K. Teuchnerci a!. Journal of Luminescence60&61 (/994) 520 522
calculatedvaluesfor the relaxationof the S,, level
(t
1) are included in Table I.
Ll0161cm2! S~~1 ~L 4. Conclusions/PH /
The radiative lifetimes for the series ChIa—~
25~
[3-acetyl]-Chla —~ [3’-OH]-BChla —+ [3-vinyl]-
BChla—+ Bchla are almostequal.However, theflu-
orescencelifetimes decreasein this order and the
_____________________________________ differencesare mainly related to the presenceor
600 650 absenceof a fully unsaturatedring B. With excep-
V~aveIeng1hlnm]
tion of [3-acetyl]-Chla this correlateswith in-
creasedISC. For all compoundsstrong excited-Fig. 1. Cross-sectionsof the excitedsinglet absorptionno~)bar
graph)in comparison to the ground-stateabsorption cross- state absorptionswithin the S~—+ S
1 absorption
sections00 (curves) for )1) ChIa and (2) [3-acetyl]-Chla in bandwere found.
diethyletherat room temperature;Chla: = I x 10 M. [3-
acetyl]-Chla:c= 2.5 x 10 6 M; inset: energylevel schemefor
simulationof nonlinearabsorptioncurves(cf. text).
Acknowledgement
_____ —- This work wassupportedby the DeutscheFor-
5 schungsgemeinschaft(Le 729/1-1, Sche140/13-1).
0.1016
1cm 2! References
2.5 [1] D. Leupold,A. Struck,1-I. Stiel, K. Teuchner. S. Oberländer
and H. Scheer, Chem. Phys. Lett. 170 (1990) 478: A Pfar-
rherr. K. Teuchner, D. Leupold and P. Hoffmann, J. Photo-
chem.Photobiol. B: Biol. 9(1991) 35.
[2] M. Becker,V. Nagarjan,D. Meddendorf.MA. Shield and
W.W. Parson, in: Current Researchin Photosynthesis.
750 Vol. 1, ed. M. Baltscheffsky(Kiuwer. Dordrecht. 1990) p.Waveiengthlnm]
101.
[3] H. Scheer and A. Struck, in: PhotosyntheticReaction
Fig. 2. Cross-sectionsof the excited singlet absorption00 (bar Center,eds.JR.Norris andJ. Deisenhofer(AcademicPress.
graph) in comparisonto the ground-stateabsorptioncross- New York), in press.
sections00 (curves) for (1) BChla, (2) [3-vinyl]-BChla and )3) [4] K. Teuchner, A. Pfarrherr, H. Slid, W. Freyer and D.
[3’-OU]-BChIa in diethylether at room temperature;BChla: Leupold, Photochem.Photobiol.57 (1993)465.
c = 4.4 x 10
6M. [3-vinyl]-BChla: c 2.9x 10 6 M. [3i~0H]~ [5] J.S. Connolly, E.B. Samueland A.F. Jansen,Photochem.
BChla:c = 2.6 x 10 6M. Photobiol.36 (1982) 565.
[6] H. Stiel, K. Teuchner,W. Becker, Exp. ‘Iechn. Phys. 39
(1991) IS; H. Stiel, K. Teuchner.D. Leupold,S. Oberländer,
Strongexcited-stateabsorptionsin the region of S Ehlert and R. Jahnke,Intell Instr Camp 9 (1992) 79
the ground-stateabsorptionband could be found [7] G.P.Gurinovich,AN. Losevand El. Segun,J. App!. Spec-
for all pigmentsinvestigated(cf. Figs. I and2). The trosc. (USSR) 26 (1976) 740.


From chlorophyll a towards bacteriochlorophyll a: Excited-state processes of modified pigments

Open Access LMU ( Ludwig-Maximilians-Univ. München)

JOURNAL OFLUMINESCENCEELSEVIER Journal of Luminescence 60&61 (1994) 520-522From chlorophyll a towards bacteriochiorophyll a: excited-stateprocesses of modified pigmentsK. Teuchner*, H. Stiel, D. Leupold, 1. Katheder’, H. Scheer’A4ax—Born—lnstitul fur iVichilineare Optik and Kur::eit.spcktro.ckopic. Rudower (haussec 6. D—12474 Berlin, (Jcr,nanvAbstractBy means of fluorescence spectroscopy and nonlinear absorption experiments, excited-state processes of the modifiedpigments [3-acetyl]-chlorophylla, [31-OH]-bacteriochlorophyl!a and [3-vinyl]-bacteriochlorophylla were investigatedand compared with those of chlorophyll a and bacteriochlorophyll a.I. Introduction because the structural differences between ChIa andBChla involve the degree of unsaturation (chlorinExcited-state properties of pigments of higher versus bacteriochlorin) as well as a changed sub-plant and bacterial photosynthesis and of related stituent at C-3 (vinyl versus acetyl), these modifiedmodified pigments are of multifarious interest, e.g., pigments characterize two ways of this transit. Alsoas basic information for molecular (excited-state) investigated was the [3’-OH]-BChla, in which theengineering, also with respect to the photophysical C-3 substituent has no double bonds capable ofprocesses of photosynthesis and their alteration in conjugation with the macrocycle.case of pigment exchange, as well as with respect tophotochemistry in view of photodynamic therapy.Some were published recently, especially those of2. Experimentalchlorophyll a, bacteriochlorophyll a, chlorophyllb and 20-chloro-chlorophyll a [1,2]. For a moredetailed characterization of the effect of the The pigments investigated were prepared as de-scribed in [3]. The solvent diethylether was oftransit chlorophyll a (ChIa) —+ bacteriochlorophyllUVASOL grade. Fluorescence spectra, emissiona (BChla) on the excited state properties, furthercross-sections, quantum yields, decay times andfluorescence spectroscopy and nonlinear absorp- ISC rates were determined according to Ref. [4]tion studies were carried out with the modifiedand literature cited therein. For determination ofpigments [3-acetyl]-Chla and [3-vinyl]-BChla. the fluorescence quantum yields of [3-vinyl]-BChlaand [3’-OH]-BChla, the reference compound wasBChla (i~F= 0.19, [5]), whereas the quantum yieldof [3-acetyl]-Chla was calibrated against ChIa* Corresponding author.Botanisches Institut der Universität MOnchen. Menzinger Sir. (~. = 0.32, [1]). The nonlinear absorption appar-67, D-80638 München, Germany. atus and the data processing were described in0022-2313’94/$07.00 ~ 1994-——Elsevier Science B.V. All rights reserved.S~SDI0022-231 3(93(E0452-4K. Teuchner ci a!. / Journal of Luminescence 60&61 (1994) 520—522 521Ref [6]. Excitation was performed by a dye laser larged by a factor of about two. Probably, thispumped by a nitrogen laser (pulse duration: 1.4 ns, could be explained by the loss of conjugation of thepulse energy: 6—12 j.1J). For further details cf. [1]. C-3 substituent with the macrocycle leading to anadditional energy dissipation by the rotation of thisgroup.3. Results and discussion3.2. Excited-state absorptions3.1. Fluorescence, internal conversion and intersys-tern crossing The values for the excited-singlet-state absorp-tion cross-sections (cf. bar graphs in Figs. 1 and 2)In Table 1 the excited state deactivation para- were calculated by curve simulation of intensity-meters are summarized. The radiative lifetime (i/kR) dependent transmission curves measured for dis-of all pigments investigated is approximately the tinct excitation wavelengths. For this an energysame. The differences in the fluorescence lifetime (t) level scheme with two absorption steps in theare mainly caused by intersystem crossing (ISC). singlet and one in the triplet system (cf. inset ofChange to a C7—C8 single bond gives increased Fig. 1) was utilized considering the rate constantsISC in both cases (Chla—~[3-vinyl]-BChla; [3- of Table 1. The Franck—Condon relaxationacetyl]-ChIa —~ BChla), whereas in cases of a (FC) and the triplet parameters were generallyvinyl —+ acetyl transition the ISC change within the set to kFc = 1 x 1012s’, k~h= 1 x 104s’,same macrocycle conjugation system in minor. Our aT <5 x 10-17 cm2, kTfl = lx 1012 51 Further-results for BChla differ from that of Connolly et a!. more, it proves necessary to consider the cross-[5], who discussed smaller ISC yields (4jS. ~0.4) sections for stimulated emission acm at least for theobtained from theoretical calculations, and corre- long-wavelength side of the S1 absorption bandlate with earlier experimental results of Gurinovich ~.(nm)/aem x 1016 (cm2): Chla — 666/2.6, 669/2.5;eta!. [7]. The rate constants for internal conversion [3-acetyl]-Chla — 677/2.3, 686/3.4; [3’-OH]-BChla(k~~)are about one order of magnitude lower than —. 730/2.3, 734/3, 738/3.3, 740/3.3; [3-vinyl]-BChlafor intersystem crossing and do not differ markedly. — 750/2.5, 755/2.9, 760/3, 770/2.2; BChla —. 775/3.8,An exception is [3’-OH]-BChla where k1~ is en- 780/4.3, 785/4.4, 790/3.6).Table IExcited-state deactivation channels of Chla, [3-acetyl]-Chla, [3’-OH]-BChla, [3-vinyl]-BChla and BChla in diethyletherCompound t (ns)4~sc 4ic Ts~(ps)kR(s’) k,,~(s”’)ChIa 6.0 ±0.2 0.32 0.60 0.085.310~ iiO~ l.310~[3-acetyl]-Chla 5.9 ±0.2 0.41 0.49 0.10 ~506.910~ 8.310~ 1.710~[3’-OH]-BChla 2.9 ±0.2 0.23 0.67 0.10 ~507I0~ 210~ 3.410~[3-vinyl]-BChla 3.1 ±0.2 0.20 0.75 0.056.510~ 2.410~ 1.610~BChla 3.0 ±0.2 0.19 0.76 0.05 106.310~ 2.510~ I.7l0~522 K. Teuchner ci a!. Journal of Luminescence 60&61 (/994) 520 522calculated values for the relaxation of the S,, level(t1) are included in Table I.Ll0161cm2! S~~1 ~L 4. Conclusions/PH /The radiative lifetimes for the series ChIa —~25~ [3-acetyl]-Chla —~ [3’-OH]-BChla —+ [3-vinyl]-BChla —+ Bchla are almost equal. However, the flu-orescence lifetimes decrease in this order and the_________________________ _____________ differences are mainly related to the presence or600 650 absence of a fully unsaturated ring B. With excep-V~aveIeng1hlnm]tion of [3-acetyl]-Chla this correlates with in-creased ISC. For all compounds strong excited-Fig. 1. Cross-sections of the excited singlet absorption no~)bargraph) in comparison to the ground-state absorption cross- state absorptions within the S~—+ S1 absorptionsections 00 (curves) for )1) ChIa and (2) [3-acetyl]-Chla in band were found.diethylether at room temperature; Chla: = I x 10 M. [3-acetyl]-Chla:c = 2.5 x 10 6 M; inset: energy level scheme forsimulation of nonlinear absorption curves (cf. text).Acknowledgement_____ —- This work was supported by the Deutsche For-5 schungsgemeinschaft (Le 729/1-1, Sche 140/1 3-1).0.10161cm 2! References2.5 [1] D. Leupold, A. Struck, 1-I. Stiel, K. Teuchner. S. Oberländerand H. Scheer, Chem. Phys. Lett. 170 (1990) 478: A Pfar-rherr. K. Teuchner, D. Leupold and P. Hoffmann, J. Photo-chem. Photobiol. B: Biol. 9(1991) 35.[2] M. Becker, V. Nagarjan, D. Meddendorf. MA. Shield andW.W. Parson, in: Current Research in Photosynthesis.750 Vol. 1, ed. M. Baltscheffsky (Kiuwer. Dordrecht. 1990) p.Waveiength lnm]101.[3] H. Scheer and A. Struck, in: Photosynthetic ReactionFig. 2. Cross-sections of the excited singlet absorption 00 (bar Center, eds. JR. Norris and J. Deisenhofer (Academic Press.graph) in comparison to the ground-state absorption cross- New York), in press.sections 00 (curves) for (1) BChla, (2) [3-vinyl]-BChla and )3) [4] K. Teuchner, A. Pfarrherr, H. Slid, W. Freyer and D.[3’-OU]-BChIa in diethylether at room temperature; BChla: Leupold, Photochem. Photobiol. 57 (1993) 465.c = 4.4 x 106M. [3-vinyl]-BChla: c 2.9 x 10 6 M. [3i~0H]~ [5] J.S. Connolly, E.B. Samuel and A.F. Jansen, Photochem.BChla: c = 2.6 x 10 6M. Photobiol. 36 (1982) 565.[6] H. Stiel, K. Teuchner, W. Becker, Exp. ‘Iechn. Phys. 39(1991) IS; H. Stiel, K. Teuchner. D. Leupold, S. Oberländer,Strong excited-state absorptions in the region of S Ehlert and R. Jahnke, Intell Instr Camp 9 (1992) 79the ground-state absorption band could be found [7] G.P. Gurinovich, AN. Losev and El. Segun, J. App!. Spec-for all pigments investigated (cf. Figs. I and 2). The trosc. (USSR) 26 (1976) 740.

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From chlorophyll a towards bacteriochlorophyll a: Excited-state processes of modified pigments

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