- Email: [email protected]
Time resolved fluorescence in the picosecond region
Volume 29, number 3 . .
:.
I Decembc:
CHEMICAL. PHYSICS LETTERS
:.
..
.’
1974
:
,. 0
-,
TIhiiZ RESOLtiD FL~O~E~CE~~E IN THE PKXXECOND FWXOti _’ G. PORTER, ES. R&D and C.J. TREDWELL Davy Furodqv Research Laborarory ofTheRoynfins!~tuti~l~, LOllLicwlwsx43s, UK .’
‘Received 12 August 1974
.:
Time resolved ~uorescence~~dies of four organic molecules in soluiion show that, contrary ta an earlier report,’ the relaxed fluorescent S1 s!ates are formed within 10 ps of excitation even when excitation is to hQhhcr states. Fiucresccnco lifetimes for fluorescein and its halogen substituted derivatives vary over a factor of 40 owing to enhakced intersystem crossing. Measured radiative Lifetimes agree with those calculated from integkted absorption intensities and are relatjvely constant.
:
the spontaneous fluqrescence of erythrosin and other molecules in solution in none of which do we observe ~du~~~on periods of fluorescence longer than the time resolution of the apparatus (IO ps).
1..In~roduct~on
Alfano and Stiapiro [I] have rece&y reporled a subwnanosecond ‘grow in’ time for the sponianeous fluorescence from a dye (erythrosin) dissolved in water or methanol. They attribute this to vibrational relaxation in the excited singlet state, prior to fluorescence, and quote a lifetime of 30-43 ps for the piocess. Their data do not, however, eliminate the possib& Ety of other processes such as solvent o~entation re@&ion [2] which could cause time dependent spectral sltifts. Also, their quoted vibrational relaxation rates are smaller than those measured for other dye k?lecules in solution [3] or calculated from gas-phase data’ [4,5]. We report further picosecond studies of
2. Expe&ntal The experimen~~ a~~nge~eR~, ic sho&n in fig. !. A bode-lo~~ed Nd3+ glass laser-osciliator praduces,, at each firing, a train of SO-80
pulses of 1060 nm ta-
diatior., each of $-la ps durations 2s measured by two-photon fluorescence. These pulses are frequencydoubled with lo-15 5%efficiency in 2 temperaturetuned caesium dihydrogen arsenate crystal @DA).
._
-PuoToMMTIPLiER
Fig. 1. ‘I’hc Iasq arrangement
:
picosecond
fiUorescence lif&imes.
.’
_’
-
-. .
for metiur&g
t’
‘_ ‘.
‘I
1
,.,
.‘_._
.’ ‘,
(.
. . ., :..
469 ,.
:
...TrtiJ.ume29, npmbcr 3, ‘_ ,. 1 l&cnbcr 1974 CHEMICAL PH.QlCS LETTl:RS ._ .., .,, .. ‘. -. : :, .I,‘., : The’pidsei produced at 530 nm are again f:equencyThe energy of the switching pulses is monitored via -doubled with about 3-4 % efficiency in ,a’temperature,tiphotodiode as a check on the performance of the tuned crystal.of’ammonium djhydrogeri phosphate laser. Extinction ratios of up to 50 000 : I can be ob(ADP).,A beam splitter (90 % reflection at 26.5 nm, 4‘ : tained using.Polaroid’HN22 polarisers which give signal/noise ratios of 5:l for ti;e fluorescence signals ‘. 70 at.530 MI) separates the laser beam into two porfor these polartions. One portion is filtered (FL) to excite the sample .. ‘measurefd here. The extinction.ratios (S) with either 265 nm or 5’30 nm radiation. ’ isers &kavelength sensitive zind the figures quoted :
The-fluoresc&ce
froth the &ple
is colle&d,and
.. focussed through a shutter, comprising crosscd polarisers.(PL , p2) and-a 1 cm ceil of CS2 1as originally described by Duguay and Hansen[6]. Any fluorescence passing through this shutter is incident upon an
f-4 mono&rcmator, set at 10 nm bandpass, ind is detected by. a 1K!g photomultiplier, The shutter is ,, opened by the-second portion of the beam which is sent through a variable optical delay, faltered (Fi). and focussed slightly into the CS, cell, thrrs allowing ‘the tempora! variation of the fluorescence to be monitpred over a series of firings of the laser. The operation of this shutter has been described most fully by Duguay and Mattick [7]. _
are-the optimum obtainable. The zero time is deteimin-
:
ed by switching the excitationpulse itself with solvent alone in the sample cell. The-plot thus ob tamed represents a convolution of the excitation and-switching pulses and has a half width of 10 ps;indicating that
both the 530 nni and 265 nm pulses have pulse widths similar to that of the 1060 nm pulses, Optimum signal/ noise ratios at peak transmission in these.experiments ‘.. g, 50: 1. The delay position corresponding to the peak transmission point is taken.as the zero time and subsequent times are calculated from this iero point. It should be noted thiit the zero time for the 530 mm pulse occurs 25 ps before that of the 265 nm pulse which indicates
,.
.,..
. . ~H~~ICALP~YSiCS
.Ygiume’z?, riumber 3 .,
.’
&ElTERS
4 Decdtiber 1974
:
:
,-
:
_. ‘.
;
“’ -
‘.
..;
&xc&d
..,I
at i301im
Monikorcu
ut580nm
:’
‘.
)’ I.
-no
26
4o’e.a
ecJ
IQ0
120
140
160
iI30
200
220
240
263
PIC0SEC0H0S
Fig.3. ~~~th~~~~ nuorescence.
a delay between the two pulses. This delay has yet tq be explained but must be taken into account when .comparing data at the two wavelengths. Fluoreseenck lifetimes from 0.01-l ns can be measured using this technique. Eositi and erythrosin were purified chromat~gra~h- .. ically and dissolved in distilled water at PM’?. Perylene was obtained from Sigma Ltd. and dissolved in speciro-’ scq& grade cyclohexane without further pu~~cation:
”
:
., ‘_ 1...,
._:’
Most of the scatter can be att~buted to ~a~atiuns in
the ‘average peak power iA,the, switching beam which alters the transmission of the shutter. Simifar results we’re obtained across the fluorescence spectrum from ‘520 nm to 610’nm, and by monitoring v&h the first polariser either parallel or at right angles to the polari* sation. of the exciting beam. Fig. 3 shqws the results ~obtain~dfroth erythrosin where, asa&, instrument-limited rise-times were obtained..A fluorescence lifetime of 4 IO”_20ps was obtained .by ri least squares fit of the experimental data to an ‘.: 3. Resules’ exponential decay; this Gt is shown 2s the smooth t ‘.~uw~. Similar instrument-li~ted,n‘se-times were ob._ ‘, t&d f&m all molecu!es studied and the measured We have measured the picosecond time-resolved ~fet~mes are summa~sed in table I. Care was taken to spontaneous fluorescence intensities of eosin, erythrosin, and Buore&n in aqueous soluti
‘., . . .... __ ‘.:_ . .‘. ..:..
-. “
“ . ” .. ‘,.__. . .,.,, ., _ . ‘.
I_:
.. ,,c.L ..
471 .’ ‘.,.
‘.
‘.
.‘I
~olumc,29,n,umbci3
,,.,
CHEtiICALPH+
..
*. .:me; : (, ‘, . .* :. .). &tioresc~&k’I× of fluorcs~eindkivatives’, “ . ‘_ ‘. .:.. .Cornpound iexp ‘. bJ. Trad 7;ad (Cak) QXp .” ‘._.. ‘-. (ns) ‘. (nsl’.. tn;) ; .. ..(-fqj’.’
emin
., L.. :
.: ,’ m fj114.) ~ery?hro&n
3.6 a)..
‘1’ ~o.%l
..,3.6
0.92 0.19 ,’
: 0.1;
O.O!.
: d’
‘4.11 :.
4:7 ,,
‘.
4.26
:
T,, 5:5
.; ,’ ..:. ,‘I,.:
”
.. . . % -, ; ffzese.t&
‘,.;,
. Ru&escein
LETTERS ‘.
,4.36
-.~t-Ella),
1
December.1974
fluolesce& de&&es; The &&irnental values are in reasonable agreement With values C&XI. lated fro?? the inte&ited absoIptioh intensities [I I] (table.1): The vari~tion.in lifetime with h+ldge? substit~~~on’~sconsistent ~~.~ea~.atom enhanced iti-’ tersysteni &ossing drid with, published tr&,fet qutiturn yi$d” fl2] ; _‘. .. . ”
,. :,
:.
,.
,Ac~.ow~e~gemen~
:
‘:
: ._,
‘a) s&&f;‘lilj; b) seerefs, (IC,IZ~. .. ‘. _. : .) ” ._, ” :. ,’ ‘, Sl’ state or a higher dlectrkic state:We can therefore
l?e’wjs:! to th&k&e Science Research Council for the award of StudentshiPs to ES.& and C.J.T. We should $sO like to thank Dr. Colin Lewis for .many helpful discussions, and Mr. D. Madill for technical assistance.,
‘. conclude that internal conversion rates are.> 10” s-l,
in agreement with earlier predictions [9]. Vib;ation& ‘ly egcited S, states are formed following internal con- .’ version from higher glectroni!: states; ffuorescence -from these levels is possible ~t~lou~ we would exp& ‘, .. some broadening &d.a waveiiengih $ift compared with fluorescence .frog t&em-tally equilibrated levels. ... We ‘observed no change in the fluorescence spectruni of either. eosin in aqueous solution or perylene 5-icp :-clohexane, as a function of time after.excitation into -.. &$I electron& fevels & in the case of perylene). The .; rr&ure or magnitude of the expecte.d spectral shifts are ngi known but the absence of any spectral char&es vindicates that vibrational relaxation is also complete i&Z iO-1L s. Similar results were obtained from all the molecules studied, irkluding ei-ythrosin ..We theref&e stiggest‘that the ‘grow in’ time observed by Alfano tid Shrilfiirp wasa fortuitous combination of experimental ~uctua~ions. : ,, y‘The measured fluorescence lifetimes ,of erythrosin arid eosin, &ong with published quantum yield data (101 lrillow an estimate of the radiati~e.~fetjm~.of ‘, ,. ..
. : “’ “1’‘,.
.,
-.
“
Refereric&% /l 1 R,R. lilfano
and S.L. Shapiro, Opt. Conu-nun.6 (‘1972)
f 2j ?k.
YWe,SK Lee, GJ. Brant aad PP. Chow, 3. Chem. Phys. 54 (1971) 4729. [3j &JR.Ibpp, PX Rentzep’is and R,P. Jones, Chem. Phys. Letter; 9 (1971) 1.. : (41 ,S.J. Formosinho, G. Porter and M.A. West, PJOC. Roy. Soc.A333 (1973) X9.. -[.5j G.S. B:ddard, O.L.J. Gijieman, G.R. Fleming and G. Porter, Proc. Rdy. Sot. (19741, [6] hf.+ Duguay’and J.W. Hansen, (1969) 192. [7] M.A;Duyay and A.T. Mattick, 2162. [8] AX!. Albrecht, Progr. Reactibn
to be pub~shed. Appi. Phys. Lelten
15
Appl. Opt. 10 (1971) Kinetics 5 (1970) 301.
(91 M. Ka.sita,DiscussionsFaraday Sot. 9 (1950) 14. [JO] G. Weter qnd I;. Y@aIe,Trans. Faraday Sot. 53 (1957) ,646. [II j PG. Seybold,‘M. Goiterman tid J. CoBis,,Photochem. Photobiol. 9 (1369) 229. {131 PG. Bowersand G. Forter, Prqc. Roy. Sac. A299 : ps7)
34%
I
-,
-.
:.
I Decembc:
CHEMICAL. PHYSICS LETTERS
:.
..
.’
1974
:
,. 0
-,
TIhiiZ RESOLtiD FL~O~E~CE~~E IN THE PKXXECOND FWXOti _’ G. PORTER, ES. R&D and C.J. TREDWELL Davy Furodqv Research Laborarory ofTheRoynfins!~tuti~l~, LOllLicwlwsx43s, UK .’
‘Received 12 August 1974
.:
Time resolved ~uorescence~~dies of four organic molecules in soluiion show that, contrary ta an earlier report,’ the relaxed fluorescent S1 s!ates are formed within 10 ps of excitation even when excitation is to hQhhcr states. Fiucresccnco lifetimes for fluorescein and its halogen substituted derivatives vary over a factor of 40 owing to enhakced intersystem crossing. Measured radiative Lifetimes agree with those calculated from integkted absorption intensities and are relatjvely constant.
:
the spontaneous fluqrescence of erythrosin and other molecules in solution in none of which do we observe ~du~~~on periods of fluorescence longer than the time resolution of the apparatus (IO ps).
1..In~roduct~on
Alfano and Stiapiro [I] have rece&y reporled a subwnanosecond ‘grow in’ time for the sponianeous fluorescence from a dye (erythrosin) dissolved in water or methanol. They attribute this to vibrational relaxation in the excited singlet state, prior to fluorescence, and quote a lifetime of 30-43 ps for the piocess. Their data do not, however, eliminate the possib& Ety of other processes such as solvent o~entation re@&ion [2] which could cause time dependent spectral sltifts. Also, their quoted vibrational relaxation rates are smaller than those measured for other dye k?lecules in solution [3] or calculated from gas-phase data’ [4,5]. We report further picosecond studies of
2. Expe&ntal The experimen~~ a~~nge~eR~, ic sho&n in fig. !. A bode-lo~~ed Nd3+ glass laser-osciliator praduces,, at each firing, a train of SO-80
pulses of 1060 nm ta-
diatior., each of $-la ps durations 2s measured by two-photon fluorescence. These pulses are frequencydoubled with lo-15 5%efficiency in 2 temperaturetuned caesium dihydrogen arsenate crystal @DA).
._
-PuoToMMTIPLiER
Fig. 1. ‘I’hc Iasq arrangement
:
picosecond
fiUorescence lif&imes.
.’
_’
-
-. .
for metiur&g
t’
‘_ ‘.
‘I
1
,.,
.‘_._
.’ ‘,
(.
. . ., :..
469 ,.
:
...TrtiJ.ume29, npmbcr 3, ‘_ ,. 1 l&cnbcr 1974 CHEMICAL PH.QlCS LETTl:RS ._ .., .,, .. ‘. -. : :, .I,‘., : The’pidsei produced at 530 nm are again f:equencyThe energy of the switching pulses is monitored via -doubled with about 3-4 % efficiency in ,a’temperature,tiphotodiode as a check on the performance of the tuned crystal.of’ammonium djhydrogeri phosphate laser. Extinction ratios of up to 50 000 : I can be ob(ADP).,A beam splitter (90 % reflection at 26.5 nm, 4‘ : tained using.Polaroid’HN22 polarisers which give signal/noise ratios of 5:l for ti;e fluorescence signals ‘. 70 at.530 MI) separates the laser beam into two porfor these polartions. One portion is filtered (FL) to excite the sample .. ‘measurefd here. The extinction.ratios (S) with either 265 nm or 5’30 nm radiation. ’ isers &kavelength sensitive zind the figures quoted :
The-fluoresc&ce
froth the &ple
is colle&d,and
.. focussed through a shutter, comprising crosscd polarisers.(PL , p2) and-a 1 cm ceil of CS2 1as originally described by Duguay and Hansen[6]. Any fluorescence passing through this shutter is incident upon an
f-4 mono&rcmator, set at 10 nm bandpass, ind is detected by. a 1K!g photomultiplier, The shutter is ,, opened by the-second portion of the beam which is sent through a variable optical delay, faltered (Fi). and focussed slightly into the CS, cell, thrrs allowing ‘the tempora! variation of the fluorescence to be monitpred over a series of firings of the laser. The operation of this shutter has been described most fully by Duguay and Mattick [7]. _
are-the optimum obtainable. The zero time is deteimin-
:
ed by switching the excitationpulse itself with solvent alone in the sample cell. The-plot thus ob tamed represents a convolution of the excitation and-switching pulses and has a half width of 10 ps;indicating that
both the 530 nni and 265 nm pulses have pulse widths similar to that of the 1060 nm pulses, Optimum signal/ noise ratios at peak transmission in these.experiments ‘.. g, 50: 1. The delay position corresponding to the peak transmission point is taken.as the zero time and subsequent times are calculated from this iero point. It should be noted thiit the zero time for the 530 mm pulse occurs 25 ps before that of the 265 nm pulse which indicates
,.
.,..
. . ~H~~ICALP~YSiCS
.Ygiume’z?, riumber 3 .,
.’
&ElTERS
4 Decdtiber 1974
:
:
,-
:
_. ‘.
;
“’ -
‘.
..;
&xc&d
..,I
at i301im
Monikorcu
ut580nm
:’
‘.
)’ I.
-no
26
4o’e.a
ecJ
IQ0
120
140
160
iI30
200
220
240
263
PIC0SEC0H0S
Fig.3. ~~~th~~~~ nuorescence.
a delay between the two pulses. This delay has yet tq be explained but must be taken into account when .comparing data at the two wavelengths. Fluoreseenck lifetimes from 0.01-l ns can be measured using this technique. Eositi and erythrosin were purified chromat~gra~h- .. ically and dissolved in distilled water at PM’?. Perylene was obtained from Sigma Ltd. and dissolved in speciro-’ scq& grade cyclohexane without further pu~~cation:
”
:
., ‘_ 1...,
._:’
Most of the scatter can be att~buted to ~a~atiuns in
the ‘average peak power iA,the, switching beam which alters the transmission of the shutter. Simifar results we’re obtained across the fluorescence spectrum from ‘520 nm to 610’nm, and by monitoring v&h the first polariser either parallel or at right angles to the polari* sation. of the exciting beam. Fig. 3 shqws the results ~obtain~dfroth erythrosin where, asa&, instrument-limited rise-times were obtained..A fluorescence lifetime of 4 IO”_20ps was obtained .by ri least squares fit of the experimental data to an ‘.: 3. Resules’ exponential decay; this Gt is shown 2s the smooth t ‘.~uw~. Similar instrument-li~ted,n‘se-times were ob._ ‘, t&d f&m all molecu!es studied and the measured We have measured the picosecond time-resolved ~fet~mes are summa~sed in table I. Care was taken to spontaneous fluorescence intensities of eosin, erythrosin, and Buore&n in aqueous soluti
‘., . . .... __ ‘.:_ . .‘. ..:..
-. “
“ . ” .. ‘,.__. . .,.,, ., _ . ‘.
I_:
.. ,,c.L ..
471 .’ ‘.,.
‘.
‘.
.‘I
~olumc,29,n,umbci3
,,.,
CHEtiICALPH+
..
*. .:me; : (, ‘, . .* :. .). &tioresc~&k’I× of fluorcs~eindkivatives’, “ . ‘_ ‘. .:.. .Cornpound iexp ‘. bJ. Trad 7;ad (Cak) QXp .” ‘._.. ‘-. (ns) ‘. (nsl’.. tn;) ; .. ..(-fqj’.’
emin
., L.. :
.: ,’ m fj114.) ~ery?hro&n
3.6 a)..
‘1’ ~o.%l
..,3.6
0.92 0.19 ,’
: 0.1;
O.O!.
: d’
‘4.11 :.
4:7 ,,
‘.
4.26
:
T,, 5:5
.; ,’ ..:. ,‘I,.:
”
.. . . % -, ; ffzese.t&
‘,.;,
. Ru&escein
LETTERS ‘.
,4.36
-.~t-Ella),
1
December.1974
fluolesce& de&&es; The &&irnental values are in reasonable agreement With values C&XI. lated fro?? the inte&ited absoIptioh intensities [I I] (table.1): The vari~tion.in lifetime with h+ldge? substit~~~on’~sconsistent ~~.~ea~.atom enhanced iti-’ tersysteni &ossing drid with, published tr&,fet qutiturn yi$d” fl2] ; _‘. .. . ”
,. :,
:.
,.
,Ac~.ow~e~gemen~
:
‘:
: ._,
‘a) s&&f;‘lilj; b) seerefs, (IC,IZ~. .. ‘. _. : .) ” ._, ” :. ,’ ‘, Sl’ state or a higher dlectrkic state:We can therefore
l?e’wjs:! to th&k&e Science Research Council for the award of StudentshiPs to ES.& and C.J.T. We should $sO like to thank Dr. Colin Lewis for .many helpful discussions, and Mr. D. Madill for technical assistance.,
‘. conclude that internal conversion rates are.> 10” s-l,
in agreement with earlier predictions [9]. Vib;ation& ‘ly egcited S, states are formed following internal con- .’ version from higher glectroni!: states; ffuorescence -from these levels is possible ~t~lou~ we would exp& ‘, .. some broadening &d.a waveiiengih $ift compared with fluorescence .frog t&em-tally equilibrated levels. ... We ‘observed no change in the fluorescence spectruni of either. eosin in aqueous solution or perylene 5-icp :-clohexane, as a function of time after.excitation into -.. &$I electron& fevels & in the case of perylene). The .; rr&ure or magnitude of the expecte.d spectral shifts are ngi known but the absence of any spectral char&es vindicates that vibrational relaxation is also complete i&Z iO-1L s. Similar results were obtained from all the molecules studied, irkluding ei-ythrosin ..We theref&e stiggest‘that the ‘grow in’ time observed by Alfano tid Shrilfiirp wasa fortuitous combination of experimental ~uctua~ions. : ,, y‘The measured fluorescence lifetimes ,of erythrosin arid eosin, &ong with published quantum yield data (101 lrillow an estimate of the radiati~e.~fetjm~.of ‘, ,. ..
. : “’ “1’‘,.
.,
-.
“
Refereric&% /l 1 R,R. lilfano
and S.L. Shapiro, Opt. Conu-nun.6 (‘1972)
f 2j ?k.
YWe,SK Lee, GJ. Brant aad PP. Chow, 3. Chem. Phys. 54 (1971) 4729. [3j &JR.Ibpp, PX Rentzep’is and R,P. Jones, Chem. Phys. Letter; 9 (1971) 1.. : (41 ,S.J. Formosinho, G. Porter and M.A. West, PJOC. Roy. Soc.A333 (1973) X9.. -[.5j G.S. B:ddard, O.L.J. Gijieman, G.R. Fleming and G. Porter, Proc. Rdy. Sot. (19741, [6] hf.+ Duguay’and J.W. Hansen, (1969) 192. [7] M.A;Duyay and A.T. Mattick, 2162. [8] AX!. Albrecht, Progr. Reactibn
to be pub~shed. Appi. Phys. Lelten
15
Appl. Opt. 10 (1971) Kinetics 5 (1970) 301.
(91 M. Ka.sita,DiscussionsFaraday Sot. 9 (1950) 14. [JO] G. Weter qnd I;. Y@aIe,Trans. Faraday Sot. 53 (1957) ,646. [II j PG. Seybold,‘M. Goiterman tid J. CoBis,,Photochem. Photobiol. 9 (1369) 229. {131 PG. Bowersand G. Forter, Prqc. Roy. Sac. A299 : ps7)
34%
I
-,
-.