“…The growth time constants for both Ret-8 and Ret-9 were estimated by fitting the picosecond data on a shorter time window of ≈500 ps and were 31 and 34 ± 6 ps, respectively. These match the fluorescence decay lifetimes measured for all - trans -retinal of between 17 and 30 ps. , The kinetic traces for Ret-8 and Ret-9 are shown in Figure . 2 Transient absorption kinetics observed for (a) Ret-8 and (b) Ret-9 at 396 nm with excitation at 355 nm in hexane solution obtained with the picosecond pump−probe spectrometer.…”
Section: Resultssupporting
confidence: 78%
“…We measured directly the growth of the triplet−triplet absorption signal on the picosecond time scale to be very fast (<40 ps) and thus estimate τ S ≤ 40 ps based on the picosecond pump-probe work or τ S < 2 ns based on the nanosecond emission techniques. Fluorescence lifetimes for native retinal have been reported in the literature to be between 17 and 30 ps. , …”
Section: Resultsmentioning
confidence: 99%
“…Solution Photochemistry of 11-cis-Retinal. In the photolysis of native 11- cis -retinal a very short-lived singlet state decays rapidly, exhibiting weak fluorescence and fast intersystem crossing (isc). , The photoisomerization of 11- cis -retinal to all - trans -retinal occurs with a quantum yield of 0.2. , The triplet quantum yield is 0.61 . Apparently adiabatic cis−trans isomerization occurs on the triplet surface on the picosecond time scale.…”
The photophysics and photochemistry of cis-locked retinal analogues have been investigated by steady-state and by picosecond and nanosecond time-resolved techniques. We have found that retinal analogues locked into the 11,12-cis configuration via bridged 8-and 9-membered rings, Ret-8 and Ret-9, respectively, are restricted in twisting about the 11,12 double bond in the first triplet state, T 1 . The twisting is restricted to different extents depending on the size of the ring. In the case of Ret-8, no geometric isomerization occurs following photoexcitation. This contrasts cis-cyclooctene derivatives which can be photoisomerized to thermodynamically less favored trans-cyclooctene. The result is rationalized by noting that in Ret-8 the ring incorporates four consecutive sp 2 carbons whereas the latter has only two. For Ret-9 which has one extra carbon in the ring, however, "cis-trans isomerization" becomes possible resulting in shorter-lived excited states and a detectable transient on the nanosecond time scale which is assigned to a short-lived (τ ≈ 110 ns) transoid ground state species.
“…The growth time constants for both Ret-8 and Ret-9 were estimated by fitting the picosecond data on a shorter time window of ≈500 ps and were 31 and 34 ± 6 ps, respectively. These match the fluorescence decay lifetimes measured for all - trans -retinal of between 17 and 30 ps. , The kinetic traces for Ret-8 and Ret-9 are shown in Figure . 2 Transient absorption kinetics observed for (a) Ret-8 and (b) Ret-9 at 396 nm with excitation at 355 nm in hexane solution obtained with the picosecond pump−probe spectrometer.…”
Section: Resultssupporting
confidence: 78%
“…We measured directly the growth of the triplet−triplet absorption signal on the picosecond time scale to be very fast (<40 ps) and thus estimate τ S ≤ 40 ps based on the picosecond pump-probe work or τ S < 2 ns based on the nanosecond emission techniques. Fluorescence lifetimes for native retinal have been reported in the literature to be between 17 and 30 ps. , …”
Section: Resultsmentioning
confidence: 99%
“…Solution Photochemistry of 11-cis-Retinal. In the photolysis of native 11- cis -retinal a very short-lived singlet state decays rapidly, exhibiting weak fluorescence and fast intersystem crossing (isc). , The photoisomerization of 11- cis -retinal to all - trans -retinal occurs with a quantum yield of 0.2. , The triplet quantum yield is 0.61 . Apparently adiabatic cis−trans isomerization occurs on the triplet surface on the picosecond time scale.…”
The photophysics and photochemistry of cis-locked retinal analogues have been investigated by steady-state and by picosecond and nanosecond time-resolved techniques. We have found that retinal analogues locked into the 11,12-cis configuration via bridged 8-and 9-membered rings, Ret-8 and Ret-9, respectively, are restricted in twisting about the 11,12 double bond in the first triplet state, T 1 . The twisting is restricted to different extents depending on the size of the ring. In the case of Ret-8, no geometric isomerization occurs following photoexcitation. This contrasts cis-cyclooctene derivatives which can be photoisomerized to thermodynamically less favored trans-cyclooctene. The result is rationalized by noting that in Ret-8 the ring incorporates four consecutive sp 2 carbons whereas the latter has only two. For Ret-9 which has one extra carbon in the ring, however, "cis-trans isomerization" becomes possible resulting in shorter-lived excited states and a detectable transient on the nanosecond time scale which is assigned to a short-lived (τ ≈ 110 ns) transoid ground state species.
“…While the protonated Schiff base of retinal is responsible for these biological functions, a free retinal itself has also been one of the central issues of photochemical studies because of its characteristic features in photoisomerization: the photoisomerization from mono- cis -retinal takes place efficiently and predominantly yields all - trans -retinal, whereas the photoisomerization from all - trans -retinal is much less efficient and the major product is 13- cis -retinal. − Owing to the significant difference in the photoisomerization efficiency of trans and cis isomers, the photoisomerization of this molecule is sometimes called “one-way isomerization”. , Time-resolved spectroscopy has been playing a crucial role in the elucidation of the mechanism and the dynamics of the photoisomerization of this molecule. Nanosecond and picosecond time-resolved spectroscopies such as UV−vis absorption, ,− infrared absorption, spontaneous Raman, − and 2D-CARS (CARS, coherent anti-Stokes Raman spectroscopy) have been applied to this molecule and afforded detailed information about the potential curves and dynamics of the excited state. Such time-resolved spectroscopic approaches, so far, have been mainly focused on the excited triplet state since the efficient isomerization from cis to trans takes place in the triplet manifold…”
The femtosecond time-resolved fluorescence of
all-trans-retinal in hexane was measured by using
the
fluorescence up-conversion method. It was found that the
fluorescence consists of ultrafast (τ = 30 ± 15 fs
and λmax ≈ 430 nm), fast (τ = 370 ± 20 fs and
λmax ≈ 440 nm), and slow (τ = 33.5 ps and
λmax ≈ 560 nm)
components. These three components were assigned to fluorescences
from the 1Bu, 1Ag, and
1
nπ* states,
respectively, which are successively populated during the relaxation
process in the singlet manifold after
photoexcitation. The oscillator strengths of the three excited
singlet states were determined to be 1.0
(1Bu),
0.024 (1Ag), and 0.0018
(1
nπ*) on the basis of the obtained
time-resolved fluorescence data. The state ordering
in the singlet manifold, as well as quantitative characterization of
the three low-lying excited singlet states,
is discussed.
“…This spectrum was replaced on a time scale of 34 ± 5 psec by strong absorption in the region 400-500 nm, the spectrum of which agreed with the well-known triplet-triplet absorption of all-trans retinal. Spectral and kinetic results were similar at 3000K and in a rigid glass at 77°K (48). The authors suggest that the first intermediate is an excited singlet state, rather than a higher triplet state, and that 34 psec is an upper limit for the intersystem crossing time to the triplet.…”
Three years ago one of us was asked by a funding agency to dust off his crystal ball and assess the fu ture importance of picosecond studies to chemistry. After a careful "objective" review of what had been accomplished up to then, and trying hard not to appear self-serving, he boldly concluded that a modest increase in the level of fu nding for picosecond instrumental developments appeared to be justified. In the light of what has occurred since then, this recommendation can only be considered cowardly. Almost all application of picosecond techniques in biology and biophysics has taken place in the past 2 or 3 years. Valuable new insights have been gained and in some areas, notably photosynthesis, striking ad vances in understanding have been made. Why? What special magic do picosecond techniques hold for biology? To answer this question we must trace its roots back to chemistry. The vast majority of chemical and biochemical reactions are composed of many elementary steps. The primary steps, which involve energy migration, bond breakage, molecular rearrangements, and charge transfer, all occur in the time range fr om about 10-14 to 10-8 sec. The "slowness" of an overall reaction is usually determined by other considerations, such as steric fa ctors and diffusion of reactants to the site of reaction. Picosecond spectroscopy enables us for the fi rst time to take a look at these primary steps.In this review we fo cus on the new insights that picosecond studies have provided in several important areas of biology. The area that has received the greatest emphasis to date is photosynthesis, which undoubtedly is appropriate, since we are all dependent upon photosynthesis both for our origin and for our continued survival. Picosecond fluorescence studies in both plants and bacteria show that excitation energy migrates fr om the antenna or light-harvesting system to the . reaction center in times that range fr om 10 psec to about I nsec, depending upon 189
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