We used ultrafast transient absorption spectroscopy to study excited-state dynamics of two keto-carotenoids, siphonaxanthin and siphonein. These two carotenoids differ in the presence of dodecanoyl-oxy group in siphonein, which is attached to the C19 carbon on the same side of the molecule as the conjugated keto group. We show that this dodecanoyl-oxy group, though not in conjugation, is still capable of modifying excited state properties. While spectroscopic properties of siphonein and siphonaxanthin are nearly identical in a non-polar solvent, they become markedly different in polar solvents. In a polar solvent, siphonein, having the dodecanoyl-oxy moiety, exhibits less pronounced vibrational bands in the absorption spectrum and has significantly enhanced characteristic features of an intramolecular charge-transfer (ICT) state in transient absorption spectra compared to siphonaxanthin. The presence of the dodecanoyl-oxy moiety also alters the lifetimes of the S1/ICT state. For siphonaxanthin, the lifetimes are 60, 20, and 14 ps in n-hexane, acetonitrile, and methanol, whereas for siphonein these lifetimes yield 60, 11, and 10 ps. Thus, we show that even a non-conjugated functional group can affect the charge-transfer character of the S1/ICT state. By comparison with fucoxanthin acyl-oxy derivatives, we show that position of the acyl-oxy group in respect to the conjugated keto group is the key feature determining whether the polarity-dependent behavior is enhanced or suppressed.

• Klíčová slova
• Carotenoid, Charge-transfer state, Excited-state dynamics, Ultrafast spectroscopy,
• MeSH
• acetonitrily chemie   MeSH
• hexany chemie   MeSH
• karotenoidy chemie   MeSH
• molekulární struktura MeSH
• rentgenová absorpční spektroskopie přístrojové vybavení   metody   MeSH
• rozpouštědla chemie   MeSH
• vodíková vazba MeSH
• xanthofyly chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• acetonitrile MeSH Prohlížeč
• acetonitrily MeSH
• fucoxanthin MeSH Prohlížeč
• hexany MeSH
• karotenoidy MeSH
• n-hexane MeSH Prohlížeč
• rozpouštědla MeSH
• siphonaxanthin MeSH Prohlížeč
• xanthofyly MeSH

We used ultrafast transient absorption spectroscopy to study excited-state dynamics of the keto-carotenoid fucoxanthin (Fx) and its two derivatives: 19'-butanoyloxyfucoxanthin (bFx) and 19'-hexanoyloxyfucoxanthin (hFx). These derivatives occur in some light-harvesting systems of photosynthetic microorganisms, and their presence is typically related to stress conditions. Even though the hexanoyl (butanoyl) moiety is not a part of the conjugated system of hFx (bFx), their absorption spectra in polar solvents exhibit more pronounced vibrational bands of the S2 state than for Fx. The effect of the nonconjugated acyloxy moiety is further observed in transient absorption spectra, which for Fx exhibit characteristic features of an intramolecular charge transfer (ICT) state in all polar solvents. For bFx and hFx, however, much weaker ICT features are detected in methanol, and the spectral markers of the ICT state disappear completely in polar, but aprotic acetonitrile. The presence of the acyloxy moiety also alters the lifetimes of the S1/ICT state. For Fx, the lifetimes are 60, 30, and 20 ps in n-hexane, acetonitrile, and methanol, whereas for bFx and hFx, these lifetimes yield 60, 60, and 40 ps, respectively. Testing the S1/ICT state lifetimes of hFx in other solvents revealed that some ICT features can be induced only in polar, protic solvents (methanol, ethanol, and ethylene glycol). Thus, bFx and hFx represent a rather rare example of a system in which a nonconjugated functional group significantly alters excited-state dynamics. By comparison with other carotenoids, we show that a keto group at the acyloxy tail, even though it is not in conjugation, affects the electron distribution along the conjugated backbone, resulting in the observed decrease of the ICT character of the S1/ICT state of bFx and hFx.

• MeSH
• molekulární konformace MeSH
• simulace molekulární dynamiky * MeSH
• xanthofyly chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• fucoxanthin MeSH Prohlížeč
• xanthofyly MeSH

Excited state dynamics of two apo-carotenals, retinal and 12'-apo-β-carotenal, were studied by femtosecond transient absorption spectroscopy. We make use of previous knowledge gathered from studies of various carbonyl carotenoids and suggest that to consistently explain the excited-state dynamics of retinal in polar solvents, it is necessary to include an intermolecular charge transfer (ICT) state in the excited state manifold. Coupling of the ICT state to the A(g)(-) state, which occurs in polar solvents, shortens lifetime of the lowest excited state of 12'-apo-β-carotenal from 180 ps in n-hexane to 7.1 ps in methanol. Comparison with a reference molecule lacking the conjugated carbonyl group, 12'-apo-β-carotene, demonstrates the importance of the carbonyl group; no polarity-induced lifetime change is observed and 12'-apo-β-carotene decays to the ground state in 220 ps regardless of solvent polarity. For retinal, we have confirmed the well-known three-state relaxation scheme in n-hexane. Population of the B(u)(+) state decays in <100 fs to the A(g)(-) state, which is quenched in 440 fs by a low-lying nπ* state that decays with a 33 ps time constant to form the retinal triplet state. In methanol, however, the A(g)(-) state is coupled to the ICT state. This coupling prevents population of the nπ* state, which explains the absence of retinal triplet formation in polar solvents. Instead, the coupled A(g)(-)/ICT state decays in 1.6 ps to the ground state. The A(g)(-)/ICT coupling is also evidenced by stimulated emission, which is a characteristic marker of the ICT state in carbonyl carotenoids.

• MeSH
• časové faktory MeSH
• hexany chemie   MeSH
• karotenoidy chemie   MeSH
• methanol chemie   MeSH
• retinaldehyd chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• hexany MeSH
• karotenoidy MeSH
• methanol MeSH
• retinaldehyd MeSH

A series of unsymmetrical tetrapyrazinoporphyrazines (TPyzPzs) from the group of azaphthalocyanines with one peripherally attached amino substituent (donor) were synthesized, and their photophysical properties (fluorescence quantum yield and singlet oxygen quantum yield) were determined. The synthesized TPyzPzs were expected to undergo intramolecular charge transfer (ICT) as the main pathway for deactivating their excited states. Several structural factors were found to play a critical role in ICT efficiency. The substituent in the ortho position to the donor center significantly influences the ICT, with tert-butylsulfanyl and butoxy substituents inducing the strongest ICTs, whereas chloro, methyl, phenyl, and hydrogen substituents in this position reduce the efficiency. The strength of the donor positively influences the ICT efficiency and correlates well with the oxidation potential of the amines used as the substituents on the TPyzPz as follows: n-butylamine < N,N-diethylamine < aniline < phenothiazine. The ICT (with conjugated donors and acceptors) in the TPyzPz also proved to be much stronger than a photoinduced electron transfer in which the donor and the acceptor are connected through an aliphatic linker.

• MeSH
• fluorescenční spektrometrie MeSH
• oxidace-redukce MeSH
• porfyriny chemie   MeSH
• transport elektronů * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• porfyriny MeSH

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8'-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8'-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.

• Publikační typ
• časopisecké články MeSH

Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties were compared to corresponding macrocycles that do not bear any donor centers. The data showed high feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of non-donor peripheral substituents on ICT was also described. The results imply that tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in applications based on ICT.

• MeSH
• fluorescenční spektrometrie MeSH
• hořčík chemie   MeSH
• indoly chemie   MeSH
• isoindoly MeSH
• komplexní sloučeniny chemie   MeSH
• kvantová teorie MeSH
• singletový kyslík chemie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• hořčík MeSH
• indoly MeSH
• isoindoly MeSH
• komplexní sloučeniny MeSH
• phthalocyanine MeSH Prohlížeč
• singletový kyslík MeSH

A series of octasubstituted zinc(II) tetrapyrazinoporphyrazines (TPyzPz), aza-analogues of phthalocyanines, differing in the number of peripheral N,N-diethylamino (n = 0-8) and tert-butylsulfanyl substituents (m = 8-n) has been synthesized. All possible congeners were characterized including adjacent and opposite isomers. Steady-state (UV-vis, fluorescence) and time-resolved (fluorescence, femtosecond transient absorption) spectroscopies, redox and photochemical (singlet oxygen formation) properties were investigated and compared. The peripheral tertiary amino substituents (donor) induce a new competitive relaxation pathway to fluorescence and intersystem crossing due to the mixing of the first excited state S(1) of the TPyzPz macrocycle with a nearby intramolecular charge transfer (ICT) state. The fluorescence quantum yield and fluorescence lifetime of 6Zn bearing one N,N-diethylamino substituent (n = 1, m = 7) decreased with increasing solvent polarity, while the same observables of 5Zn with no donor centre (n = 0, m = 8) were not affected. Protonation of the N,N-diethylamino substituent in 6Zn led to a strong increase of the fluorescence intensity. The cyclic voltammetry data, the steady-state and time-resolved emission and transient absorption studies revealed strong electronic coupling between the TPyzPz moiety and N,N-diethylamino substituents. ICT is an extremely rapid process occurring with a time constant of 10 ps and 7 ps in 6Zn (n = 1, m = 7) and 11Zn (n = 8, m = 0) in pyridine, respectively. The ICT efficiency decreased in non-polar solvents. The presence of two N,N-diethylamino substituents in 7Zn (n = 2, m = 6) considerably quenched the S(1) states in pyridine (polar, coordinating), toluene (non-polar, non-coordinating) and toluene-1% pyridine (v/v) (non-polar, coordinating). The photophysical properties of compounds with more donor substituents on the periphery (n > 2, m < 6) were similar to those of 7Zn.

• MeSH
• fluorescence MeSH
• fotochemické procesy MeSH
• indoly chemická syntéza   chemie   MeSH
• isoindoly MeSH
• kvantová teorie MeSH
• oxidace-redukce MeSH
• singletový kyslík chemie   MeSH
• spektrofotometrie ultrafialová MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• indoly MeSH
• isoindoly MeSH
• phthalocyanine MeSH Prohlížeč
• singletový kyslík MeSH

Single crystals of Diglycine Picrate (DGLP) were grown by slow evaporation technique and the vibrational spectral analysis is carried out using FT Raman and FT-IR spectroscopy, supported by Density Functional Theoretical (DFT) computations to derive equilibrium geometry, vibrational wavenumbers and first hyperpolarizability. The vibrational spectra confirm the existence of NH3(+) in DGLP. The influence of Twisted Intramolecular Charge Transfer (TICT) caused by the strong ionic ground state hydrogen bonding between charged species making DGLP crystal to have the non-centrosymmetric structure has been discussed. The Natural Bond Orbital (NBO) analysis confirms the occurrence of strong intermolecular N-H⋯O hydrogen bond. The HOMO-LUMO energy gap and the first order hyperpolarizability were calculated and it supports the nonlinear optical activity of the Diglycine Picrate crystal.

• Klíčová slova
• DGLP, FT-IR, FT-Raman, ICT, NBO,
• MeSH
• elektrony * MeSH
• krystalizace MeSH
• molekulární konformace MeSH
• nelineární dynamika * MeSH
• optické jevy * MeSH
• pikráty chemie   MeSH
• Ramanova spektroskopie * MeSH
• spektroskopie infračervená s Fourierovou transformací MeSH
• vibrace * MeSH
• vodíková vazba MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• picric acid MeSH Prohlížeč
• pikráty MeSH

The intramolecular charge transfer (ICT), which is a pathway for excited state relaxation, was studied on the newly synthesized zinc(ii) complexes of tetrapyrazinoporphyrazines bearing one fixed donor (i.e., a dialkylamino substituent). The rest of the peripheral substituents on the core was designed with respect to their different electronic effects (OBu, neopentyl, StBu, COOBu). The photophysical (singlet oxygen and fluorescence quantum yields) and electrochemical (reduction potentials) properties were determined and compared within the series and with compounds that did not contain a donor moiety. The ICT efficiency correlated well with both the electron-deficient character of the core and the Hammett substituent constants σp. The most efficient ICT was observed for the core with the most electron-accepting substituent (COOBu), and the lowest ICT efficiency was detected for the least electron-deficient core (substituted by OBu). Titration of DMSO solutions of target compounds with H2SO4 indicated that basicity of the azomethine bridges was largely influenced by the character of the peripheral substituents while the dialkylamino donor center remained nearly unaffected. Furthermore, protonation of the donor nitrogen caused partial restoration of the fluorescence quantum yield (increase up to 90 times) due to blocking of ICT. The results implied that the ICT efficiency was strongly dependent on the electron-accepting properties of the core whose properties can be readily affected by suitable selection of peripheral substituents.

• MeSH
• elektrochemie MeSH
• elektrony MeSH
• fluorescence MeSH
• indoly chemie   MeSH
• isoindoly MeSH
• organokovové sloučeniny chemie   MeSH
• singletový kyslík chemie   MeSH
• sloučeniny zinku MeSH
• spektrofotometrie ultrafialová MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• indoly MeSH
• isoindoly MeSH
• organokovové sloučeniny MeSH
• singletový kyslík MeSH
• sloučeniny zinku MeSH
• Zn(II)-phthalocyanine MeSH Prohlížeč

Light-harvesting complexes ensure necessary flow of excitation energy into photosynthetic reaction centers. In the present work, transient absorption measurements were performed on LH1-RC complexes isolated from two aerobic anoxygenic phototrophs (AAPs), Roseobacter sp. COL2P containing the carotenoid spheroidenone, and Erythrobacter sp. NAP1 which contains the carotenoids zeaxanthin and bacteriorubixanthinal. We show that the spectroscopic data from the LH1-RC complex of Roseobacter sp. COL2P are very similar to those previously reported for Rhodobacter sphaeroides, including the transient absorption spectrum originating from the intramolecular charge-transfer (ICT) state of spheroidenone. Although the ICT state is also populated in LH1-RC complexes of Erythrobacter sp. NAP1, its appearance is probably related to the polarity of the bacteriorubixanthinal environment rather than to the specific configuration of the carotenoid, which we hypothesize is responsible for populating the ICT state of spheroidenone in LH1-RC of Roseobacter sp. COL2P. The population of the ICT state enables efficient S1/ICT-to-bacteriochlorophyll (BChl) energy transfer which would otherwise be largely inhibited for spheroidenone and bacteriorubixanthinal due to their low energy S1 states. In addition, the triplet states of these carotenoids appear well-tuned for efficient quenching of singlet oxygen or BChl-a triplets, which is of vital importance for oxygen-dependent organisms such as AAPs.

• MeSH
• bakteriální proteiny chemie   metabolismus   MeSH
• bakteriochlorofyly chemie   MeSH
• karotenoidy chemie   MeSH
• kinetika MeSH
• přenos energie MeSH
• Rhodobacter sphaeroides metabolismus   MeSH
• Roseobacter metabolismus   MeSH
• Sphingomonadaceae metabolismus   MeSH
• světlosběrné proteinové komplexy chemie   metabolismus   MeSH
• xanthofyly chemie   MeSH
• zeaxanthiny MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyly MeSH
• karotenoidy MeSH
• spheroidenone MeSH Prohlížeč
• světlosběrné proteinové komplexy MeSH
• xanthofyly MeSH
• zeaxanthiny MeSH