PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 3823373

Photosynthetic efficiency.

W Gebhardt
View original source ↗Export metadata ↓

Abstract

The efficiency of photosynthesis is discussed in analogy to the solar cell. The total efficiency eta can be written as a product of factors eta i concerning different loss processes. The fraction of photon energy hv which is available for photosynthesis in the membrane, usually called the thermodynamic efficiency eta th, is calculated. An upper limit of eta th is found by means of the second law of thermodynamics. Other factors take into account losses by reflection, absorption and by various irreversible processes of the photochemical pathways.

Explore related subjects

PhotochemistryPhotosynthesisThermodynamicsJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

W Gebhardt. 1986. Photosynthetic efficiency.. https://doi.org/10.1007/bf01214641

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2006

Internal conversion to the electronic ground state occurs via two distinct pathways for pyrimidine bases in aqueous solution.

The femtosecond transient absorption technique was used to study the relaxation of excited electronic states created by absorption of 267-nm light in all of the naturally occurring pyrimidine DNA and RNA bases in aqueous solution. The results reveal a surprising bifurcation of the initial excited-state population in <1 ps to two nonradiative decay channels within the manifold of singlet states. The first is the subpicosecond internal conversion channel first characterized in 2000. The second channel involves passage through a dark intermediate state assigned to a lowest-energy (1)npi* state. Approximately 10-50% of all photoexcited pyrimidine bases decay via the (1)npi* state, which has a lifetime of 10-150 ps. Three- to 6-fold-longer lifetimes are seen for pyrimidine nucleotides and nucleosides than for the corresponding free bases, revealing an unprecedented effect of ribosyl substitution on electronic energy relaxation. A small fraction of the (1)npi* population is proposed to undergo intersystem crossing to the lowest triplet state in competition with vibrational cooling, explaining the higher triplet yields observed for pyrimidine versus purine bases at room temperature. Some simple correlations exist between yields of the (1)npi* state and yields of some pyrimidine photoproducts, but more work is needed before the photochemical consequences of this state can be definitively determined. These findings lead to a dramatically different picture of electronic energy relaxation in single pyrimidine bases with important ramifications for understanding DNA photostability.

Photochemistry↗
PubMed2006

Synthesis of 7-azaserotonin: its photophysical properties associated with excited state proton transfer reaction.

We report the synthesis of 3-(2-aminoethyl)-5-ol-1H-pyrrolo[2,3-b]pyridine (7-azaserotonin), which may potentially serve as an agonist or antagonist of serotonin receptors. In alcohols, the solvent (e.g., ethanol) catalyzed proton-transfer reaction takes place for 7-azaserotonin in the excited state, resulting in dual emission. Conversely, excited-state deprotonation takes place in neutral aqueous solution. The unique excitation behavior makes 7-azaserotonin versatile as a potential bioprobe.

Photochemistry↗
PubMed2005

Ultrafast dynamics of all-trans--carotene explored by resonant and nonresonant photoexcitations.

Excitation energy dependence of transmittance change has been investigated in -carotene. The signal induced by nonresonant excitation is ascribed to the ac Stark effect and the two-photon absorption of the excitation and probe pulses in three-level systems. The ultrafast response following resonant excitation is assigned to the two-photon absorption and the transient absorption of the photogenerated S(2) state with a lifetime of 150 fs. The long-debated S(2)-S(1) relaxation in beta-carotene can be explained by a two-state model (S(2), S(1)) without involving any intermediate states.

Photochemistry↗