Electronic excited states of D-(-)-luciferin and related chromophores

Yamada

et al. 2013

Assignment of the fluorescence spectrum of firefly luciferin in aqueous solutions was achieved by utilizing not only emission energies but also theoretical absorption spectra and relative concentrations as estimated by pKa values. Calculated Gibbs free energies were utilized to estimate pKa values. These pKa values were then corrected by employing the experimental results. It was previously thought that the main peak near 550 nm observed in the experimental fluorescence spectra at all pH values corresponds to emission from the first excited state of the luciferin dianion [Ando et al. (2010) Jpn. J. Appl. Phys. 49, 117002-117008]. However, we found that the peak near 550 nm at low pH corresponds to emission from the first excited state of the phenolate monoanion of luciferin. Furthermore, we found that the causes of the red fluorescence at pH 1-2 are not only the emission from phenol monoanion but also the emission from the protonated species at nitrogen atom in the thiazoline ring of dianion.

Section: Resultsmentioning

confidence: 97%

Theoretical Study of Fluorescence Spectra Utilizing the pK_a Values of Acids in Their Excited States

Yamada

et al. 2013

“…The theoretical studies on luciferin were accelerated by the success in obtaining its X‐ray structure , because quantum chemistry calculations at that time needed information on molecular structures . Wada et al .…”

Section: Introductionmentioning

confidence: 99%

“…In 1975, Jung et al . reported the oscillator strength for luciferin using the SCF MO CI Pariser‐Parr‐Pople. In 2012, Anselmi et al .…”

Section: Introductionmentioning

confidence: 99%

Analysis of Photoexcitation Energy Dependence in the Photoluminescence of Firefly Luciferin

Mochizuki

et al. 2014

The whole pathways for photoluminescence, which include absorption, relaxation and emission, of firefly luciferin in aqueous solutions of different pH values with different photoexcitation energies were theoretically investigated by considering protonation/deprotonation. It is experimentally known that the color of fluorescence changes from green to red with a decrease in the photoexcitation energy. We confirmed with the theoretical analysis that the peak energy shift in the fluorescence spectra with varying photoenergies is due to a change in photoluminescence pathway. When the photoexcitation energy is decreased, the red emission from a monoanion form of firefly luciferin with carboxylate and phenolate groups and N-protonated thiazoline ring occurs irrespective of the pH values. However, because the species abundant in the solution and those excited by the photon depend on the solution pH, the pathway leading to the monoanion form changes with the solution pH.

“…According to previous theoretical studies (5), the first excited state of luciferin is represented by the excitation from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), wherein HOMO and LUMO have π symmetries. These excited states are valence excited ones in nature, although excitations induce significant reorganization of charge distribution.…”

mentioning

confidence: 99%

Theoretical Study of Absorption and Fluorescence Spectra of Firefly Luciferin in Aqueous Solutions

Yamada

et al. 2012

The absorption and fluorescence spectra of firefly luciferin, which is an analog of oxyluciferin, are investigated by performing the density functional theory (DFT) calculations, especially focusing on the experimentally unassigned peaks. Time-dependent DFT calculations are performed for the excited states of firefly luciferin and its conjugate acids and bases. We find that (1) the peaks in the experimental absorption spectra correspond to the excited states of not only (6'O(-), 4COO(-)) and (6'OH, 4COO(-)), but also (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (2) the peaks in the experimental fluorescence spectra correspond to the excited states of not only (6'O(-), 4COO(-)), but also (6'OH, 4COO(-)), (6'O(-), 4COOH), (6'OH, 4COOH) and (6'OH, 3H(+), 4COOH); (3) the unassigned peak near 400 nm in the experimental absorption spectra at pH 1 is assigned to the absorption from the equilibrium ground state to the first excited state of (6'OH, 3H(+), 4COOH); and (4) the unassigned peak at 610 nm in the experimental fluorescence spectra corresponds to the transition from the equilibrium first excited state to the ground state of (6'OH, 4COO(-)).