Charge Transfer and π to π* Transitions in the Visible Spectra of Sulfheme Met Isomeric Structures

Abstract

Since the 1863 discovery of a new green hemoglobin derivative called "sulfhemoglobin", the nature of the characteristic 618 nm absorption band has been the subject of several hypotheses. The experimental spectra are a function of the observation time and interplay between two major sulfheme isomer concentrations (a three- and five-membered ring adduct), with the latter being the dominant isomer at longer times. Thus, time-dependent density functional theory (TDDFT) was used to calculate the sulfheme excited states and visualize the highest occupied molecular orbitals (HOMOs) and lowest unoccupied MOs (LUMOs) of both isomers in order to interpret the transitions between them. These two isomers have distinguishable a and a HOMO energies. Formation of the three-membered ring S isomeric structure decreases the energy of the HOMO a and a orbitals compared to the unmodified heme due to the electron-withdrawing, sulfur-containing, three-membered ring. Conversely, formation of the S isomeric structure decreases the energy of the HOMO a and a orbitals due to the electron-withdrawing, sulfur-containing, five-membered ring. The calculations reveal that the absorption spectrum within the 700 nm region arises from a mixture of MOs but can be characterized as π to π* transitions, while the 600 nm region is characterized by π to d (d , d) transitions having components of a deoxy-like derivative.

Synthesis, Characterization, Bioactivity Screening and Computational Studies of Diphenyl−malonohydrazides and Pyridines Derivatives

“…According to the computed percentage contributions of several electronic transitions, the ICT transition for molecules ( 3,11 a – j ) appeared at a higher wavelength in the range of (269∼325 nm), which could be related to the large percentage contributions of HOMO→LUMO transition. Meanwhile, the π→π* electronic transitions of molecules ( 3,11 a – j ) appeared at a lower wavelength in the 225∼268 nm range, owing to the significant percentage contributions of HOMO+n to LUMO‐n transitions [55] . From the results, it was obvious that the intramolecular charge transfer (ICT) of ( 3 a – j ) are hypsochromic shifted corresponding to its analogous ( 11 a – j ).…”

“…Meanwhile, the π!π* electronic transitions of molecules (3,11 a-j) appeared at a lower wavelength in the 225 ∼ 268 nm range, owing to the significant percentage contributions of HOMO + n to LUMO-n transitions. [55] From the results, it was obvious that the intramolecular charge transfer (ICT) of (3 a-j) are hypsochromic shifted corresponding to its analogous (11 a-j). On the other hand, (11 a-j) showed a higher maximum molar absorptivity(ε) in the range of (2.51 × 10…”

Design, synthesis, and performance evaluation of TiO2-dye sensitized solar cells using 2,2′-bithiophene-based co-sensitizers

“…From their FMOS, the distribution of the electrons in the HOMO is concentrated on the whole molecule, whereas in the LUMO, there was a shift to the acceptor part toward the cyano-moiety. The computed contributions of various electronic transitions, presented in Table 1 (supplementary file), suggest that the ICT in co-sensitizers 3a-c and 5a-c is characterized by a peak absorption in the 470–478 nm range, related to the large contribution of HOMO to LUMO transitions Meanwhile, the π–π* electronic transitions of the compounds, due to significant contributions of HOMO-n to LUMO + n transitions 50 . Using the same basis set and functional energy, we calculated the electrostatic potentials (MEPs) of the dyes under investigation.…”

Liquid-crystalline circularly polarised fluorescent emitters with a high luminescence dissymmetry factor

“…27 This implies that the binaphthalene moiety has only a small effect on the excited state properties and the broad, structureless emission spectrum suggests that it originates from a charge-transfer (CT) excited state. 28 Large, positive solvatochromism was observed for the solvent-dependent emission spectra (Fig. 3b), further indicative of the strong charge-transfer nature of the excited state.…”