Electronic properties of N(5)-ethyl flavinium ion.
We investigated the electronic properties of N(5)-ethyl flavinium perchlorate (Et-Fl(+)) and compared them to those of its parent compound, 3-methyllumiflavin (Fl). Absorption and fluorescence spectra of Fl and Et-Fl(+) exhibit similar spectral features, but the absorption energy of Et-Fl(+) is substantially lower than that of Fl. We calculated the absorption signatures of Fl and Et-Fl(+) using time-dependent density functional theory (TD-DFT) methods and found that the main absorption bands of Fl and Et-Fl(+) are (π,π*) transitions for the S(1) and S(3) excited states. Furthermore, calculations predict that the S(2) state has (n,π*) character. Using cyclic voltammetry and a simplistic consideration of the orbital energies, we compared the HOMO/LUMO energies of Fl and Et-Fl(+). We found that both HOMO and LUMO orbitals of Et-Fl(+) are stabilized relative to those in Fl, although the stabilization of the LUMO level was more pronounced. Visible and mid-IR pump-probe experiments demonstrate that Et-Fl(+) exhibits a shorter excited-state lifetime (590 ps) relative to that of Fl (several nanoseconds), possibly due to faster thermal deactivation in Et-Fl(+), as dictated by the energy gap law. Furthermore, we observed a fast (23-30 ps) S(2) → S(0) internal conversion in transient absorption spectra of both Fl and Et-Fl(+) in experiments that utilized pump excitations with higher energy.
Department of Chemistry, Bowling Green State University, Bowling Green, Ohio 43403, United States.
Vincent
V
Sichula
Pavel
P
Kucheryavy
Renat
R
Khatmullin
Ying
Y
Hu
Ekaterina
E
Mirzakulova
Shubham
S
Vyas
Samuel F
SF
Manzer
Christopher M
CM
Hadad
Ksenija D
KD
Glusac
D004581:Electronics; D004583:Electrons; D005415:Flavins / Q000737:chemistry*; D005453:Fluorescence; D008958:Models, Molecular; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet
D005415:Flavins; C556459:N(5)-ethyl flavinium; C008465:3-methyllumiflavin