Optical Spectra of Oligofurans: A Theoretical Approach to the Transition Energies, Reorganization Energies, and the Vibronic Activity

Abstract

There is experimental evidence of high vibronic activity that accompanies the allowed transition between the ground state and the lowest electronic singlet excited state of oligofurans that contain two, three, and four furan rings. The absorption and emission spectra of the three lowest oligofurans measured at liquid nitrogen temperature show distinct fine structures that are reproduced using the projection-based model of vibronic coupling (with Dushinsky rotation included) parameterized utilizing either Density Functional Theory (DFT, with several different exchange-correlation functionals) or ab initio (CC2) quantum chemistry calculations. Using as a reference the experimental data concerning the electronic absorption and fluorescence for the eight lowest oligofurans, we first analyzed the performance of the exchange-correlation functionals for the electronic transition energies and the reorganization energies. Subsequently, we used the best functionals alongside with the CC2 method to explore how the reorganization energies are distributed among the totally symmetric vibrations, identify the normal modes that dominate in the fine structures present in the absorption and emission bands, and trace their evolution with the increasing number of rings in the oligofuran series. Confrontation of the simulated spectra with the experiment allows for the verification of the performance of the selected DFT functionals and the CC2 method.

Theoretical Investigation of a Coumarin Fluorescent Probe for Distinguishing the Detection of Small-Molecule Biothiols

“…The lower ALIE value of the Se atom compared to the S atom indicated the higher sensitivity of the CouSeNO 2 probe to biothiols than the CouSNO 2 probe, which was also testified within the experiment work. large reorganization energy and Huang-Rhys factors [27,28] for some normal vibration modes, as shown in Figure 4 To illustrate the electron excitation process from S0 to S1 within the CouSNO2 and CouSeNO2 probes, the hole-electron (brown and green colors, respectively, in Figure 5) analyses were performed based on the TDDFT results. It could be informed that the electron was mainly excited from the benzene ring part to the main planar part of the probes.…”

“…The dihedral angle, α, between the benzene ring and the main molecular plane of the CouSNO 2 probe variated from 59 • to 108 • when the molecule was excited from S 0 to S 1 ; this change in α was from 56 • to 108 • in the CouSeNO 2 probe. This large structural difference between S 0 and S 1 within the CouSNO 2 and CouSeNO 2 probes would lead to large reorganization energy and Huang-Rhys factors[27,28] for some normal vibration modes, as shown in Figure4(CouSNO 2 was only shown for clarity consideration). It could be seen that the vibration mode with large Huang-Rhys factors were just corresponding with the swing of the benzene ring in the probe molecule.…”