Analysis of the S₂←S₀ vibronic spectrum of the ortho-cyanophenol dimer using a multimode vibronic coupling approach

Abstract

Articles you may be interested inExcitonic splitting and vibronic coupling in 1,2-diphenoxyethane: Conformation-specific effects in the weak coupling limit J. Chem. Phys. 138, 204313 (2013); 10.1063/1.4807300The S 1/S 2 exciton interaction in 2-pyridone·6-methyl-2-pyridone: Davydov splitting, vibronic coupling, and vibronic quenching J. Chem. Phys. Analysis of the S 2 ← S 0 vibronic spectrum of the ortho-cyanophenol dimer using a multimode vibronic coupling approach The S 2 ← S 0 vibronic spectrum of the ortho-cyanophenol dimer (oCP) 2 is analyzed in a joint experimental and theoretical investigation. Vibronic excitation energies up to 750 cm −1 are covered, which extends our previous analysis of the quenching of the excitonic splitting in this and related species [Kopec et al., J. Chem. Phys. 137, 184312 (2012)]. As we demonstrate, this necessitates an extension of the coupling model. Accordingly, we compute the potential energy surfaces of the orthocyanophenol dimer (oCP) 2 along all relevant normal modes using the approximate second-order coupled cluster method RI-CC2 and extract the corresponding coupling constants using the linear and quadratic vibronic coupling scheme. These serve as the basis to calculate the vibronic spectrum. The theoretical results are found to be in good agreement with the experimental highly resolved resonant two-photon ionization spectrum. This allows to interpret key features of the excitonic and vibronic interactions in terms of nodal patterns of the underlying vibronic wave functions. C 2015 AIP Publishing LLC. [http://dx

Do Hydrogen Bonds Influence Excitonic Splittings?

“…[9] The S 0 → S 1 spectra of mCP and mCP- 13 C were used to determine the isotopic contribution ∆ iso = 3.3 cm However, these splittings do not take the redistribution of the electronic TDM into vibronic TDMs into account, and can therefore not be directly compared to the determined excitonic splittings ∆ exc . [3][4][5][6][7]9,10] To calculate the vibronic quenching factor Γ = Π i exp(-S i ) = exp(-Σ i S i ), we employed the Huang-Rhys factors � = � 2 � ℏ � � , where i numbers the totally-symmetric intramolecular vibrations of the BN or mCP monomer. [3][4][5][6] The experimental S i yielded Γ exp = 0.213 for (BN) 2 and Γ exp = 0.043 for (mCP) 2 .…”

“…[3][4][5][6][7]9,10] To calculate the vibronic quenching factor Γ = Π i exp(-S i ) = exp(-Σ i S i ), we employed the Huang-Rhys factors � = � 2 � ℏ � � , where i numbers the totally-symmetric intramolecular vibrations of the BN or mCP monomer. [3][4][5][6] The experimental S i yielded Γ exp = 0.213 for (BN) 2 and Γ exp = 0.043 for (mCP) 2 . [9,13] The vibronic coupling hence larger than the excitonic splittings and are heavily influenced by the hydrogen bond strengths.…”

“…Our group has been studying the excitonic S 0 → S 1 /S 2 splittings in rigid, doubly hydrogen-bonded dimers such as (2-pyridone) 2 , (2-aminopyridine) 2 , (benzoic acid) 2 , (benzonitrile) 2 and (ortho-cyanophenol) 2 . [2][3][4][5][6] They are centrosymmetric, meaning that the electronically excited S 1 (and higher S n ) states of monomers A and B are degenerate and excitonically coupled. [2][3][4][5][6][7][8] Upon dimerization the transition dipole moment (TDM) vectors of the monomers combine in a parallel and antiparallel manner, giving rise to an antisymmetric (A u , B u ) and a symmetric (A g ) excited state combination.…”

“…[2][3][4][5][6] They are centrosymmetric, meaning that the electronically excited S 1 (and higher S n ) states of monomers A and B are degenerate and excitonically coupled. [2][3][4][5][6][7][8] Upon dimerization the transition dipole moment (TDM) vectors of the monomers combine in a parallel and antiparallel manner, giving rise to an antisymmetric (A u , B u ) and a symmetric (A g ) excited state combination. [9] Thus, either the S 0 → S 1 or the S 0 → S 2 transition is electric-dipole (g↔u) allowed, while the other is electric-dipole (g↔g) forbidden.…”

“…[3,6] The observed splittings are up to a factor 40 smaller than the purely electronic (Davydov) exciton splittings ∆ calc that are predicted by high-level ab initio calculations. This so-called 'vibronic quenching' of the excitonic splitting ∆ calc can be obtained [3][4][5][6][7][8][9][10] by taking the Huang-Rhys factors S i into account within Förster's perturbation theory approach [7] or the Fulton-Gouterman model. [11,12] Applying the resulting quenching factor Γ to the calculated exciton splitting ∆ calc results in vibronic splittings ∆ vibron that are very close to the experimentally observed S 1 /S 2 splittings.…”