S 1 /S 2 exciton splitting in the (2-pyridone)2 dimer

Abstract

The S1↔S0 and S2↔S0 vibronic spectra of the supersonically cooled 2-pyridone dimer (2PY)2 and its 13C-, d1-, and d2-isotopomers were investigated by two-color resonant two-photon ionization and fluorescence spectroscopies. For the C2h symmetric (2PY)2–h2 and (2PY)2–d2 complexes, the 2PY moieties are equivalent and the S1↔S0 (1Ag↔1Ag) transition is forbidden. A single H/D or 12C/13C isotopic substitution reduces the symmetry to Cs, so that (2PY)2–13C and (2PY)2–d1 both exhibit S1↔S0 and S2↔S0 transitions. The S1/S2 state exciton splittings are 43.6 cm−1 and 52.4 cm−1, respectively. These are analyzed in terms of a Frenkel model and compared to calculated splittings based on ab initio monomer transition dipole moments. For (2PY)2–d1, whose 2PY subunits are different, an excitation transfer time of 318 fs is calculated from the exciton splitting. The S1↔S0 and S2↔S0 spectra are analyzed and assigned. Several bu intermolecular vibrations of S1 appear via vibronic coupling to the S2(Bu) state. Combination of the fluorescence data from excitation of the S1 and S2 origins and vibrational excitations of (2PY)2–h2, (2PY)2–d1, and (2PY)2–d2 allows the determination of the six S0 state intermolecular vibrational frequencies.

Excitonic Splitting, Delocalization, and Vibronic Quenching in the Benzonitrile Dimer

“…With this angle and the C 2h symmetry of the dimer, the higher-lying transition to the S 2 (B u ) state is fully allowed while the transition to the lower-lying S 1 (A g ) state is strictly electric dipole forbidden. This situation is closely analogous to other Hbonded self-dimers such as (2-pyridone) 2 , 23,31,32 (2-aminopyridine) 2 , 20,23 and (benzoic acid) 2 . 24 The BN monomer has been extensively studied by LIF and fluorescence emission spectroscopy.…”

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

“…The examples chosen were typically doubly H-bonded aromatic and heteroaromatic species, most notably the 2-aminopyridine (2AP) 2 , ortho-cyanophenol (oCP) 2 , 2-pyridone (2PY) 2 , and related molecular dimers. [6][7][8][9][10][11] The systems all show similar excitonic splitting schemes, with a (mostly) forbidden S 1 ← S 0 transition, that becomes slightly allowed upon asymmetric isotopic substitution.…”

“…Very satisfactory agreement with the observed S 1 /S 2 energy splittings could be obtained, 6,7,12 thus reconciling the large discrepancy between ab initio theory and experiment that existed before. 8 We have adopted and compared two different approaches using Förster perturbation theory and an effective mode ansatz that yielded a complementary description of the phenomenon. 12,13 We furthermore analysed the quenching in terms of a nonadiabatic tunneling splitting on the lower adiabatic potential energy surface (PES).…”

Excited-State Double-Proton Transfer in the 7-Azaindole Dimer in the Gas Phase. Resolution of the Stepwise versus Concerted Mechanism Controversy and a New Paradigm

“…Recently, the exciton resonance interaction has been studied for similar double hydrogen-bonded dimers, such as pyridone dimer [73][74][75] and anthralinic acid dimer 76 in the gas phase. The exciton resonance interaction strongly depends on the distance between the two monomer moieties as well as on the magnitude of the transition dipole moment.…”