Resonance Raman Intensity Analysis of the Excited-State Proton-Transfer Dynamics of 2-Hydroxybenzaldehyde in the Charge-Transfer/Proton-Transfer Absorption Band

Abstract

Resonance Raman spectra were obtained for 2-hydroxybenzaldehyde (OHBA) in cyclohexane solution with excitation wavelengths in resonance with the first charge-transfer/proton-transfer (CT/PT) band absorption. These spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion predominantly along the nominal C=CH in-plane bend+ring deformation modes (nu9, nu10, nu14, nu16, nu18, nu19, nu20, nu26, nu30, nu31, and nu35) accompanied by a smaller amount of motion along the nominal C=O stretch mode (nu7), the nominal C=C-C(=O) in-plane bend modes (nu33 and nu37), and the nominal ring C-O-H in-plane bend modes (nu9 and nu14). A preliminary resonance Raman intensity analysis was done, and these results for the OHBA molecule were compared to results previously reported for the 2-hydroxyacetophenone (OHAP) molecule. Several proton-transfer tautomers in the ground and excited states were predicted from the results of B3LYP/cc-PVTZ, UB3LYP/cc-PVTZ, and CASSCF/cc-PVDZ level of theory computations. The differences and similarities between the CT/PT band resonance Raman spectra and the vibrational reorganizational energies for the OHBA molecule relative to those for the OHAP molecule are briefly discussed.

Decay dynamics of α,β-carboxylic methyl esters (CH3OCOCH:CHR) in the lower-lying excited states—Resonance Raman and complete active space self-consistent field calculation study

“…This indicates that the major part of structural dynamics associated with the ultrafast S 2,FC →S 2 /S 1 decay process can be probed via the resonance Raman scattering as indicated from our previous studies on related but different systems. 16,[39][40][41][42][43] The vertical π →π * electronic transition of α,β-enones or α,β-carboxylic methyl esters is localized on the C α =C β or C α =C β -C4=C5 moiety without significantly involving the C=O moiety, and this causes a sudden excited state deconjugation between the O=C and the C α =C β moieties. The short-time structural dynamics of 3M3P2O is distinctly different than that of ethylene in that 3M3P2O does not have the C α =C β torsional vibration to accompany the C α =C β stretch motion in the Franck-Condon region.…”

A Complete Active Space Self-Consistent Field and Density Functional Theory Study of S0, T1, S1 States of Five Phenol ortho-Derivatives

“…Excitation energies: Table-1 lists the CASSCF/ cc-pVDZ adiabatic excitation energy (Ea) values and the TD B3LYP/6-311+g(d, p) vertical excitation energy (Ev) values for the S1, T1 states and the oscillator strengths are also tabulated. The available experimental values are also given 10,11 in Table- The calculated results also show that the oscillator strengths (f) are 0.0553, 0.0528, 0.0697, 0.1004 and 0.0825 for the S0→S1 absorption bands of 2-nitrophenol, salicylaldehyde, 2-acetylphenol, salicylamide, salicylic acid. The experimental f values of S0→S1 absorption bands of 2-nitrophenol and salicylaldehyde are 0.0689, 0.0667, respectively, which agree with the calculated values very well.…”

“…Additionally, similar to 2-nitrophenol, all their T1 and S1 structures are H transfer geometries. Zheng et al 11 and Peteanu & Mathies 12 studied the S0→S1 resonance Raman spectroscopy of salicylaldehyde and 2-acetylphenol and their results indicate in the Franck-Condon region the proton-transfer dynamics of salicylaldehyde are similar to that of 2-acetylphenol and all their short-time proton-transfer dynamics being distributed over a wide range of vibrational modes without involving the O-H stretching coordinate. That's to say, S1 IESPT processes of salicylaldehyde and 2-acetylphenol are barrierless too.…”

“…Zheng et al found that the IESPT bands for 2-nitrophenol, salicylaldehyde, 2-acetylphenol come from S0-S1 transition and these three electronically excited molecules are evolved rapidly in the Franck-Condon region along a large number of skeletal coordinates without involving the O-H stretching coordinate by resonance Raman spectroscopy technique. These facts indicate that the IESPT for 2-nitrophenol, salicylaldehyde and 2acetylphenol would be barrierless processes [10][11][12][13][14][15] . The CASPT2 and TD-DFT energy calculations also predicted no barrier in the ESIPT reaction of 2-acetylphenol 16,17 .…”

Structural dynamics of 4‐pyrimidone in lower‐lying excited States

“…It appears that the structural dynamics along NH/CH bend reaction coordinates of 2TPM and 4PMO consists with the photoinduced hydrogen atom detachment‐attachment or excited state ESIPT mechanism since the NH/CH bend motions + C = O stretch motion is dynamically required for proton to move from N atom to S or O atom for TPM or 4PMO, and this causes NH/CH bends and C = O stretch reaction coordinates to become dynamically active. It seems that the variety of the NH/CH bend + C = O stretch reaction coordinates could be served as the marker for hydrogen‐detachment‐attachment or ESIPT reaction initiated in Franck–Condon region for TPM, 4PMO and other similar ESIPT molecules, as is such for 2‐hydroxybenzaldehyde (OHBA) and 2‐hydroxyacetophenone (OHAP), in which the ESIPT reactions take play in about a hundred femtosecond time‐scale, and the variety of the characteristic C = C–H/C–O–H/C = C–C(=O)/C = C–C(–OH) in‐plane bend modes also served as the marker for the ESIPT reaction in the charge‐transfer/proton‐transfer absorption bands. Therefore, the very similar structural dynamics between 4PMO and 2TPM in terms of the variety of the CH/NH bend + C = O stretch modes characteristic to ESIPT reaction suggests that the initial excited state dynamics of 4PMO is likely towards the intramolecular proton‐transfer reaction.…”