Time‐dependent density functional theory study on the absorption spectrum of Coumarin 102 and its hydrogen‐bonded complexes

Abstract

The effect of both solvent polarity and hydrogen bonding (HB) on the electronic transition energy of Coumarin 102 (C102) has been examined using the time-dependent density functional theory (TDDFT). Solvent effect on both geometry and electronic transition energy is evaluated using the polarizable continuum model (PCM). A linear relation of the absorption maximum of C102 with the solvent polarity function Δf is found using the TDDFT-PCM method for all solvents except dimethyl sulfoxide. The solvent polarity and the type B HB between the carbonyl oxygen and solvent hydrogen atom make the absorption wavelength redshift, whereas the type A HB between the amino nitrogen atom and solvent hydrogen atom has an opposite effect on the absorption wavelength. The calculated absorption wavelengths of C102 with two type B HB between the carbonyl oxygen and solvent hydrogen atom are in excellent agreement with experimental measurements. The solvatochromism of C102 is analyzed in terms of the Kamlet-Taft equation and the parameters s and a are discussed.

Spectroscopic Study of Solvent Effects on the Electronic Absorption Spectra of Flavone and 7-Hydroxyflavone in Neat and Binary Solvent Mixtures

“…Zhao et al . have studied the solvatochromism of Coumarin 102 by means of TD-DFT methods and they observed the same deviation in DMSO [24]. These authors attribute this anomaly to strong long-range bulk electrostatic effects and a very large π* value of DMSO.…”

“…For this aim, two hybrid functionals have been used: B3LYP and PBE0 [35,36] in combination with the PCM method. The PBE0 does not contain any adjustable parameter fitted to specific property, and recent studied on coumarins suggests that provides more reliable results compared with experimental results [24,37,38]. To simulate the UV-visible spectra only the excitation energies with oscillator strength ( f ) higher than 0.01 were used.…”

Theoretical studies on absorption, emission, and resonance Raman spectra of Coumarin 343 isomers

“…In the past decades, in fact, stable ground states and pure electronic absorption spectra of coumarin derivatives in gas phase and in solution have been studied by using quantum chemical methods. [32][33][34][35][36][37][38][39][40][41][42][43] For instance, in the framework of density functional theory (DFT), Preat et al 33 investigated the UV electronic absorption spectra of substituted coumarins with various basis sets and functionals. It turns out that the Becke-Lee-Yang-Parr functional (B3LYP) together with the polarized continuum model (PCM) provides valid ground-state geometries and the consistent UV spectra with experimental measurements.…”

Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins

“…7-aminocoumarins are commonly used as laser dyes due to their high quantum yields of emission and low lying ππ* excited states of essentially HOMO to LUMO character. [40][41][42][43][44][45] The first excited singlet states of the 7-aminocoumarins exhibit relatively strong solvatochromic behavior, which has been widely attributed to partial intramolecular charge transfer character (ICT) between the nitrogen atom and carbonyl oxygen atom following extensive studies using TDDFT, [41][42][43][44][45] together with emission and absorption spectroscopy. [46][47][48] Despite this charge separation, unsubstituted 7-aminocoumarins are too small for the partial ICT character to be considered as a long-range charge transfer excited state in TDDFT, and B3LYP therefore performs adequately for calculating excitation energies.…”

“…[46][47][48] Despite this charge separation, unsubstituted 7-aminocoumarins are too small for the partial ICT character to be considered as a long-range charge transfer excited state in TDDFT, and B3LYP therefore performs adequately for calculating excitation energies. [41][42][43][44][45] This is important for comparing with TRIR data, as the B3LYP functional is also known to reproduce ground state experimental frequencies well using both scaled harmonic 49,50 and anharmonic 2, 51 techniques, while other commonly used functionals, such as PBE0 52 or CAM-B3LYP 25 and other range corrected functionals often predict frequencies of significantly lower quality. 50,53 Coumarins containing an unsubstituted 7-NH 2 group also show higher fluorescent quantum yields in polar solvents than in non-polar solvents, 54,55 attributed to an increase in positive charge on the N-atom and simultaneous flattening of the 7-NH 2 group in polar solvents, leading to suppression of non-radiative decay from the excited state.…”