The excited state dipole moments of betaine pyridinium investigated by an innovative solvatochromic analysis and TDDFT calculations

Abstract

This work reports on the solvatochromic properties of a simple heterocyclic betaine pyridinium, 2-(1-pyridinio)benzimidazolate (SBPa), having promising potentialities in non-linear optics. From advanced PCM-TDDFT calculations, the solvatochromism of SBPa was found to be unusual, involving two different electronic states for absorption (S(0)→ S(2)) and emission (S(1)→S'(0)). To account for this behavior, we developed an innovative physical treatment which consists in a non-linear fit of the solvatochromic data using the Bilot-Kawski theoretical model and visualizing the least-square coefficient χ(2) on a 2D map as a function of the solute polarizability and gas phase absorption energy. In parallel, Kamlet-Taft correlations were undertaken to select a propitious set of electrostatic solvents usable in this treatment. Protic solvents that lead to specific interactions and nonpolar solvents that favor dimerization processes were excluded. From a choice of aprotic solvents with sufficiently high polarity, 4 dipole moments μ(g)(S(0)) = +9.1 D, μ(e)(S(2)) = -1.5 D, μ(e)(S(1)) = 0 D and μ(g)(S'(0)) = +3.31 D were determined, the 3 former values being in close agreement with TDDFT values, although the solute polarizability values seem underestimated. Anyhow, disregarding this discrepancy, we evaluated the static hyperpolarizability to β(0) = -64 × 10(-30) esu from the solvatochromic data in close agreement with DFT calculations.

Excited-state dynamics of thiophene substituted betaine pyridinium compounds

“…As evidenced from Fig. 1(a), the 400-450 nm band can be safely assigned to the CT absorption band reported for the SBPa parent molecule 14 that was concerning the shape, similar band position, and negative solvatochromic effect (B2700 cm À1 blue-shift for Th 2 SBPa and B3000 cm À1 for SBPa on going from toluene to MeCN). According to TDDFT calculations able to reproduce the experimental solvatochromism (see oscillator strengths in Fig.…”

“…19b PCM-TDDFT calculations of the vertical absorption transition energy, oscillator strength, and contour plots of the involved molecular orbitals (MO) of Th 2 SBPa and Th 4 SBPa in MeCN, toluene, and THF solvents were done at the PCM-TD-PBE0/6-311++G(2d,p)// PBE0/6-311G(d) level using the Gaussian 09 package 21 as previously calculated for SBPa. 14,16 Solvent contributions were introduced by using the Polarizable Continuum Model (PCM). 22…”

“…7,8,12,13 These conclusions were nicely supported by the excited-state dipole moment and hyperpolarizability values determined from an extensive quantitative analysis of the solvatochromism of SBPa in solution and TDDFT calculations. 14 On the other hand, in order to get a real understanding of the photoinduced ICT process in SBPa at the molecular level, femtosecond photoionization (gas phase) and transient absorption (solution) spectroscopic experiments have been recently performed 15 and complemented by PCM-TDDFT calculations. 15,16 From this ensemble of data, a complex photophysical relaxation scheme has been derived, which involves two distinct ICT excited states of planar geometries, S 1 (CT) and S 2 (CT).…”

0–0 Energies Using Hybrid Schemes: Benchmarks of TD-DFT, CIS(D), ADC(2), CC2, and BSE/GW formalisms for 80 Real-Life Compounds

“… 152 For XVI , negative solvatochromism is indeed observed experimentally, and a full theoretical rationalization of this outcome is already available. 87 , 153 The three compounds undergoing the largest positive solvatochromism are LVI , LIX , and LXV , three very strong CT dyes. To our knowledge, no detailed experimental investigations of solvatochromic effects (e.g., from apolar to strongly polar solvents) have been made for these three derivatives.…”

Solvation effect and binding of rhaponticin with iron: a spectroscopic and DFT/TDDFT study

“…The value of the solute cavity radius a was calculated from the molecular volume by Suppan's equation: 19 a ¼ 3M…”