Tuning Wavefunction Mixing in Push–Pull Molecules: From Neutral to Zwitterionic Compounds

Abstract

A new pushpull molecule, containing an (alkylamino)thiophene as electron donor and 1,3-bis(dicyanomethylidene)-2-indenylindene as electron acceptor, has been synthesized and characterized in the solid state by X-ray crystallography, in solution by UV/Vis and NMR spectroscopy and by theoretical calculations. The quinoidal zwitterionic form of this compound was underscored both in the solid state and in moderately polar solvents. Experimental and theoretical analyses were also performed on two similar pushpull molecules, selectively chosen to vary basic chemical features such as the resonance energy of the aromatic group and the steric hindrance of the attractor. Comparative analysis of the three compounds has shown that steric hindrance, resonance energy and the polarity of the environment play a significant role in stabilizing one limiting resonance form over the other. By varying these chemical variables, fine tuning of the electronic ground state of a pushpull molecule, from the neutral aromatic form to the charge-separated zwitterion, passing through a form in which the two limiting forms contribute almost equally (the cyanine limit), can be achieved

DFT predictions of the oxidation potential of organic dyes for opto-electronic devices

“…M06 overestimates oxidation free energies of 6 and 7 by ca 0.1 eV, M05-2X and M06-2X by 0.2 eV. Note however that a nearly halved error (% 0:1 eV) is obtained by high exchange meta functionals for 8, the only chromophore of the indane series possessing push-pull character [30], for which self-interaction error is expected to be more pronounced as also shown by the good result of CAM-B3LYP.…”

“…[49,50,11,51]; that choice was dictated by the fact that electron densities and optimum geometries of some of the investigated dyes exhibit a large dependence on the dielectric environment [30]. For the same reason we have not tested the SMD solvation model [48], a method designed to compute absolute solvation energies starting from gas-phase optimization/Hessian calculations, although there is evidence that SMD is capable of very accurate predictions of redox free energy for small molecules [9,10].…”

“…The chromophores (6)(7)(8) are examples of molecules whose electronic wavefunctions change from zwitterionic (6) to donoracceptor push-pull (8) [30]. Those highly polarized compounds represent a difficult case for density functional computations because of the well known problem of self electron interactions in approximate functionals [31].…”

Novel pyran based dyes for application in dye sensitized solar cells

“…As shown in previous works reported in the literature, the use of functionalizing group with different electron acceptor strength on the same molecular fragment results in the tuning of the optical absorption properties of the dyes so that different parts of the visible spectrum can be covered [12,21,22]. The pyran core is symmetrically linked to phenothiazine groups; phenothiazine is a heteroaromatic system characterized by a strong electron donor ability as a consequence of the presence of electron rich nitrogen and sulfur atoms contained in it.…”

First Principle Analysis of Charge Dissociation and Charge Recombination Processes in Organic Solar Cells

“…The M05-2X functional has been adopted because, holding a high percentage of Hartree-Fock exchange, it yields more accurate results than standard hybrid functionals for donor-acceptor conjugate dyes, reaching the quality of explicitly correlated methods. [24][25][26] Effects due to the polarization of solvent were included by using a polarizable Rate constants have been evaluated by using the Fermi Golden Rule (FGR) expression of the rate of a radiationless transition between two electronic states,…”