Tuning First Molecular Hyperpolarizabilities through the Use of Proaromatic Spacers

Abstract

In this paper, we describe the second-order nonlinear optical properties of a series of 1,3-dithiole-based electron donor-acceptor systems incorporating proaromatic donor and spacer groups. Modification of the proaromaticity of the quinoid spacer gives rise to NLO-phores with mubeta values ranging from -2000 x 10(-)(48) esu to +3000 x 10(-)(48) esu. Quite surprisingly, compounds with a p-benzoquinoid spacer and a strong acceptor group show negative mubeta values, usually associated to zwitterionic ground states, and yet they are largely quinoid, as evidenced by crystallographic data and theoretical calculations. Progressive benzoannulation of the spacer and introduction of alkylsulfanyl substituents on the dithiole donor unit result in a shift to more positive mubeta values. DFT and ab initio calculations verify these empirical trends.

First Principle Calculations of the Electronic and Vibrational Properties of the 3-(1,1-Dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole Molecule

“…The Fig. 8 shows that the DCNP molecule is characterized predominantly by aromatic ground states and according to the work of Andreu et al 67 this kind of D-π-A system should favour the intramolecular charge transfer process.…”

Scope and Limitations of Baird's Theory on Triplet State Aromaticity: Application to the Tuning of Singlet–Triplet Energy Gaps in Fulvenes

“…Especially in donor-p-acceptor systems, in which the aromaticity varies upon excitation, peripheral sulfur atoms have proved important in affecting the hyperpolarizability of such chromophores. [14] Even though this present investigation is fundamental in character, we thus hope that the results presented here can also initiate further investigations in more applied research areas.…”

Solvent-Dependent Structural and Electronic Behaviors of a Push−Pull Molecule: {4-[4,5-Bis(methylsulfanyl)-1,3-dithiol-2-ylidene]cyclohexa-2,5-dien-1-ylidene}malononitrile

“…1 It has been reported that the second-order nonlinear optical property of such push-pull molecules can be modified by changing the bridge. 2 These molecules are expressed by a resonance hybrid between two canonical structures for neutral and zwitterionic forms. In the report the first hyperpolarizabilities measured were analyzed for the respective molecules by considering two canonical structures in both the ground and excited states for each molecule.…”