Nonlinear optical chromophores based on Dewar's rules: enhancement of electro-optic activity by introducing heteroatoms into the donor or bridge

Abstract

In this work, we investigated the enhancement of the electro-optic response by introducing electron-rich heteroatoms as additional donors into the donor or bridge of a conventional second-order nonlinear optical chromophore. A series of chromophores C2-C4 based on the same tricyanofuran acceptor (TCF) but with different heteroatoms in the alkylamino phenyl donor (C2 or C3) or thiophene bridge (C4) have been synthesized and systematically investigated. Density functional theory calculations suggested that chromophores C2-C4 had a smaller energy gap and larger first-order hyperpolarizability (β) than traditional chromophore C1 due to the additional heteroatoms. Single crystal structure analyses and optimized configurations indicate that the rationally introduced heteroatom group would bring larger β and weaker intermolecular interactions which were beneficial for translating molecular β into macro-electro-optic activity in electric field poled films. The electro-optic coefficient of poled films containing 25 wt% of these new chromophores doped in amorphous poly-carbonate afforded values of 83 and 91 pm V(-1) at 1310 nm for chromophores C3 and C4, respectively, which are two times higher than that of the traditional chromophore C1 (39 pm V(-1)). High r33 values indicated that introducing heteroatoms to the donor and bridge of a conventional molecular structure can efficiently improve the electron-donating ability, which improves the β. The long-chain on the donor or bridge part, acting as the isolation group, may reduce inter-molecular electrostatic interactions, thus enhancing the macroscopic EO activity. These results, together with good solubility and compatibility with the polymer, show the new chromophore's potential application in electro-optic devices.

Verbenone‐based push–pull chromophores with giant first hyperpolarizabilities: A new structure–property correlation study

“…The frontier molecular orbitals are often used to characterize excitation properties, photophysical properties, charge transfer interaction and electronic properties of D-π-A molecules [47][48][49][50]. Figure 3 depicts the electron density distribution of the HOMO and LUMO structures.…”

Organic Electro‐Optic Mach–Zehnder Modulators: From Physics‐Based to System‐Level Modeling

“…This in turn leads to a modulation of the absorption profile and, from the Kramers–Kronig relationships, a variation of the real refractive index. To achieve high EO activity, dipolar NLO chromophores with high molecular hyperpolarizability β and good thermal stability have to be designed (through ab initio simulation techniques and computational chemistry tools) and synthesized, see the study by Xu et al [ 17 ] and references therein. If the chromophore dipole moments have a random orientation after dispersion in a polymer matrix, the average influence of the RF electric field will be zero.…”

Synthesis and characterization of Y-shaped optical nonlinear chromophores with strong acceptors

“…12 Organic second-order nonlinear optical molecules are usually composed of an electron donor (D), electron acceptor (A), and electron bridge (p), which is known as D-p-A structure. 13 Various kinds of alkyl anilines, 14,15 and triarylamino derivatives 16 were the most common donor structures. While heterocyclic or polyene bridge [17][18][19][20][21][22] (thiophene, pyrrole, isophorone derivatives, etc.)…”