jp8b08016_si_003.cif (99.42 kB)
Molecular Origins of the Nonlinear Optical Responses of a Series of α‑(X-2-Pyridylamino)‑o‑cresol Chromophores from Concerted X‑ray Diffraction, Hyper-Rayleigh Scattering, and Ab Initio Calculations
dataset
posted on 2018-12-10, 00:00 authored by Christopher
M. Ashcroft, Jacqueline M. Cole, Edward A. Boardman, Tze-Chia Lin, Javier Perez-Moreno, Koen ClaysFaster transmission rates are desperately
needed in the telecommunications
industry, given that global demand for signal transmission already
outstrips supply. New organic nonlinear optical (NLO) materials offer
a prospective solution for the telecommunications industry given that
they exhibit shorter optical response times compared to their inorganic
counterparts. α-(X-2-Pyridylamino)-o-cresol-type
motifs with their donor−π–acceptor (D−π–A)
architecture and high level of π-conjugation are expected to
afford high levels of intramolecular charge transfer (ICT). Such ICT
phenomena will contribute to these types of molecules having faster
optical response times and large (hyper)polarizabilities. The linear
and second-order NLO properties of three new α-(X-2-pyridylamino)-o-cresol motifs (X = 4-CH3 (1);
5-Cl (2); 3,5-Cl (3)) were hence evaluated.
NLO structure–function relationships were established in terms
of their ICT characteristics and molecular hyperpolarizabilities (β).
Given the typically large errors (10–30%) that are associated
with determinations of β coefficients, three independent methods
were used to enumerate β: (i) direct optical measurements using
hyper-Rayleigh scattering, (ii) ab initio density
functional theory (DFT) calculations, and (iii) X-ray wavefunction
refinement (XWR). In the third case, a pseudoexperimental wavefunction
of the compounds under investigation is afforded, from which its molecular
properties are derived. The β values obtained from these three
different methods are subsequently compared and assessed in terms
of the effects of phase state on each chromophore on the NLO response.
In terms of a materials-centered scientific interpretation, these
β determinations reveal that compound 3 is the
most promising candidate for use as an NLO chromophore owing to the
presence of its withdrawing 3,5-chloro substituents. More generally,
the correlation of the molecular structures of these α-(X-2-pyridylamino)-o-cresol chemicals to their linear and nonlinear optical
properties extends the growing knowledge base of molecular design
rules for organic NLO materials and specifically highlights the implications
of ICT between two moieties in an NLO chromophore, causing a diminutive
effect upon their NLO responses. This augments already well-established
structure–property rules for the molecular engineering of NLO
chromophores and points toward the ultimate goal of being able to
tailor-make organic molecules to suit a given NLO device application.