Nonlinear optical crystals designed with 4-nitrophenolate chromophores: Anengineering route using a multidipolar chromophore, 3-hydroxy-2,4,6-trinitrophenolate

4-Nitrophenol derivatives are interesting chromophores for nonlinear optics (NLO), being typical donor-acceptor system connected by pi conjugation. Du e to the presence of the acidic phenolic proton, they also readily form sal ts with suitably selected organic and metallic bases. The so-formed l -nitr ophenolates have increased molecular hyperpolarizabilities (beta). The phen olate and nitro oxygens are strong hydrogen bond accepters and the nitro gr oup has a tendency to coordinate with metal centers. This opens up two diff erent engineering routes to build NLO materials from these chromophores: (a ) organic-organic and (b) metal-organic salts. This paper reviews the cryst al packing and nonlinear optical (NLO) efficiency in nitrophenolate crystal s engineered through these routes and presents the crystal structure of a n ew NLO efficient organic-organic salt. 1-hydroxy-3-methylpyridinium 3-hydro xy-2,4,6-trinitrophenolate (P2(1)) In this crystal both the multidipolar an ion and dipolar cation are NLO chromophores. The anions form herringbone me diated chain with intra and intermolecular O-H . . . .O hydrogen bonds and the cations are attached to them through strong O-H . . . .O- hydrogen bond s.