Self-assembled organic nonlinear optical crystals based on pyridine derived fluorenone

Abstract

Organic π-conjugated materials have demonstrated superior nonlinear optical (NLO) performance and serve as ideal candidates for photonic devices. However, the design of organic NLO materials with well-defined architectures and highly efficient second-order NLO properties remains a significant challenge. Here, pyridine groups with different N-substitution positions have been incorporated into the fluorenone skeleton to obtain target compounds 3-DPyFO and 4-DPyFO with modulated intermolecular interactions and self-assembly behaviors. Noncentrosymmetric 3-DPyFO-α exhibits thermal-induced phase transition and unusual multi-response fluorescence including thermochromic and mechanochromic luminescence. Meanwhile, 4-DPyFO-α shows highly efficient second- and third-order NLO effects, along with a resonance enhancement of second harmonic generation (SHG) and two-photon excited fluorescence (TPF). This study on NLO properties of pyridine functionalized fluorenone derivatives will enrich the fluorenone based NLO materials for photonic device applications.