Highly efficient acido-triggered reversible luminescent and nonlinear optical switch based on 5-π-delocalized-donor-1,3-di(2-pyridyl)benzenes

The acidochromic behaviour of trans-5-(p-(N,N-diphenylamino)styryl)-1,3-di(2-pyridyl)benzene (1) and 5-(p-(N,N-diphenylamino)phenylethynyl)-1,3-di(2-pyridyl) benzene (2) was investigated, both in solution and doped into films, studying their linear and nonlinear optical properties. Remarkably, the efficient luminescence of 1 drops drastically upon protonation and is restored upon deprotonation - both in solution and in the solid state - leading to an excellent on/off emissive acido-triggered reversible switch. In parallel, protonation leads to a large enhancement of the second-order NLO response, as determined by the EFISH technique, which is reversible upon deprotonation. The related methylated salts of 1 and 2 are similarly characterized by a high NLO response.