# Symmetrical D–π–A–π–D indanone dyes: a new design for nonlinear optics and cyanide detection

## TL;DR

This paper introduces new indanone dyes that show strong nonlinear optical properties and can detect cyanide through color changes.

## Contribution

The novel symmetrical D–π–A–π–D indanone dye design offers new potential for nonlinear optics and cyanide sensing.

## Key findings

- The dyes exhibit strong second-order nonlinear optical responses measured via EFISH.
- The dyes selectively detect cyanide with a visible color change in various media.
- DFT calculations and NMR studies confirm the interaction mechanism with cyanide.

## Abstract

Three indan-2-one-based donor–π–acceptor–π–donor type dyes with symmetric donor groups were synthesized and characterized to study their nonlinear optical (NLO) properties and their potential use in the rapid and selective determination of cyanide. The designed structures feature symmetrical alkylaminophenyl donor groups and a strong electron-withdrawing dicyanovinylene as an acceptor connected through vinyl groups as a π-bridge. These strongly π-conjugated organic dyes can absorb in the NIR region, and they showed sensitivity towards the polarity of solvents with colorimetric and optical changes. Because of the strong donor–acceptor structure, second-order NLO properties were studied by measuring electric field-induced second harmonic (EFISH) values, which showed significant second-order NLO responses. The experimental results were explained using density functional theory (DFT) methods. The dyes also exhibit chemosensor properties, showing selectivity for cyanide via a Michael addition mechanism that causes the disappearance of the ICT band, and a significant color change was observed in both organic and aqueous media. In addition, the interaction mechanism between cyanide and the chemosensor is determined by a 1H NMR study and explained by DFT calculations.