# Pyrene-Chromone Schiff Base Molecules with Tunable Fluorescence: Structure–Property Relationships and Substituent Effects

## TL;DR

This paper explores how substituents affect the fluorescence of pyrene-chromone molecules, revealing structure-property relationships useful for optoelectronic and sensing applications.

## Contribution

The study introduces three novel pyrene-chromone Schiff base derivatives and demonstrates how substituents modulate their photophysical properties.

## Key findings

- The compounds exhibit intense absorption in the 430–440 nm range and tunable emission in the 540–565 nm region.
- Nitro-substituted derivatives show reduced optical band gaps and fluorescence quenching due to enhanced charge transfer.
- Concentration-dependent studies confirm linear Beer–Lambert behavior and no aggregation in the tested range.

## Abstract

The fluorescence properties of organic molecules are largely determined by molecular architecture, π-conjugation, and electronic substituent effects. In this study, three novel pyrene-chromone Schiff base derivatives were designed and synthesized to investigate substituent-driven modulation of photophysical behavior. The compounds were obtained via condensation of 1-aminopyrene with three different chromone-based aldehydes and fully characterized by FT-IR, 1H-NMR, and mass spectrometry. The molecular design involves a donor-π-acceptor architecture: pyrene donates electrons, while the chromene moiety accepts them, enabling charge transfer upon excitation. UV-Vis and fluorescence spectroscopy revealed intense absorption in the 430–440 nm range and tunable emission in the 540–565 nm region, corresponding to large Stokes shifts (107–125 nm). Substituent effects significantly influenced optical band gaps and emission intensities, with the nitro-substituted derivative exhibiting a reduced band gap and pronounced fluorescence quenching due to enhanced intramolecular charge transfer. Concentration-dependent absorption studies demonstrated linear Beer–Lambert behavior, indicating the absence of aggregation within the investigated range. These results establish clear structure–property relationships in pyrene-chromene Schiff bases and highlight their potential as promising candidates for optoelectronic and fluorescence-based sensing applications.