Pyrene-pyrazole systems – Elucidating the impact of substitution patterns in the group of Mono-, Di-, Tri- and tetrasubstituted derivatives on emission behaviour through experimental and theoretical approaches

Pyrene derivatives have garnered significant attention in the scientific community due to their fascinating luminescent properties, which can be finely tuned through structural modifications. However, existing modifications predominantly rely on altering substituents. To address this limitation, this work investigates the nuanced influence of substitution patterns on emission behaviour, focusing on pyrene-pyrazole systems P1-P8. Through a meticulous integration of experimental and theoretical methodologies, a series of mono-, di-, tri-, and tetrasubstituted pyrene derivatives containing substituents at non-K region (positions 1-, 3-, 6-, 8-) as well as at nodal positions (position 2-, 7-) were synthesised and characterised. Quantum chemical calculations provided insights into molecular orbitals and energy gaps, elucidating electronic structure–property relationships. Thermal stability assessments revealed how substitutions affect compound stability. Experimental spectroscopic studies across various solvents unveiled subtle solvatochromism and red-shifted emissions with increasing substituents. Clarifying substitution-induced effects on emission behaviour provides significant knowledge for developing customised luminophores that possess the intended optical characteristics, especially those based on the unsymmetrically substituted pyrenes at positions 1,3,6- and 1,7-. This comprehensive investigation lays the groundwork for the rational design of novel materials with tailored emission properties for optoelectronics, fluorescence, and beyond. This study elucidates the experimental and theoretical intricacies of substitution patterns and their effects on emission characteristics while highlighting the advantages of both area-nodal position and non-K region, as well as relatively unexplored 1,3,6-trisubstituted derivatives for maintaining expected luminescent properties.