Peri-Substituted Acyl Pyrrolyl Naphthalenes: Synthesis, Reactions and Photophysical Properties

Area of Science:

• Organic Chemistry
• Photophysics
• Supramolecular Chemistry

Background:

• Synthesis of novel organic compounds with potential photophysical applications.
• Understanding the influence of solvent environment on molecular fluorescence.
• Exploring intramolecular charge transfer (ICT) phenomena in excited states.

Purpose of the Study:

• To report the synthesis of 1-acyl-8-pyrrolylnaphthalenes and a pyrrolone derivative.
• To investigate the detailed photophysical properties of the fused, planar derivative 6.
• To elucidate the mechanisms behind solvent-dependent fluorescence enhancement.

Main Methods:

• Organic synthesis for compound preparation.
• Spectroscopic techniques (UV-Vis absorption, fluorescence emission) to study photophysics.
• Preferential solvation studies, multilinear regression analysis, and computational modeling.

Main Results:

• Successful synthesis of compounds 5, 6, and 8, with challenges noted for other derivatives.
• Compound 6 displays significant solvatochromism in fluorescence due to ICT.
• Fluorescence intensity of compound 6 increases linearly with solvent H-bond donating strength.
• Inhibition of intersystem crossing (ISC) from singlet to triplet states is identified as the primary cause of fluorescence enhancement.
• Both dielectric stabilization and hydrogen bonding contribute to stabilizing the excited singlet state and reducing ISC.

Conclusions:

• The photophysical behavior of 1-acyl-8-pyrrolylnaphthalene derivative 6 is strongly influenced by solvent polarity and hydrogen bonding.
• Hydrogen bonding plays a crucial role in enhancing fluorescence by suppressing non-radiative decay pathways, specifically ISC.
• The findings provide insights into designing fluorescent organic molecules with tunable emission properties through solvent interactions.