The electronic origin of the ground state spectral features and excited state deactivation in cycloalkanones: the role of intermolecular H-bonding in neat and binary mixtures of solvents

Ibrahim Ahmed Z Al-Ansari

doi:10.1007/s00894-019-4015-6

Abstract

In this study, a D–A cycloalkanone (K1) has been investigated by steady state absorption and fluorescence in neat solvents and in three binary mixtures of nonpolar aprotic/polar protic, polar aprotic/polar protic, and polar protic/polar protic solvents. The experimental findings were complemented by density functional theory (DFT), time-dependent density functional theory (TD-DFT), and NBO quantum-mechanical calculations. Experimentally, effective changes in absorption and fluorescence were observed by solute–solvent interaction. The binary K1-solvent1-solv2 configuration, modeled at the B3LYP-DFT level, confirms involvement of inter-molecular H-bonding with the carbonyl C=O in the fluorescence deactivation process (quenching). This is supported by considerable electron delocalization from C=O to the solvent’s hydroxyl (nO → σ*H-O). This type of hyperconjugation was found to be the main driver for solute–solvent stabilization.

Highlights

Molecular π-systems with electron donating (D) and electron accepting (A) substituents generally are known as push–pull systems and characterized by intramolecular charge transfer (ICT) [1]
The complete ground state absorption and excited state emission results were given in our earlier work [18]
Our TD-density functional theory (DFT) calculations, show that the origin of the LW band is S0 → S1 1(π,π*), whereas the weak band in the middle region of 300–340 nm is due to S0 → S3 transition and possess a 1(n,π*) signature

Summary

Introduction

Molecular π-systems with electron donating (D) and electron accepting (A) substituents generally are known as push–pull systems and characterized by intramolecular charge transfer (ICT) [1]. Our interest in these important biologically active cycloalkanones came due to the fact that the complete mechanism for their interaction with DNA and protein is still not completely understood [16, 17]. In this work, we continue our investigation on one of the cycloalkanones we previously synthesized [18] This push–pull compound with the carbonyl motif (denoted as K1), is built on a strong donor N,Ndimethyl-aniline unit (D) connected to the acceptor (A) cyclic benzoyl group, via a cyclic five-membered ring

Methods

Results

Conclusion