Fluorescent carbazole based pyridone dyes – Synthesis, solvatochromism, linear and nonlinear optical properties

Abstract

Carbazole based pyridone dyes are investigated for their non-linear optical (NLO) properties. They exhibit positive solvatochromism and charge transfer character with a high fluorescence quantum yield which encouraged us to study their NLO characteristics. Photophysical properties of dyes in different solvents are evaluated and correlated with computational optical absorption and fluorescence emission using global hybrid (B3LYP) and long range separated functional (CAM-B3LYP) with 6–31G(d) basic set. Frontier Molecular Orbital analysis and Generalised Mulliken Hush analysis reveal a strong intramolecular molecular charge transfer character in these dyes. DFT and TD-DFT are performed to understand the electronic and photophysical properties of dyes. The resultant decrease in the HOMO-LUMO energy gap is responsible for bathochromic shift. Large enhancement in the non-linear optical properties are seen for these dyes than urea confirming their use in non-linear optical materials. The MEP analysis reveals the sites for electrophilic and nucleophilic attack in the dye. The experimental data are in good agreement with those obtained by computation (DFT) method. Fundamental limiting values of β, γ for dyes are observed within the estimated limits.