Synthesis and comparative solvatochromic studies of simple and donor acceptor benzimidazole incorporated naphthyridine systems

Abstract

Benzimidazo[1,2-a]benzo[g]-1,8-naphthyridine (<strong>NB-1</strong>) and its donor-acceptor analog, 11-morpholino-benzimidazo[1,2-a]benzo(g)-1,8-naphthyridine-6-carbonitrile, (<strong>NB-2</strong>) have been synthesized and investigated for their optical and solvatochromic properties. Absorption and emission maxima of the push-pull chromophore, <strong>NB-2</strong> were red shifted in comparison to <strong>NB-1</strong> lacking in donor-acceptor motif. Both systems are highly fluorescent (φ = 0.74-0.84) and exhibit positive solvatochromism. Using solvatochromic shift method, we estimated 2 fold higher dipole moment in the excited state for <strong>NB-2</strong> over <strong>NB-1</strong>. High degree of electronic charge redistribution in <strong>NB-2</strong> seems to be responsible for its optical spectral red shifts and higher dipole moments compared to <strong>NB-1</strong>.