Solid-State Photodimerization Reaction with Photosalient Effect and Photophysical and Electrochemical Properties of <i>N</i>-Methylated 1-Naphthylvinyl-4-Quinoline
Tamil Selvan Kannan, Subrata Munan, Murugavel Kathiresan, Animesh Samanta, Goutam Kumar Kole
Abstract
Crystal packing-dependent photochemical reactions of several functional olefins have been explored, but not for 1-naphthylvinyl-4-quinoline ( NVQ ) and analogous N -methylated 1-naphthylvinyl-4-quinoline cation ( MNVQ ). Herein, crystal structure elucidation and photophysical and electrochemical properties for both NVQ and MNVQ, and photodimerization reaction with a photosalient effect for MNVQ have been investigated for the first time. The neutral compound NVQ stacks parallel in its crystal; however, having a distance of 4.43 Å between the C═C bonds, it remained photoinert. Upon methylation at the quinoline- N, the resulting MNVQ cations stack parallel in a head-to-tail fashion with a distance of 3.6 Å between the C═C bonds, and consequently it underwent [2 + 2] photocycloaddition reaction quantitatively to MQNCB dication, when irradiated under visible light (∼410 nm). Monitoring closely the single crystals of MNVQ under blue light showed that they burst upon exposure for 1 min, signifying a photosalient behavior. Measurements of photophysical properties showed that MNVQ exhibited a bathochromic shift in both absorption (by 4772 cm –1 ) and emission (by 6198 cm –1 ) compared to the neutral NVQ . Upon photodimerization, the MQNCB dication exhibited a hypsochromic and hypochromic shift both in absorption and emission compared to the MNVQ cation, a signature of cessation of conjugation. Cyclic voltammetry (CV) measurements showed that all three compounds are redox active and exhibit a reversible reduction event in the range of −0.6 to −0.9 V (vs Ag/AgCl). Experimental results have been substantiated by theoretical calculations.