Anthracene-naphthylacetonitrile fluorescent isomers and Cl/H substituent dependent molecular packing, solid-state fluorescence and mechanofluorochromism

• Published in: CrystEngComm 2023-11, Vol.25 (45), p.633-639
• Main Authors: Ravi, Sasikala, Priyadharshini, Prakash, Karthikeyan, Subramanian, Pannipara, Mehboobali, Al-Sehemi, Abdullah G, Madhu, Vedichi, Moon, Dohyun, Anthony, Savarimuthu Philip
• Format: Article
• Language: English
• Subjects: Acetonitrile; Aldehydes; Anthracene; Bonding strength; Carbonyls; Charge transfer; Chloroform; Crushing; Crystal lattices; Crystallization; Dichloromethane; Fluorescence; Heating; Isomers; Phase transitions; Single crystals; Solid state; Switching; X ray powder diffraction
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/d3ce00718a

The condensation reaction between naphthylacetonitrile isomers and anthracene aldehyde produced unexpected highly twisted AIEgens (2-(naphthalen-1-yl)-2-(10-oxo-9,10-dihydroanthracen-9-yl)acetonitrile ( 1 ) and ( Z )-3-(anthracen-9-yl)-2-(naphthalen-2-yl)acrylonitrile ( 2 )). 1 and 2 exhibited strong solid-state fluorescence and mechanical stimuli-induced reversible fluorescence switching. Crystallization of 2 in acidic CHCl 3 -CH 3 OH produced Cl substituted anthracene ( 2 -Cl ), whereas in CH 2 Cl 2 pure crystals of 2 were produced. Single crystal analysis of 1 revealed a twisted conformation in the middle ring of anthracene due to carbonyl introduction. The carbonyl oxygen and cyano nitrogen are involved in the H-bonding interactions in the crystal lattice. 2 showed slipped stacking between naphthyl units whereas 2 -Cl exhibited intermolecular H-bonding between Cl and anthracene hydrogens. 1 exhibited strong solid-state fluorescence ( λ max = 541 nm, quantum yield ( Φ f ) = 18.2%), whereas 2 and 2 -Cl displayed tunable and relatively low fluorescence efficiency ( λ max = 547 ( 2 ), 489 nm ( 2 -Cl ), Φ f = 6.3 ( 2 ) and 3.6% ( 2 -Cl )). Computational studies suggested clear intramolecular charge transfer (ICT) in 1 compared to 2 and 2 -Cl . Further, 1 and 2 -Cl showed mechanical crushing and heating induced reversible fluorescence switching but 2 did not show any fluorescence switching. Powder X-ray diffraction indicated a reversible phase transformation upon crushing and heating that caused reversible fluorescence switching. Hence, the present study provides insight into the subtle structural impact on intermolecular interactions and solid-state fluorescence. Anthracene aldehyde with naphthylacetonitrile isomers produced unusual and expected fluorophores that showed molecular packing-controlled stimuli-induced reversible fluorescence switching and solid-state fluorescence.