Inter and Intra-Stacking Influenced Charge Hoping Interactions in Core-Substituted Squarylium Dye Derivatives: A Computational Investigation

Abstract

The stacking arrangement and associated interactions within crystal packing of ten core substituted squaraine (CSQ) dyes that are symmetric dicyanovinyl (DCV) acceptor group functionalized squaraine derivatives with distinct electron rich side donor moieties containing various substituents have been assessed by computational methods. Out of three sets, two are containing indolenine and quinolinium donor moieties as side substitution. In first set, the halogen substituent’s on indolenine donor moieties (such as –Cl, –Br, and –I) exhibit monoclinic polymorphism while –F substituted one is with triclinic polymorphism. Though, triclinic and orthorhombic polymorphs are known for the absence of any substituent. Another group of two CSQ dyes has quinolinium donor units that differ in length of alkyl chain substitution found in monoclinic polymorphism. The next set of CSQ contains monoclinic polymorphism in which one indolenine CSQ contains a chiral center while the other one is with benzothiazole ring. Here, we investigate the impact of DCV acceptor moiety present at the central C4 ring of squaraine dyes along with functionalization of side donor groups on the inter and intra-stacking patterns at crystal packing to establish the charge transfer protocol. Theoretical calculations including geometrical analysis, internal reorganization energy, charge transfer integral, drift mobility and interaction energy along with complete investigation of the Hirshfeld surface analysis have been performed. The distinctive geometrical changes upon electron gain and loss have been observed at different moieties of the respective CSQ i.e. side aromatic rings and central C4 ring respectively. Inter or intra-stack cofacial interactions between side substituted donor rings offer electron transfer character while participation of slip-stacked central C4 rings proportionate hole transfer character in all CSQs. Although much meager participation of DCV group in inter and intra-stacking interactions of all motifs studied, indirect influence is noted through geometrical impacts. Such packing effects give insights into inter- and intra-stack interactions, possibly guiding experimentalists' ideas for shaping and using promising squaraine derivatives in advanced functional materials.