NIR-emitting squaraine J-aggregate nanosheets

Abstract

Click chemistry and Yamamoto coupling afforded a S-shaped pi-scaffold composed of two directly connected dicyanomethylene-substituted squaraine dyes. This bis(squaraine) self-assembles into nanosheets in a cooperative self-assembly process, affording an absorption...

Polymorphism in Squaraine Dye Aggregates by Self‐Assembly Pathway Differentiation: Panchromatic Tubular Dye Nanorods versus J‐Aggregate Nanosheets

“…BisSQ2 was synthesized following the route shown in Scheme 2. Suzuki coupling reaction of compound 1 [17] with 1,4-benzenediboronic acid bis(pinacol) ester (2)afforded the target bis(squaraine) BisSQ2.The crude product was purified by recycling gel permeation chromatography (GPC) to give the pure BisSQ2 in ayield of 23 %. Fordetails on the synthetic procedures and characterizations of all new compounds,s ee the SI.…”

“…However,asignificant decrease in the fluorescence quantum yield to 42 %and areduced fluorescence lifetime of 3.01 ns in comparison to SQ1 (79 %a nd 4.78 ns,r espectively) are Scheme 1. Chemical structure of reference squaraine SQ1 and bis(squaraine) dyes BisSQ1 [17] and BisSQ2 with graphical illustrationo f the orientation of the permanent and transitiond ipole moments, indicated by purple and orange arrow,r espectively.…”

Polymorphism in Squaraine Dye Aggregates by Self‐Assembly Pathway Differentiation: Panchromatic Tubular Dye Nanorods versus J‐Aggregate Nanosheets

“…Prominent examples are benzene‐1,3,5‐tricarboxamide molecules (BTAs) whose regular self‐assembly into 1D fibers [31] was transformed into 2D and 3D morphologies by additional H‐bonding interactions by shielding carboxyl groups in a hydrophobic environment [5b] or by alteration of the alkyl chain length for porphyrin molecules, likewise transforming the self‐assembly into 1D fibers [5a] by increasing the lateral van der Waals forces to afford a 2D sheet‐like morphology. In this context, it is intriguing that we observed polymorphism for BisSQ2 , but not for BisSQ1 despite of the absence of specific measures as described above for the BTAs and alkyl porphyrins [17] . Both molecules consist of two squaraine dyes connected in the same angle.…”

“… Chemical structure of reference squaraine SQ1 and bis(squaraine) dyes BisSQ1 [17] and BisSQ2 with graphical illustration of the orientation of the permanent and transition dipole moments, indicated by purple and orange arrow, respectively.…”

“…Aliphatic and hydrophilic side chains were attached to enhance microphase segregation. Interestingly, whilst BisSQ1 self‐assembly afforded only one type of dye aggregate that consists of a nanosheet structure with slip‐stacked packing arrangement of the dyes and concomitant J‐type exciton coupling, [17] our in‐depth UV/Vis/NIR spectroscopic analysis of BisSQ2 reveals the formation of two dye aggregate polymorphs with entirely different morphologies, i.e., nanorod and nanosheet, as well as optical properties, i.e., panchromatic and red‐shifted absorption bands, respectively. Based on a combined effort by experimental work (microscopy and X‐ray scattering) and theoretical calculations, we were able to derive reliable packing models for both polymorphs and to establish structure‐function relationships.…”