Aggregation Modes of Chiral Diketopyrrolo[3,4‐c]pyrrole Dyes in Solution and Thin Films

Abstract

The chiroptical features of chiral diketopyrrolo [3,4c]pyrrole (DPP) derivatives have been only marginally investigated to date. In this regard, we have synthesized ad hoc four chiral DPP dyes, functionalized with enantiopure alkyl groups from natural sources either on the lactam moieties or on the terminal positions of the π-conjugated backbone, to promote an efficient self-assembly into chiral supramolecular structures. For each of them, the aggregation modes has been investigated by absorbance and ECD spectroscopies in conditions of solution aggregation and on thin films, considering the effects of deposition technique (drop casting vs. spin coating) and post-deposition operations (solvent and thermal annealing). The effect of the structure of lateral πconjugated units attached to the central DPP scaffold, as well as that of the position of the alkyl chiral group, has been assessed. ECD revealed superior capability, compared to absorbance spectroscopy, to provide information on the aggregation modes and to detect the possible co-existence of multiple aggregation pathways.

Chiral diketopyrrolopyrrole dyes showing light emission in solid and aggregate states

“…The thiophene rings were functionalized with phenyl, 4-(diphenylamino)phenyl or tetraphenylethylene (TPE) substituents; the former two gave intense ECD spectra of the aggregates in solution, whereas TPE yielded no measurable optical activity. 17 Due to the distance between the stereogenic carbon and the DPP core, isolated molecules remained CD silent in solution in all the derivatives. 17 In general, all the studies on chiral DPP dyes refer to emissive properties in solution, as for those derivatives, ACQ appeared to be dominant in the solid phases.…”

“…17 Due to the distance between the stereogenic carbon and the DPP core, isolated molecules remained CD silent in solution in all the derivatives. 17 In general, all the studies on chiral DPP dyes refer to emissive properties in solution, as for those derivatives, ACQ appeared to be dominant in the solid phases. In some cases, the ACQ phenomenon can be prevented by using molecular motifs displaying the property of aggregation-induced emission (AIE) that is the opposite phenomenon to ACQ.…”

“…17 Due to the distance between the stereogenic carbon and the DPP core, isolated molecules remained CD silent in solution in all the derivatives. 17…”

“…ECD spectroscopy can indeed deliver precious information about the configurational and conformational composition of a sample and its supramolecular organization. [16][17][18] In the case of radiative relaxation in an excited state, left and right polarizations are emitted differently, which amounts to circularly polarized luminescence or CPL. CPL can be quantified by the dissymmetry factor defined as g lum = 2(I L À I R )/(I L + I R ), where I L and I R are the intensities of the left-and right-handed circularly polarised emitted lights, respectively.…”

Self‐assembly of chiral diketopyrrolopyrrole chromophores giving supramolecular chains in monolayers and twisted microtapes

“…[22][23][24][25][26] Broadly speaking, the aryl substituent, in the most part, typically dictates the intended application of the DPP molecule, with thiophene-based systems (ThDPP, Supporting information S1: ESI 5.1) being used for organic electronic applications thanks to their planarity, good charge transport, and straightforward polymerization, whereas phenyl-based systems (PhDPP, Supporting information S1: ESI 5.1) are synonymous with sensors and imaging agents given their excellent emissive properties in both the solution and the solid state. [27][28][29][30][31][32][33][34][35][36][37] For DPP systems, there have been several strategies to impart hydrogen bonding 38 and chiral motifs [39][40][41] that promote self-assembly and modulate π-π stacking interactions, to ultimately evaluate their impact on the compounds' optoelectronic performance. DPPs inherently suffer from solubility issues given the strong intermolecular interactions driven by π-π stacking and hydrogen bonding through the lactam moiety.…”