J-aggregation, its impact on excited state dynamics and unique solvent effects on macroscopic assembly of a core-substituted naphthalenediimide

Abstract

Herein we reveal a straightforward supramolecular design for the H-bonding driven J-aggregation of an amine-substituted cNDI in aliphatic hydrocarbons. Transient absorption spectroscopy reveals sub-ps intramolecular electron transfer in isolated NDI molecules in a THF solution followed by a fast recombination process, while a remarkable extension of the excited state lifetime by more than one order of magnitude occurred in methylcyclohexane likely owing to an increased charge-separation as a result of better delocalization of the charge-separated states in J-aggregates. We also describe unique solvent-effects on the macroscopic structure and morphology. While J-aggregation with similar photophysical characteristics was noticed in all the tested aliphatic hydrocarbons, the morphology strongly depends on the "structure" of the solvents. In linear hydrocarbons (n-hexane, n-octane, n-decane or n-dodecane), formation of an entangled fibrillar network leads to macroscopic gelation while in cyclic hydrocarbons (methylcyclohexane or cyclohexane) although having a similar polarity, the cNDI exhibits nanoscale spherical particles. These unprecedented solvent effects were rationalized by establishing structure-dependent specific interactions of the solvent molecules with the cNDI which may serve as a general guideline for solvent-induced morphology-control of structurally related self-assembled materials.

Solvent Geometry Regulated Cooperative Supramolecular Polymerization

“…In a “good” solvent such as CHCl 3 , the monomeric state exhibits sharp absorption bands at 353 and 370 nm together with an intramolecular charge‐transfer band at 600 nm. In methylcyclohexane (MCH) or decane, bathochromically shifted almost identical absorption bands indicate J‐aggregation . In the 1 H NMR spectra in MCH or decane, no aromatic peaks were visible for the NDI or benzene ring (Figure S1 in the Supporting Information), which can be attributed to the line broadening as reported for strongly self‐assembled other organogelators .…”

“…To this aim, the majority of the focus has been directed towards understanding the effect of structural nuances of the building block, whereas any direct role of the solvent molecules on devising the cooperative supramolecular polymerization remains limited to only a few examples . Recently, we have reported J‐aggregation of a core‐substituted naphthalene‐diimide (NDI) derivative (NDI‐1, Scheme ) with the primary objective to understand the effect of self‐assembly on excited state dynamics . Subsequently, we realized this system represents a rare example of self‐assembly where the macroscopic structure is strongly dependent on the geometry of the hydrocarbon solvent as it showed spontaneous gelation in linear hydrocarbons whereas a free‐flowing solution in cyclic hydrocarbons (Scheme ) although similar J‐aggregation was evident in both types of solvents.…”

Rational Design for Complementary Donor–Acceptor Recognition Pairs Using Self‐Complementary Hydrogen Bonds

“…However, the magnitude of the upfield shift for NDI‐2 ring protons was less than that in the D–A complex and the peak for homo‐assembly completely disappeared in the mixed sample, indicating an absence of NDI–NDI homo‐assembly in the presence of Py‐3 . For only Py‐3 , there was a minor difference in the chemical shifts of the aromatic protons in CDCl 3 and in MCH, which can be attributed to a mere solvent effect and not necessarily to homo‐assembly. Indeed, that was confirmed by the identical UV/Vis spectra of Py‐3 in CHCl 3 and in MCH (see the Supporting Information, Figure S19).…”

Solvent‐Dependent Nanostructures Based on Active π‐Aggregation Induced Emission Enhancement of New Carbazole Derivatives of Triphenylacrylonitrile

“…The leveling‐off of the tail absorption is attributed to the Mie scattering in the aggregate state. In a “good” solvent such as THF, sharp absorption bands ( λ max ) are noted (Figure ) at 355 and 362 nm for 2‐CTPAN and 2,2′‐CTPAN, respectively, due to π–π* transitions . From UV/Vis spectra (Figure S8) it can be seen that at 80 % and 70 % of water fraction, aggregation occurs for 2‐CTPAN and 2,2′‐CTPAN, respectively, and is responsible for the redshift of the absorption maxima .…”

“…In a "good"s olvent such as THF,s harp absorption bands (l max )a re noted ( Figure 1) at 355 and 362 nm for 2-CTPAN and 2,2'-CTPAN, respectively,d ue to p-p*t ransitions. [42] From UV/Vis spectra ( Figure S8) it can be seen that at 80 %a nd 70 %o f water fraction, aggregation occurs for 2-CTPAN and 2,2'-CTPAN, respectively,a nd is responsible for the redshift of the absorption maxima. [43] Above 90 %w ater content,a ll vibronic features of the spectra are completely lost and the p-p*a b-Scheme1.Structure of 2-CTPAN and 2,2'-CTPAN.…”