We present a theoretical investigation of small aggregates of quadrupolar (A-π-D-π-A or D-π-A-π-D) charge-transfer dyes, with attention focused on the role of intermolecular interactions in determining their optical properties. We tackle the theoretical issue by adopting essential-state models (ESMs), which describe an isolated molecule in terms of a minimal number of electronic states, corresponding to the resonance structures. ESMs quite naturally describe intermolecular interactions relaxing the dipolar approximation and accounting for molecular polarizabilities. The approach is applied to curcuminoid and squaraine dyes, two families of chromophores with weak and strong quadrupolar character, respectively. The method is validated against experiment and for curcuminoids also against time-dependent density functional theory. ESMs rationalize the strong ultra-excitonic effects recurrently observed in the experimental optical spectra of aggregates of highly polarizable quadrupolar dyes, offering a valuable tool to exploit the supramolecular design of material properties.

We investigate the energetics, electronic structure, optical properties, and charge transfer characteristics of coronene and its imide-functionalized derivatives using quantum chemical calculations. We analyze the formation feasibility of pristine coronene and its different imide monomers, namely, coronene-5-diimide, coronene-6-diimide, and coronene-tetraimide, from a common parental compound, coronene octacarboxylic acid, and find that the most favorable derivative is the pure coronene. Our results also show that coronene-6-diimide is preferred over other possible imide compounds, which is well in accordance with the relative experimental abundance of coronene-6-diimide. The absorption characteristics obtained for both the monomer and dimer of coronene imides show bathochromic shifts for the low-energy peak positions in comparison to the pristine coronene because of the presence of the electron withdrawing imide groups, and the trend in transition energy follows the order of the electronic gap. Interestingly, we find a larger extent of red shift for the absorption maxima of the synthetically more feasible coronene-6-diimide among others. Moreover, our analysis also shows that the extent of red shift strongly depends on the position and orientations of the imide groups, and the low-energy peaks solely correspond to the π–π* electronic transitions. Furthermore, we also calculate the charge (electron and hole) transfer integrals for the plausible stable dimers, and find that effective hole transfer integrals are significantly larger than the electron transfer integral except for the coronene-tetraimide, for which the electron transfer integral is found to be greater than the hole transfer integral. The calculated carrier mobilities for the coronene crystal show that the hole mobility is significantly larger, almost 15 times, than the electron mobility. Our study provides a detailed understanding of the tunable optical and charge transfer properties for imide-functionalized coronene derivatives, and suggests their potential use in optoelectronic and field effect transistor devices.

A bottom-up modelling strategy is adopted to discuss the linear and nonlinear optical spectra of a prototypical push-pull dye, 4-dimethylamino-4'-nitrostilbene (DANS), in different environments, from solutions to linear aggregates, fully accounting for the molecular polarity and polarizability. In particular, we demonstrate a large amplification of the first hyperpolarizability of linear aggregates with a superlinear dependence on the aggregate size. Results are discussed with reference to recent experiments for DANS molecules aligned inside single-wall carbon nanotubes, leading to a complete and internally consistent description of the observed spectral properties in terms of ∼7 aligned molecules, reducing by an order of magnitude the size of the aggregate estimated in the hypothesis of linear amplification, as expected for non-interacting molecules. This has important implications for material design: it is possible to obtain a large amplification of the first hyperpolarizability by aligning just a few DANS molecules (or more generally, a few polar dyes showing normal solvatochromism) without the need to grow large ordered systems.

A flexible twofold interpenetrated MOF reversibly switches between closed, narrow and large pore forms. In situ crystallographic analysis of a narrow-pore intermediate phase provides a detailed explanation of a plateau observed during desorption.

The electronic structures, optical and charge transport properties of various boron–nitrogen (BN) substituted hexagonal graphene nanoflakes (h-GNFs) are investigated with the aim of tailoring the intrinsic properties of pristine h-GNFs using first-principles density functional theory.