Exciton Coupling of Merocyanine Dyes from H- to J-type in the Solid State by Crystal Engineering

Abstract

A key issue for the application of π-conjugated organic molecules as thin film solid-state materials is the packing structure, which drastically affects optical and electronic properties due to intermolecular coupling. In this regard, merocyanine dyes usually pack in H-coupled antiparallel arrangements while structures with more interesting J-type coupling have been rarely reported. Here we show that for three highly dipolar merocyanine dyes, which exhibit the same π-scaffold and accordingly equal properties as monomers in solution, the solid-state packing can be changed by a simple variation of aliphatic substituents to afford narrow and intense absorption bands with huge hypsochromic (H) or bathochromic (J) shifts for their thin films and nanocrystals. Time-dependent density functional theory calculations show that the energetic offset of almost 1 eV magnitude results from distinct packing motifs within the crystal structures that comply with the archetype H- or J-aggregate structures as described by Kasha's exciton theory.

Fused Pyrazine‐ and Carbazole‐Containing Azaacenes: Synthesis and Properties

“…The third band absorption spectrum of thin film of 4 a is bathochromically shifted by approximately 15 nm compared with the solution absorption spectrum, indicating J‐type aggregation in the solid state, while the absorption spectrum of 4 b in thin‐film is very similar with that in solution. For 5 b , the thin film absorption spectrum is blue‐shifted by about 10 nm compared with solution absorption, indicating H‐type aggregation in the solid state . Different aggregation behavior of these azaacenes in the solid states indicates that both the alkyl chain and core conjugated length can influence the aggregation greatly.…”

“…The thin-film UV-Vis absorption spectra of 4 a, 4 b and 5 b are shown in Figure S7. The third band absorption spectrum of thin film of 4 a is bathochromically shifted by approximately 15 nm compared with the solution absorption spectrum, indicating J-type aggregation in the solid state, [14] while the absorption spectrum of 4 b in thin-film is very similar with that in solution. For 5 b, the thin film absorption spectrum is blue-shifted by about 10 nm compared with solution absorption, indicating H-type aggregation in the solid state.…”

“…For 5 b, the thin film absorption spectrum is blue-shifted by about 10 nm compared with solution absorption, indicating H-type aggregation in the solid state. [14] Different aggregation behavior of these azaacenes in the solid states indicates that both the alkyl chain and core conjugated length can influence the aggregation greatly. The fluorescence spectra of compounds 4 a, 4 b, and 5 b in chloroform were measured and shown in Figure S8.…”

Synthesis and crystal structure of N,N-dimethylformamide solvate of thiocyanuric acid

“…All chemical shifts were referenced to the residual solvent protons/carbons of the solvent indicated. 1 …”

“…

Abstract Considerable attention has been paid recently to crystal engineering; which involves the design and preparation of new crystalline molecular solids with desired properties [1][2][3][4]. Crystalline materials with specific properties find applications in petrochemical industry for separation and purification.

…”