Experimental and theoretical investigations are presented on four quadrupolar molecules constituted of a central electron-acceptor 2,1,3-benzothiadiazole conjugated at both sides with electron-donating thiophene (or 2,2′-bithiophene) substituted groups. Previous investigation of their physicochemical properties demonstrated that thermally induced self-organization might be achieved for one of them. In this study, we further explore the structure−properties relationships for these quadrupolar chromophores also examining their aggregation behavior in organic nanoparticles. Strong spectroscopic evidence of Jaggregates formation is obtained, favored by the presence of branched terminal alkyl chains. The surprisingly low fluorescence quantum yield of these J-aggregates is rationalized within the essential-state model approach.

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We report the first macrocycle-based ratiometric molecular thermometer exploiting the conformational thermosensitivity of a calixarene functionalized with two different fluorophores.

A family of multipolar V-shaped chromophores bearing an A'-D-A-D-A' structure were investigated, where 2,1,3-benzothiadiazole, acting as the central electron acceptor (A), is linked to two thiophene-based electron-donating moieties (D) end-capped with alkyl-cyanoacetate substituents (A'). The spectroscopic properties of thin films and powders were investigated and were compared to solutions and nanoaggregates. The optical properties strongly depended on the aggregation state and could be tuned by means of thermal treatment (annealing) of the films and through mechanical treatment (grinding) of the powders, demonstrating that these materials are multistimuli responsive. The spectroscopic analysis revealed the partial formation of J-aggregates both in the films and in powders, despite the weak luminescence. This behavior was interpreted as due to the partial formation of poorly fluorescent red-shifted aggregates acting as a sink in an efficient excitation energytransfer process from J-aggregates.

The photophysics of a structurally unique aza‐analogue of polycyclic aromatic hydrocarbons characterized by 12 conjugated rings and a curved architecture was studied in detail. The combined experimental and computational investigation reveals that the lowest excited state has charge‐transfer character, in spite of the absence of any peripheral electron‐withdrawing groups. The exceptionally electron‐rich core comprised of two fused pyrrole rings is responsible for it. The observed strong solvatofluorochromism is related to symmetry breaking occurring in the emitting excited state, leading to a significant dipole moment (13.5 D) in the relaxed excited state. The anomalously small fluorescence anisotropy of this molecule, which is qualitatively different from what is observed in standard quadrupolar dyes, is explained as due to the presence of excited states that are close in energy but have different polarization directions.