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Helicenes and helicenoid structures are promising candidates for future applications exploiting circularly polarized light. Ideal candidates should possess near‐quantitative photoluminescence quantum yield, a high luminescence dissymmetry factor and an adjustable HOMO‐LUMO gap. However, carbo[n]helicenes are poorly luminescent compounds and they absorb light mainly in the ultraviolet region. Here we show that the incorporation of a carbonyl group into helical scaffold significantly improves the fluorescence quantum yield and shifts the absorption to visible region. Although the carbonyl group is commonly considered as detrimental to efficient emission, fluorescence quantum yields up to Φ=0.43 were recorded. A straightforward synthetic approach to a highly luminescent tetraceno[6]helicenone and an aza analogue has been developed. The key step is a radical cyclization which is achieving dehydrative π‐extension. The aza‐analogue was incorporated as an emitter in organic light emitting diodes (OLEDs) and showed good performance. [ABSTRACT FROM AUTHOR] more...

Absorption, fluorescence, and phosphorescence spectra of single crystals of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) and BTBT dispersed in frozen n-nonane, n-hexadecane, and dichloromethane matrices were studied at 5 K. Observation of a new absorption band and related changes in the fluorescence to phosphorescence intensity ratio, when the concentration of BTBT in the matrix increased above 10−4M, indicated the presence of BTBT aggregates. Quantum-chemistry calculations performed for the simplest aggregate, isolated dimer, showed that its structure is similar to the "herringbone" element in the BTBT crystal unit cell and the lowest electronic excited singlet state of the dimer has the intermolecular charge-transfer character. A qualitatively different nature of this state in dimers and in crystals, when compared with the situation in BTBT monomer [locally excited (LE) state], is associated with a decrease in the intersystem crossing yield. The structured vibronic structure of phosphorescence spectra in the studied systems indicated LE character of the triplet states. [ABSTRACT FROM AUTHOR] more...

Four tris(salicylideneanilines) (TSANs) with gradually increased steric interactions between the keto–enamine moiety and neighbouring phenyl substituent are presented. The steric interactions are induced by placing two alkyl groups at the ortho position in the N-aryl substituent. The impact of the steric effect over the radiative channels of deactivation of the excited state was evaluated through spectroscopic measurements and theoretical calculations using ab initio techniques. Our results show that the emission occurring after excited state intramolecular proton transfer (ESIPT) is favoured by placing the bulky groups in the ortho position of the N-phenyl ring of the TSAN. However, our TSANs seem to offer the opportunity to obtain a pronounced emission band at higher energy, significantly increasing the coverage of the visible spectrum, resulting in the enhancement of the dual emissive properties of tris(salicylideneanilines). Thus, TSANs may be promising molecules capable of white-like emission for use in organic electronic devices such as white OLEDs. [ABSTRACT FROM AUTHOR] more...

The internal conversion (IC) in 1-aminonaphthalenes are studied. It is shown that a fast thermally activated IC reaction occurs in 1N5, 1N4 and 1DMAN in n-hexane. However, the IC reaction slows down in the polar solvent acetonitrile due to the polarity-dependent increase in the IC activation energy. Correlations between the IC efficiency in 1-aminonaphthalenes and the theta twist angle are also observed. more...

Helicenes are very attractive chiral non-planar polycyclic aromatic hydrocarbons possessing strong chiroptical properties. However, most of the helicenes absorb light mainly in the ultraviolet region, with only a small segment in the blue part of the visible spectrum. Furthermore, carbo[ n ]helicenes exhibit only weak luminescence that limits their utilization. Herein, we demonstrate that peripheral decoration of the helicene backbone with an aryl-carbonyl group shifts the absorption to the visible region and simultaneously improves their fluorescence quantum yields. We thus show that the carbonyl group, commonly considered as detrimental to emission, has the capability of improving optical and photophysical properties. Two different families, aceno[ n ]helicenones and fluoreno[ n ]helicenes, are presented with comprehensive spectrochemical characterization. TD-DFT calculations were implemented to clarify their electronic profiles. We show that increasing the helical length in aceno[ n ]helicenes increases absorption onset, g abs and g lum . Extension of the peripheral aromatic part in fluoreno[ n ]helicenes leads to a blue shift in both absorption and emission., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.) more...