Impact of Heterocycle Annulation on NIR Absorbance in Quinoid Thioacene Derivatives

Abstract

The synthesis and characterisation of a homologous series of quinoid sulfur-containing imidazolyl-substituted heteroacenes is described. The optoelectronic and magnetic properties were investigated by UV/vis, fluorescence and EPR spectroscopy as well as quantum-chemical calculations, and were compared to those of the corresponding benzo congener. The room-temperature and atmospherically stable quinoids display strong absorption in the NIR region between 678 and 819 nm. The dithieno[3,2-b:2',3'-d]thiophene and the thieno[2',3':4,5]thieno[3,2-b]thieno[2,3-d]thiophenederivatives were EPR active at room temperature. For the latter, variable-temperature EPR spectroscopy revealed the presence of a thermally accessible triplet state, with a singlet-triplet separation of 14.1 kJ mol À 1 .

Synthesis of Thiophene‐fused Helicenes

“…for the synthesis of phenanthrenes and related compounds from 2‐ethynylbiphenyls [22] . This method has already been applied to a cyclization of analogous thiophene‐derived precursors [15b–d] . In our adaption of this protocol we intended to cyclize di(thienyl)di(alkynyl)arenes to the respective penta‐ and hexahelicenes.…”

Experimental and computational study of the exchange interaction between the V(iii) centers in the vanadium-cyclal dimer

“…This equation follows from assuming that the relevant 〈 Ŝ 2 〉 expectation values are equal to 6 ħ 2 and 2 ħ 2 , thereby neglecting the dependence of the geometry on these expectation values. 21–23…”

Heteroatom-Based Diradical(oid)s

“…When diradicals are stable at high temperatures above room temperature, this equation is a fairly powerful method for determining the singlet−triplet energy gaps. 369 A typical example in given in Figure 27. The anionic boronand carbon-based Kekulédiradicaloids 113 Dipp and 113 iPr spanned by a p-phenylene bridge are dark-red crystalline solids.…”

“…It is treated as an arbitrary temperature-independent scaling factor that is adjusted to fit the absolute intensity of I false( T false) = C T true( 1 3 + normalexp ( − 2 J / k T ) true) to the uncalibrated EPR peak-to-peak signal intensities. When diradicals are stable at high temperatures above room temperature, this equation is a fairly powerful method for determining the singlet–triplet energy gaps …”