Optical and Conformational Studies on Benzobisthiazole Derivatives

Abstract

2,6-Didodecyl-4,8-diphenyl-benzo[1,2-d;4,5-d']bisthiazole (3) and 2,6-didodecyl-4,8-dipyrrole-2-yl-benzo[1,2-d;4,5-d']bisthiazole (5) were synthesized, and their optical properties were investigated in solution and in the solid state. Compounds 3 and 5 were excited with the 325 nm He-Cd laser line to produce blue and green luminescence, respectively. The luminescence of 5 (Phi = 14%) was more efficient than that of 3 (Phi = 5%). Structural and optical properties were further determined with DFT and ZINDO calculations. The planar structure of 5 results in pi --> pi* electronic transitions from the pyrrole moiety to the benzobisthiazole frame, while the twisted geometry of 3 results in luminescence strongly associated with the pi --> pi* transitions within the benzothiazole frame. The effect of solvent on the luminescence properties of 5 is summarized as competition between intra- and intermolecular NH...N hydrogen bonds.

Substituents Destabilize the Molecule by Increasing Biradicaloid Character and Stabilize by Intramolecular Charge Transfer in the Derivatives of Benzobis(thiadiazole) and Thiadiazolothienopyrazine: A Computational Study

“…For example 9,10-bis(2-thienyl)anthracene shows an absorption maximum of 404 nm and for 4,8-dipyrole-2-yl-benzo [1,2-d;4,5-d']bisthiazole it is around 450 nm. [68,69] We calculated the excitation energies using the B3LYP/cc-pVTZ method under the TDDFT formalism (Table 3). It is clear from Table 3 that the B3LYP results seem to be close to experiment only for bare TTP.…”

A quantum-chemical perspective into low optical-gap polymers for highly-efficient organic solar cells

“…Density functional theory (DFT) has also been extensively applied to the geometric and electronic description of DA oligomers. 12,20,26,48,49,51,62,68,70,75,[129][130][131][132][133][134][135][138][139][140]144,145,[147][148][149]151,153 DFT tends to provide a good balance between chemical accuracy and computational cost, though limitations in system size do arise because of larger computational demands in comparison to semiempirical methods since DFT methods normally scale as c 4 ; however, it should be noted that considerable efforts have been devoted to reduce this scaling, e.g., via linear scaling techniques, [159][160][161][162][163] to allow DFT methods to be applied to very large systems. Additionally, traditional DFT methods suffer from the self-interaction error (the fact that an electron can interact with itself), which generally leads to an over-delocalized description of the wave function, and artifacts due to the approximations needed to describe the exchange functional.…”

“…With a proper description of the geometric and electronic structure, quantum-chemical methods can be used to describe the processes involved during photoexcitation and exciton formation. As with the determination of the geometric properties, the most widely used methods for the determination of the (singlet) excited-state properties of DA oligomers are based on semiempirical HF 8,75,[127][128][129][130]138,141,142,146,150,151 and (time-dependent) density functional theory. 48,49,51,70,[129][130][131][132][133][134]136,[138][139][140]144,145,147,153 The most common semiempirical HF method employed to date uses the Intermediate Neglect of Differential Overlap (INDO) Hamiltonian coupled with a Configuration Interaction scheme that allows for excitations of single electrons (CIS).…”

To bend or not to bend – are heteroatom interactions within conjugated molecules effective in dictating conformation and planarity?

“…Extension of the conjugated unit through the 2,6-sites has been well studied, but the attachment of conjugated units at the 4,8-positions has been extremely limited. [11][12][13][14] The latter approach provides a better template for intramolecular non-covalent contacts, resulting in an extended p-system with a disc-like structure (see 13, Fig. 4) and this has been realised through compounds 6-12.…”