Conformationally-restricted bicarbazoles with phenylene bridges displaying deep-blue emission and high triplet energies: systematic structure–property relationships

Twelve bicarbazole derivatives with emission ranging from blue-green to deep-blue, and E_T 2.6–3.0 eV.

Radical cation and dication of a 4H-dithieno[2,3-b:3′,2′-e][1,4]-thiazine

4H-Dithieno[2,3-b:3’,2’-e][1,4]-thiazine (DTT), and its radical cation and dication were synthesized, characterized (EPR spectroscopy and spectroelectrochemistry) and interpreted (DFT and TD DFT calculations).

Synthesis and electronic properties of 3,7-dianilino substituted N-hexyl phenothiazines

3,7-Diaminophenothiazine derivatives are readily synthesized via two-fold Buchwald-Hartwig coupling of 10-hexyl 3,7-dibromo-10H-phenothiazine with a series of primary and secondary anilines and amines. All derivatives possess two reversible oxidations at low potentials with remarkable semiquinone formation constants. The electronic structure of this novel class of phenothiazinyl-oligoanilines is additionally studied and rationalized by DFT computations and correlation studies between selected experimental and computational electronic data.

4H-dithieno[2,3-b:3',2'-e][1,4]thiazines--synthesis and electronic properties of a novel class of electron rich redox systems

Quantum chemical screening reveals that 4H-dithieno[2,3-b:3',2'-e][1,4]thiazines possess the highest HOMO among four constitutional isomers, even 0.27 eV higher in energy than the well established 10H-phenothiazine. N-Substituted 4H-dithieno[2,3-b:3',2'-e][1,4]thiazines are readily accessible by twofold Pd-catalyzed amination. According to cyclic voltammetry dithienothiazines are reversibly oxidized and can be considered as new donors for functional π-systems.

A Theoretical, Spectroscopic, and Photophysical Study of 2,7-Carbazolenevinylene-Based Conjugated Derivatives

A combined theoretical and experimental study of the structure, optical, and photophysical properties of four 2,7-carbazolenevinylene-based derivatives in solution is presented. Geometry optimizations of the ground states of PCP, PCP-CN, TCT, and TCT-CN were carried out using the density functional theory (DFT/B3LYP/6-31G*). It is found that PCP and TCT are nearly planar in their ground electronic states (S0), whereas the cyano derivatives are more twisted. The nature and the energy of the first singlet-singlet electronic transitions have been obtained from time-dependent density functional theory (TDDFT) calculations performed on the optimized geometries. For all the compounds, excitation to the S1 state corresponds mainly to the promotion of one electron from the highest-occupied molecular orbital to the lowest-unoccupied molecular orbital, and the S1 <-- S0 electronic transition is strongly allowed and polarized along the long axis of the molecular frame. The optimization (relaxation) of the first singlet excited electronic state (S1) has been done using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. It is observed that all four investigated compounds become more planar in their S1 relaxed excited state. Electronic transition energies from the relaxed excited states have been obtained from TDDFT calculations performed on the S1-optimized geometries. The absorption and fluorescence spectra of the carbazolenevinylenes have been recorded in chloroform. A good agreement is obtained between TDDFT vertical transitions energies and the (0,0) absorption and fluorescence bands. The change from phenylene to thiophene rings as well as the incorporation of cyano substituents induce bathochromic shifts in the absorption and fluorescence spectra. From the analysis of the energy of the frontier molecular orbitals, it is believed that thiophene rings and CN substituents induce some charge-transfer character to the first electronic transition, which is responsible for the red shifts observed. Finally, the fluorescence quantum yield and the lifetime of the compounds in chloroform have been obtained. In sharp contrast with many oligothiophenes, it is observed that TCT possesses a high fluorescence quantum yield. On the other hand, the CN-containing derivatives exhibit much lower fluorescence quantum yields, probably due to the combined influence of steric effects and charge-transfer interactions caused by the cyano groups.

A first principles calculations and experimental study of the ground- and excited-state properties of ladder oligo(p-aniline)s

The molecular structure of three ladder oligo(p-aniline)s, 5,11-diethyl-6,12-dimethylindolo[3,2-b]carbazole (DIMER 2P), 14-ethyl-5,8-dihydro-diindolo[3,2-b:2',3'-h]carbazole (TRIMER 2P), and 5,8,14-triethyl-diindolo[3,2-b:2',3'-h]carbazole (TRIMER 3P) were investigated by first principles calculations at the Hartree-Fock (HF6-31G*) and density functional theory (DFTB3LYP6-31G*) levels. It is found that the agreement between theoretical and x-ray geometrical parameters is good and rather similar for both theoretical methods. The nature and the energy of the first two singlet-singlet electronic transitions have been obtained by Zerner intermediate neglect of differential overlap/spectroscopy semiempirical calculations performed on the HF6-31G* and DFTB3LYP6-31G* optimized geometries, as well as time-dependent density functional theory (TDDFT) calculations performed on the DFTB3LYP6-31G* optimized structures. For all the compounds and for all the theoretical approaches, it is observed that the S(1)<--S(0) electronic transition (pipi*) is weakly allowed and polarized along the short axis (y) of the molecule. On the other hand, the S(2)<--S(0) electronic transition of each oligomer possesses a much larger oscillator strength and is polarized along the long (x) molecular axis. It is found that TDDFT calculations provide the best overall agreement between the energies and the corresponding optical transitions obtained from the absorption bands (0-0 peaks) measured in dichloromethane as well as providing a good evaluation of the bathochromic shifts caused by the increase in the conjugation length or by the presence of extra alkyl chains on the nitrogen atoms in TRIMER 3P compared to TRIMER 2P.