Thiophene-based donor–acceptor co-oligomers by copper-catalyzed 1,3-dipolar cycloaddition

• Stefanie Potratz,
• Amaresh Mishra and
• Peter Bäuerle

Beilstein J. Org. Chem. 2012, 8, 683–692, doi:10.3762/bjoc.8.76

• unit could be observed. From the optoelectronic data we deduced a HOMO–LUMO energy level diagram including band gaps for the novel donor–acceptor materials 5, 6 and 10–14 (Figure 2). HOMO values were taken from the onset of oxidation and the internal reference Fc/Fc+ was set to −5.1 eV versus vacuum

• , 121.89, 125.26, 126.59, 128.56, 132.63, 136.68, 143.41; CIMS m/z: (M + H) 377, (M − N2) 349, (M − N4) 320; HRMS–ESI (m/z): (M + Na) calcd for C18H12N6NaS2, 399.0457; found, 399.0452. UV–vis spectra of 5, 10 and 11 (a) and 12–14 (b) in dichloromethane ([c] = 5 × 10−5 M) at room temperature. HOMO–LUMO

Synthesis, solid-state fluorescence properties, and computational analysis of novel 2-aminobenzo[4,5]thieno[3,2-d]pyrimidine 5,5-dioxides

• Kenichirou Yokota,
• Masayori Hagimori,
• Naoko Mizuyama,
• Yasuhisa Nishimura,
• Hiroshi Fujito,
• Yasuhiro Shigemitsu and
• Yoshinori Tominaga

Beilstein J. Org. Chem. 2012, 8, 266–274, doi:10.3762/bjoc.8.28

• reproduced by a series of ab initio quantum-chemical calculations. Keywords: amino group; fluorescence; HOMO/LUMO; pyrimidine; solid-state; Introduction Solid-state fluorescent compounds are currently attracting considerable interest from both theoretical and practical standpoints [1][2][3][4]. Recently

• structures, the HOMO and LUMO of 3a are depicted in Figure 1. The λmax was assigned as the HOMO–LUMO π–π* excitation (configuration weight = 0.697) with an oscillator strength of 0.096 at 335 nm. The next theoretical peak appeared at 290 nm, derived from (HOMO − 1) to LUMO excitations, considerably separated

• carried out ab initio molecular-orbital calculations, focused on 3a (Figure 3). The computed key bond lengths are shown in Table 3. Comparison of the S0 (DFT) and S1 (CIS) bond lengths shows that the S0→S1 (dominant HOMO→LUMO) transition is reflected in the bond-length variations. The C4–C5 bond, with a

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

• Jiří Kulhánek and
• Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

• chromophore π-conjugated backbone. In contrast to 88–93, the presence of two (or four) N,N-dimethylamino donors and the systematic extension of the π-linkers in 95–100 resulted in a bathochromically shifted CT-band, lowered electrochemically measured and calculated HOMO–LUMO gaps, and enhanced first-order

Sexithiophenes as efficient luminescence quenchers of quantum dots

• Christopher R. Mason,
• Yang Li,
• Paul O’Brien,
• Neil J. Findlay and
• Peter J. Skabara

Beilstein J. Org. Chem. 2011, 7, 1722–1731, doi:10.3762/bjoc.7.202

• with the increase in π-electron delocalisation due to the addition of the conjugated phenyl ring. This increase in conjugation is also evidenced by a slight reduction in the optically determined HOMO–LUMO gap of 1a and 1b (2.2 eV for both, Table 2). The solid-state absorption spectra of 1a and 1b are

• very similar, but the optical HOMO–LUMO gaps in the solid state are red-shifted compared to those in solution (2.0 eV). UV–vis spectroelectrochemical measurements (SEC) were performed in acetonitrile on functionalised sexithiophene 1b and nonfunctionalised sexithiophene 2b as thin films drop-cast onto

• separation potentials of 1b in the solid state compared to 2b. The HOMO–LUMO gap was determined from the difference in the onsets for the reduction and first-oxidation processes. Comparison of the optical properties of 1a, 1b, 2a and 2b in solution and solid state. The HOMO–LUMO gap was determined from the

Predicting the UV–vis spectra of oxazine dyes

• Scott Fleming,
• Andrew Mills and
• Tell Tuttle

Beilstein J. Org. Chem. 2011, 7, 432–441, doi:10.3762/bjoc.7.56

• 0.4–0.6, while the major contribution (HOMO–LUMO) remains constant across the series, resulting in the slight variation in the Λ values observed for this dye. Figure 5 illustrates that the orbital overlap for the solvent phase calculations is largely unaffected by the choice of functional. This is due

• primarily to the fact that the predominant contribution to the excitation energy and the nature and overlap of the orbital pair (HOMO–LUMO) is conserved across the different methods. In the gas-phase TD-DFT calculations the number of orbital pairs contributing towards the λmax excitation varies with respect

• to the solvent calculations – two orbital pairs contribute in the gas-phase calculations for 2, 3, 5, 7, 9, and 10 – however, a comparable Λ value is obtained in most cases due to the dominance of the HOMO–LUMO contribution in these excitations as well. The strong overlap between the occupied and

Syntheses and properties of thienyl-substituted dithienophenazines

• Annemarie Meyer,
• Eva Sigmund,
• Friedhelm Luppertz,
• Gregor Schnakenburg,
• Immanuel Gadaczek,
• Thomas Bredow,
• Stefan-S. Jester and
• Sigurd Höger

Beilstein J. Org. Chem. 2010, 6, 1180–1187, doi:10.3762/bjoc.6.135

• thiophene-based (well-established) materials, compounds with additional electron-poor moieties are in focus, as they are known to shift the HOMO and LUMO levels towards lower energies, thus increasing the compounds' stability against oxidation. In addition, the HOMO-LUMO gap is reduced (by the donor

• ). It has to be kept in mind that the calculated values correspond to vertical excitation energies between electronic states while the measured optical spectra include vibronic effects. The dominating signals in the spectra of quaterthiophene 19 and sexithiophene 20 correspond to the HOMO-LUMO

• larger delocalized π-system, which lowers the HOMO-LUMO gap as discussed above. The difference density of 12a (Figure 2c) shows that the S0-S1 excitation leads to an intramolecular charge transfer (CT) from the thiophenes to the phenazine part of the molecule. These calculations verify our initial

Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

• Ritesh Nandy and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2010, 6, 992–1001, doi:10.3762/bjoc.6.112

• . These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO–LUMO energy gaps have been

• substituted with electron withdrawing groups on the phenyl ring. HOMO–LUMO energy gaps have been estimated based on electrochemical studies and compared with those obtained from absorption spectroscopy. Results and Discussion Synthesis 2-Ethynyltriphenylene (4) was synthesized by coupling 2-iodotriphenylene

• potentials, as well as to estimate the HOMO–LUMO gap of these derivatives [31][32][33][34][35]. All the compounds showed a single irreversible oxidation peak and multiple reduction peaks. The HOMO–LUMO gap was estimated from the CV data as the difference between the oxidation peak potential and the reduction

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• the “normal” 5-substituted isoxazoline is formed. Hence, the nitrodecene 123 gives rise to only the nine-membered carbocycle 125 upon reaction with phenyl isocyanate. The matching HOMO-LUMO interactions for such cycloadditions favour the formation of 126 but ring strain and transannular steric effects

Convenient methods for preparing π-conjugated linkers as building blocks for modular chemistry

• Jiří Kulhánek,
• Filip Bureš and
• Miroslav Ludwig

Beilstein J. Org. Chem. 2009, 5, No. 11, doi:10.3762/bjoc.5.11

• formation of the target molecule [19][20] or a separate preparation of the donor as well as the acceptor moieties and their final combination [21][22]. It is already well known that the HOMO/LUMO gap and polarizability of the push-pull systems with the given donors and acceptors can be finely tailored by

High stereoselectivity on low temperature Diels- Alder reactions

• Luiz Carlos da Silva Filho,
• Valdemar Lacerda Júnior,
• Mauricio Gomes Constantino,
• Gil Valdo José da Silva and
• Paulo Roberto Invernize

Beilstein J. Org. Chem. 2005, 1, No. 14, doi:10.1186/1860-5397-1-14

• less reactive, while β-methylated cycloenones (4 and 6) did not react at all. The rather perplexing low reactivity of β-methylated cycloenones was already observed by Wenkert et al. [17]. We are presently carrying out HOMO-LUMO and transition state calculations, seeking for the reasons that could

• product. This would increase the usual difference between the two transition states, normally due mainly to π orbital overlaps. As already mentioned, we are performing HOMO-LUMO and transition states calculations to verify some structural factors influences on the course of these reactions. Conclusion