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Materials for Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
A simple one-dimensional analog of the bulk solid is provided by an infinite chain of carbon atoms, in which individual atoms are separated by distance a (Wang and Herron 1991) (Figure 2.11a). Moreover, each atom carries one pπ orbital (polyene, an idealized polyacetylene chain). This infinite chain is equivalent to an N-annulene, where N is infinite. Annulene is a class of monocyclic hydrocarbons (having a molecular structure with only one ring) with conjugated double bonds (two or more double bonds separated by single bonds; conjugation is possible by means of alternating single and double bonds). The main ideas behind the quantum size effects of semiconductor QDs are understood by investigating the length dependence of N-annulene or N-polyene; polyene is an unsaturated compound containing more than two double bonds. (a) Orbitals of a chain of carbon atoms. (b) Splitting of the energy level of the orbital into levels for bonding, nonbonding, and antibonding orbitals. (c) Plot of E(k) against k. (Wang, Y. and Herron, N., J. Phys. Chem., 95, 525, 1991.)
Application Of Computational Methods To The Rational Design Of Photoactive Materials For Solar Cells
Published in Tanmoy Chakraborty, Prabhat Ranjan, Anand Pandey, Computational Chemistry Methodology in Structural Biology and Materials Sciences, 2017
The basic concept for the design of new photoactive materials in this case study is to reconstruct the donor (D) moiety of the reference compound. As shown in Figure 6.2, the D-moiety of the TA-St-CA reference dye consists of three aromatic annulenes which join at the center N atom. Annulenes, such as benzene, are conjugated monocyclic hydrocarbon rings without side chains. The general formula for an annulene is given as CnHn (if n is an even number) or CnHn+1 (when n is an odd number) [25]. Figure 6.3 gives some examples of annulenes.
The evolution of the principle of circumscribing
Published in Molecular Physics, 2023
Altans are generated by a specialised type of circumscribing in which the encircling annulene is attached via its alternate degree-2 vertices to the degree-2 vertices of a core structure like benzene, naphthalene, or triangulene [2,4]. The generation of monocapped nanotube altans can begin with cyclopentadienyl or benzene as done by Dias in reference 5 but omitting the final end capping step and continuing circumscribing indefinitely. Figures 7 and 8 present this process with all the eigenvalue data for monocapped nanotubes which are (altan)n-benzenes. Note that 0.0 and 0.414214, −2.414214 are additional unique eigenvalues that occur in all monocapped members of this series (Figure 7). The other unique eigenvalues (Figure 8) differ from member to member but are identical for the same membership in Figures 7 and 9. Figure 9 gives all the eigenvalue data for monocapped nanotubes which are (altan)n-cyclopentadienyl. Both the series in Figures 7 and 9 have rotational symmetry and therefore possess corresponding unique eigenvalues presented in Figure 8 for the same tier membership.
Stability, optical and charge transport properties of saddle-shaped cyclooctatetrathiophene (COTh) isomers: a theoretical study
Published in Journal of Sulfur Chemistry, 2022
Anuj Tripathi, Vipin Kumar, Prabhakar Chetti
Recent years have witnessed reintroduced interest in the approach to, and synthesis of, cyclic π-conjugated systems that consist of an anti-aromatic ring. Cyclooctatetraene (COT) is one of the conventional π-conjugated flexible molecules with an 8π annulene framework having D2d symmetry containing an integrally nonplanar saddle-shaped geometry. Because of the presence of angle strain and antiaromaticity in COT, it prefers to possess a nonplanar conformation rather than a planar conformation [1–4]. Its planar structural homologues can be obtained by oxidation and reduction reactions, which is a classical example of the influence of Huckel’s rule [5–8]. This was demonstrated by Yamaguchi et. al., who recently reported that the configuration of thiazole fused COT changed from a tub-shape to a planar geometry via reduction and oxidation as predicted by Huckel’s rule [9]. COT-based materials show fascinating behaviors such as cavity control in the size of cage molecules, buckycatchers, electromechanical actuators, organic field-effect transistors (OFETs) and molecular tweezers [10–14].
Comprehensive study of the correlations that exist among the members of the [n]cyclacene series and the Möbius[n]cyclacene series
Published in Molecular Physics, 2018
Tables 2 and 3 present various HMO trends of among the [n]cyclacene series versus the Möbius[n]cyclacene series. The topological conjugation energy per π-bond (TCE/π-bond) of both [n]cyclacenes and Möbius[n]cyclacenes are very similar and approach the same limit of TCE = 0.767 β with increasing size (Table 2). Because of its Hamiltonian circuit which is twice the size of the largest circuit of its [n]cylcacne isomer, Möbius[n]cyclacenes approach the limit of TCE = 0.767 β faster. The electronic properties of HOMO–LUMO gap, %TRE and BRE of the [n]cyclacene series exhibit an oscillatory behavior with increasing size (Table 3) consistent with that observed at higher level calculation (TAO-DFT for n ≤ 30).[5] This oscillatory behavior in %TRE is indicative of alternating aromaticity and antiaromaticity of the rims for smaller members of this series. Such oscillatory behaviour is absent in the Möbius[n]cyclacene series because they all have a single 4n π–electron Hamiltonian rim. By the %TRE index, the members of the Möbius[n]cyclacene series appear to be slightly more aromatic than the smaller members of the [n]cyclacene series but by the BRE measure are less aromatic. It is of interest to note that the Huckel 4n/4n+2 antiaromaticity/aromaticity rule is reversed in Möbius annulenes [13,26]. Benzene has %TRE = 3.528 and BRE = 0.2726. %TRE is a measure of global aromaticity and BRE is a measure of LA associated with the relevant ring [31]. The double Clar sextet in [3]cyclacene (Figure 13) makes it exceptional as it has %TRE = 2.865 and BRE = 0.2262. Also [2]cyclacene has two antiaromatic [4]annulene rim circuits, one at the upper and one at the lower zigzag edge, resulting in %TRE = ‒8.958 and BRE = ‒ 0.1768 which can be compared to [4]annulene (cyclobutadiene) which has %TRE = ‒23.46 and BRE = ‒ 1.226.