π-electron calculations of polarizabilities in conjugated systems

Abstract

Articles you may be interested in πelectron polarizabilities of infinite organic polymers J. Chem. Phys. 97, 9389 (1992); 10.1063/1.463315Ultraviolet photoemission study of oligothiophenes: The effect of irregularity on πelectron systems A screened potential molecularorbital calculation of the πelectron systems of metalloporphin, metallochlorin, and metallobacteriochlorin A screened potential molecularorbital calculation of the πelectron system of porphyrin Finite-field technique has been applied to the calculation of 1T molecular polarizabilities within the P~~ser-Parr-Pople Hamiltonian. This formalism allows to analyze large oligomers contammg up to 400 atoms, and asymptotic behaviors may be attained in some cases. We have investigated the role of the polymer size, the backbone geometries, the presence of neutral and charged defects (solitons, polarons, bipolarons), the chemical nature of the monomeric unit on the polarizabilities. Generally, the polarizabilities are not deeply modified by a change of the geometrical characteristics, and may lead to huge values for sufficiently large chains. Besides, the charge of the system is the leading factor which determines the values of this property. The evolution of the polarizability with the number N of 1T atomic centers, au depends largely on the charge, and on the defect. For the neutral systems, the polarizability per monomeric unit au increases smoothly, and then exhibits an asymptotic behavior with N. For polymers with a defect, this variation is different: au first increases with N, reaches a maximum a for N and finally tends to an asymptotic value. The values of a umax for N max depend onuili~ type of ax , defect (soliton vs polaron) and are rather sensitive to the dependence of the first-neighbor oneelectron interaction with the interatomic distance. A large number of results on polyacetylene and poly heterocycles shows that there exists a simple law between the polarizability and the electronic gap, independently of the type of the monomeric unit. But this relation shows a deviation from a simple proportionality behavior, as soon as a reaches large values (as for example in polymers with defects).

π-electron polarizabilities of infinite organic polymers

“…13 The only change is relative to the parametrization of the bielectronic PPP integrals. The previous results obtained on long oligomers including topological defects (solitons, polarons, and bipolarons) have shown that the commonly used Ohno integrals (see, e.g., Ref.…”

“…The polarizability per unit cell has been calculated for different values of this alternation and compared to results obtained on the same type of calculation on long 0ligomers. 13 The Fock matrix elements of an infinite system described by the Pariser-Parr-Pople approximations is…”

“…(4) presents no particular difficulty. As noted by these authors, the numerical instabilities may be controlled from the requirement of the antihermiticity criterion of the elements of the matrix n, (13) In order to check the antihermiticity of the n matrix, the polarizability is calculated at each SCF iteration using formula (4) and the alternative expression which is equivalent to Eq. (4) once Eq.…”

“…The PPP polarizabilities are not directly comparable to previous calculations 13 because of the choice of the bielectronic integrals as discussed above. Moreover, in the present paper, the SOS polarizabilities have been calculated while evaluating the difference in the state energies [see expression (2)] as the difference of the molecular energies (calculation referenced by SOS-1 in our previous paper 13 ). The variations of the polarizabilities per unit au as a function of the chain length are given in Tables I and II for polyacetylene (PA), polypyrrole (PY), and poly thiophene (PT) within the Hiickel and PPP formalisms, respectively.…”

Conjugated Molecules for the Smart Filtering of Intense Radiations

“…A prominent class of materials displaying NLO absorption and concomitant generation of the OL effect is constituted by conjugated organic molecules [13] which are characterized by the presence of an extended network of loosely bound π-electrons with oxidation energies ranging within the approximate interval 6.5-8.5 eV [14]. The most relevant feature of the π-electrons is their high polarizability [15,16]. This allows a quasi-instantaneous response of the molecule to the perturbations induced by rapidly variable external electric fields and the interaction between light and conjugated molecule generally brings about low losses and scarce dispersion of the energy transported by the optical wave [5].…”