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Model calculations of the first hyperpolarisability per unit cell of finite and infinite polymethineimine chains

The longitudinal component of the static first hyperpolarizability per unit cell of model finite and infinite polymethineimine chains has been computed at the uncoupled Hartree-Fock level of approximation. Particular attention has been paid to the correspondence between the results associated with the large oligomers and the direct polymeric results. We have investigated as a function of increasingly large chain length the effects of the heteroatomicity and the bond alternation upon the electron density alternation and centro-symmetry which modulate the amplitude of the longitudinal first hyperpolarizability per unit cell.