Relations of two-photon absorption property and molecular structure in phenylenevinylene chromophores

Abstract

In this paper, we performed experimental and quantum-chemical studies on a series of symmetrically substituted phenylenevinylene chromophores with different lengths of conjugated chains and different electro negativity of substitution groups to provide an insight into the nature of the two-photon absorption (TPA) processes and to reveal structure-property relations. TPA spectra were obtained at the wavelengths ranging from 600 to 1000 nm with 6ns laser pulses of 10Hz repetition rate. The TPA spectra show that absorption band is mainly related to the transition of electrons btween the orbital localized at phenyl rings of the conjugated chains. Quantum-chemical calculations were performed with MOLCAO (Molecular Orbital as a Linear Combination of Atomic Orbitals) method to calculate the positions of the electronic levels and the shapes of the molecular orbitals. Considering all of the series of symmetrically substituted phenylenevinylene chromophores, the planar structure and the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is influenced significantly by the length of conjugated chains and the electro negativity of substitution groups. Structure-property relations revealed that the TPA cross section tends to be enhanced by an increase in the electro negativity of the substitution groups and tends to be reduced by an interruption of the conjugated chain.