The aggregation effects on the two-photon absorption properties of para-nitroaniline polymers by hydrogen-bond interactions

This paper has theoretically designed a series ofaggregate polymers on the basis of several para-nitroanilinemonomers by hydrogen-bond interactions. At the level oftime-dependent hybrid density functional theory, it has optimizedtheir geometrical structures and studied their two-photon absorption(TPA) properties by using analytical response theory. The calculatedresults exhibit that the aggregation effects not only bring out theconsiderable red shift of the excited energies but also greatlyenhance the TPA intensities of the aggregate polymers in comparisonwith the para-nitroaniline monomer. The aggregate configurationsalso have an important influence on the TPA abilities of thepolymers; the trimer has the largest TPA cross section. The electrontransitions between the molecular orbits involving the strong TPAexcitations of the trimer are depicted to illuminate therelationship between the intermolecular charge transfer and the TPAproperty.