DESIGN OF ORGANIC-MOLECULES WITH LARGE 2-PHOTON ABSORPTION CROSS-SECTIONS

A strategy for the design of molecules with Large two-photon absorptio n cross sections, delta, was developed, on the basis of the concept th at symmetric charge transfer, from the ends of a conjugated system to the middle, or vice versa, upon excitation is correlated to enhanced v alues of delta. Synthesized bis(styryl)benzene derivatives with donor- pi-donor, donor-acceptor-donor, and acceptor-donor-acceptor structural motifs exhibit exceptionally Large values of delta, up to about 400 t imes that of trans-stilbene. Quantum chemical calculations performed o n these molecules indicate that substantial symmetric charge redistrib ution occurs upon excitation and provide delta values in good agreemen t with experimental values. The combination of Large delta and high fl uorescence quantum yield or triplet yield exhibited by molecules devel oped here offers potential for unprecedented brightness in two-photon fluorescent imaging or enhanced photosensitivity in two-photon sensiti zation, respectively.