Two-photon or higher-order absorbing optical materials and methods of use

DETAILED DESCRIPTION Many of the compounds useful according to the invention can be described by one of four structural motifs.
These compounds exhibit enhanced two-photon or multi-photon absorptivities and allow one to control the position of two-photon or multi-photon absorption bands.
The motifs may be generally categorized as follows: a) molecules in which two donors are connected to a conjugated .
pi.
(pi)-electron bridge (abbreviated "D-.
pi.
-D" motif); b) molecules in which two donors are connected to a conjugated .
pi.
(pi)-electron bridge which is substituted with one or more electron accepting groups (abbreviated "D-A-D" motif); c) molecules in which two acceptors are connected to a conjugated .
pi.
(pi)-electron bridge (abbreviated "A-.
pi.
-A" motif); and d) molecules in which two acceptors are connected to a conjugated .
pi.
(pi)-electron bridge which is substituted with one or more electron donating groups (abbreviated "A-D-A" motif).
We have found that molecules which take these forms can be designed to operate in methods wherein the compounds undergo simultaneous two-photon (or higher-order) absorption, forming compositions which include molecules in an electronically excited state.
These excited state species can be used in a great variety of subsequent method steps.