INVESTIGATION OF THE LINEAR AND NONLINEAR-OPTICAL RESPONSE OF EDGE-LINKED CONJUGATED ZINC PORPHYRIN OLIGOMERS BY OPTICAL SPECTROSCOPY AND CONFIGURATION-INTERACTION TECHNIQUES

We present a joint experimental and theoretical investigation of the l inear and nonlinear optical response of butadiyne-linked zinc porphyri n oligomers. Efficient overlap between the chromophores leads to a lar ge red-shift of the Q absorption band together with a splitting of the B band into two components when increasing the chain length from one to two repeating porphyrin units. Ultrafast pumb-probe measurements pe rformed on these compounds show several well-defined features, associa ted with singlet excited state absorption. We also find clear evidence for the formation of longer-lived triplet excitons, resulting from ve ry efficient singlet-triplet intersystem crossing processes, For the m onomers, the assignment of the observed linear and photoinduced absorp tion features is supported by a Configuration Interaction description of the singlet and triplet excited states. In the case of the porphyri n dimer, agreement with the experimental results can only be obtained by considering a sizable cumulenic contribution in the excited-state g eometry used as input for the CI calculations. The potential of porphy rin systems for Reverse Saturable Absorption and Nonlinear Optics is e mphasized. (C) 1997 American Institute of Physics.