Spiroconjugated intramolecular charge-transfer dyes

Novel organic spiroconjugated dyes have been prepared using simple condensation reactions between substituted ninhydrins (acceptors) and various diamines, dialcohols, dithiols, aminothiols and hydroxythiols (donors). The donor and acceptor components (based on 1,3- or 1,2-indandione skeleton) were connected in a spiro fashion that allowed for interactions between their orthogonal {dollar}pi{dollar}-systems. The extent of interactions (spiroconjugation) is controlled by the symmetry and energy of the interacting orbitals.; The spiro dyes showed distorted geometry in their crystal structures. These distortions were related to the pyramidalizations of nitrogens of the donor moieties and could be explained by a shift in electron density from the donor fragment to the acceptor moiety. In compounds with 1,3-indandione acceptor, the ground states had dipoles ({dollar}rmmusb g{dollar}) along the long axis of the molecule with the indandione moiety being the electron deficient end.; All spiro dyes showed electronic transitions in the visible region that were attributed to intramolecular charge-transfer (CT) from the highest occupied molecular orbital (HOMO) of the donor components to the lowest unoccupied molecular orbital (LUMO) of the acceptor moiety. In compounds where donor and acceptor frontier orbitals had the same symmetry, the CT transition probabilities were significantly greater than those in dyes built from donors and acceptors with frontier orbitals of different symmetry. The position of the CT bands depended upon the frontier orbital energies of the donor and acceptor moieties as well as the extent of spiroconjugation in these compounds.; Negative solvatochromism and electrooptical absorption (EOA) measurements on the CT bands indicated that excited-state dipole moments ({dollar}murmsb e{dollar}) were in opposite direction to {dollar}rmmusb g.{dollar} These observations confirm the premise that the excited-state of the spiro dyes can be perceived as a radical cation of the donor and radical anion of the acceptor.; Comparison of results from EOA measurements and electric field-induced second harmonic generation (EFISH) studies indicated that the molecular hyperpolarizabilities ({dollar}beta{dollar}) of the spiro compounds had two opposing contributions: one from the CT transition and another from the acceptor chromophore. The first generation of these novel spiro dyes showed {dollar}beta{dollar} values comparable to that of p-nitroaniline, a standard in the field of non-linear optical materials.