Photoinduced 1,3-proton shift in methyldithiepines as a potential way of modulating hyperpolarizabilities.

Reversible disruption of conjugation is a useful technique for affecting electronic properties of organic compounds. One can readily envision, for instance, a formal scheme involving a 1,3-H shift in a 1,2-propenylidene fragment connecting the donor (D) and acceptor (A) that is expected to exert a dramatic effect on properties such as UV-vis absorption, dipole moment, polarizability, and hyperpolarizability. Modulating the latter is a challeng-