Tetrathiafulvalene-Polychlorotriphenylmethyl Dyads: Influence of Bridge and Open-Shell Characteristics on Linear and Nonlinear Optical Properties

Three conjugated donor--acceptor radical systems (1a-1c) were prepared by bridging a tetrathiafulvalene (TTF) electron-donor unit to a polychlorotriphenylmethyl (PTM) electron-acceptor radical through vinylene units of different lengths. The dependence of the intramolecular charge transfer on the length of the conjugated bridge has been analyzed by different electrochemical and spectroscopic techniques. Linear optical properties and the second-order nonlinear optical (NLO) response of these derivatives have been computed by comparing systems 1a-1c with the non-radical analogues (2a-2c). Interestingly, an enhanced NLO response is predicted for dyads 1a-1c with PTM in the radical form and for compounds with longer vinylene bridges. Calculations confirm the active role the bridge plays for electronic communication between the donor TTF and the acceptor PTM units.