Lewis acids and bases can interact to form either Lewis adducts or, in some cases, unbound, frustrated Lewis pairs (FLPs). Depending on the strength of the interaction, diverse chemical reactivity and photophysical properties may be expected. π-Conjugated systems bearing Lewis acidic boron centers, especially those with electron rich backbones, have been proposed for intriguing applications as luminescent materials and chemical sensors due to their highly favorable charge-transfer character and ion-binding capabilities. We report here a system in which a Lewis acidic dimesitylboryl center and Lewis basic phosphine or phosphine oxide group are attached pendant to a π-conjugated thiophene-based backbone. These systems show temperature and solvent dependent switching between Lewis adduct and unbound Lewis pair, giving rise to drastically different absorbance and emission colors. The synthesis and structure of these compounds will be presented, and the photophysical behavior, switching mechanism and potential applications will be discussed.