Exciplex Ensemble Modulated by Excitation Mode in Intramolecular Charge-Transfer Dyad: Effects of Temperature, Solvent Polarity, and Wavelength on Photochemistry and Photophysics of Tethered Naphthalene–Dicyanoethene System

Solvent, temperature, and excitation wavelength significantly affected the photochemical outcomes of a naphthalene–dicyanoethene system tethered by different number (<i>n</i>) of methylene groups (<b>1</b>–<b>3</b>). The effect of irradiation wavelength was almost negligible for <b>2a</b> but pronounced for <b>3a</b>. The temperature dependence and theoretical calculations indicated the diversity of exciplex conformations, an ensemble of which can be effectively altered by changing excitation wavelength to eventually switch the regioselectivity of photoreactions