Picosecond molecular switch based on the influence of photogenerated electric fields on optical charge transfer transitions

A concept for a picosecond molecular switch is demonstrated using a photoinduced electron transfer reaction in a covalently linked, fixed distance donor-acceptor molecule D-A linked to a perylene-3,4-dicarboximide chromophore, C. The chromophore C possesses a strong charge transfer transition in its optical spectrum. Selective excitation of C within D-A-C using 530 nm, 130 fs laser pulses produces ^1*C, which undergoes singlet-singlet energy transfer to produce ^1*D, which in turn transfers an electron to A. If the D-A-C system is selectively excited with 416 nm, 130 fs laser pulses to produce D⁺-A^--C prior to excitation of C with 530 nm, 130 fs laser pulses, a 25% lower yield of ^1*C is generated. The intense local electric field produced by D⁺-A^- causes a 15 nm electrochromic red shift of the charge transfer absorption of C. Thus, the absorption of C at 530 nm is significantly diminished by the presence of D⁺-A^-. The need to use two laser pulses with different wavelengths to observe these effects, and the resulting picosecond time response makes it possible to consider applications of this concept in the design of molecular switches.