Bending Effect on the Electronic Properties and Nonlinear Optical Responses of Linear Porphyrin Oligomer

Physical bending provides a more stable and controllable method to modify the electronic properties and device applications compared to chemical doping/surface modification in traditional optoelectronic materials. The bending effect on the electronic properties and nonlinear optical (NLO) responses of linear porphyrin oligomer is explored using quantum chemistry methods by designing a series of curved structures with different bending degrees. The highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap (E-gap) of the linear porphyrin oligomer decreases after being bended to form the curved structures, and the E-gap values and orbital distributions show independent behavior on bending degree. In the electronic absorption spectra, the maximum absorptions mainly come from the S-0 ? S-1/S-0? S-2 transitions with the characteristic of local excitation. The NLO response presents a tendency to increase and then decrease with decreasing the bending degree, which is in good accordance with the widely used two-level model. The curved frameworks as well as the results offer guidelines for novel organic NLO device design and fabrication.