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 (Egap) of the linear porphyrin oligomer decreases after being bended to form the curved structures, and the Egap values and orbital distributions show independent behavior on bending degree. In the electronic absorption spectra, the maximum absorptions mainly come from the S0 → S1/S0 → S2 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.