Photo-tunable linear and nonlinear optical response of cyclophanediene-dihydropyrene photoswitches.

Cyclophanediene (CPD)-dihydropyrene (DHP) is a negative T-type photochrome pair having a thermodynamically stable colored form, i.e., DHP. Interconversion between cyclophanediene and dihydropyrene is associated with significant changes in dipole moment, absorption wavelength and polarizability, which can impart substantial linear and nonlinear optical response. In this study, phototunable linear and nonlinear optical response of cyclophanediene-dihdyropyrene photoswitches is described. Cyclophanedienes and dihydropyrenes are functionalized at the internal position for maximum changes in volume and polarizability. The UV-Vis spectra are calculated at É·B97XD, which was validated through a benchmark approach. An excellent correlation is observed between theoretical and experimental absorption spectra. Several CPD-DHP pairs have been recognized for clean interconversion in UV-Vis light without formation of a photostationary state. Nonlinear optical response of dihydropyrenes is remarkably higher than that of cyclophanedienes. In general, the calculated hyperpolarizability values of dihydropyrenes are about two to three orders of magnitude higher than those for cyclophanedienes. The trends in calculated hyperpolarizabilities are rationalized through two level method. The high nonlinear optical response of dihydropyrenes stems from low excitation energies. The remarkable difference in hyperpolarizabilities of these isomeric forms paves path for the design of phototunable nonlinear optical materials.