Theoretical Study On The Second-order Nonlinear Optical Properties Of Metal Corrole Complexes

Organic nonlinear optical?NLO?materials have potential application in optical switching,optical signal processing and optical data storage due to their easy chemical modification,fast optical response and high damage threshold.The second-order nonlinear optical coefficient is an important parameter to measure the nonlinear optical responses of the materials.Among organic NLO materials,organic conjugated macrocyclic compounds such as porphyrins have large second-order nonlinear optical responses due to their effect of peripheral substituents.As a kind of porphyrinoids,corrole is an 18-?electron conjugated macrocycle having a direct pyrrole–pyrrole linkage and four pyrrole units in corrole macrocycle are linked with just three meso carbons.This difference leads to its non-centrosymmetric structure.Therefore,corrole is a promising candidate for second-order NLO materials due to its intrinsic structural feature.Among these novel corrole compounds,metallocorroles have become a hotspot in corrole chemistry,but the theoretical study of metallocorroles on nonlinear optical responses is rarely reported.Herein,we will focus theoretical investigation on the second-order nonlinear optical properties of metallocrroles.In this paper,to check central metal ion effect on the second-order NLO properties of corrole,we performed density functional theory?DFT?study by using 5,10,15-tripentafluorophenyl corrole and its Mn,Cu and Ga complexes as model compounds.Firstly,the ground state structures of corroles were optimized at B3LYP/6-31G?d?/SDD level without any symmetry constraints.Herein,the 6-31G?d?basis set was adopted for nonmental atoms,yet SDD basis set associated with pseudo potentials was utilized for metal elements.To consider the solvent effect,polarizable continuum model?PCM?was employed in calculations.After that,the frequency calculation was conducted at the same level and it confirms that optimized geometrical structure corresponds to a minimum without imaginary frequency.Based on optimized ground state structures,the electronic structure,electronic absorption spectra have been investigated by DFT calculations.More significantly,the second-order NLO properties have been probed by means of sum-over-states?SOS?method and hole-electron distribution analysis has been adopted to study electron excitation.The computational results show that Cu?TPFC?complex has the largest first hyperpolarizability value??₀=4402 a.u.?,whereas the metal complexes Mn?TPFC?and Ga?TPFC?complexes own smaller?₀ values?2032 a.u.and 1912 a.u.?as compared to parent TPFC molecule??₀=3770 a.u.?,the second-order NLO responses for these compounds are mainly from the contributions of?_y component.The hole-electron distribution analysis indicates that the contributions to large?₀ value for free-base TPFC mainly originate from intramolecular charge transfer on corrole macrocycle.While the metal ions are introduced,the second-order NLO responses for Cu?TPFC?and Mn?TPFC?complexes are mainly from the contributions of intraligand charge transfer?ILCT?transition on corrole macrocycle and the strongest second-order NLO responses for Cu?TPFC?come from?-HOMO to?-?LUMO+1?and?-?HOMO-8?to?-LUMO molecular orbital transition,whereas the contributions to?₀ for Ga?TPFC?complex derive from ILCT transition on corrole macrocycle,showing weakest second-order NLO responses.Therefore,central metal ion with different electron configurations is an important factor affecting second-order NLO responses.In addition,the first hyperpolarizability values of 5,15-pentafluorophenyl-10-?2-aminophenyl?corrole(F₁₀Cor)and its metal complexes also have been calculated to explore the central metal ion and substituent effects.The calculated results show that the?₀ value of F₁₀Cor increases to 4389 a.u.as compared to A₃-type corrole TPFC due to the electron-donating effect.It is worthy to note that the second-order NLO responses for these compounds are also mainly from the contributions of?_y component and F₁₀CorCu complex has the largest?₀ value?6685 a.u.?.The hole-electron distribution analysis demonstrates that the second-order NLO responses for F₁₀CorCu complex are derived from?-HOMO-1 to?-LUMO transition,exhibiting intraligand charge transfer?ILCT?transition between 2-aminophenyl and corrole macrocycle.Hence it demonstrates that the second-order NLO responses for corrole complexes can be influenced by central metal ion effect.