Extension of Intramolecular Charge-Transfer State Lifetime by Encapsulation in Porous Frameworks

Abstract

Control over excited-state lifetimes and relaxation pathways in chromophoric materials is a major challenge in the optimization of photovoltaic energy conversion and photochemical energy storage mechanisms. In light of experimental evidence that the charge-transfer excited-state lifetime of 9-mesityl-10-methylacridinium ion (MesAcr+) can be dramatically extended via encapsulation in the mesoporous aluminosilicate AlMCM-41, we employ multiscale simulations to uncover a mechanism for the suppression of charge recombination of MesAcr+ in AlMCM-41. The simulations reveal that solvation in acetonitrile and encapsulation in AlMCM-41 have opposing effects on the reorganization energy of MesAcr+: solvation substantially raises the reorganization energy while the encapsulation lowers it. Because charge recombination in MesAcr+ takes place deep within the Marcus inverted region, the smaller reorganization energy observed in solvent-free AlMCM-41 raises the activation barrier for excited-state charge recombination. ...