Nonequilibrium bandgap modification in porphyrin-based metal-organic frameworks revealed by transient absorption spectroscopy

Modifying the equilibrium bandgap has proven to be an effective strategy for optimizing photocarrier properties in metal-organic frameworks (MOFs). In this work, we have investigated the nonequilibrium bandgap modification in cobalt porphyrin-based MOF (Co-TCPP MOF) nanofilms through transient absorption spectroscopy. Our results reveal a captivating redshift–blueshift crossover in the nonequilibrium bandgap of Co-TCPP MOFs, with a staggering maximum shifting value of approximately 170 meV, achieved with an excitation fluence of 96 μJ/cm2. This phenomenon sets the stage for further investigations into harnessing nonequilibrium bandgap modification as a powerful tool for tailoring photocarrier properties. Another key facet of our research is the revelation that the bandgap modification effect observed in Co-TCPP MOFs is strongly dependent on the excitation fluence and is absent in disordered porphyrin molecules. This observation suggests a correlation between the bandgap modification and the amplified many-body interactions present within the ordered MOF structure, thus offering valuable insights into the intricate relationship between bandgap modification, excitation fluence, and ordered MOF structures.