Directional Excited-State Polarization in a 3,6,9,12-Connected Rectangular Chrysene Network: A Range-Separated Fragment Comparison with a Dibenzochrysene Benchmark

Abstract

A central question for chrysene-based artificial-photosynthetic materials is whether visible-light excitation can produce spatially directed electronic response rather than absorption alone.  We examine a finite fragment
representing the longer C12-C6 direction of a 3,6,9,12-connected rectangular substituted-chrysene network and compare it with a finite fragment derived from a reported dibenzochrysene (DBC) photocatalytic framework.  Ground states were calculated using density-fitted CAM-B3LYP/STO-3G.  The excited-state response was evaluated by the Tamm--Dancoff approximation in a frontier space containing the six highest occupied and six lowest virtual orbitals, with density-fitted Coulomb and seminumerical exchange response.

The three lowest rectangular-fragment roots occur at (2.0468), (2.4360), and (2.9513 eV), corresponding to (605.8), (509.0), and (420.1 nm), with oscillator strengths of (1.8765), (0.5229), and (0.3139).  Their electron--hole centroid separations are (4.258), (3.946), and (5.301 Angstrom).  More than (99.1%) of each displacement lies along the core-centroid connection axis.  The final (5x5) to (6x6) active-space energy changes are below 0.0035 eV, and the assembled response matrix is Hermitian to approximately 10^{-7}E_h.

Relative to the ordinal DBC-fragment roots, the rectangular roots are 0.124 - 0.324 eV lower and have centroid separations 0.433 - 0.741 Angstrom larger, although their oscillator strengths are smaller.  Fragment populations show that the states remain predominantly bridge-centered; the results therefore establish directional excited-state polarization, not complete core-to-core charge separation.  The calculation supports weak optical-directional admissibility while leaving charge-separation free energy, recombination competition, catalyst extraction, and hydrogen evolution unresolved.  These distinctions motivate an uncertainty-aware inverse-design objective combining optical response, directional displacement, electron--hole overlap, redox alignment, kinetics, and synthetic feasibility.