# Beyond-Kasha Photochemistry in a Heteroleptic Platinum–Dithiolene Complex

## TL;DR

This paper explores a platinum complex that shows non-Kasha photochemistry, enabling new types of light-responsive materials.

## Contribution

The study identifies a heteroleptic platinum–dithiolene complex exhibiting beyond-Kasha photochemistry with excitation-dependent behavior.

## Key findings

- The complex undergoes conformational changes only when higher excited states are excited.
- These changes lead to HCl detachment and a blue-shift in the S1–S0 gap within 70 ps.
- The system demonstrates excitation-dependent photochemistry, enabling new material applications.

## Abstract

Kasha’s rule
implies that photochemical reactions
occur
in the lowest excited state, regardless of excitation wavelength.
Only a few chromophores have been reported to exhibit efficient non-Kasha
responses. While these are rare, their exploitation could revolutionize
multiresponsive materials, improve solar energy utilization, and advance
light-driven chemical reactions. Studying non-Kasha dynamics enhances
the understanding of excited-state processes and could broaden the
range of usable chromophores in real applications. This article focuses
on the anionic heteroleptic dithiolene complex [Pt­((R)-α-MBAdto)­(quinoxdt)]− ((R)-α-MBAdto = (R)-(+)­α-methylbenzyl-dithiooxamidate; quinoxdt = [1,4]­dithiino­[2,3-b]­quinoxaline-2,3-bis­(thiolate)) in acetonitrile, which
undergoes long-lived conformational changes exclusively upon excitation
of higher excited states. In its tight ion-pair adduct with HCl, these
changes drive HCl detachment within 70 ps, trigger a dramatic blue-shift
in the
S

1
–
S

0
gap, and lead
to aggregate formation. Although these processes ultimately occur
in the lowest excited state, they rely on non-Kasha isomerization,
representing a “beyond-Kasha” process. Such systems
pave the way for innovative multiresponsive materials and non-Kasha
excitation-dependent photochemical applications.