posted on 2023-12-07, 18:40authored bySamara Medina Rivero, Matías J. Alonso-Navarro, Claire Tonnelé, Jose M. Marín-Beloqui, Fátima Suárez-Blas, Tracey M. Clarke, Seongsoo Kang, Juwon Oh, M. Mar Ramos, Dongho Kim, David Casanova, José L. Segura, Juan Casado
A new
family of molecules obtained by coupling Tröger’s
base unit with dicyanovinylene-terminated oligothiophenes of different
lengths has been synthesized and characterized by steady-state stationary
and transient time-resolved spectroscopies. Quantum chemical calculations
allow us to interpret and recognize the properties of the stationary
excited states as well as the time-dependent mechanisms of singlet-to-triplet
coupling. The presence of the diazocine unit in Tröger’s
base derivatives is key to efficiently producing singlet-to-triplet
intersystem crossing mediated by the role of the nitrogen atoms and
of the almost orthogonal disposition of the two thiophene arms. Spin–orbit
coupling-mediated interstate intersystem crossing (ISC) is activated
by a symmetry-breaking process in the first singlet excited state
with partial charge transfer character. This mechanism is a characteristic
of these molecular triads since the independent dicyanovinylene-oligothiophene
branches do not display appreciable ISC. These results show how Tröger’s
base coupling of organic chromophores can be used to improve the ISC
efficiency and tune their photophysics.