Broadband near-IR absorbing trans-bis(trialkylphosphine) Pt(II) bisacetylide binuclear complex (Pt–1) was prepared with boron-dipyrromethene (Bodipy) and styrylBodipy acetylide ligands. Pt–1 shows strong absorption bands at 731 and 503 nm. Singlet energy transfer (EnT) and efficient intersystem crossing of the central coordinated Bodipy ligand were proposed to be responsible for the efficient funneling of the excitation energy to the triplet-state manifold. Reference complexes containing only a single Bodipy ligand were prepared for comparison (with styrylBodipy ligand Pt–0 or Bodipy ligand Pt–2). The molecular structures were confirmed by single-crystal X-ray diffraction. The photophysical properties were studied with steady-state and time-resolved transient absorption spectroscopies, electrochemical characterization, and density functional theory/time-dependent density functional theory calculations. Dual fluorescence was observed for Pt–1. Singlet EnT in Pt–1 was proposed based on the fluorescence quenching/excitation spectra, and femtosecond transient absorption spectra (energy transfer rate constant kEnT = 2.2 × 1010 s–1). With nanosecond transient absorption spectra, intramolecular triplet-state energy transfer in Pt–1 was proved. Gibbs free energy changes of charge separation indicate that the photoinduced intramolecular electron transfer in Pt–1 is thermodynamically prohibited. Intermolecular triplet transfer between Pt–2 and L–1 was studied with nanosecond transient absorption spectra; the EnT rate and energy transfer efficiency were determined as 3.6 × 104 s–1 and 94.5%, respectively. The singlet oxygen (1O2) photosensitizing of Pt–1 was improved as compared to the complexes containing only a single visible-light-absorbing chromophore.

A triad based on naphthalenediimides (NDI) was prepared to study the intersystem crossing (ISC), the fluorescence-resonance-energy-transfer (FRET), as well as the photoinduced electron transfer (PET) processes. In the triad, the 2-bromo-6-alkylaminoNDI moiety was used as singlet energy donor and the spin converter, whereas 2,6-dialkylaminoNDI was used as the singlet/triplet energy acceptor. This unique structural protocol and thus alignment of the energy levels ensures the competing ISC and FRET in the triad. The photophysical properties of the triad and the reference compounds were studied with steady-state UV–vis absorption spectra, fluorescence spectra, nanosecond transient absorption spectra, cyclic voltammetry, and DFT/TDDFT calculations. FRET was confirmed with steady-state UV–vis absorption and fluorescence spectroscopy. Intramolecular electron transfer was observed in polar solvents, demonstrated by the quenching of both the fluorescence and triplet state of the energy acceptor. Nanosecond transient absorption spectroscopy shows that the T1 state of the triad is exclusively localized on the 2,6-dialkylaminoNDI moiety in the triad upon selective photoexcitation into the energy donor, which indicates the intramolecular triplet state energy transfer. The intermolecular triplet state energy transfer between the two reference compounds was investigated with nanosecond transient absorption spectroscopy. The photophysical properties were rationalized by TDDFT calculations.