We have constructed a broadband ultrafast time-resolved infrared (TRIR) spectrometer and incorporated it into our existing time-resolved spectroscopy apparatus, thus creating a single instrument capable of performing the complementary techniques of femto-/picosecond time-resolved resonance Raman (TR ³ ), fluorescence, and UV/visible/infrared transient absorption spectroscopy. The TRIR spectrometer employs broadband (150 fs, ∼150 cm ⁻¹ FWHM) mid-infrared probe and reference pulses (generated by difference frequency mixing of near-infrared pulses in type I AgGaS ₂ ), which are dispersed over two 64-element linear infrared array detectors (HgCdTe). These are coupled via custom-built data acquisition electronics to a personal computer for data processing. This data acquisition system performs signal handling on a shot-by-shot basis at the 1 kHz repetition rate of the pulsed laser system. The combination of real-time signal processing and the ability to normalize each probe and reference pulse has enabled us to achieve a high sensitivity on the order of ΔOD ∼ 10 ⁻⁴ –10 ⁻⁵ with 1 min of acquisition time. We present preliminary picosecond TRIR studies using this spectrometer and also demonstrate how a combination of TRIR and TR ³ spectroscopy can provide key information for the full elucidation of a photochemical process.

The photophysical properties of fac-[Re(CO)₃(dppz)(py)]⁺ (1, where dppz = dipyrido[3,2-a:2′,3′-c]phenazine) in CH₃CN have been investigated using a series of complementary techniques including visible and infrared transient absorption and resonance Raman spectroscopy on the picosecond and nanosecond timescales. The results confirm previous reports that the lowest-lying emissive state in 1 is a triplet intra-ligand (³IL) state localised on the dppz ligand and have provided detailed information on the dynamics of 1 upon photoexcitation, including the relative energies of the excited state species encountered and the electronic distribution within these. If the dppz ligand is viewed in terms of phenanthroline (phen) and phenazine (phz) moieties, the emissive state is probably more accurately described as a ³π→π*(phz) IL state. The picosecond studies have shown that this emissive state is formed, at least in part, within 30 ps of excitation from a precursor, which is possibly a ³π→π*(phen) IL state. On the nanosecond timescale, TRIR has been employed to elucidate further dynamics and reveal the presence of an energetically close-lying state in equilibrium with the emissive state. This has tentatively been assigned as being ³dπ(Re)→π*(phz) metal-to-ligand charge transfer (MLCT) in nature. A summary of the photophysics is proposed in the form of a Jablonski scheme. Time dependent density functional theory (TD-DFT) calculations support the relative ordering and suggested electronic character of the excited state species involved.

A phenanthridine derivative covalently linked to a ruthenium complex yields an imaging probe whose fluorescence intensity and lifetime change substantially in the presence of RNA.

Time-resolved infrared (TRIR) spectroscopy, a combination of UV flash photolysis and fast infrared detection, is a powerful technique for probing excited states and detecting reaction intermediates. In this Perspective we highlight the application of TRIR to excited states by probing the nature of the lowest excited states of fac-[Re(CO)₃(dppz-Cl₂)(R)]ⁿ⁺ (R = Cl⁻ (n = 0), py (n = 1) and 4-Me₂N-py (n = 1); dppz-Cl₂ = 11,12-dichlorodipyrido[3,2-a:2′,3′-c]phenazine) in CH₃CN. The characterisation of [Cr(η⁶-C₆H₆)(CO)₂Xe] and [Re(η⁵-C₅H₅)(CO)₂(C₂H₆)] in supercritical Xe and liquid ethane solution exemplifies how this technique can be applied to detect new organometallic species.