Photochemistry and Photophysics of Charge-Transfer Excited States in Emissive d10/d0 Heterobimetallic Titanocene Tweezer Complexes.

Transition-metal complexes that undergo ligand-to-metal charge transfer (LMCT) to d0 metals are of interest as possible photocatalysts due to the lack of deactivating d-d states. Herein, the synthesis and characterization of nine titanocene complexes of the formula Cp2Ti(C2Ar)2·MX (where Ar = phenyl, dimethylaniline, or triphenylamine; and MX = CuCl, CuBr, or AgCl) are presented. Solid-state structural characterization demonstrates that MX coordinates to the alkyne tweezers and CuX coordination has a greater structural impact than AgCl. All complexes, including the parent complexes without coordinated MX, are brightly emissive at 77 K (emission max between 575 and 767 nm), with the coordination of MX redshifting the emission in all cases except for the coordination of AgCl into Cp2Ti(C2Ph)2. TDDFT investigations suggest that emission is dominated by arylalkynyl-to-titanium 3LMCT in all cases except Cp2Ti(C2Ph)2·CuBr, which is dominated by CuBr-to-Ti charge transfer. In room-temperature fluid solution, only Cp2Ti(C2Ph)2 and Cp2Ti(C2Ph)2·AgCl are emissive, albeit with photoluminescent quantum yields ≤2 × 10-4. The parent complexes photodecompose in room-temperature solution with quantum yields, Φrxn, between 0.25 and 0.99. The coordination of MX decreases Φrxn by two to three orders of magnitude. There is a clear trend that Φrxn increases as the emission energy increases. This trend is consistent with a competition between energy-gap-law controlled nonradiative decay and thermally activated intersystem crossing between the 3LMCT state and the singlet transition state for decomposition.

Ligand-to-Metal Charge-Transfer Photophysics and Photochemistry of Emissive d0 Titanocenes: A Spectroscopic and Computational Investigation.

Complexes with ligand-to-metal charge-transfer (LMCT) excited states involving d0 metals represent a new design for photocatalysts. Herein, the photochemistry and photophysics of d0 titanocenes of the type Cp2Ti(C2R)2, where C2R = ethynylphenyl (C2Ph), 4-ethynyldimethylaniline (C2DMA), or 4-ethynyltriphenylamine (C2TPA), have been investigated. Cp2Ti(C2Ph)2 and Cp2Ti(C2DMA)2 have also been characterized by single-crystal X-ray diffraction. The two aryl rings in Cp2Ti(C2DMA)2 are nearly face-to-face in the solid state, whereas they are mutually perpendicular for Cp2Ti(C2Ph)2. All three complexes are brightly emissive at 77 K but photodecompose at room temperature when irradiated into their lowest-energy absorption band. The emission wavelengths and photodecomposition quantum yields are as follows: Cp2Ti(C2Ph)2, 575 nm and 0.65; Cp2Ti(C2TPA)2, 642 nm and 0.42; Cp2Ti(C2DMA)2, 672 nm and 0.25. Extensive benchmarking of the density functional theory (DFT) model against the structural data and of the time-dependent DFT (TDDFT) model against the absorption and emission data was performed using combinations of 13 different functionals and 4 basis sets. The model that predicted the absorption and emission data with the greatest fidelity utilized MN15/LANL2DZ for both the DFT optimization and the TDDFT. Computational analysis shows that absorption involves a transition to a 1LMCT state. Whereas the spectroscopic data for Cp2Ti(C2TPA)2 and Cp2Ti(C2DMA)2 are well modeled using the optimized structure of these complexes, Cp2Ti(C2Ph)2 required averaging of the spectra from multiple rotamers involving rotation of the Ph rings. Consistent with this finding, an energy scan of all rotamers showed a very flat energetic surface, with less than 1.3 kcal/mol separating the minimum and maximum. The computational data suggest that emission occurs from a 3LMCT state. Optimization of the 3LMCT state demonstrates compression of the C-Ti-C bond angle, consistent with the known products of photodecomposition.

Comparative analysis of viral infection outcomes in human seminal fluid from prior viral epidemics and Sars-CoV-2 may offer trends for viral sexual transmissibility and long-term reproductive health implications.

BACKGROUND: Viral detection in seminal fluid indicates their potential for both sexual transmission and impairment of reproductive health. Review of the mechanistic entry, sexual transmission and viral impacts for patients during major recent viral outbreaks of Zika virus (ZIKV), Ebola virus (EBOV), severe acute respiratory syndrome (SARS)-coronavirus (CoV), and SARS-coronavirus 2 (CoV-2) (the virus which causes COVID-19) provides a framework to discuss this potential. AIM: Comparative analysis of prior viral presence on seminal fluid against current (preliminary) findings for SARS-CoV-2 to predict biological implications of the novel coronavirus upon current sexual transmissibility, viral presence, and reproductive health. METHODOLOGY AND FINDINGS: Literature review was conducted using PubMed and Google Scholar databases. ZIKV and EBOV were found to be present in semen and to be sexually transmitted, leading the World Health Organization (WHO) to update their guidelines on prevention of the two viruses to include refraining from sexual contact. There are conflicting studies regarding the presence of SARS-CoV in male reproductive tissue, but it has been linked to testicular atrophy and orchitis. To date, two studies have detected SARS-CoV-2 RNA in semen, while seven studies have reported no positive detection. CONCLUSIONS: Though unlikely in the majority of cases, SARS-CoV-2 can potentially be present in seminal fluid, although there are no reports of sexual transmission to date. Prior epidemics raise significant concerns regarding the long-term reproductive health capacity for patients who are affected by entry of Sars-CoV-2 into the reproductive tract, therefore more study is needed to clarify the impacts to reproductive health.

This review describes the detection of viruses in seminal fluid and their sexual transmission, focusing on the major viral outbreaks of Zika virus (ZIKV), Ebola virus (EBOV), severe acute respiratory syndrome (SARS)-coronavirus (CoV), and SARS-coronavirus 2 (CoV-2). ZIKV and EBOV were found to be present in semen and to be sexually transmitted, leading the World Health Organization (WHO) to update their guidelines on prevention of the two viruses to include refraining from sexual contact. There are conflicting studies regarding the presence of SARS-CoV in male reproductive tissue, but it has been linked to testicular atrophy and orchitis. To date, two studies have detected SARS-CoV-2 RNA in semen, while seven studies have reported no positive detection. More studies must be completed to accurately determine its risk of sexual transmission to ensure mitigation of further transmission and understand the long-term implications of SARS-CoV-2 on the reproductive health of recovered patients.

Testosterone-Induced Central Serous Chorioretinopathy Mimicking a Choroidal Mass.

PURPOSE: To describe a case of supplemental testosterone-induced central serous chorioretinopathy (CSCR) mimicking a choroidal mass in a 63-year-old male. METHODS: Case report. PATIENT: A 63-year-old male patient on self-prescribed supplemental testosterone with CSCR mimicking a choroidal mass. RESULTS: A 63-year-old male presented with new onset vision loss, subretinal fluid, and choroidal mass in his left eye. Intravenous fluorescein angiography showed an enhancing choroidal mass involving the fovea. B scan ultrasonography revealed diffuse choroidal thickening. Given concern for a diffuse uveal melanoma, the lesion was biopsied showing non-diagnostic rare, atypical melanocytes. Four months after initial presentation, the patient was diagnosed with polycythemia vera. Fourteen months after diagnosis, he admitted to testosterone supplementation. Upon cessation of the testosterone supplement, the lesion progressively flattened to a chorioretinal scar with subretinal fluid resolution, and the return of normal choroidal thickness over the next 14 months. DISCUSSION: Testosterone supplementation has been linked to erythrocytosis and polycythemia vera. In the retina, testosterone supplementation has been linked to CSCR and both central and branch retinal artery and vein occlusions. This case demonstrates the importance of inquiring about all prescribed and over the counter medications in patients presenting with retinal lesions of unknown origin.

Oxidatively stable ferrocenyl-π-bridge-titanocene D-π-A complexes: an electrochemical and spectroscopic investigation of the mixed-valent states.

The synthesis, spectroscopic, and electrochemical characterization of oxidatively stable D-π-A compounds of the form (Me2CpC2Fc)2TiCl2 and RCp2Ti(C2Fc)2CuX (where Fc = ferrocenyl) are reported. Oxidative stability enabled by the addition of CuX is evidenced by voltammagrams of the RCp2Ti(C2Fc)2CuX compounds which all display two chemically-reversible 1e- FeIII/II couples, indicative of electronic communication between the Fc- termini. Differential pulse voltammetry (DPV) in CH2Cl2/[n-Bu4N][PF6], demonstrated that the redox potential difference between the two 1e- FeIII/II couples (ΔE1/2) is between 112 mV and 146 mV, being most pronounced with the electron rich Cp*2Ti(C2Fc)2CuBr. The ΔE1/2 values were unaffected by solvent (THF) and displayed only a small dependence on the identity of the counterion, either PF6- or B(C6F5)4-. For each complex with a measurable ΔE1/2 value, spectroelectrochemical experiments were performed in CH2Cl2/[n-Bu4N][PF6] and gave clear evidence of both the one-electron oxidized mixed-valent (MV) state and the two-electron oxidized state, each with distinct spectroscopic signatures. The MV states of these complexes showed absorbance between 820 and 940 nm which were replaced with a higher energy feature following a second oxidation. A very similar absorption band was also observed in the one-electron oxidized state of an analogue with only a single Fc substituent, namely TMSCp2Ti(C2Fc)(C2Ph)CuBr, suggesting this feature is not an FeII/FeIII intravalence charge-transfer (IVCT) band. Despite DFT calculations suggesting a pathway exists for electronic coupling, NIR spectroscopy on the MV states gave no evidence of an FeII/FeIII IVCT. Possible contributions to ΔE1/2 from inductive effects and a superexchange mechanism are discussed.