The convergence of blockchain, the Internet of Things (IoT), and artificial intelligence (AI) is widely heralded as transformative for advancing the Sustainable Development Goals (SDGs) and reshaping responsible investment, yet the literature remains profoundly fragmented across technological, sustainability, and financial silos. This study addresses this gap through a rigorous qualitative meta synthesis of 33 peer reviewed studies published between 2021 and 2026, deliberately prioritizing interpretive depth and thematic integration over Qualitative Meta-Synthesis quantification to extract causal mechanisms and contextual contingencies. Anchored in the resource based view, dynamic capabilities, institutional, stakeholder, information asymmetry, and socio technical systems theories, our analysis delineates eight interconnected thematic categories and three core causal pathways transparency and trust infrastructures, real time sensing with operational optimization, and predictive and prescriptive intelligence. Critically, the synthesis uncovers four persistent paradoxes the energy throughput trade off, transparency obfuscation dynamics, governance accountability voids, and digital divide exclusion tensions that collectively qualify prevailing technology optimism narratives and position digital technologies as conditional enablers rather than panaceas. Building upon these insights, we advance the Digital Integrated Mechanisms for Transformation (DIMT) Framework, positing that sustainability outcomes are not technologically determined but critically contingent upon data maturity, regulatory coherence, stakeholder literacy, and institutional readiness. Empirical evidence further reveals that synergistic integration of all three technologies remains empirically scarce, comprising merely 2.7% of the corpus, marking a paramount frontier for future inquiry. This review consolidates fragmented knowledge, explicates implementation paradoxes, and offers actionable guidance for policymakers, investors.